Author Topic: Simple Power limiting/ Stepping.  (Read 740 times)

glort

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Simple Power limiting/ Stepping.
« on: January 11, 2019, 09:12:52 AM »

As I have mentioned before, my house is on 3 phase power. I have 2 Spinny meters which spin very nicely in a backwards direction when fed with solar power and one electronic meter which registers any current flow as a charge.

The only 3 Phase thing I have is the ducted AC so I am able to run it for free on 2 phases and pay for the 3rd.
Sounds OK but the recent hot weather and the need to have the thing on constantly has meant that one leg of power has been costing upwards of $6 a day just for the AC.  May not sound much but we are fast heading to $400 just for the AC this quarter.

I have been trying to appreciate the low cost power I have with teh other 2 phases but having an excess of power on both of them and having to cut down on the AC just because of one phase has got the better of me.
Spoke to my mate in the AC game yesterday and he " approved" my idea for feeding the 3rd phase with solar and said it should not cause any problems with the phase rotation or voltage sensing.  I pulled the cover off the thing today and started digging round the boards etc and should be no problem getting to what I want.

The grand plan is to stick another array of about 4KW on the roof with a 2 Kw inverter and feed that to the L1 Phase which is the electronically metered one. I can tap into the compressor Contactor and turn on a relay with that which I can then switch the inverter in and out with. This won't be perfect, will only work during the day which will be better for cooling than heating but anything will be a help. There will also be a delay between the compressor cutting in and the inverter booting up but again, better than nothing and on really hot or cold days the thing will be barely switching out anyway.

I ran the AC today and took some measurements with my clamp meter.  19XX Watt on that phase which is the most loaded one with the compressor running, about 800 with the fan only running on the evaporator which runs all the time on cooling even when the compressor shuts off. The fan of course runs on the L1 phase which is exactly the one I don't want it to run on and can't be changed.
I am OK with having an array strictly for the AC only but I also intend to run a DPDT relay with the inverter output so when the AC is not running, the relay will be feeding power to one of the other phases. This will be a help in winter especially when power generation is short.

The thing I'd like to do to make the most of this is be able to limit the output power for the Evap fan as well.  Don't care about " wasted" output, I would like to be able to reduce the power when the fan was running then have another relay bypass what ever limiting device I put in place to give full power when the compressor kicks in. This would have the double advantage of keeping the inverter on song as well which would mean a big power saving in both powering the blower and the inverter being already booted up to supply the main power for the compressor. 

Question is, what is the best practical way to limit the current when only the blower is running?
Thoughts run to using a 500W halogen flood light tube ( or 2 as I'm not sure they will pass 500W when used like this?) or maybe a PWM controller which is then bypassed for full power with another relay.
 
That's probably my preferred option and would allow a lot of fine tuning on the PWM but wondering if the educated people here have a better idea?

It would be nice to be able to limit the solar feed in, I could then direct the unused array to another inverter BUT, solar generation is highly variable and what is producing 1kw in summer sure as heck won't be in winter nor on a cloudy day. Regulating DC is a pain as I have not seen any PWM's capeable of handling the voltage and current anyway.
As such the control of the AC side seems much simpler and easier.

My mate was concerned about Voltage drop on the solar phase until I explained that the mains would be Connected at all times and the feed in would be to supplement that just like it is now on the other phases.  I am also hoping that the PWM won't cause any problems as I know it makes some of my inverters hum a bit when on the line but I am more concerned about the board on the AC.  Not sure if a cap in circuit would help with that?

Anyway, that's the Bright idea, any Ideas, suggestions or heads up on anything I may have over looked or forgotten?


BruceM

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Re: Simple Power limiting/ Stepping.
« Reply #1 on: January 11, 2019, 03:49:30 PM »
Sensing the compressor relay on to connect the GTI to the digital metered phase seems straight forward...and down regulating the backfeed via a fixed load for fan only should suffice. 

You have to design for the max array output with some headroom, and then live with whatever you get which is less.  Pity there is no dynamically controlled DC PWM module.


