Small A/C problems with off-grid solar

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  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar
    bmet wrote: »
    Switching power supplies are robust. Their rectification produces very good, flat DC.

    Yeah, I think some are so robust they would work from 30 to 500+ Hz..
    And they would work, if you applied the right DC voltage. Zero Hz.. :p
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Small A/C problems with off-grid solar

    The issue with bypassing the bridged rectifier may be feedback. Some switching supplies use an optical sensor as both feedback and isolation safety.
    XRinger wrote: »
    Yeah, I think some are so robust they would work from 30 to 500+ Hz..
    And they would work, if you applied the right DC voltage. Zero Hz.. :p
  • rplarryrplarry Solar Expert Posts: 203 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Sueco
    Are you still trying to use your A/C unit? If so, and if you ever do get it running you will find that it uses so much power from your battery bank that you probably will not have any charge left to run your night time loads. I used to have a similar problem. I needed A/C during the night so I could sleep. I found that a Honda 2000 ran my 6000 btu room A/C with just a little power left over, which I used to charge my battery bank. My Honda ran for 10 hours a night and used a little more than 2 gallons, I had an external fuel tank. So in your case if it runs anything like mine, you should be able to run yours for 4 or 5 hours during the day on the one gallon that the generator holds. A much cheaper solution than trying to run an A/C on a solar system.
    Just a thought.
    Larry
  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar
    bmet wrote: »
    The issue with bypassing the bridged rectifier may be feedback. Some switching supplies use an optical sensor as both feedback and isolation safety.

    Why would you have to bypass the diodes? Diodes won't block DC.. :p
  • BB.BB. Super Moderators, Administrators Posts: 32,013 admin
    Re: Small A/C problems with off-grid solar

    Many PFC computer supply designs will work on 100-264 VDC just fine...

    Many Non-PFC computer supplies would have to run on high voltage DC to charge the input caps (115/230 VAC would be 300-360 VDC or so).

    Obviously, none of these should be attempted without knowledge of the specific power supply design.

    -Bil
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ssunssun Registered Users Posts: 5
    Re: Small A/C problems with off-grid solar

    New to the forum. I recently tested a 12V Cobra 1000W inverter using my truck battery (good Energizer) to see if it could start my refrigerator. (I'm reading here that most do not do that and the MSW inverter is not good for motors, so I may need to rethink my plan.) However, what I found was that the inverter was faulting on compressor motor start only because the battery voltage was dipping too much. The inverter handled it fine when I paralleled a 20A charger with the battery and waited until it was charged above 14.5V. Whether it was more due to initial motor current draw or inverter inefficiency I cannot say, but ultimately more battery capacity solved the problem.

    I would definitely be going to 24V and am intrigued with the kicker-capacitor idea. But before I think about that, if I go ahead with the plan for solar powered refrigeration (I have my reasons to still consider it), does y'all think I'm doing damage to my refrigerator motor with MSW? cuz that woodent be worth it.

    Thanks,

    ~Dan

    "The dollar isn't worth the digital paper it's not printed on." -Gerald Celente
  • BB.BB. Super Moderators, Administrators Posts: 32,013 admin
    Re: Small A/C problems with off-grid solar

    Another issue may have been is the cable/connections from the battery to the inverter--Clip on leads just do not work at high current.

    For example, a 1,000 watt inverter may supply upwards of 2,000 watt surge--All of that energy has to come from the battery directly (there is very little energy storage on the inverter itself). Assuming the battery drops to 11.5 volts plus 1 volt wiring drop and 85% efficient inverter, the maximum surge current for a 12 volt bank 2kW surge would be:
    • 2,000 watts * 1/10.5 volts * 1/0.85 = 224 amps
    That requires a lot of copper and very good/short connections to operate at 12 volts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    How badly did the compressor motor "rattle" when it started?
    I ran my 'frige off a MSW 3kW 12 Volt Xantrex at first. You could hear it struggle to start. That is not good for the motor. Switched to the Outback sine wave inverter; motor starts as quiet as can be.
    That's (some of) the difference between a $500 MSW inverter and a $2,000 PSW inverter.
  • ssunssun Registered Users Posts: 5
    Re: Small A/C problems with off-grid solar

    did not rattle at all.
  • PhotowhitPhotowhit Solar Expert Posts: 5,656 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Well I don't know if the original poster is still out there, I too, live in Missery (Misssouri) and run a window AC off of a small battery bank. The AC is a 5300btu 10.7 seer(?). I still have a tiny battery bank of 4 6volt golf cart batteries set up in a 24 volt bank.

    I use a 1800 watt prosine inverter(true sine wave) with out any problems. In the past I have used a 1400 watt, semi-pure sine wave(more steps) inverter with it that might be cost effective for you, drop me a PM and I'll discuss the Ebayer I purchased through.

