Lister Engine Forum
How to / DIY => Everything else => Topic started by: BruceM on July 29, 2018, 03:12:30 AM
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I thought I should play nice and quite stuffing this in Glort's PV -grid tie work. While I did add 1500 watts of panels to my existing 875 for this project, I'm now down to the inverter work.
A little review:
I live off grid and have lived with my own 120VDC system and Listeroid for AC and compressed air for a long time. In preparation for adding inverter power to my system, I upgraded my 120VDC PV charge regulator to handle up to 3000 marketing watts of PV. It's linear, not pulsing, for very clean DC.
My 120VDC input inverter design is based on the venerable Trace SW series which does low frequency switching of transformers with secondaries in series to create a sine. That general concept is about all I'm using. I'm using very soft (slow) switching plus snubbers and minimal passive filtration to generate AC with no audible (via AM radio) EMI on the AC or DC supply. I'm only using 2 transformers of equal output secondaries, and they are used to make a 5 step sine wave; zero plus two steps up and two steps down. I originally did a 7 step sine but found 5 step better. The 5 step sine gets the THD down below my ST3 generator head, and eliminates the typical 20% motor heating loss of a MSW inverter. I use 120VDC for my home and shop power, and have been using a Listeroid 6/1 for AC generation for well pumping and washing machine.
I have previously done quite a bit of testing of the prototype on motor starting at 120VAC output; it would start a 1.5HP tile saw like grid power, instant and effortless. I ran into a bunch of trouble when I switched transformers for 230VAC output; ultimately I tracked it down to huge inrush surge current. Until I worked up a software solution of soft starting the transformers, I could only test by starting the processor and H-bridges with 0 volts input, then switching on the 120VDC through two huge chokes and 30K uF of DC filter caps. This provided a slowly increasing voltage which kept inrush current minimal. The massive DC filter was needed for keeping AC off my clean 120VDC. With the filter in place, I now have 1 millivolt of AC ripple with 1000 watts of load. Backfeeding 230VAC to my step down transformer outside the shop, I've run a couple loads of laundry in the washer (about 1100 watt load also) with no trouble and barely warm heatsink on the H-bridges. I've also been testing with 500, 1000, and 1500 watts of heat lamps in the shop.
I got the prototype jury rigged on the floor of the battery bank shed and then found that due to my new short 120VDC supply wires to the 10K uF fiter output capacitor, the old Antek transformer inrush current problem came back and bit me. I should have tested with small fuses, but I got cocky...with 4 mosfets, 3 ICs, and 2 transistors fried the result. I got it repaired, changed the soft start to extend from 50 usec to 5 millisecond pulses, and now she starts and stops nicely on small fuses, again.
Tomorrow I'll test on my 1/2 HP Franklin submersible well pump. It pumps from a depth of 200 feet. It normally runs at 1150 watts, with starting peak over 3400. The issue to be tested will be surge load capability and compatibility with the operation of the Franklin QD solid state capacitor start relay.
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My intentionally minimalist design with PICOscope measured 8% THD does not comply with the THD specifications for grid tie inverters (5%). My primary goal for an off grid inverter was to have the lowest possible EMI, while being able to run single phase induction motors efficiently. I intentionally sacrificed THD to allow for slow switching times and reduced EMI, as long as motor efficiency was not significantly affected; keeping induction motors happy was my requirement. Most generators are in the 9-15% THD range. My ST-3 THD measured at 12%. So "generator" class THD was sufficient for my needs, and I did beat that, just, when I got rid of the waveform distortions of slow switching a 7 step sine and went to the simpler 5 step.
The large toroidal transformers will always be costly, and this will always pressure designers away from this approach, especially when EMI is not even considered.
For the low THD required for GTI inverters, the designer has no choice but to do 100x faster switching, even while using a low frequency design per the original 3 transformer Trace SW series. The sine wave must be built with many small steps; Trace used 32 steps per half wave. The same Trace SW approach with a modern microcontroller can be done, but even with very well designed snubbing, the faster switching design will require substantially more passive filtering of the AC and DC. AC filtering in particular is costly in efficiency. For example, only 10 microfarads of total capacitance line to line at 230VAC draws 1 amp (230 watts) continuously. Capacitance to ground in microfarad levels is largely a "beat the test" farce since the earthing system in the real world is NOT a copper plane from which all measurements are referenced. Capacitance to ground in larger values, for AC or DC typically just turns the entire grounding system into an EMI radiator. I combat that problem by spending a fortune on the earthing system; I use copper flashing, buried, with rods connected, and copper flashing extending all the way to the filter enclosure, typically.
The large toroidal transformers used in my design are heavy and expensive. The mass market for GTI's has driven them to make them smaller, cheaper, lighter. Low frequency, transformer isolated designs were well proven as being the most durable and reliable.
My usual plea to those adding inverters to their homes:
To avoid developing Electrical Sensitivity and to greatly reduce the risk of accelerated cancer growth and autoimmune diseases (arthritis, thyroid, diabetes, cardiac) I urge everyone with an inverter (GTI or off grid) to add a commercial grade two stage common mode choke filter to both PV input and AC output. This will greatly reduce the EMI radiating from the home and PV wiring. These passive filters are available at any big electronics component supplier, and they run $70-$250 each depending on size. They will not adversely affect inverter efficiency or performance. They are likely to provide -20 to -30dB worth of filtering up to 50MHz, where must of the switching EMI energy will be. DO NOT buy plug in "filters" such as Stetzer or Greenwave. They are nothing but 22uF motor run capacitors and will void the warranty of your inverter, will likely cause it to fail, dramatically reduce it's efficiency and will provide absolutely zero common mode filtering. Anyone promoting them is utterly incompetent, knows nothing of the engineering field of EMC, and should be given a good tar and feather job.
