Inverter chokes under load

SurfMonkey

Solar newbie here . . .
I am trying to run a small chest freezer that operates at:
124.4v, 60Hz
.79 amp
61.8 watts

My inverter is a Kisae 2000w 12v pure sine unit
Single 12.8v 280AH LiFePO4 battery

When I switch the inverter on, with in about 15 seconds, the fans kick in and the inverter shuts off the power. This always happens to this appliance. Other things run just fine.

Any suggestions appreciated!

B in San Diego

AzSun

What are the other items that run just fine? Do you have any test equipment such as a DC voltmeter, DC clamp on amp meter, or clamp on AC amp meter? Does the freezer start up "efforlessly" when connected to utility power? Freezers and refrigerators do take a fair amount of power to start up but I would think your setup should be able to handle the one you have. It seems like you are getting an overload or large voltage drop your inverter cannot handle.   

BB.

As AzSun says--Measure the AC side (voltage, current) using a current clamp meter or kill-a-watt meter, or similar.

Also, on the DC side, measure the DC battery bus voltage to the AC inverter's input.

An induction motor (AC compressor for fridge) probably draws at least 5x running Watts (VA) input surge. The DC bus voltage should be between 10.5 and 15.5 VDC:

https://www.kisaepower.com/products/sw1220/

The AC inverter should manage close to 4,000 VA surge for at least a few seconds.

I don't see anything "wrong" with your hardware. What AWG (diameter) and length of cable do you have on the DC power side? The estimated worst case starting of 600 Watts would be:

• 600 Watts * 1/0.85 typical inverter eff * 1/10.5 volt voltage cutout = 67 Amps estimated max DC current for inverter starting the fridge

Too long/too small of DC power cable from battery to inverter could hit the low voltage cutoff of the inverter (do you get any warning lights?). Note for (full power) inverter wiring, they recommend 300 Amp cabling and fusing for DC side.

Page 9 of manual for inverter error codes:

https://www.kisaepower.com/wp-content/uploads/2015/07/MW_SW_Series_MU_MW1215_RevB.pdf

-Bill

SurfMonkey

Thanks for the prompt responses and thanks for your patience with my newbie question.
I am including some photos that may be helpful.

I have run a bar fridge, power tool battery charger, various lights without problem.

The readings I am using for the freezer were taken from a Kill-a-Watt meter. VA readings were not taken and to be honest, I am not that familiar with the impact volt-ampere would have on a system.
I am using 4 awg cables from battery with a switch and 100 amp fuse as shown.

I am getting 13.22v (at the lugs on the inverter without a load.
 
Too long/too small of DC power cable from battery to inverter could hit the low voltage cutoff of the inverter (do you get any warning lights?). Note for (full power) inverter wiring, they recommend 300 Amp cabling and fusing for DC side.

This may be a problem. Please see photos. The inverter is mounted with lights pointed down but I can get a mirror down there to see if any error lights come on.

Thanks again for your help.
b

BB.

Technically, Watts is equal to or less than VA... The math:

Watts = Volts * Amps * PF (power factor, typically between 0.50 and 1.00)
Watts = Volts * Amps * Cosine phase angle between Volts and Amps (i.e., cosine of Zero Degrees = 1.00)

Basically, think of VA * PF like peddling a bicycle where your pushing irregularly on the peddles, that is PF less than 1.0

If your force on the peddles is "optimum to peddle position" (no pressure when peddles are "vertical" and max pressure when peddles are horizontal) and very smooth--Then that is PF approaching 1.0

More or less, 'poor PF' is a less efficent usage of current... I.e., your loads with poor PF draw more Amps out of phase with the voltage. So the wiring, transformers, inverters, AC generator wiring/etc. has to be heavy enough to manage the higher current of a poor PF system. Some AC loads can approach a PF of 0.5 so your loads draw 2x more current to operate--Wiring, fuses, inverter "see" and must support that larger current.

However, Watts (V*A*PF=Watts) is what the battery supplies, geneset, inverter supply in terms of power... They "care about Watts" (fuel consumption, Amp*Hours from battery bank, etc.). So both Watts and VA are useful for system design and debugging.

More or less, a Kill-a-Watt meter can do either Watts/VA/PF measurements. And a Volt/Amp/Current clamp meter can only measure Volts and Amps, and cannot quantify the phase angle between Volts and Amps (or "pulsed current") and  technically all you can read is Volt*Amps. (need to measure voltage and current at the same time, and "do the math" to get phase angle and PF measurements).

Since you need to design for actual Amperage flow--VA is important for a safe design--And Watts is always equal to or less than VA).

I don't think you have a VA or Watts issue here... The basic wiring certainly seems hefty enough for a 60 Watt fridge. As well as the battery bank/AC inverter/etc... Note that a "typical" AC fridge runs between (roughly) 0.65 and 0.90 PF.

Your battery is capable (typically for Lithium Ion) powering:

12 volts * 280 AH (i.e., 1 hour discharge, or 280 Amps) = 3,360 Watts @ 12 VDC continuously
12 volts * 150 Amps * 0.85 AC inverter eff = 1,530 Watts typical max continuous 120 VAC loads with 150 Amp @ 12 VDC fuse

At this point, measuring the DC voltage at the inverter's input when the fridge is starting, and again measuring the AC voltage (fridge starting) would my next two steps.

If you had a "bad battery" or a poor electrical connection somewhere, you should be able to track that down.

Also, you could put on a 1,000 Watt electrical heater and do those DC and AC measurements too... And not worry about the few seconds of motor starting surge...

-Bill

SurfMonkey

VA reading comes in at 99/101 on Kill-a-Watt.
Thanks for the suggestions. Heaters or heat guns are always a good test!