    I moved to an idea location with the intent of running an AC on solar, I figured my need was for 500 watts of array as minimal just to run the fridge and rest of household, and 1200 watts as minimal for running household and AC for 3-4 hours a night. Also note I build the tiny cabin(10x16) just for AC, built in the shade with 6" thick well insulated walls, floor and ceiling. So my duty cycle is fairly low ( the amount of time the AC actually runs) So unless you have an additional power source I think you are seriously short on Array.

    I have use this setup to survive the last 4 summers, I have increased my array size with the intent of purchasing a forklift battery this summer and running the AC round the clock, haven't gotten there yet, the 4 - 6 volt Golf Cart batteries get pushed to 50% capacity often in the summer, they are hanging in there though showing their age going into their 5th summer of abuse and 6th summer of life.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar
    ssun wrote: »
    did not rattle at all.

    That's a good sign.

    If you've got an AC clamp meter you might check the current and see if it's within specs for the 'frige.
    Otherwise, heed Bill's advice regarding wire sizes and connections and it should be good if not exercised too much (kids holding the door open in August while slowly deciding what to drink).
  • ssunssun Registered Users Posts: 5
    Re: Small A/C problems with off-grid solar

    Thanks, Cariboocoot. I'm starting to think that since I've seen so many comments about it that I should shell out the extra moola for a PSW. I'm guessing that just because I hear no noise, that doesn't mean the fridge isn't getting treated too harshly. The price tag of the system is already over my head so I might as well resign myself to $500 more. Thanks for the input.

    Is there any difference between "pure" sine wave and "true" sine wave? I'm seeing both advertised.

    ~Dan
    0 panels, 0 controller, 0 batteries, 1 refrigerator.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Small A/C problems with off-grid solar

    both pretty much mean the same even though neither is an accurate description of the waveform that is present. the waveforms really aren't perfect, but those references are used to distinguish this good waveform that is closer to a pure sine wave with less than a 5% total harmonic distortion from those that have up to about 28% thd for a square waveform. less than 5% thd is what utility companies are required to have and shows how far off of a sine wave it is.
    i know this is more than you wanted to know, but usually those descriptions are of the 5% thd or less waveforms. be careful as some use deceptive wording, but an example escapes me at present and that usually occurs with small computer ups.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Small A/C problems with off-grid solar
    XRinger wrote: »
    Why would you have to bypass the diodes? Diodes won't block DC.. :p
    Is that a joke? Sure they will. One direction only, of course.
  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar

    Yes, I was joking, but maybe for those that didn't get it,
    I should have specified "Unless it's a half wave rectifier"..

    Since a bridge rectifier will pass a DC source.

    018_03.gif
    http://iccircuit.blogspot.com/2010/07/full-wave-bridge-rectifier.html

    Meaning that some Switching power supplies can be plugged right into a DC outlet.. (Given the correct DC voltage) :p
  • ssunssun Registered Users Posts: 5
    Re: Small A/C problems with off-grid solar

    thanks niel. no, more information is better. 'preciate it.

    ~dan
    0 panels, 0 controller, 0 batteries, 1 refrigerator
    hoping for 12 panels, MidNite Classic 150, 8-12 Trojan-105's
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Small A/C problems with off-grid solar
    XRinger wrote: »
    Why would you have to bypass the diodes? Diodes won't block DC.. :p

    I did not say I wanted to bypass diodes. I was responding to another poster. At any rate, some switching power supplies employ optical isolation as a required design spec. In medical equipment this is especially true. Every time electrodes get hooked up to a human for EEG, ECGs, or whatever electrical monitoring device that is being used, they are optically isolated from the wall outlet power. Bypassing the bridge would shut the device down automatically.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Small A/C problems with off-grid solar

    To the OP,

    What size wire is between the battery bank and inverter, and how long is it?
  • CVN-71CVN-71 Solar Expert Posts: 54 ✭✭
    Re: Small A/C problems with off-grid solar

    Last week during the "heat wave", we lost power here at the house, on two days. I used my off grid 24v battery bank to run the a/c, and two refers, plus aquarium. Fortunately it was during peak sun and the batteries did not get depleted much, at 7pm I was still at 90%. My system didn't have problems running the 600w a/c on low and 2 fridges. I'm assuming my 4000w inverter was powerful enough to do the job. Boy was i glad I had this set up. I simply can't run a generator and then go to work leaving it unattended.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Small A/C problems with off-grid solar
    CVN-71 wrote: »
    Last week during the "heat wave", we lost power here at the house, on two days. I used my off grid 24v battery bank to run the a/c, and two refers, plus aquarium. Boy was i glad I had this set up. I simply can't run a generator and then go to work leaving it unattended.

    Nice system you have there CVN. Not kidding!
  • BB.BB. Super Moderators, Administrators Posts: 32,013 admin
    Re: Small A/C problems with off-grid solar

    Always keep a close watch on your battery bank connections... That is a lot of current and you don't want a dirty connection to over heat or stress the other 1/2 of your battery bank from the heavy current use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CVN-71CVN-71 Solar Expert Posts: 54 ✭✭
    Re: Small A/C problems with off-grid solar

    Thanks Bill, good point!
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