Small A/C problems with off-grid solar

suecosueco Registered Users Posts: 22
I have a small (5000 BTU/580W) A/C that I'm trying to run during the heat of the day. I have 6 12V batteries, 3 125W panels, and a Cobra 1500W (3000W peak) 12V to 120 V inverter.

I can make coffee (900W), make bread (750W), make rice, etc. However, when I try to run the 580W A/C, the inverter gives an "overload protection" error.

Now, the A/C has that GFI (?) style plug, with the shielded cord, with the trip and reset at the plug-in. Is that causing the problem? It doesn't trip, but is it causing the inverter to trip?

Any ideas what I can do to correct what is causing the OLP so I can run my A/C?

As an FYI - I've added another solar panel (giving me 500W total), and purchased yet another inverter, to move my system to 24V. However, I'm not sure that any of this will fix the A/C problem.

This is surprising to me, because I would think that MOST people run small A/C's on their solar systems in the summer, and these new plugs are pretty standard, now - even my old ones have them.
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Comments

  • VicVic Solar Expert Posts: 3,113 ✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Am certain the the problem you are seeing is just as you said ... The power required to start the A/C compressor exceeds the capability of the inverter. Motors are hard to start, and require large surge capacity from inverters and batteries.

    If you had an Inverter generator, you should be able to start the A/C ... usually a 2000 watt genset is required (at least if it is a Honda EU 2000isa, anyway).

    Your move to a 24 V system and new inverter may help. Many inexpensive inverters have VERY OPTIMISTIC specs.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • suecosueco Registered Users Posts: 22
    Re: Small A/C problems with off-grid solar

    The inverter has a 3000W surge limit. Are you telling me that the small compressor motor exceeds 3000W???? Surely not. Also, there are 6 deep cycle batteries - any one of them should be able to start this motor....
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    Wrong on most counts.
    Most people do not run A/C on their off-grid systems because any form of refrigeration compressor is a bleedin' power hog with massive start-up surge.
    The "surge rating" on inverters, especially inexpensive ones, tends to be a figment of the imagination of the marketing department, not a number you can rely on for actual use.
    A 5000 BTU unit can easily overwhelm a 1500 Watt inverter. Especially an MSW inverter, which essentially has a 20% power shortage as far as any induction motor is concerned. Trying running that thing through a Kill-A-Watt meter and see what it really draws. It won't catch the start surge (probably in excess of 15 Amps) but it will give you some interesting insight into the fluctuating power draw of motors; they are far from steady-state devices.

    I'm sorry to say you seem to be yet another innocent victim of exaggerated advertising claims. Hopefully we can help you save at least your system if not your sanity. :p
  • suecosueco Registered Users Posts: 22
    Re: Small A/C problems with off-grid solar

    Already ran through my Kill-o-Watt - my good friend (even has a name "Kiwally"). You are right, it didn't catch the surge. And, yes, Kiwally already indicated that the manufacturer's specs did underestimate the actuals of running...

    and, I don't mind being wrong.... as long as I learn. In this case, a very important piece of information - that it's not the shielded cable sending some signal because of the surge. I won't tell you what I was getting ready to try.....

    So, suggestions on the best solution? generator inverter? just for power-up? I'm already moving to 24 V; however, same size 24V-120V inverter (1500W (3000W peak) probably a mistake).

    Can you recommend a good 24V inverter? I'd could probably spend up-to $750, but really would like to keep it much cheaper. I wrestle with spending the extra ? $600 just to kick the condenser, when most of the time the extra won't be needed....
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    See, here's the problem; cheaper doesn't just mean "less expensive". It also means "not as good". In the world of inverters it inevitably means "MSW type that motors don't play well with". That gets into the whole thing of Multiple Stepped Wave trying to be sine wave and the horrors of Power Factor, as well as improperly formed magnetic fields and their relationship inside a small-frame motor. The short version is that the cheap inverters look like 20% less power to the motors, which if they do run at all will wind up slowly, draw more current, and fail prematurely as a result of being worked too hard.

    There are inexpensive sine wave inverters. Samlex is one brand. And if you look at our host's selection you will notice this curious warning: "Note: We do not recommend Samlex for use with heavy startup loads, such as refrigerators or any other motor driven appliance that might have a large starting surge."
    They can't take it.