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I did the inverter test on my Franklin "1/2 HP" well pump this morning. Success! I'm pleased with the results. It starts faster than on the my ST-3/Listeroid which sags a little. Running current at 235V was down to 5.9 amps in 2 seconds for a total of 1386 watts. That's a bit higher than expected but the pump is over 10 years old and main winding resistance is out of range, slightly. The pump controller lid specs say 6 amps at 230VAC, even though Franklin literature claims 1150 watts for the pump.
I did a comparison to ST-3/ Listeroid power. With the same RMS volts and RMS clamp on amp meters in place; results- 6.1 amps 232VAC. 1415 watts. The frequency was 60.1 Hz which might account for the small increase. Certainly the inverter has performed at least as well as ST-3 generator for motor driving efficiency.
I did find a software bug which is intermittently affecting remote shut down. Otherwise, I'm ready to get on with proper job of packaging and installation; at present it is just a jury rig of boards and wires on the floor of the shed.
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Franklin rates it's submersible motors on pumping HP, apparently. It's nuts. The rated current/volts for their "1/2 HP" is more typical for a 1.5 to 2 HP motor. Don't ask my why. Horse power is generally untrustworthy in American marketing- you can only look at rated current and voltage and service factor and go from there.
For the typical two stage commercial filter power filters, here's a page full of models about right for a 5KW output GTI. If you drill down further you will see that the more expensive ones use larger common mode chokes, which have better performance, especially at lower frequencies. Data sheets give you an insertion loss plot for each one. I make my own filters, but I wanted to keep this simple for those who might be daunted. They are not that expensive and even the cheapest one's will reduce the home power EMI dramatically.
https://www.digikey.com/products/en/filters/power-line-filter-modules/838?k=&pkeyword=&pv2155=u25A&pv2155=u30A&pv2155=u36A&FV=ffe00346%2C5400d2%2C33c02b2&quantity=0&ColumnSort=0&page=1&stock=1&pageSize=25
For installation, these need to be mounted inside a junction box, since the terminals are exposed.
Commercial electronics are not designed for ease of maintenance, just as cars are not anymore, either. It's all about the race to the bottom. When I build something, the components alone might cost me 20 times the price of a finished product from China, and they have a custom molded plastic case.
The challenge for my inverter install is to make it easy for myself for any troubleshooting and maintenance. I have the luxury of not caring about size, weight. I want to locate the two H-bridges so I have ready access the top side of the boards for o-scope checkout; the processor board can just unplug, and I'll add some test points on the top side of the power control/remote control board. The little voltage sense transformer plus rectifier for computing RMS voltage needs a top side test point also. Fortunately, what commercially would be stuffed in a small shoebox, I'm putting in a 15x15x6 inch box. I haven't decided on whether the heat sink should be split in two and extend outside the box, or whether I'll just have lots of screened vents on the box and let the heat sink help drive the thermally driven airflow. The latter probably, as it gives me better access.
I was too scramble brained from the live testing this AM to do the software debug work. Hopefully tomorrow AM I'll be smarter. It's the damned grossly overtaxed RMS voltage routine that's got the bug- that makes it ignore the shut down request signal...after traversing the voltage timing table upwards to a large amount. I'm going to have to do some recording with the Picoscope logic analyzer function again, while flipping some spare port bits in the code so I can figure out what's happening in real time. I'll be able to use an Arduino Uno board hooked up to a breadboard for simulating a few signals and a pot for AC sense voltage. It would just be a whole lot faster if I didn't have to go into the house to operate the picoscope, but I can't work near it or the computer.
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My inverter logs my 1/2 hp Franklin well pump motor right at 1Kw. Poor Power Factor on the motor is what kicks it up over 800w/hp
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Good point on PF, Mike. I've got to try adding some motor run caps and see if I can lower the power draw a bit or if Franklin already has it optimized.
I also thought about reducing power frequency and voltage a bit after it's started, but I'd need a faster and more capable (ram, faster ADC, priority interupts) controller processor as the little ATmega328P is tapped out.
Franklin has a PV direct inverter for running their single phase pumps. About $3K and no doubt an EMI monster. But I was able to comb through their literature to find out what they are up to. It slows down to 30Hz and reduced voltage if PV power drops. They can go no lower than 30 Hz or their pump's hydrostatic bearings fail.
I don't need full power flow at all, it will just be topping off a 2400 gallon gravity feed storage tank on sunny days. I expect their controller also replaces the standard motor control box so they can manage their own soft start on the start windings. A bit more of a project than I wanted to handle right now. With 3 of my soft switch H-bridge boards and a bigger, faster processor I could also do 3 phase MSW (3 step). 6 H-bridges for 5 step sine.
I did get my two 1000 watt transformers wrapped with 3/4" mylar strip tonight, and also wrapped my 14mH gapped, laminated toroidal choke.
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I've got the inverter installed in the battery bank shed and am running my washing machine PV power using the remote start. Voltage and frequency are perfect. Battery bank is holding in float at 139V thanks to the new 1500W array addition to my old 875W panel array.
It was a relatively uneventful installation but I had an interesting problem with the generator/inverter 230V switchover coil relay; it was chattering during the transformer soft start, even though voltage during the soft start is limited to single transformer, only 150V max. The soft start failed as it was also connecting to remote step down transformers and blew the fuses. I figured it out after some end to end testing. I've temporarily bypassed the offending relay and tomorrow will add a time delay module on the coil so that it won't kick in until transformer soft start is complete and the the output has stabilized at 230V.
