Author Topic: More panels!  (Read 29756 times)

broncodriver99

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Re: More panels!
« Reply #105 on: July 19, 2018, 09:38:21 PM »
My concerns about window AC units converted to propane are- can they be used on fuel grade propane, and how do I insure the right type and amount of oil...and concerns about purging the original oil. I have 10 gallons of white mineral oil so of course that is an appealing lubricant.

I don't know that there is anything to be gained from converting window AC's to propane. They have to meet pretty strict energy requirements now so any modifications made would likely be detrimental to their efficiency and performance. I would run them as is and if one fails and you are inclined to experiment with it then so be it but you will likely never get it to produce the same cooling for the same amount of energy by changing the refrigerant and taking it out of design. Not to mention longevity.

About the best thing going these days is inverter driven mini-split systems. The efficiency they are getting out of them has gone through the roof in the last few years. Typical now is ~30 SEER which use ~40% less energy than a higher end EnergyStar window banger. They also perform very well in hot arid environments. Mitsubishi just came out with the smallest one on the market @6000 BTU which sounds about right up your alley, it has the ability to modulate down to about 1700 BTU/hr or overdrive up to about 9000 btu/hr when needed. There is also a company that makes one that can use solar PV directly into the units inverter to offset some of the load required on the AC(power) side of things. I will see if I can find their info for you.

The big question is how well they will run on an inverter and whether they will introduce any unwanted EMI to your situation. They do make some that can be ducted and you could likely then counteract any EMI if it is an issue.
« Last Edit: July 19, 2018, 09:47:14 PM by broncodriver99 »

BruceM

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Re: More panels!
« Reply #106 on: July 20, 2018, 12:34:05 AM »
The only point of changing refrigerant is that I have to modify the plumbing to add a stainless flat plate exchanger to cool the water so would have to evacuate and recharge. Propane is essentially free.  But I can keep it the same. Do you see a problem with using a stainless flat plate collector as the water cooler/evaporator?  I was thinking of some 1/4 tubing inside my gas hot water heater (used as a low BTU boiler) as an alternative. 

I agree split systems are a good choice, but fan motors in the house are a bust for me.  I can look into split system compressors, and see if there are any small enough.  The existing in floor system provides a way to extract the heat from the slab without and noise or motor EMFs and winding/bearing odors.  I'm not well at all, I didn't do a 120VDC powered, paintless and fanless interior home for sport, it's so I can function well enough to live independently.  I don't last long in normal homes.

I just finished fixing my inverter h-bridge with the 2 popped mosfets and one fried IC. Back in working order and tested out fine.

I decided to go for the PCB modification to solve my remote inverter on/off design goof.  I modified them both with 8 cuts and jumps each to reverse the polarity of the low side switches. Now with the microcontroller off, the H-bridge can be left powered, still drawing only 5ma of 12v and no extra solid state HV DC switching is required for my remote on/off control. The low side switches are both on, so the "resting state" is now with transformers shorted, and this keeps the floating high side powered (and off). (The design of powering the high side via capacitor, charged only when the output is being pulled low by the low side is commonly known as the bootstrap capacitor method.) When operating the inverter draws about 50 ma total of 12V, but when operating it is powered by a low voltage winding off one of the transformers.

Next up I have carefully modify the 19 step data table for the inverter gate control bits. I've got to invert just the low side bits.  It won't be pretty if I screw up, there is no built in hardware protection to prevent high/low dead shorts.  I didn't want to add the additional logic ICs and instead check the outputs via logic analyzer after every software change, no matter how trivial.






BruceM

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Re: More panels!
« Reply #107 on: July 20, 2018, 12:56:32 AM »
I just looked at some split system condenser units-  there are some small ones that fit my power budget, and would be perfect for my water chilling approach if only I can sort out the water chiller part.  Thanks BroncoDriver!

Looked again.  Alas, they are using "inverter" drives for variable speed operation, so I won't be using these. They are an EMI bomb.  I need something with a regular single phase motor, no frills.

« Last Edit: July 20, 2018, 01:20:25 AM by BruceM »

broncodriver99

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Re: More panels!
« Reply #108 on: July 20, 2018, 02:48:43 AM »
Bruce I didn't put two and two together that you were modifying the window units to be the water chiller you mentioned. I must have missed it somewhere, it makes more sense now. I see no reason a stainless brazed plate HX wouldn't work just fine. They make plenty that are refrigerant rated. I will look through some of my tech books and see if there is a compatibility issue with POE oil, the oil likely in a window unit compressor, and propane. I have never seen them recommended for use together but it doesn't mean they aren't miscible.

As far as the mini-splits I thought the inverters may be a problem. There are a couple of companies starting to make small chillers with them but I think 18,000 Btu is as small as they go.