Fan only load relay (NO) would be coil connected to the fan power, with a second relay in series (NC) with coil powered by the compressor power.




glort

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Re: Simple Power limiting/ Stepping.
« Reply #2 on: January 11, 2019, 05:19:28 PM »

  Pity there is no dynamically controlled DC PWM module.


Do you know of an AC type that could be set to a fixed voltage or current and maintain that  regardless of input?

Upon further head scratching and splinter removal from my fingers, I saw a couple of flaws in my thinking.
The switching part is easy, the control part is not.
I doubt a PWM would work.  Would have to allow the inverter to sync up and once it did the inverter would ramp up the voltage trying to get it through till it tripped out on high Voltage.  I could run a dump load but that would have to be switched from the DC side or else at night I'd be running the AC AND the dump load.
I May be able to just use a simple Plug pack type transformer from the solar input as they normally rectify  the AC to DC anyway so some type should work then I could use that to drive a SSR to switch in the dummy load.
Getting messy.

Think I have the solution though.
I'll simply Move the L1 phase to one of the spinny meters that I can backfeed.  That is the main phase for the AC with the highest loading so if I swap phases and put the Digital meter on another phase and the L1 on a spinny meter, the phase on the digital meter will only come on with the compressor.  I can get a 1.5Kw inverter and switch that straight in and out.
I'll put the feed from the inverter to a DPDT so when the AC is off, it goes to another phase and syncs with that. When the  Compressor of the AC comes on, the relay will switch, the inverter will drop out and re sync to that phase and supply the compressor till it drops out again.

While I will loose about a minute before the inverter kicks in when the compressor switches, the L2 and 3 have lower draw and only power the compressor, not the condenser fans and the evaporator blower.  The L1 has higher draw and much longer run time as well especially in cooling.  I would guess this will cut consumption down to around 50% or less.

I think this will be the most practical way of tackling the problem. The only other way would be to use 2x 1KW inverters which are not going to be easy to find.  I can't think of any practical way to limit a 2 Kw inverter down.  It will have to be well Overclocked on panels to allow for winter fall off and I could never regulate the DC input effectively, power or cost wise.

If there was a current limiting relay like the Voltage monitoring relays I have it would be fine. Couldn't be that hard to design for a company in the electronics field or expensive for the Chinese to Knock off.  :laugh:

Hopefully this will be mainly a summer thing. I want to get started on the oil burning heater for winter. Spose I better drag out the oil oil pump and collection drum and start getting in some fuel while the getting is good. Usually plenty around in summer, Bugger all in winter when you need it like everything else.

Hard to imagine that in one standard 50? Gallon/ 200L Drum there is 2000Kwh worth of energy.  My main solar array only made 3500Kwh of power all last year. Just 2 Drums and I would have beat that less the greatly reduced efficiency. I'll get in an IBC of oil and should be OK.

Been thinking of spark Control for a wood fire Pizza oven. Would have to be careful of hot sparks blowing round here.  Now thinking if I make it an oil fired oven, I should have all the benefits and none of the dangers. I don't think it is the fuel source that matters as much as the Thermal mass and stored heat.

BruceM

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Re: Simple Power limiting/ Stepping.
« Reply #3 on: January 11, 2019, 07:47:11 PM »
Regulating with only the simplest of controls is tough, so moving the fan seems reasonable if it makes things simpler.

Current sensing relays (AC current) are readily available, there are plenty on Ebay but I didn't see any China made knockoffs.  Many have an adjustable trip current.

Soon I expect many of the power management features you want in an inverter will be incorporated into come commercial inverter, but I expect you will be able to do nearly as much by other means.

Besides shunt-dump loading the AC, loading the PV supply side is also doable via DC solid state relays and the same sort of resistive dump loads, assuming PV voltage compatibility.






glort

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Re: Simple Power limiting/ Stepping.
« Reply #4 on: January 14, 2019, 10:59:57 AM »

Saw my mate on the weekend and asked him about moving the phases on the meters. He's a bit concerned over having things in order and said the work he had been doing lately had been closely inspected for things to all run 1,2,3 right though. He's going to talk to some other guys he knows to see what they think and if there would be any potential repercussions if things were moved and discovered in time.