I still have some work to do; I haven't installed the earth grounding system for EMI filtering. Grounding the center tap of secondary side the two 1000W transformers completely eliminates the very low end of the AM band EMI. It's like adding a shield ground between the two sets of windings, which is what I'd probably do if I was having them custom made. Since this is a low budget DIY project, I just rewound the secondaries of some stock Antek transformers. They aren't ideal for this application since they buzz with the non-sine primary input, even with no load. The laminated cores aren't adequately bonded for that.
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Light white smoke this AM (more distant fire) with no taste and less misery for me so I got up at 4AM and tried to get something done before the worst of the heat and smoke.
I did get the software updated with a slightly better version of RMS voltage sensing. I added a second 65 sample half wave with 1/2 a sample time shift. It's adequate now, +-1%. I can improve it more by exceeding the best accuracy speed of the ADC and doubling the sample rate but will wait until I have finished the grounding system as the little bit of common EMI on the AC now is likely affecting the RMS accuracy. It's also only a 10 bit analog to digital converter (ADC) so that may be the limiting factor at this point. Hot rodding the ADC may only make accuracy suffer further.
I topped up the water tank with about an hour of running at 1385 watts in 93F heat. The transformers were barely warm, the heat sink on the 2 H-bridges was also barely warm. No need for fans.
I tried a new transformer soft start routine, with both transformers pulsed at the same time, in opposite polarity so that the net AC volts would be zero until soft start was almost complete. Alas, it blew a 3A (gentle testing) fuse and I don't have enough 3A spares to continue with trying new variations to see what keeps the Antek transformers happy. After I cool off for a bit I'll install the time delay controller on the output relay, and then I'll be able to switch between Listeroid 6/1 and inverter power from in my shop. The inverter gets priority- if it's on, it steals the 6 gauge twisted pair coming down the hill.
I'll do a video when we have a windless AM without too much smoke.
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I got the earth grounding system put in over the last few days. That was a lot of dirty work. I did hook the transformer secondary "center" to ground, but still have to modify the H-bridge output filters to add capacitors to ground. For all the bench work, I didn't have a decent ground so couldn't test that for effectiveness.
Got the 3A test fuses so back to the start up relay issue.
Tried the ICM 102 delay on make controller- it is either defective for won't work for a 230V coil relay. The spec sheet that came with it says 40ma minimum current...a detail left out in the sales literature. It was just turning on immediately. I took it down to my shop and tried it on generator 230V, with another Omron relay with 230V coil. Yep, that didn't work. Coil is being fed 80VAC when "off". ICM in Syracuse, NY, blew this one.
I decided to have another go at a zero voltage output transformer soft start. Why add hardware with some new software can do it instead? With keeping zero output voltage in mind, I wrote a new version pulsing one transformer positive while the second negative, then vice-versa, increasing the pulse width by 50usecs each time. The transformers are the same, so outputs in opposite polarities in series cancel. I carefully matched the pulse and delay timing of the old successful routine. Voila, it worked on the first go. Figures now that I had an open bag of 20- 3A fuses! I can hear the distinctive buzz-winding down sound of the soft start, with zero volts on the meter, then snap, voltage goes to 230 and the output switch-over relay goes clack. So I don't need the delay on make relay controller anymore.
I put the covers on all the boxes yesterday and cleaned up the chaff on the shed floor. Looks pretty decent. All that's left is the final EMI cleanup.
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Thanks, Glort. Open sourcing this hardware and software and my 120VDC battery management hardware is one possibility. I'm afraid most need a finished product, competent installation, and lots of support. Precious few are well enough (or have the resources) to tackle living off grid after becoming ill.
Wish I could use a MIG welder and plasma torch. Now I have to get back a few hundred feet from those. I wasn't too bad with a stick welder/cutting rod at one time.
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Thanks, Glort. Because of MS and autoimmune thyroid disease that has caused alternating episodes of hypo and hyper thyroid, depression has often been a serious problem for me. Just in the last year, I found that by taking just 1/4 grain of natural (pig) thyroid plus Cynomel by Grossman, I can manage and not have the horrible aggravation of my epilepsy that thyroid meds have always caused. I need something that's in the natural stuff, but only a little. The Grossman generic Cytomel feels MUCH better to me, is head and shoulders above the US generics, and 1/4 the price. When I'm naturally hyperthyroid, my epilepsy is markedly better (7 years was my longest stretch), despite the difficulty in sleeping; so I know the thyroid medications are the culprit.
"Modern" medicine assumes that hormones that are not the same as your natural ones, but are similar molecules that can be patented, must be good enough, even when patients claim otherwise. I think that's nonsense, and that for profit medicine with it's patent medicines is hardly in the best interest of the public. I have similar problems with the hydrocortisone I inject. It's NOT the same as having normal adrenal output, and even in injectable form causes gastric distress, yet for me, compared to the other two patented synthetic analogs to cortisol, dexamethasone and prednisone it is the lesser of evils.
I'd sure like to see truely bioidentical hormones available; I think millions would benefit greatly. Right now our pharma industry with their regulatory capture makes that impossible, as does their control of the legislature.
Depression has a dozen different causes, biologically, and is serious business. It may be the harbinger of neuro-degenerative diseases. The conventional approach of just giving SSRI drugs for "depression" will be viewed in the future as dark ages, incompetent medicine. I highly suggest reading Datis Kharrazian's books. His functional medicine approach, in looking deeper for the underlying problem, may not be as profitable as 8 minute medicine, but seems a hell of a lot better for the patient.
