inverter problem

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rialtaguy

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Aug 29, 2017
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Installing a 110v fridg in RV to be powered by inverter.  Fridge draws 85 w and inverter is 750.  When I turn on fridg it starts, the inverter alarm goes off and the fridg shuts down.  Obviously, I'm doing something wrong.  Tried another appliance on it and same results.  Help!!!

2000 Winnie Rialta, Haier 2.7 cu ft fridge, Harbor Freight inverter, two deep cycle batteries.  Tried hammer drill as well.

Also, should I wire a fuse into this circuit?

Rialtaguy
 
Welcome to the forum.

It would help if you told us more.

What RV?
What Fridge?
What Inverter?
What battery?  Only 1 battery?

What other appliance did you try?
 
More details would help but you have some main issues that have to be correct. The inverter is best if located close to the battery. You must have the appropriate cable size and you must have enough battery capacity. There is also a big difference between the running draw and the start up draw. Some frigs want a pure sine wave inverter. I have heard of people using modified but often we use pure sine.

Look at your frig compressor or book and it may give a LRA locked rotor amps. Mine is about 10 amps so for the instant when the compressor starts it may draw near that. I'm not a frig tech but that's the basics of it. If it's pulling 10 amps AC and you convert that to DC amps it would be 100 DC  10 A of AC x 10 = 100 amps DC.  100 amps DC x 12 volts = 1200 watts plus you have to factor in inverter inefficiency. If your inverter isn't pure sine it may be a problem. If your surge capacity isn't high enough it may be a problem. If your cables are too small it may be a problem.

Yes, it MUST be fused. If I had to guess I'd think your cables are too small, then I'd guess your surge is too low or it's modified sine and it doesn't like the compressor motor.  ANL fuses  and holders or an manual reset breaker are a pretty cheap and easy way to fuse it.
 
I found these specs for a Haier frig "Local Walmart store had this on display @ 8/17/2016. Specs tag on the back stated Running: 1.5 amps, Startup: 4.5 amps"

4.5 amps AC = 45 amps DC. 45 amps x 12 volts =  540 watts so the inverter size should work but again the type of inverter may be an issue and the cable size absolutely has to be large enough.

i just looked at two Harbor freight 750 inverters which were both modified sine and UP TO 87% efficient so bump that amp draw by another 20% and call it 650 which is under 750 and far under the 1500 surge that they list. I'm guessing cables. I'd suggest throwing some jumper cables onto the existing cables to boost it's amp carrying capacity but you are flirting with fire when you operate with out fuses.
 
Hey QZ - Thanks for all your thought and ideas.  They are appreciated.  The cables are 1/0 - the conductor is about 1/4" in diameter.  When I tried the drill it would start and cut out repeatedly, presumably as the inverter cuts off and resets.  Will definitely fuse this.  Open to other ideas from anyone.
 
With it hooked up, put a voltmeter on the DC input terminals on the inverter and start the fridge.  See what the voltage drops to.  Anything much below 12V will kick out most inverters. 
 
As boatbuilder said use a voltmeter but the start up is so fast that you may not see a low voltage. Two gc2 6 volts should be plenty to run it. Before I installed a 10.7 residential I had ran a smaller dorm style frig on a 1000 watt Xantrex Prowatt pure sine just to see how it worked. It had a small freezer but was probably a little bigger than the model you bought.  My 10.7 resi is running off six GC2 batteries on a Xantrex Prowatt 2000 along with televisions etc. It seems you have cabled it large enough so could you buy 1000 watt or so  pure sine somewhere with a friendly return policy.
 
Are you also positive that your battery is fully charged and water level is up? If you let it sit a few hours with no draw and not being charged it  should be sitting at 12.6 or so volts. If the battery is in good shape you should also have a good specific gravity reading with a hydrometer. Good battery, proper cables and the right inverter that frig should run.
 
Once again, thanks to you all.  I'm still working on it.  Some updated info: I'm mistaken about brand.  It's a Cen-tech modified sine wave, not that that should make a difference.  There are 2 batteries as previously noted, the electrolyte level is where it should be, and voltage is 12.7+.  I just tried a 150 watt floodlight and that works fine.  Please... keep those ideas coming.
 
The inverter shuts down because the battery voltage drops too low when the inverter load comes on. As QZ explained, there is a brief draw in excess of 45A when the compressor kicks in. That's a huge draw if you have only modest battery bank, e.g. 100AH or so.  Small cables or poor connections will also cause voltage drop when the load suddenly increases.

Is the battery(s) new and well charged? Specific gravity where it should be?
 
rialtaguy said:
Once again, thanks to you all.  I'm still working on it.  Some updated info: I'm mistaken about brand.  It's a Cen-tech modified sine wave, not that that should make a difference.  There are 2 batteries as previously noted, the electrolyte level is where it should be, and voltage is 12.7+.  I just tried a 150 watt floodlight and that works fine.  Please... keep those ideas coming.
Click to expand...

Picture the flood light like slowly rolling a ball under hand across the floor.  The bulb filiment starts to glow as the current in it builds. Picture the frig compressor as a baseball bat slamming a tree very momentarily. The compressor armature is stopped but went the electricy touches it it instantly wants to be at 1,750 rpm or whatever. That modified inverter MAY just say I aint gunna do it. As I mentioned I have heard of people using modified but I'd also bet that it was of a larger capacity as compared to the load.  The resi refrigerators are excellent but they do have specific criteria that must be met to even start or live a long life.

The flood light is like a heating element and although it appears to pop on quickly it is actually somewhat slow. Again, the compressor is like slamming full demand on. It is a momentary demand but it's still there and the inverter sees it. 
 
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