I told Just move them, can always play Dumb and deny any knowledge.

In the meantime and with  40o+ ( for the people in the US using that antiquated system, 40oF is...... Bloody hot) days predicted for the rest of the week, I got out and set up my solar relay system.  Came out very neat actually.
Have DPDT relay powering up and switching off the compressor contactor.  That switches the output from the solar inverters back to the mains feed on the L1 line which is the one most power is pulled from and the one I can't backfeed. Yet.

Dropped the amps from the meter from around 12 to 4 which is a good saving.  Tried getting it lower but that's a bit tricky.
Getting the array output to match the demand isn't easy when you set the arrays up for full output. I tried mixing and matching the array outputs but couldn't do any better. 

I'm thinking tomorrow I might try using a PWM on a make up output to see if I can fine tune things a bit better. I know the solar outputs will vary and therefore so will the balance but I'd like to get it right at least part of the day and I can go out every hour or so and tweak it for good measure.

it's a bit tricky finding the sweet spot for this. I was looking at 3 Different meters today and none of them were giving me the same numbers.  It's also clear it's not hard to over shoot and feed more power back upping the amps to the meter which measures either way as a cost. I want to get the mains feed al low in amps as possible but annoying when you have to run from one meter to the other every time you make a change and they don't add up and you can't actually tell which way the current is now flowing.

Hopefully the PWM won't upset anything and I can stand there and dial it and watch the clamp meter do down.
Would love some Device that you could just dial in an output and that's what the thing delivered as long as it was supplied sufficient power.

I'll run the thing flat out all day to keep the house as cool as possible and reduce the need to cool at night.  Setting the Thermostat to it's lowest setting seems to stop the compressor running all the time which saves the boot up time on the inverters. The next thing will be to add another relay and 2 step the supply to run the Evap fan and the compressor and fans together.  That might only be 3 amps which does add up but a piddling amount to set up a whole array for.

I'm definitely getting old. The heat knocks me around Physically and mentally these days.
Even though I have got my Bikini body ready and it's High season, I'll be staying indoors  from about 10 am to ...... maybe midnight.  Wasn't that hot today and I left doing the lawn till 7, when it's real hot the night time temps are still uncomfortable.

Might put the mist sprayer on the Condenser  this week too.  The heat they are predicting is going to push the unit way off it's curve so  bit of Evaporative mist spraying will make a big difference.

broncodriver99

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Re: Simple Power limiting/ Stepping.
« Reply #5 on: January 14, 2019, 02:46:38 PM »
In the meantime and with  40o+ ( for the people in the US using that superior system, 40oF is...... Bloody hot)

Fixed it for you.  ;) It is 40 degrees here too, and 6" of snow on the ground. That's 153 mm.
« Last Edit: January 14, 2019, 02:54:00 PM by broncodriver99 »

BruceM

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Re: Simple Power limiting/ Stepping.
« Reply #6 on: January 14, 2019, 07:43:41 PM »
The F scale isn't bad- 0 to 100 for damn cold to damned hot.  Better resolution in the livable range. 

Your meters are likely cheap approximating types, not true RMS amps.  The PWM load will only make the errors worse.  All meters may be affected by the EMI injected by your inverter an other switching power supplies, etc.

If you get your total power use down too low, your pirate system may attract unwanted attention.   Good job on the digital meter phase,  compressor compensation.



 

   




ajaffa1

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Re: Simple Power limiting/ Stepping.
« Reply #7 on: January 14, 2019, 09:09:52 PM »
Need to increase the range a bit Bruce, 40 Centigrade is 104 Fahrenheit, 50 Centigrade is a nasty 122 Fahrenheit. Yes it does get that hot here sometimes. Expecting a nice 34 degrees today.