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Neurology and Psychiatry are both still pretty much dark ages. They apply labels to symptoms and call that a diagnosis, and then start trying drugs at random. There is no science to what drugs may temporarily help for someone and what will not, or worse. All you can do is just keep trying. I had a horror show for a life for a few years, trying drug after drug to try to get some control of my epilepsy while new MS lesions were showing at every new MRI. The horrible depression of being seriously autoimmune-hypothyroid, just taking enough Cytomel to keep me from suicide, since taking more turned up the epilepsy dangerously. The rapid downward slide gradually stopped when someone visited with a meter, showed me the high readings. and I cleaned up my home, EMF wise. A lot of misery and holes in my brain for the lack of a couple wire nuts in the right boxes. I owe my life to the person who spoke up and stuck a meter in my face.
Doing laundry on the inverter with the latest software version now. Did some checking and found an issue I have to work on besides cleaning up some EMI. The PV charge regulation is going oscillatory at higher loads- this in the late AM when there is plenty of excess amps beyond what the inverter is calling for. I see a 1V peak to peak sine ripple at about 6.6Hz on the 120VDC. The battery regulators are flashing visibly. This is the hassle of closed loop analog control systems. I can twiddle with the values of the net charge dampening term...I suspect that when I last jacked that up to improve response to sudden shedding or adding of 1200W loads, I may have affected stability for the minutely pulsing nature of the inverter. It's going to take some time to sort it out. I have a solderless breadboard that can take over that part of the control, getting the essential signals from the PCB and generating the drive signal for the PV current regulator. I just hope I can make it happen without the inverter on, as I can't stand there for more than 30 seconds with that on.
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The other thing I found very helpful in the last year is the Gundry low lectin diet. Reduced my headaches, brain fog and muscle pain dramatically. Don't think I could have finished the inverter project otherwise. Software was beyond me, totally.
Learned an important lesson today. I forgot and started the inverter with the step down transformer turned on. The new soft start can't handle that either, it blew the 16a fuse for each h-bridge, and the same two mosfets on each board. No other casualties. I MUST add a time delay relay control to the output so that soft start is ALWAYS with no loads.
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More EMI testing and DC ripple measurement today led to an annoying discovery. I use 4- 800 w toroidal step down transformers in parallel (not ideal) outside the shop to get 120VAC for the washing machine, a friend's welder, etc. On occasion, when remotely switching on those transformers via relay, I get the same old toroid transformer inrush current spike- and it blew fuses and 3 mosfets. So I will have to add a relay time delay controller (Siemens), another relay, and 400 watts of 50 ohm resistors. The resistors will limit the start current, then the relay will short them out after 3 seconds.
Toroids are very efficient, and a bit of a pain.
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Yes, when I did all my testing, there was a long 12 gauge pair leading from the shop bench to the 230V outlet, which was also 12 gauge back to the shop power panel, and I think 12 or 10 gauge to to the power pedestal in the hard with the transformers.
Now that I'm thinking about voltage losses, and everything is beefed up, it's been an eye opener how high the inrush currents can be for the higher efficiency toroids. The ST-3 never complained.
I found out something interesting today- I had almost 20 millivolts peak to peak of AC waveform riding on top of my 120VDC when the inverter was running and no other DC load in the shop...and it didn't change in the slightest from no load to 1500 watts load! It took me a bit to realize what was going on.
The problem is that I ran both AC and DC as 6 AWG twisted pairs in the same metal conduit (something I avoided for my neighbors setup) down the hill about 250 feet...and the 230VAC signal is coupling capacitively onto the DC line. I'll have to add capacitance from 0, and120VDC to ground at the power pedestal to help remove the AC. It should be well below 1 millivolt! The luxury of DC is that there is no loss or performance penalty for adding capacitance. I rely on clean 120VDC, it lets me use soldering irons and other resistive appliances with no health problems.
There's that old saying about 90% of the project completed, but that last 10% takes 90% of the time.
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Hey BruceM, sorry to here you have had such a rough time with your mental/physical health and the Medical professionals that are supposed to help.
I have had similar experiences and wonder at the way pills are randomly trialed on the sick. My doctor tried to prescribed a drug called lyrica, for nerve pain. I declined his kind offer as I knew that this product can cause heart attacks and I`ve already had one. He then put me on an antidepressant called Sertraline which put me back in hospital with blood pressure issues.
I went to see the cardiologist today for a check up, told him what had happened and he was appalled that my GP had tried these medications on me without consulting him.
There are some very smart doctors out there who can help, the difficulty is finding them and then having the courage to tell the mediocre medics to take a running jump.
The best news today is that I have been taken off the blood thinners. I will no longer bleed for a week from an insect bite or develop a haematoma instead of a bruise. Happy days :)
Keep up the good work, chin up,
Bob
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I think good medical practice is an extreme exception, rather than the norm. I've seen so much blatant, basic malpractice it's outrageous. Trusting any medical practitioner is a fools paradise, in my book. It's your health, and MUCH can be done to help yourself.
I'm keeping an open mind on the cause of the AC ripple on the DC. But I know it was NOT there in my bench testing; I had it down to 1-2 millivolts peak to peak at 1000 watts at the end of about 300 feet of cable. I was expecting an unmeasureable situation with the inverter near the battery bank. But given the constant level of AC ripple regardless of load, it is almost certainly capacitively coupling from the constant 230VAC pair in the same metal conduit. I was foolish to have not run a separate conduit for AC.
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Not fully believing my own findings (I was still recovering from a trip to town.) I retested today and find results similar to the bench testing. AC ripple on 120vdc supply of about 3 mv p-p at 1000w load, 1mv with 500w. I suspect operator error or a bad test lead before.
EMI on DC is non-existant, AC is barely there with AM radio oriented just right a few inches from the wire and tuned just right to the lowest portion of the AM band under even small load.
