Do I need a starter battery for <100W AC fridge?

[jaan]

Hello everyone!

Oftentimes when I'm shopping around for a lithium battery there is a clear warning "do not use as a starter battery".

I know AC fridges basically have motors, but I reckon the motors are small / very small, and using deep cycle lithium battery would be sufficient?

 

[Rednecktek]

No, a starter battery is designed to pump out hundreds of amps to turn over a big block of steel to get your engine started. A fridge is nothing compared to that. Pretty much any LFP battery out there will fire up a fridge just fine.

 

[efficientPV]

My fridge took 120A peak to start and a 100AH lithium can supply that for very short periods of time.

 

[Supervstech]

Hello everyone!

Oftentimes when I'm shopping around for a lithium battery there is a clear warning "do not use as a starter battery".

I know AC fridges basically have motors, but I reckon the motors are small / very small, and using deep cycle lithium battery would be sufficient?

How large a fridge?

Average small fridges at 120v pull 7 to 25A startup whichnwould be 70 to 250A or so with 12V
250A would be considered a starter load...
So, find out how much inrush, or LRA your compressor pulls before deciding.

 

[robbob2112]

Somewhere on the fridge there is a model number sticker/plate .. take a picture and post it. On that is usually current listed for running. Sometimes it lists start current.

 

[Mattb4]

Hello everyone!

Oftentimes when I'm shopping around for a lithium battery there is a clear warning "do not use as a starter battery".

I know AC fridges basically have motors, but I reckon the motors are small / very small, and using deep cycle lithium battery would be sufficient?

I wont get into the chemistry and construction of various battery types but I will mention that LiFePO4 batteries should come with a BMS. That BMS has a current limit both running and instantaneous. If what you are operating needs more than the BMS allows it will trip.

 

[jaan]

Thanks for the responses!

If I understand correctly, to know for sure I'll need to find exactly the specs of the compressor motor.

This information does not seem to.be readily available, I found some general fridge specs though (I don't have the fridge yet):

1.
127l
139 kWh/year
230v
50hz
100w

2.
107l
90 kWh/year
220 - 240V ~ 50HZ
Total current 0.55A

(Unfortunately no start current was listed)

Since it gets pretty hot during the summer here, often up to 40°C (104°F), I’m guessing the fridge would use more energy rather than less than specified. That does not matter for the start current I'm guessing, just that it'll be starting up more often?

The battery I'm eyeing is LiTime 12V 230Ah, here are BMS details:

BMS：200A
Max. Continuous Output Power：2560W
Max. Continuous Charge Current：200A
Max. Continuous Discharge Current：200A
Max. Discharge Current 5 Seconds：600A

To my eyes, and given the responses above, it looks like the fridge will be able to.start no problem and there will be even a large margin left?

 

[zanydroid]

600 * 12 = 7kW, I'd be worried more about voltage drop than the battery capability at that point, given that this is a 12V system.

What is the surge rating of the inverters that you have in mind? And you are going with what would be a mainstream inverter (from the POV of DIY power forums), therefore PSW, and not some random thing you buy at the store, which could very likely not be PSW? I made the mistake of buying a random inverter during a power outage last year, and it turned out to be MSW and pretty low surge. Even when I could get motors started with it, the motors sounded extremely unhappy, because of the terrible waveform shape.

I don't think there's really such a thing as deep cycle lithium. They're all "deep-cyclable" in the sense that word is used for lead acid.

 

[jaan]

600 * 12 = 7kW, I'd be worried more about voltage drop than the battery capability at that point, given that this is a 12V system.

You mean generally that the Max. Discharge Current 5 Seconds of this battery is too large, or in the specific scenario with the fridge that would be a problem?

As for the inverter I want PSW, and surge rating whatever the fridge wattage I end up buying times ~ 5 I guess

 

[zanydroid]

You mean generally that the Max. Discharge Current 5 Seconds of this battery is too large, or in the specific scenario with the fridge that would be a problem?

Large is good. What I meant was, at 400A-600A range you will have a good chunk of voltage drop that may need to be factored in.

I think with the size of fridges you listed above (which looks small), if you can surge to the ampacity of the circuit type the fridge can plug into, it should be fine.

If you have the largest fridge commonly installed on that kind of circuit, you probably want more.

Also need to consider whether the inverter is a trustworthy brand, where the surge ratings etc mean something.

 

[Rednecktek]

Your LFP will be plenty. Even at 5x starting load that's still only 500w which is less than 50a on a 12v system. Not a problem.