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24V Output Question

gmcconnell

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May 24, 2021
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Hello!

I have a question that I think I know the answer to, but wanted to make 100% sure I didn’t have something backwards because it has been confusing me a little.

I am drawing up some plans for solar on my Airstream. I’d like to use a 24V system and around 200Ah. I want to be able to power a 3000W inverter so will need over 100A to do so.

I’m looking at the SOK batteries. I am planning on running 4x of the 100Ah batteries in a 2S2P configuration. I figure this will give me a 24V 200Ah battery capable of outputting 200A.

However, I just wanted to make sure that was how the BMS works. I understand the battery capacity is added when paralleled, but is output also?

I would like to buy 2x of the 12V 206Ah and run them in series to save $220 but I think that will only output 100A, correct?

Or buy 2x of the 24V 100Ah and run them in parallel which will also save the money, but would output 200A if I’m thinking of everything correctly. Unfortunately I don’t know when/if they will be back in stock. Anybody have any insight?

Thanks everybody, learning a lot on here!
 
You are correct. The max continuous discharge current of the SOK 12V 100Ah, SOK 12V 206Ah, and SOK 24V 100Ah batteries is 100A. Two in parallel gives you 200A max continuous discharge current. A 3000W inverter at 24V requires 3000W / 24V / 0.85 which is about 150A.

4 SOK 12V 100Ah batteries in 2S2P will give you 24V and enough discharge current to run a 3000W inverter.

2 SOK 12V 206Ah batteries in 2S will only give 100A which would only support a 2000W inverter, not 3000W.

2 SOK 24V 100Ah batteries in 2P gives 200A discharge current which can run the 3000W inverter.
 
Where will be batteries be physically located and could they be exposed to freezing temperatures? If yes, Li batteries could get destroyed getting one single charge at freezing. You might want to look at 6V golf-cart batteries as an alternative. Costco has them on sale now for 99$ each.
 
You are correct. The max continuous discharge current of the SOK 12V 100Ah, SOK 12V 206Ah, and SOK 24V 100Ah batteries is 100A. Two in parallel gives you 200A max continuous discharge current. A 3000W inverter at 24V requires 3000W / 24V / 0.85 which is about 150A.

4 SOK 12V 100Ah batteries in 2S2P will give you 24V and enough discharge current to run a 3000W inverter.

2 SOK 12V 206Ah batteries in 2S will only give 100A which would only support a 2000W inverter, not 3000W.

2 SOK 24V 100Ah batteries in 2P gives 200A discharge current which can run the 3000W inverter.
Perfect, thank you for confirming for me!

Have you heard any update on the 24V 100Ah batteries?
 
Have you heard any update on the 24V 100Ah batteries?
I only know what I can see on their website. Min is usually good about responding to support emails. Send them an inquiry.
 
You are correct. The max continuous discharge current of the SOK 12V 100Ah, SOK 12V 206Ah, and SOK 24V 100Ah batteries is 100A. Two in parallel gives you 200A max continuous discharge current. A 3000W inverter at 24V requires 3000W / 24V / 0.85 which is about 150A.

4 SOK 12V 100Ah batteries in 2S2P will give you 24V and enough discharge current to run a 3000W inverter.

2 SOK 12V 206Ah batteries in 2S will only give 100A which would only support a 2000W inverter, not 3000W.

2 SOK 24V 100Ah batteries in 2P gives 200A discharge current which can run the 3000W inverter.

What would happen if the battery bank was undersized for the inverter, continuous current discharge-wise?

Lets say the same scenarios but with a bigger inverter (6KW). Would the inverter work as long as the load isnt bigger than the 200a the batteries can push out? In the case the load exceeded the max discharge current, would the BMS turn off the batteries?

Thanks in advance!
 
What would happen if the battery bank was undersized for the inverter, continuous current discharge-wise?
The bms will trip.
You inverter will stop inverting.
Tripping a bms under max load repeatedly will likely cause the bms to fail.
If you are lucky it will fail open and you will need to replace the bms.
If you are unlucky it will fail closed and you will only find out there is a problem when your battery is destroyed.
Neither of those options are very good considering the batteries you are using are sealed units.
 
The bms will trip.
You inverter will stop inverting.
Tripping a bms under max load repeatedly will likely cause the bms to fail.
If you are lucky it will fail open and you will need to replace the bms.
If you are unlucky it will fail closed and you will only find out there is a problem when your battery is destroyed.
Neither of those options are very good considering the batteries you are using are sealed units.

Short Answer: Dont do it!

Got it. Thanks!!!
 
Short Answer: Dont do it!

Got it. Thanks!!!
I will add that the SOK does support a peak discharge current of 200A for up to 3 seconds. So if you have a brief surge from a load you may be OK. Just don't try to push that too long.
 
You could fuse the batteries so the fuse blows at the battery's max continuous current (or a bit above). This would help protect the battery of you use too much of the inverter. If you later add more battery in parallel you can update the fuse appropriately. Obviously the most important thing is that the fuse protects the wire properly but undersizing the fuse to also protect the battery is an option.
 
If they are 206 Ah each... they would give 206 Ah at 24V, where does the 100 come from?
206Ah (amp-hours) is the capacity of each battery. The 100A (amps, no hours) is the max continuous discharge current. You can find that value listed on the spec sheet for the battery. The capacity and the discharge current have absolutely nothing to do with each other. The capacity comes from the size of the cells and the number in parallel (internal to the battery). The discharge current is controlled (at least for LiFePO4) by the BMS.

Note that discharging a 206Ah battery at 100A means the battery will be fully depleted in just over 2 hours.
 
I see. I just hadn't thought anyone would think of actually using a 3 KW inverter at 3 KW anywhere near continuously.
I have a 3 KW inverter. With 210 Ah of batteries, at 24V. It runs 50-100W "continuously", and still complains about it :·)
 
I see. I just hadn't thought anyone would think of actually using a 3 KW inverter at 3 KW anywhere near continuously.
I have a 3 KW inverter. With 210 Ah of batteries, at 24V. It runs 50-100W "continuously", and still complains about it :·)
Im glad I asked about it because now I know what to look for in a battery. I previously was looking at just 1 "Powerwall" with decent capacity due to the aesthetics if having the battery wallmounted, but Ive noticed most of them (at 48v) have very low continuous discharge current.

Here is an example:

The Simpliphis Ive seen also have very low discharge amps.
 
That KiloVault has a max continuous discharge current of 60A. But it's at over 51V. That will handle a 3kW inverter.
 
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