The EMI is around 1MHz, so as one should expect, it didn't significantly jump to the DC wires in the same conduit, or what did is the same as what bled off to the buried metal conduit.
This is substantially better than my partially EMI suppressed Listeroid/ST-3 power.
I have yet to add the 0.1 ohm capacitors to ground on the H bridge output filter boards, which I will try, since the earth grounding system was such a project! Right now they are just a toroidal common mode choke and snubber. The only ground connection at present is the center connection of the two transformer secondaries.
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Hi BruceM, used to get the same sort of problems with control cables in factories, always ran unshielded twisted pairs at least a meter away from single or three phase cables. The worst offender was florescent lighting with starter modules.
Where we had no choice but to lay cabling next to power cables, we ran shielded cables all grounded to earth. Gets real expensive in some situations where you might need 30 or more control/data wires.
Bob
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Hi Bob, Yep, industrial control is often one of the worst EMI environments out there; fiber, both plastic and mulitmode glass, has made big inroads there for good reason. I use Industrial Fiber Optics POF products for both analog/control and digital data regularly. My home's audio, thermostat, central vac, computer on/IR controls, keyboard/trackball and IR rear projection controls are all IFO product based, my own designs. In my case it's because the home is shielded to -110dB so all signals have to either be filtered or fiber.
Today I did add 0.01 uF caps to the earthing system on the AC output of the H-bridges. Connection was easy as I ran sheet copper (16 oz/SF copper flashing) up behind the steel box and could just screw to the box and copper anywhere. It did improve both the DC (nothing audible at all now) and AC. AC with any load is only audible on the AM radio around 560KHz, within 1/2 inch of the wire with the radio oriented just right. No load EMI on the 230VAC can be picked up at 6 inches. I'll have to think about that one. During testing I experimented with a snubber on the AC output, a motor run cap about 6 uF and 2-10 ohms on my earlier 120V version. It worked well but I don't like that solution as it's a power sucker.
I thought about adding the 4 - 250 uH toroidal chokes to the 2 h-bridge output filter boards again. The chokes "round the corners" of the stepped waveform quite nicely but do nothing for the EMI whatsoever. They do get hot at full load and add about 1% power loss. While the waveform is softer, it doesn't do anything appreciable for THD or motor efficiency so I'm reluctant to add them in.
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Hi BruceM, I am struggling to understand your set up. I know that your health issues make you very susceptible to EMI. Why do you have any AC (shielded or not) in, or near, your home?
DC is more dangerous but produces so much less EMI. You write that you have some 300 m of underground cabling, which suggests that you require both in your home space. Why?
Some domestic equipment runs only on AC, while some runs an AC but then transform it and rectifie it to DC at various voltages.
Can you not keep it simple and put all AC appliances, generators, invertors and etc at a safe distance from your home, with remote start switching. Build a Faraday cage (preferably in the ground) closer to the house and fill it with the transformers and etc to run everything else on DC.
There is a very lazy man living near me who worked out that he would expend a lot less personal effort if his washing machine was next to his rotary washing line. He put up a small shed and ran an extension lead and hose pipe. He now lifts the wet washing out of the washer straight onto the line. I can only admire his inventiveness, sadly I expect the time he saves himself is spent sat on his arse in front of the TV.
I know I have come late to this conversation and apologise as you have probably answered most, if not all, of these questions in previous posts. (I`m too lazy to read the last 1500 posts) :laugh:
Fiber is the future of all terrestrial communication and data control, it is very difficult to hack and immune to EMP from solar flares or nuclear blasts( the routing systems are not). It is however fragile, I suspect that this is why the military rely so heavily on satellite communications and why the US, the former Soviet Union and China are investing so heavily in space defense capabilities.
Keep well,
Bob
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Bob, I use 120VDC for my home, plus some 12VDC for controls, etc. Both filtered with -110dB from 10K to 2GHz military grade filters and in EMT conduit with compression fittings. I don't use AC in the home because it's only useful function is for running motors, which I don't use in the home because of sound and the ELF magnetic fields. The inverter is using my 120VDC battery bank/PV charge controller as the source, and it's output shares the same conduit as the shop and house feeds (as does my ST-3 output).
I have 250 feet of conduit from the battery bank building to the shop/house, so 76 meters. The building was located on a hill which is ideal for a wind generator, but I found PV was more than adequate even in winter, here.
You mention DC as being less safe, when in fact, this is not true. For any given voltage, DC is about 4x safer, including the "can't let go" threshold. This is well established. I thought otherwise myself until I did some research.
There is no difference between AC and DC for power emission as far as higher frequency EMI. I have misled you - I am only talking about the EMI on the DC and inverter generated AC wires, now measured in my shop while the inverter is switched on. The same switching power supply for computer equipment on my 120VDC system makes just as much EMI on the DC as it does on AC. (I have a 7 stage LC filter for the computer gear.) The difference is that filtering of DC is much easier and more efficient, since capacitors don't heat/dissipate 60/50Hz power while trying to remove high frequencies. There is no limit on inductors, either. You can add as much capacitance and inductance as you need, though the same EMC rules regarding stages for "woofer", "midrange", and "tweeters" apply.