    In fact the air conditioning unit's demands can be so high that nothing short of a 3 kW rated sine wave inverter may take it. It could be difficult to start even off a 2 kW gen set.

    You've got three things working against you on that load: the wave form discrepancy, the start-up surge, and the DC Voltage drop/current rise. To solve all three will cost a lot of money. Have you read the thread about the Sanyo mini-split AC? Located here: http://forum.solar-electric.com/showthread.php?t=5104 Sometimes the solution is to change the load.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Another thing to keep in mind, a 900watt coffee maker and the 750 watt bread maker have no start-up surge, and cycle their resistive load on and off once they're up to temperature, using only enough power to maintain that temp. The AC on the other hand is sucking back a lot of power non-stop, trying to cool your house. It's hard enough to run a fridge on solar, and that's easy compared to cooling a house:cry: You also don't mention the size of your batteries, or their amp hour rating. I can run a 6200 btu Energy Star AC on my high surge capable Xantrex pure sine wave 1800 watt inverter while the sun is shining, but I have 1000 watts PV, and 1200 AH battery. Could probably run it some at other times, but have no desire to run down my batteries. BTW, it's interesting that your 5000 btu AC sucks back almost 600 watts. My Energy Star 6200 BTU uses roughly 450 watts. Yours, considering normal inefficiencies, could easily be sucking a 60 amp draw on your batteries and more if using a MSW inverter. Just some food for thought:-)
  • suecosueco Registered Users Posts: 22
    Re: Small A/C problems with off-grid solar

    MSW - I assumed was "modified sine wave". it appears that's is not correct... or is multiple step the same as modified sine?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar
    sueco wrote: »
    MSW - I assumed was "modified sine wave". it appears that's is not correct... or is multiple step the same as modified sine?

    "Modified Sine Wave" is a misnomer, or "lie", used by manufacturers to make their product sound better. Semantically, that would be a sine wave that has been modified. There's no point in doing that, of course, and it is really Multiple Step (or Square) Waves which give an imitation of a sine wave. Sometimes it's a fairly good imitation: lots of steps. Sometimes it's not so good: very few steps.

    Basically an inverter is either the MSW type (call it what you will) with a less-than-ideal waveform (to put it mildly) or a PSW type (sometimes called "pure", sometimes "true" - again neither is exactly accurate) with a waveform that is close to that of utility power. In some cases it is better than certain utility co's.
  • bluewickedburnerbluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Doesn't help you right now but you can try a DC Ac typically used for truck cabins. Nice little things designed to run for quite a while from a smaller battery bank.

    One thing I haven't seen mentioned. Try hooking up to starting batteries for the AC instead of deep cycle. For a heavy draw item you're better off with batteries designed to discharge faster. Lot of diesel rigs run their cabin AC with no engine running.

    For AC you need those cranking amps. Deep cycles just aren't up to it and your inverter can't get the power fast enough. You're going to be in for some serious charging after that use though.

    Just a thought.

    BTW, we have used a two compressor AC (running on one compressor) on battery and through a 2000 watt MSW inverter. Works just fine. I know the pros and cons of that but it works is all I can say. Amp draw never gets over 17 at startup and then only for a few seconds, then drops to under 10.
  • suecosueco Registered Users Posts: 22
    Re: Small A/C problems with off-grid solar

    Thanks, Bluewickedburner (I'm not going to begin to guess what that stands for).

    I thought about putting a cracking battery (or 2) on battery bank.... I know you're not supposed to mix battery types (gel w/flooded w/agm), but I wasn't sure about putting high crank battery w/deep cell - I guess it shouldn't matter since they're both flooded. I'd probably run through the cranking battery pretty fast, but it's cheap enough, and they recycle (or is that another manufacturing misrepresentation (?)).

    And I hear you about it working, possibly not the most efficient, but it works. For me, I have extra W's to use in the middle of the day, and I can "find" things for that, but what is needed the most is a little assistance for the cooling for an hour or 2 in the middle of the day.