Bob

glort

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Re: Simple Power limiting/ Stepping.
« Reply #8 on: January 14, 2019, 11:13:14 PM »

Was 46C where I was the other week.  That's 114 F.  last year we had multiple -5C Days as well.

Not going to get to 46 This week here thankfully,

Friday 18 January

Summary
    Min 21
    Max 42
    Hot and mostly sunny.
    Chance of any rain: 20%

Sydney area

Very hot and mostly sunny. Winds north to northeasterly 15 to 20 km/h tending east to northeasterly during the afternoon.

My Local Forecast.

http://www.bom.gov.au/nsw/forecasts/camden.shtml

Now I have the power compensating the compressor, the next stage will be backfeeding another phase while the AC isn't on from the other side of the relay. I'll do some switching tests today, if I don't get cooked from the heat, with the inverters and their trip/ reset time. I'm pretty sure they have to do it in milliseconds when the power goes out but I'll put it to the test first to make sure  they are not going to try to connect to the other phase at the wrong frequency. Also have to see if the PWM will play nice with everything else.


I am aware of getting too greedy with the solar so I do make sure to have some Reasonable bill.  Generally leave enough usage where I can to give about a $300 Bill.  Winter was higher because I couldn't keep up and this one is getting away a bit on the AC phase so definitely won't be questioned. The average bill here has no real average as such.  People with pools and have kids (adults) with them can be paying $2k quarter and older couples whom are away traveling more than they are at home might pay as little as $300.

A realistic average would be around $1200 I'd say for a family but again If I think of the people in the street near me....
Couple with 4 Adult Kids one house, next door is 4 adults, next to that couple with 5 Kids, professional couple never home, old man on his own, another old couple, working couple no kids, my neighbour one side is retired couple often away but also often doing a lot of work in the shed welding running compressors etc and the one the other side Married working couple with adults kids turning up en masse at least once a month for a few days.

Only 3 of us have solar so all over the place.

There is a thing here now with our Privatized Fiasco of a system that has become user pays.
I was telling my mate on the weekend about someone I was talking to that had bought land about 10 years ago for their retirement. Now ready to build on the place, they have been told all the allocation for the street on teh transformer has been taken up and if they want to connect they will have to pay $40K for an upgrade.
I was saying to mate, surely that can't be right, he laughed and Pointed  to a bunch of large industrial AC units in his huge shed.

They are due to go into a hospital he looks after but first he is going to "Test " them at his place.
He has just finished Re wiring his property and is all set up for 120A per phase. They told him if he wants any more then the 63A coming to his property it will cost him $115,000 to upgrade the Transformer and wires that are probably 50+ years old and don't meet Current standards.
They told him there is only 40A available but they have to give him 63 ( same as my place) and that's all they would give him.

Next Door Neighbors both also want more power as one wants to bring his business to the property and that is the only hurdle and the other one wants to build a new dwelling but has run into the same problem.
They are organizing to basically blow the hell out the transformer and set the wires alight so a New transformer and wires have to be installed to current standards at the power co's expense.

Mate is going to hook up the AC units so He pulls his 63A per phase or close to it and the others are going to power up everything they have as well. Mate had 3 BIG Fan Blowers  sitting there he took out of a job and is going to hook them up in each neighbours place to add to the load.

I said Going to push your power bill a Bit he said not for long and certainly not for $115,000.
They are waiting till about march when the weather is milder and 2 other  neighbors on the same transformer are going to go on Holidays.  The 4th one has been let in on the plan as well and is happy as he has his own generator from way back he often uses for powering his big irrigation Pump. Mate is getting a big skid mount generator off a company he often works with on job and upgrades he does so they are all set for the week or so they expect the power to be out while they do the repairs and upgrades. 

Told him I want to come see the fire works when they do it.
mate reckons they will be obligated to do the whole road because they are at the end and everything else goes further down and they are not permitted to upgrade one part from the feeder without carrying through.  There are 2 More trannys further down the road so maybe all the other people will benefit as well.