I developed this low EMI inverter so that I could run via PV power on sunny days my well pump (1380W), which is far removed from the house and shop, and the washing machine(1100W), which is in the shop. I also wanted to test my design theory which I first applied successfully to a redesign of the electronics of the EL-SID circ pump (the only brushless DC circ pump at that time) about 17 years ago; that EMI is best controlled by slowing the slew rate of switching; that most of the losses of slow switching are compensated by reduced gate drive power. That method is now being used by Texas Instruments in their latest variable speed motor drive IC's. The industrial control situation has gotten so bad (EMI-wise) that finally designers are trying to address the problem at the source, instead of the liberal and expensive application of EMC band-aids everywhere else. I've taken the same basic approach to a more extreme level; for very slow switching of power MOSFETs, you cannot just increase gate drive resistance. It requires some additional specialized circuitry. It also requires very careful selection of the MOSFET. Today, some MOSFETs are now rated for linear operation with full safe operating area data provided. When I first applied the slow switching method to the EL-SID circulation pump, I had to test and use higher voltage MOSFETs since no linear data was available. Today it's much, much easier and some companies make great choices for slow switching that have very low on resistance (high efficiency and little heat).
It is unheard of for a 1500W (or even a 100W) inverter of any kind to produce dramatically lower EMI on the connected AC and DC cables than that produced by a typical 10 watt power supply. This one has less audible EMI at the attached cables than an LCD wrist watch. Those offered commercially today will typically obliterate the entire AM band anywhere in or near the house since all the wiring radiates this EMI. Early on in my development of my inverter, I decided to just disconnect the more extreme slew rate control circuitry to see what the emissions would be like. The entire AM band was wiped out, within 8 feet of any connected wires. So by design, I'm reducing emissions by over 90dB, with very little efficiency penalty. I am sacrificing some THD, intentionally, but 8-9% THD is better than my ST-3 at 12% and it allowed me to take slow switching to an extreme.
This is not your typical DIY inverter.
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Ruined a metal cutting bandsaw blade yesterday cutting a gap in a 450W toroid core that I stripped of wires, etc. Last time I did it by hand and it wrecked about 6 hacksaw blades. The grain oriented silicon steel is very hard, and has a thin ceramic coating which eats blades. I hoped my bandsaw would power through it easily, but NO, it was painfully slow. I filled the gap with JB weld.
Today I wound 72 feet of 10 awg magnet wire on the core- 120 turns. I've never used wire that big before and won't be doing it again. No room in the center, doesn't look nearly as nice as the 12 awg one. Next time I'll try multiple strands of smaller wire and start with a bigger core. The 12 AWG one (same cut core, same number of turns) tested well at 14 milli-Henrys. This should be close to that, but half the resistive loss. Got it installed in the place of the 5mH Hammond choke with plenty of room to spare.
I got the Siemens relay delay unit and the power resistors this afternoon, and installed that in my power pedestal outside the shop. So the 230- 120V step down transformer is now "soft start", with 40 ohms (5- 8 ohm 100W resistors in series) in series with the windings for 3 seconds, then a second relay closes and shorts the resistors. Tested it briefly with the inverter and it seems to work fine. Ran out of energy and sunlight so will do a more thorough checkout tomorrow.
I got some small toroidal 10uH inductors for the H-bridge filter boards yesterday. That's up next after some more testing.
G
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Wow Bruce, looks like you are really pushing the boundaries on this. have you tried cutting the toroid with a four inch grinder? Should do the job but the heat generated might damage the ceramic coating.
Does cutting the toroid have a significant effect on its performance as a choke? I can certainly see that trying to wind that much wire onto an intact toroid would be impossible.
I am looking out for a cheap second hand grid tied inverter to play with. I intend to try rectifying the output from a 5 Kva generator to drive it. Solar by day, Lister at night.
Finding it very difficult to get any information on how much ripple an inverter will tolerate, I guess they are intended to run off PV or batteries so no one has tested them with rectified/smoothed AC.
Bob
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Gapped laminated toroidal cores are used for large inductance DC chokes. Powdered iron toroids are used for values up to about 250 uF. The gap is needed to avoid saturation, just as powdered iron is used instead of ferrites for DC power inductors. Alas, my gapping is non-scientific, as the annealed toroid opens when it is cut so the gap varies widely between inside and outside. It has worked, though. I will look into thin kerf 10" diameter metal cutting blades for my table saw as ruining a $26 bandsaw blade for a single cut is too expensive. In quantity, manufactured gapped torroid core chokes are very reasonable in price, but the onesy-twosy prices are beyond my budget, so I've been making my own from my collection of surplus toroidal transformers.
Alas, my testing today showed that even a jury rig adding a 3rd choke and two more 10K uF capacitors made no difference in the DC ripple measured at my shop on the 120VDC supply. My new 10 awg wound choke is performing identically to the Hammond 5 millihenry choke it replaced for a range of loads.
Oddly, ripple is more than twice as high when the well pump is running instead of similar wattage of 230V heat lamps in the shop. I am at 15mv of ripple for the will pump. I must ponder this anomaly and test more to sort it out. I may move my 3rd choke to the 0V line and see how that affects the DC ripple.
I did answer the mystery of the constant 20mv of AC ripple I found a few days ago; it was idiotic operator error. There is a double pole switch for the DC near the outlet. If the switch is off, the cable just acts as an antenna, and the DC and AC cables in the shop run parallel and into the same box on the wall. I did it today, recognized the more jagged waveform instead of the 120Hz sine the inverter and DC filter makes. My IQ plummets as I start to have temporal lobe abnormalities when I'm near the oscilloscope, etc., so I struggle to keep on track and get my planned measurements done. I'd fire myself if I only I could.
Bob, I think you're right about the GTI being designed for relatively clean but variable volts/amps input. Only testing of a specific model will tell the tale. I would consider using a higher resistance choke such as a toroidal transformer operating in saturation (no gap, just use the existing windings). I have used them for chokes like this, and despite being in saturation they do work quite well. My generator charger used two 1000W transformer primaries as chokes, a 10K uF capacitor between. No capacitor needed on the battery side, they already are a capacitor. This got the ripple level down to 20 mv or so at 10 amps/146V. The voltage drop may need to be added to, as that will keep the GTI's maximum power point sweep from cyclically overloading your generator.