As an aside, just to give you more to think about, 24VDC variable speed compressors are available pretty cheaply these days. Being an electronics guy you could likely come up with a control system for one, the simplest ones just vary the voltage. Being as your load will be pretty constant and intermittent use I think you are on the right track with a modified window banger chiller though. Cheap and simple. Any idea what kind of capacity you are looking for?
« Last Edit: July 20, 2018, 02:54:35 AM by broncodriver99 »

broncodriver99

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Re: More panels!
« Reply #109 on: July 20, 2018, 03:04:20 AM »
I just looked at compatibility sheets on R-290(propane) and R-600(isobutane) and both can be used with POE oil. The only note is that it may cause increased viscosity in the oil. So, you don't have to do an oil change unless you just want to. Just make sure you don't leave the system open as moisture contaminates POE very quickly.

BruceM

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Re: More panels!
« Reply #110 on: July 20, 2018, 03:32:49 AM »
I need 10-12K BTU's cooling capacity, power budget is about 1200 watts running including the condenser fan. 
I'd love to do ground source but can't justify it for such intermittent use. 

It does begin to look like hacking a window unit is my best bet.  I liked the split system condenser approach because of the nice already built outside enclosure.  Pity they've all gone to variable speed inverter drives.  Grrr. 

The Danfoss 24V compressors are not something I'd want to use.  Again, because they are doing hard and fast switching for brushless DC motor control with no concern for conducted EMI.  Plus I don't have 24V anyway.  The beauty of induction motors is no conducted EMI.  You still have low frequency ELF magnetic fields, but distance solves that. 

I seem to be dropping words in my sentences today. Too much soldering and live circuit checkout on the inverter.  I'm tired and scatter brained.



« Last Edit: July 20, 2018, 03:42:48 AM by BruceM »

BruceM

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Re: More panels!
« Reply #111 on: July 22, 2018, 02:14:53 AM »
After another 3 blown mosfets, and a lot of bench work over the last 2 days, I THINK I finally have my inverter remote on/off issue figured out.  Previously, I manually switch on the 120VDC supply in front of a two stage, massive LC filter.  The result is the h-bridges see a slowly rising input voltage.  Ditto on shut down.  It worked well and could even startup with load connected without a problem.

Then I tried to add a feature for remote on/off, using the existing H-bridges as the solid state switch, since they only take 5ma of 12V when idle. The processor gets powered off to save power.  When I start the inverter  via powering up the processor, it is starting with full voltage, and always on the positive going half wave.  On shut down, it detects the shut down request after the positive going half wave and stops.  This leaves residual magnetism in the 1000 watt toroidal transformer core, so that on the next start, the current surge is great enough to trip the 15 amp breaker per H-bridge ...which causes an input spike (my very slow switched design is sensitive to that) which pops those mosfets.

Two days of work to figure that one out, and a whole lot of test setups.  I was just SURE the software guy screwed up...but exhaustive testing via single shot logic analyzer captures vindicated software.  Removing the transformers and driving light bulbs, the processor turn on/off works flawlessly.

Now I have to think about just sticking with the slowly ramping up/down of the voltage via a solid state relay before the big dual L-C power filter, changing my on/off remote control board significantly. Plan B:  add no new hardware by adding a bunch of tricky software to do soft "starting" of the transformer by a special ramp up of alternating polarity pulse widths.  Damn hardware guys always expect software to solve everything.  ;)

I'll have to sleep on it to decide which way to go. 


mikenash

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Re: More panels!
« Reply #112 on: July 22, 2018, 04:45:17 AM »
Good on you Bruce

When I read this, I feel like our ex-Jaffa friend who would rather discuss erectile disfunction while standing naked infront of an audience of nuns than attempt electronic work . . .

I'm glad somebody knows how to do that stuff . . .

BruceM

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Re: More panels!
« Reply #113 on: July 22, 2018, 06:12:52 AM »
The nuns and erectile dysfunction line was hilarious.  Cracked me up.

I've been forced to learn power electronics since moving off grid but it was never my field or in my experience.  Necessity being the mother of invention I have proceeded to lurch my way through with many missteps.  Highly educational though frustrating at times.  Rough spots or outright disasters are perhaps the biggest opportunities to dig deep and learn. I really enjoy learning new things, even though now the "evaporation" rate is alarming.





BruceM

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Re: More panels!
« Reply #114 on: July 24, 2018, 12:46:07 AM »
More fiddling about and some research and I solved my problem with some new "soft start always positive" and "always negative" shut down software.

It seems large toroidal transformers with high efficiency grain oriented steel laminate cores are notorious for whopping big start surge currents; so bad they typically resort to things like a current limiting power resistor with a time delayed relay to bypass it after startup. One company even sells an electronic soft starter.  For my testing I stripped down to driving a single transformer/h-bridge with a small fast blow inline fuse to protect my H-bridge circuitry.  The Antec 1000W tranformers I switched to when changing up to 230VAC would pop my 15A per H-Bridge breaker.   The surplus Toroids International 1100 watt transformers I used during all my early testing at 120VAC output (with both secondaries configured at 90V, so 180V peak) did NOT blow even a 1 amp fuse even without any soft start pulses. So the problem was clearly the start surge current of the Antec transformers.