    What's the voltage on the battery/inverter? 12V or 24V? or something higher. I don't think it SHOULD matter, but I get the impression that 24V would be easier.
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Small A/C problems with off-grid solar

    Guess it's time for me to walk away from this thread. lol
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    Some random observations, comments, and remarks:

    Yes, cranking batteries can deliver high current faster than deep cycles.
    No, they will not "enjoy" being used or recharged as deep cycles; it will shorten their life. This may not be a concern if you're not in it for the long haul.
    A trucker's AC unit is meant to cool down a much smaller space than a 5000 btu unit. Naturally it uses less power.
    A 24 Volt system (even with deep cycle batteries) will be better suited to running higher power things like air conditioning because the current is less for the same amount of Watts and Watt hours. Less heating of wires, less Voltage drop, less Amps needing to be delivered "instantly", less Amp hours over time. 48 Volt is even better. But as you go up in system Voltage there is a certain minimum extra expense involved which needs to be justified for the over-all gain, not just to run one device.

    Before you make any decisions on spending money on such things, remember whose money you'll be spending. It isn't mine. :roll:
  • suecosueco Registered Users Posts: 22
    Re: Small A/C problems with off-grid solar

    Thanks, 'Coot. Yes, right again, as usual. I did some more research here on the forum, then looked some other places, and concluded that mixing battery types isn't good for the battery, and, therefore, not good for me.....

    Still, I appreciate Bluewickedburner for being willing to step outside the box AND go against the heavies. If solar is going to get moving, we need to be willing to think differently - the technology is awesome and easy, really, to implement and it's been here for long enough. It's too expensive, yes, but get middle america hooked, and I bet you see that changed.

    And, yes, I'm already moving to 24V (previously mentioned).... we'll see if that's enough to get over this hurdle. However, I KNOW there's a way to do this - there's enough brain power on this forum to figure out how to get the dang motor STARTED, without having to reconfigure the whole solar setup. I'm thinking of contacting GA Tech EE/Controls lab and see if a grad student will take this on: for a millisec a kick is needed - every, 15-30 minutes, depending on the temperature - can this be done on the "side", somehow without having to size your system enough to launch a space station.

    I'll go sip my solar brew and contemplate some more.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Small A/C problems with off-grid solar

    There is always a way to do it. You could try a cheap kicker capactior ( $ 15 ) or a Dometic Soft Start if you want to spend $400.

    The first thing I'd look at is look at the amp draw and the voltage on the cables to the inverter and see if you have enough. On 12 V it will pull about 70 Amps LRC and drop back to about 50 Amps or so.

    If all that fails , throw the inverter in the trash and buy what you need.
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    look in to the "hard start kit". here is a link from a HVAC tech. or do a google search. http://www.youtube.com/watch?v=VZea1wC-cHU he has some good common sense info.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    On the hard start kit. Make sure you have a start capacitor you are hooking up the hard start kit to. If (many do not) you only have a run capacitor you can get a simple relay kit with the hard start kit that will kick it off after a second. Just an FYI.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    :roll: (Thinks quietly to himself): "I don't work for Emerson Electric anymore. I'm not getting paid for this. I don't have to say anything." :p
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Small A/C problems with off-grid solar

    Another trick is to put 5-10 seconds a Delay cube timer on the fan / blower motor and the compressor so they don't try to start together. Cost $20.

    I do it on boats where they start a cooling pump and blower, works on some.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    LOL....my old man is the AC king of Dallas Ft. Worth. He had me in the attics running duct when I was 10 :) Went through a lot of Emerson fan motors.....
    Many folks will not know the difference between a start capacitor and a run capacitor.
  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar
    Wrong on most counts.
    Most people do not run A/C on their off-grid systems because any form of refrigeration compressor is a bleedin' power hog with massive start-up surge.


    There is one form of AC that doesn't have a huge start-up surge.

    http://us.sanyo.com/HVAC/HVAC-Solar-Integration-Offgrid-Solar

    A mini-split (ductless) AC that uses Inverter technology, slowly ramps up
    it's power consumption. The surge is very slow on mine.
    It can take a few minutes, before dropping back down to low power.
    (Right now, it's using less than 400w to cool my house).

    My 24,000 BTUh Sanyo (36,000 BTHh heating) would most likely
    run on a 48vdc TSW (and maybe a MSW) inverter rated at 2.5kw @240vac (5kw peak).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    XRinger;

    I actually mentioned that in a subsequent post, complete with link to one of the threads that discuss them.