Even 10% ripple may be fine for your application...you'll just have to experiment.
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Hey Buddy, sorry to hear you are a bit out of sorts, hope it clears soon, how is your wife recovering from her hospital trip?
Regarding the GTI I am looking for information on how much ripple they will cope with. I have a cunning/stupid plan to use my Lister CS 6/1 to run the ST5 I now have and use it to feed my grid tied inverter at night.
The output will need to be rectified and then smoothed to a level that is acceptable to the GTI. I believe that I can probably export energy to the gird after sundown by doing this, running on waste oil. The most electrically expensive part of my day is the evening while cooking food and watching TV, so running my CS on waste oil costs next to nothing and exporting the excess cuts my energy bill and carbon footprint.
Bob
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Taking a break from the pneumatic string trimmer while the compressor catches up. Rain is rare and nice here, but damn, it makes grass and weeds grow with abandon. I made a Gast 1-AM air motor string trimmer that I can use.
I think Glort's right on using an induction motor as grid backfeed. It's the simplest and most efficient. But if you already have the ST-5 and GTI, making a bit of DC is a good plan too. Big chokes or inductors also go by other names, such as "line reactors" or "reactor" if you are looking for surplus parts as I always do. Just look at the milli-henry (MH) and amps rating. You'd like 5MH or more, and amps at greater than or equal to your max ouput. For the GTI, check out the maximum DC input voltage, and the suggested range of voltages. You must keep your DC peak below that max, with some margin. If you do that, it may work oddly but is not likely to do any harm to the GTI, regardless of how much ripple you have on your DC.
The GTI obviously things you have connected it to a PV panel array. Some will periodically decrease and then increase the current draw to see where the optimum power production is. Then settle in at that level for a minute or so. When it does this maximum power point sweep, it's expecting to see a voltage drop and total power drop when it's pulling too much. By putting in some resistance (which could be in part via inductors) you will accomodate it.
Another solution would be to NOT use an AVR, using the harmonic windings only, letting voltage and frequency drop with the load of the MPP sweep. It will take some experimenting to find the simplest solution that will keep the GTI happy enough, without grossly overloading the Lister. A governor spring which allows more rpm sag on load might be just the trick.
Sorry you're having a bad one today, Glort.
I'm sure to be laid up tomorrow after my string trimmer extravaganza.
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You can buy a meter for measuring inductance. Usually the same meter will do capacitance measurement as well, since much of the circuitry is similar. Probably some very cheap ones from China these days.
If the newer GTI's all hunt fast for the max power point, that makes some sort of resistance inline necessary. It must see a drop in voltage immediately as it tries to draw more power.
It would be time consuming to work that out (to keep it from constantly torturing the generator) but I do think it's doable.
Pity there isn't an open source GTI that could be modified to do something more civilized.
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Some of the MPPT controllers designed to work with wind turbines (Morningstar and Midnight Classic) have settings where you can limit the hunting, or use a different power curve to get a stable harvest.
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Glort is absolutely right about my skill set. My experience with advanced electronics is very limited. I`m good with cabling and motor control, I`ve built hundreds of computers but that just involves plugging bits into a motherboard.
Designing and building a custom GTI is way beyond me. Judging by how unreliable some of them are it`s also beyond some of the manufacturers.
I could just run my home off the generators at night but switching from grid to generator power resets all electronics in the house. If you have ever tried resetting digital clocks and etc you will understand the problem.
I could partially rewire the house so that water heating, cooking and other high energy appliances run off my SOM but I worry that my wife would find it too complicated.
Bob
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Yep, the power factor of the GTI (capacitor inputs) would likely goof up some generator-regulators. Most AVRs are NOT RMS regulators, and will regulate AC true RMS voltage lower when faced by this type of load. (200V instead of 230) Bob's ST-5 on harmonic would likely do fine.
With a inductor (choke or reactor) above the critical value for filtering, there will be excellent power factor and no problem with voltage regulation by the generator head, regardless.
I hope we hear from Bob soon- getting overrun by wildfire is very dangerous.
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Thanks for the update!
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Hey Guys, still here and still OK, I have just seen another two fire engines go past my home, that makes nine in the last hour. Looks like the fire service are throwing everything they have at this fire. The problem they face is lack of water due to the ongoing drought and very dry bush.
If we can stay safe till Friday we should get some rain, the first in three months. Hoping that will help extinguish some of the fires. At the moment We are sandwiched between two fires if the wind blows from the west or east we could be in serious strife.
Pray for rain, not just for us but for all those NSW farmers doing it tough.
Bob
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Hey Glort, North easterly I can cope with, the fire to the west is much closer.
Rain in Australia is a strange beast, it`s all or nothing and very localized. I can get 100 mm in an hour while my neighbor gets next to nothing. I have seen the Nymboida river rise by more than 20 meters overnight when we do get proper rain. Always breaks my heart to see it run down hill and out to sea. We need to do a lot more to capture it for use in dry spells like this. A couple of good inland dams would provide us with water, hydro electric power and fishing. Got to be a win all round but the gubermint are too busy squabbling among themselves to make any decisions or useful investment. If you want to find the source of global warming it`s coming from all the hot air and BS produced by the politicians. I wonder what the emissions are from all the journalists, analysts and TV presenters that hang on their every word? What a useless bunch of overpaid assh*les they all are. I retract that statement, assh*les are useful when you have the sh1ts, politicians, analysts and he media are not! >:(
Well, while I was typing this I got a phone call from a friend of ours who is fighting the fires. She tells me that we are not out of the woods yet. It gives me hope for humanity and enormous pride in the Australian people when a forty five year old woman is voluntarily fighting fires in the dark to protect me and mine. God bless her and all the firefighters.
