How to / DIY > Everything else
Simple Power limiting/ Stepping.
guest22972:
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:
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.
BruceM:
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.
broncodriver99:
--- Quote from: glort on January 14, 2019, 10:59:57 AM ---In the meantime and with 40o+ ( for the people in the US using that superior system, 40oF is...... Bloody hot)
--- End quote ---
Fixed it for you. ;) It is 40 degrees here too, and 6" of snow on the ground. That's 153 mm.
BruceM:
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.
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