That encouraged me to try fiddling with my own soft start routine.  After a pile of fried fuses,  I found that starting at 50usec wide 140V pulses, positive then negative, and incrementing by 50 usecs each cycle until pulse width of 3000 usecs (3 milliseconds) with a fixed 4 msecs between did the trick.  After that it starts the normal sine generation.  Now I can start the Antec transformers with the full 140VDC, even on 1 amp fuses, though they do blow after 4 starts in rapid succession. The soft start is about 1.5 seconds and makes funny winding up sound. The soft start pulsing is done so that the transformers don't add, it's only one or the other.  The inverter AC output is switched into my 230 VAC line from the generator with a 230V coil relay so it's won't attach itself to the load (and disconnect the generator) until after the soft start is complete and full voltage is available. If a motor load is left turned on, it won't see the oddball, low voltage soft start.

My next step is to modify the secondary transformer windings, again, to get my peak voltages with 140VDC input down a bit.  I overshot the last time exactly by factor of two... I goofed on the math.

I'm very pleased I was able to solve my remote start problem without adding a bunch of hardware, and I'm glad that what I've learned about large toroidal transformers answered a lot of mysterious problems I had during the switch over to 230VAC.  When it's all my own software and hardware, I tend to suspect that first...



BruceM

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Re: More panels!
« Reply #115 on: July 24, 2018, 04:03:38 PM »
Glort, please remind me, is your cloud effect overvoltage on the DC (panel) side of the inverter, and exceeding the max allowable input voltage, thus causing an inverter shut down?  If so, what's the max allowed voltage and what's your panel series configuration? 

If it's on the DC side, one (or more) panel in each series string could simply be shorted via DC SSR, dropping voltage by about 24-30 volts.  Mager brand DC SSRs from China are pretty cheap and I have a couple of their 40 amp - 230V ones I could test for you.  A simple peak voltage limiting circuit could do it automatically.


EdDee

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Re: More panels!
« Reply #116 on: July 25, 2018, 09:03:59 AM »
Hey Glort,

An insult and a compliment all in one.....

You have great taste and judgment in your current missus..... Pity she has the opposite in men!!

But seriously though... Wish her well and a speedy return to home ground...

The washing pile must be over 6ft by now!

Cheers
Ed
12/1 750RPM/9HP Roid 5kVA- WMO Disposal/Electricity & Hot Water Gen
12/1 650RPM/8HP Roid 4.5kVa - Demon Dino
Chinese Yanmar - Silent Runner with AutoStart
Classic Komatsu 1963 Dozer/Fergusson 35 Gold Belly ...
Bikes,Cars,Gunsmithing & Paintball...Oh yes, a 5Ha open air Workshop to play in!

ajaffa1

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Re: More panels!
« Reply #117 on: July 25, 2018, 09:27:38 AM »
Hey guys, before I had my accident and subsequent heart attack, my missus went to Sydney to care for her ailing parents. She was away almost six months and my electric bill dropped to almost nothing. That said I spent a small fortune on take away meals.

I finally got to the root of the problem when she returned and fired up the tumble dryer. Why anyone would use a tumble dryer on a forty degree centigrade day was a total mystery to me, she tells me it activates the fabric conditioner and removes the fluff, dog hair and etc. Sounds like a crock of sh1t to me.

Glort, hope your wife is continuing to make a good recovery.

Bob


LowGear

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Re: More panels!
« Reply #118 on: July 25, 2018, 01:56:52 PM »
Quote
Sounds like a crock of sh1t to me.

I'm sorry ajaffa1 but your missus is correct about the magic of dryers.  Well, except the fabric conditioner which falls outside my zone of understanding as well.  At 40 C it should take about 15 minutes to dry an elephant. 

The big question is what were you using for clean clothes?
NPR Tipper/Dump Truck
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Witte BD Generator
SunnyBoy 6000 + SolarWorld 245

BruceM

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Re: More panels!
« Reply #119 on: July 25, 2018, 03:56:53 PM »
Computer/projector and lighting (incandescent) are my only electrical load, besides daytime electric cooking. 
I only switch to gas cooking on dark days or nights because I'm in the habit.  I never feel like I'm short on power.
The new inverter will find sunny day uses, but won't be running at night.

I remember now about your wire size problem.  You could still use the panel shorting SSR's to limit PV input if adding loads gets to be a problem.  The Mager brand Chinese one's are about $8 each. You could test this yourself by putting in the Tee connectors for a panel and manually short it on a day when you're getting overvoltage trip outs.  The same voltage relay approach could operate the panel shorting.