Bob
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52 years ago tomorrow I was on my honey moon near Shaver lake California at her cousins cabin. under the eves were 1 pint mason canning jars upside down glued to the underside of the roof. The bottom metal screw on cap had a shot gun shell punched through it, the shot removed. I asked later what? they were filled with Borate and or baking soda. The 99 year lease from the forest service was expiring and they told the owners no renewal and no fire support any more. later a land trade was made and a volenteer fire Dept formed. they would not cover homes with the bombs installed. with the plastic bottles available now they could work even better with reduced risk to fire fighters. I was told a house fire starts under the Eves in a clockwise swirl, the bombs go off and the structure has another chance all be it slim. Maybe south of the equator the swirl goes counter clockwise? We have smoke from Canada BC and Olympics and Cascades, but nothing close. Wishing you all the best
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Thanks Tiger, I`ll look into that idea. I have shot gun cartridges and mason jars, baking soda is cheap enough. I will run the plan by some of my fire fighter friends. I expect they will be horrified! :laugh:
Most house fires here start in the gutters. Burning embers fall on the roof igniting dry matter in the gutters, The fire then burns up into the roof space. A lot of Australian homes have sprinkler systems on the roof to fight this problem.
So far we have had lots of smoke and falling ash but no burning embers, lets hope the rain continues to fall and the wind keeps down.
Bob
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I'm still working on that last 10% of my inverter install. It's been really educational. ;)
It's fully functional when I'm not pulling it apart.
What I've been working on is minimizing higher frequency EMI on AC and 120VDC lines, plus limiting low frequency ripple on the 120VDC from the inverter load. With side orders of adding an AC circuit breaker, improving AC voltage regulation, and adding soft start resistor and time delay relay to the 230 to 115V step down transformer outside the shop.
High and low frequency problem solutions tend to conflict which is why many EE's think EMC is a black art. It's not, but it sure can be a challenge.
I'm revising the grounding of the PV/battery bank system to tie it into the HF grounding system. The interaction of that system with the inverter EMI/ripple seems to be a big contributor. Even a 6 gauge kludge makes a big difference. I'll have to extend the copper flashing and add some capacitors across the load and charge shunts to "stiffen up" the ground. Once I'm finished with the EMI and ripple issues, then the PV charge regulator control circuitry will have to be revised to improve stability. Under certain inverter load and sun-PV conditions I've seen a 6 Hz oscillation of less than 1 volt which was clearly PV charge regulator. I haven't seen it lately so hopefully it will disappear when everything else is up to snuff.
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The Magnum design EE I spoke to was very much aware of his product EMI issues and even knew where some minimal filtering would have the greatest benefit (a common mode choke on the PV input to the unit significantly improved the conducted emissions on the AC output). He is of course not allowed to add it. I don't think off grid inverters have to meet any emission standards. What standards there are are to insure that radio commerce is mostly unaffected at 30 meters from the equipment...there are no standards for human health at present beyond not cooking you like a hot dog.
I keep thinking that I'm almost finished...but I'm determined to make this as good as can be practically done. The PV regulation mods are going to take some time; I can't just stand there and tinker with the wireless breadboard daughterboard if I have to have the inverter running to test it. It will be a very slow process.
I just love not having to run the Listeroid 6/1 so much. I'm going to start looking for a 1.5 hp induction motor, 230VAC air compressor that can do 150 psi. Then the inverter on PV power can handle daily topping off of my big 500 gallon air tank. I'll add a processor to do available PV and load monitoring, and top off the 2200 gallon gravity feed well storage tank and air tanks as power is available.
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A real time spectrum analyzer (the data recording/FFT type) is the right tool for capturing peak EMI levels from low frequency events (diode noise). Alas, these run over $8K plus a few thousand for ancillary gear. I do have the old Spectrum Probes from Smith Designs.
The "meter" you found is a ''toy'' broad spectrum meter, which would not detect anything from my equipment. The specifications are a farce- they mention power but then don't give power units, instead millivolts but not in units with any meaning like mv/m2.
Cornet, GHz Solutions, and Acousticom all make fairly decent, semi-calibrated broadband meters. I have an old Aaronia and a Cornet broadband meter, but they are not sensitive enough or shielded properly for conducted EMI measurment; they would only see the highest ambient radio/microwave level across their entire range of frequencies. They are useful tools, but not for this job.
For diode type noise (pulsed broad spectrum at ELF rate) the well chosen AM radio is actually the far more sensitive tool.
I did get a little work done yesterday. All is well, i found the Franklin well pump QD controller diode (Triac actually) noise is fairly well controlled with a single common mode choke. I'm considering some wiring changes for light filtering of power for the use of the well pump and future air compressor motor, with more substantial filtering of the AC distributed to the shop, since that shares the conduit with my 120 VDC line.
I've got to address the needed changes to my PV charge controller now; there is still some interaction and minor oscillation at high PV/low inverter load. The inverter load (3 mv of ripple for the well pump) is also affecting the float state circuitry- it gets kicked out to bulk charge when the inverter is running and it should stay in float.
This afternoon I should get the copper flashing to extend the HF ground over to the battery bank earth ground connection.
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I'm pretty much done now on the inverter project. I did just edit a short video that shows the installation in my battery bank shed. Some minor EMI work left- I need to replace the Siemans time delay relay controller for my 240 to 115 step down transformer as it's a noisy bastard, and I have to add a box for a small common mode choke filter for the Franklin QD pump control box, which is another minor EMI source.
https://youtu.be/U36qiYWODBk
I have more detailed videos on the design but won't put you to sleep with those.