The power co's hold all these people to randsom and won't provide the essential service they are obligated to and want to charge the end user for it when they are projecting $2.7 BILLION  dollar profits this year.
Maybe that figure is about to be a little down on what they thought.

Nothing illegal about using the amount of power you are wired up for.

I strongly suspect where I am is a bit on the edge as well. Normally high voltage on the lines on Mild days but when the heat comes and the AC obviously goes on for everyone, My voltage can be low even when I'm pumping solar power back in.
I don't want any more power, I just want the power to be closer to the standards it's supposed to be.


One day they will come and put a new meter in I won't be able to get around and I dread that day and how we will will go if we have to pay full tilt.

Sure I do use more than I could now but the thing is I don't always do that and when we have just been doing what we need and I read the meters and see what that works out at, that's when I get scared quite literally.

BruceM

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Re: Simple Power limiting/ Stepping.
« Reply #9 on: January 14, 2019, 11:51:57 PM »
Bob, I still say 0-100F is a fine and dandy range.  Anything over 100 is just too damned hot.  I admit when I lived in the Phoenix area I did acclimate and could cope with anything under 110F.  Over 110F, it was just too easy to get heat stroke when working outside.  But I was young and healthy then. 

I don't know anyone who has moved off grid that wasn't very glad they did, and wished they had done so much sooner. 

The typical power bills Glort lists are shocking to me, but I've been on an inflation shrunk fixed income for a long, long time.  I can't imagine why people would want to spend that much on power. 














glort

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Re: Simple Power limiting/ Stepping.
« Reply #10 on: January 15, 2019, 04:37:54 AM »

The typical power bills Glort lists are shocking to me,

They are to a lot of people here but they are generally suburbanites with gas and live much closer to the sea where the temperatures are much milder... and don't have pumped water or sewage digester tanks.

this isn't a cheap place to live. there are 3 homes in my street for sale atm, the CHEAPEST is $1.65M Prices here have gone down a little but below the falls the rest of Sydney has seen.

Just checked my AC setup and found no power was going back to the unit.  Traced it back to the 20A relay base had melted and lost contact. Haven't put more than 10A through it.  Running it at 8 A now and going to look for a larger unit/ better base.

Things like that really Tick me off. I bought larger than I knew I needed on purpose, double what I needed and it's still not up to scratch.

mike90045

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Re: Simple Power limiting/ Stepping.
« Reply #11 on: January 15, 2019, 04:39:19 AM »
Quote
Next Door Neighbors both also want more power as one wants to bring his business to the property and that is the only hurdle and the other one wants to build a new dwelling but has run into the same problem.
They are organizing to basically blow the hell out the transformer and set the wires alight so a New transformer and wires have to be installed to current standards at the power co's expense.

Be darn sure that your panels are not visible, or the Power Company may send you the bill because your illegal install blew up their wires !!






glort

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Re: Simple Power limiting/ Stepping.
« Reply #12 on: January 15, 2019, 08:57:25 AM »

Be darn sure that your panels are not visible, or the Power Company may send you the bill because your illegal install blew up their wires !!

Yeah, they are likely to try anything.  Can't be seen from the street but they use google earth for a lot of things now so hard to hide.

Went and Checked the replaced relay a couple of hours after installing it.  Chinese crap had packed it in already. Never had more than 8A running through it but looking for other bases I saw something that made me wonder if it were not actually a 5 A base but with typical Chinese tactic to slapping the biggest number on something regardless of actual rating.

Scrounging round I found a used base in my jun... treasures and put that in. Physically larger and said it was rated to 15A so hopefully does the Job. Think i'll buy a 25A contactor for good measure.

dax021

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Re: Simple Power limiting/ Stepping.
« Reply #13 on: January 15, 2019, 09:56:10 AM »
Ok, so at what temperature is c and F the same number?

mikenash

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Re: Simple Power limiting/ Stepping.
« Reply #14 on: January 15, 2019, 06:04:43 PM »
Must be somewhere around 10F/-10C?  or maybe 11 or 12?