    Sometimes it just takes a while for the relevant information to burble to the surface. :roll:
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Small A/C problems with off-grid solar
    sueco wrote: »
    MSW - I assumed was "modified sine wave". it appears that's is not correct... or is multiple step the same as modified sine?
    MSW does indeed stand for "modified sine wave" in the lingo of the inverter manufacturers who coined the term, but it's marketingspeak. The wording of the phrase suggests that it started as a sine wave and then was modified, when in reality it started with a square wave that merely has a bit of hysteresis added to hold it at the midpoint for a bit during each cycle. It's a little "smoother" than a square wave, but not much.
  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar

    I would like to see one of those Stepped waveforms, from one of my MSW inverters.
    But, I'm finding that Chinese MSW really means Modified Square Wave, with a tweaked duty cycle.. :(

    squarewave.jpg
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    They thought about calling them "Really Fuzzy Square Wave Inverters Whose Output In No Way Resembles An Actual Sine Wave" - but it wouldn't all fit on the box. :roll:
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    MSW has it's place in my humble opinion. I run some florescent lights and big fans off one out in the shop. Of course I have a True Sine Wave (Xantrex) inverter for the house wiring. I think some folks try and use a MSW to run computers, TV's etc. and get frustrated but they work for less "delicate" electric powered appliance/devices.
    So if your going to run aforementioned less delicate devices heck...save some money and go MSW.

    There...go ahead and dog pile an old man ....see if I care :blush:
  • XRingerXRinger Solar Expert Posts: 529 ✭✭✭
    Re: Small A/C problems with off-grid solar

    I think you might be wrong about computers that use direct AC to DC conversion. (rectification?).
    Or, anything that uses that type of power supply. (Inverter power supply?)

    All the PCs and LCD displays in the house works just fine on MSWs.
    Even my old CRT display works with MSWs.
  • The Only SargeThe Only Sarge Solar Expert Posts: 164 ✭✭✭✭✭
    Re: Small A/C problems with off-grid solar

    So does my laptop on my workbench in the shop. I often hear/read of people with PC monitors going wacky on MSW...that was the touchwood of my comment.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Small A/C problems with off-grid solar

    Things that don't like MSW are those that are waveform dependent for their operation - like induction motors - and those that need a "reference Voltage" like some battery chargers. Fluorescent lights (including some CFL's) may not work or may be noisy. Thing is not all MSW inverters have really poor waveform and not all devices that might act up will. It's a gamble of matching source with load. Since they often don't even give you THD figures for the inverter you just never know.
  • BB.BB. Super Moderators, Administrators Posts: 32,026 admin
    Re: Small A/C problems with off-grid solar

    Again, it depends on the design--and from (limited) experience, I would say that 80% will work OK.

    But, the AC to DC rectification (with voltage doubler) for computer type power supplies is very common. Until the Power Factor Correction Requirement came into EU law/requirements--PFC was rare to non-existent.

    A typical non-PFC computer type power supply input looks like some diodes and capacitors. The difference in the "edge rate" of the MSW vs TSW wave form is huge in terms of peak current through the diodes/capacitors. The RMS current is much higher, and therefore the heating effect of the high ripple current is higher too.

    PFC power supplies do not control current through input circuitry like the typical non-PFC supply does.

    Will a power supply fail immediately on a MSW inverter--not usually. Can it be a problem in that the input components run "hot"--yes.

    Now, there can be inductors and various filter circuits that will soften the MSW edge rate--so it is possible that the newer non-PFC power supplies may have less of a problem (a diode to cap rectifier circuit is very noisy electrically--so adding filters is an important part of FCC compliance).

    Also, there is some sort of power limit (below XX watts non-PFC supplies are OK, and above XX Watts, supplies must be PFC--I don't remember the limits but smaller power supplies can overheat on MSW where larger supplies from the same vendor will not).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Small A/C problems with off-grid solar

    Switching power supplies are robust. Their rectification produces very good, flat DC.
    XRinger wrote: »
    I think you might be wrong about computers that use direct AC to DC conversion. (rectification?).
    Or, anything that uses that type of power supply. (Inverter power supply?)

    All the PCs and LCD displays in the house works just fine on MSWs.
    Even my old CRT display works with MSWs.
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