LFP series/parallel

AlOnestone

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I have seen conflicting opinions wrt connecting LFP batteries in series(12x2=24) and in parallel to double the Ah. Obviously I’m ignorant wrt this topic. Please advise

Second Q is: How to calculate the battery bank energy required for a given inverter… mine is an Outback 3500W Inverter. I do not have any high surge demands over the typical skill saw and other woodworking had tools.

TIA!
 
I have seen conflicting opinions wrt connecting LFP batteries in series(12x2=24) and in parallel to double the Ah. Obviously I’m ignorant wrt this topic. Please advise
There is no simple answer to this.
Does it work? It all depends on the BMS put in the battery. If the FETs used in the BMS can handle the full 24V (nominal) voltage, then it can work. Check the specs of your battery and see if it can be put in series. Many but not all 12V LiFePO4 batteries can be put at least 2 in series.

Can there be problems? Yes. Before you put them in series you will top them both off so they will be balanced relative to each other. Over time they will drift out of balance. To counter that requires one of two things: 1) use a battery level balancer or 2) Every once in a while you take them apart and top them both off again. How often. It depends on the battery and use pattern so I hesitate to give a number. It could be every few months or it could be one or two years.
Second Q is: How to calculate the battery bank energy required for a given inverter… mine is an Outback 3500W Inverter. I do not have any high surge demands over the typical skill saw and other woodworking had tools.

There are two important calculations: 1) Current and 2) Energy.

Current: The battery must be able to supply enough current to satisfy the inverter. Without considering surge, the current could be as high as 3500W/24V = 145.8A to power a 3500W inverter. This would be the minimum continuous current the batteries should be able to provide. I don't like to run things at 100% so I would want the batteries to be able to pump out at least 200A continuous

Surge currents could make that considerably higher. With woodworking tools, I would assume some surges that could go higher.... particularly if a lot of other things are running at the same time. Some batteries don't allow much surge, while others do. It depends on how aggressively the BMS decides the surge is a bad thing and shuts down.

Energy: (Amp Hours or Watt Hours) The information provided is not sufficient to answer this question in any meaningful way. This is a factor of energy used by all of your loads, not the size of the inverter.

If you have a 100Ah battery and your average load draws 10A, the battery is good for 10 hours of run time without being recharged.
If you run the 3500W inverter full-out, a 100Ah battery will drain in about 100Ah/145A = .685 hours or about 40 Min.
 
Thanks FilterGuy
That clarifies a lot, but generally it’s ok to run the series/parallel setup that I stated?

So 200Ah from the bank should be enough?
I have very little else drawing on the system when I use the tools so I’m confident that I’m good in that situation.
 
AH is pointless of a value unless voltage is mentioned. 200ah at 12v is 100ah at 24v

That why I prefer Whr or Kwhr.

200ah at 24v is about 4.8kwhr.

As for hand power tools you’d be amazed at what new battery powered tools are able to do these days.
 
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Hello expert,

I have these two batteries and was wondering if I can connect it in series. I am thinking about connecting it into series and run a 3kw 24v all in one inverter with 9 solar panels 325 watts each. I have included two pictures, any advice will be truly appreciated.
 

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Hello expert,

I have these two batteries and was wondering if I can connect it in series. I am thinking about connecting it into series and run a 3kw 24v all in one inverter with 9 solar panels 325 watts each. I have included two pictures, any advice will be truly appreciated.
Your going to have the manufacturer give you the information or open the battery up and see what bms is being used those are your choices not all batteries can be put in series
 
Your going to have the manufacturer give you the information or open the battery up and see what bms is being used those are your choices not all batteries can be put in series
Thank you very much
 
Your going to have the manufacturer give you the information or open the battery up and see what bms is being used those are your choices not all batteries can be put in series
Here are the pictures of the inside battery. Would you be able to tell if it can be connected in series?
 

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According to the manufacturers sheet on that bms it does not support parallel configurations

that is a jbd bms you can do more research but what I read it looks like it’s a no go

it also states no series connections also
 
Last edited:
According to the manufacturers sheet on that bms it does not support parallel configurations

that is a jbd bms you can do more research but what I read it looks like it’s a no go

it also states no series connections also
Thank you very much
 
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