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Lithium experement

Found some lithium cells for sale on Craigslist.. took the chance to see how and why that makes them tick.

Have had them for a few months but havnt had a chance to really try them.. ran into some issues this weekend dry camping at the lake.. took them out today and for some reason the 4 cells in the middle of each run are lower volts per cell.

Took the low cells out of the run. 4 cells at 3.2 wired in series to get 12.8 ( approx) then wired the whole in parallel to give me a battery bank of approx 750ah of lithium.. somewhere or somehow I am not getting any ah hardly out of them.. I can watch them drop in volts in a mater of a couple hours they are under 12v from 13.8 or 14v

Ordering a new set of cells with a bms @ 400ah.. so planning on getting either 2 or 3 sets.. I want at least 800ah but I figured since I am in their order 3 sets for 1200ah and call it done.. then start playing with the AC on batteries

Didnt spend to much on this run so not to worried about costs..

Re: Lithium experement

Reply #1 –
Are these LiFePO4 (lithium iron phosphate)? or a different type of cell?
I'm only familiar with LiFePO4 so this may or not help.  It sounds like the cells all need to be individually balanced, do you have a BMS for these?
Each cell should be within 0.01 volts or so, search online for more specifics.  There are different ways of achieving balance, either top or bottom balance.  Then make sure your connections are all tight.  IIRC if a cell is truly bad the voltage on that individual cell will drop quicker than the others in that 4 cell pack so removing the bad cells is a good thing. 
How long are you charging these for?  For 750Ah if you have a 100amp charger should take 6 hours or so to achieve full charge from 20% SOC.
This is a good although somewhat dated article written by a marine electrician: LiFePO4 Batteries On Boats – Marine How To
Forest & Cindy Olivier
1987 log cabin
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no longer 1999 36' U320 build #5522
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Re: Lithium experement

Reply #2 –
Nice find! They are just out of balance. You could do the following

1. Either use a BMS to balance them or parallel them for a day to get them in balance.

2. Charge them fully: To 3.6Volts, then remove them charger.

3. Check there capacity by discharging to 2.5Volts
1997 U270 34FT Build 5140 Cummins 8.3 Allison 3060R
Solar 1920Watts, 14KWH lithium. Orion BMS.

Re: Lithium experement

Reply #3 –
I have them connected by solar 1200w and through the inverter/charger ..

I bottom balanced before I began so all were at or within the .01 or each other

How can I check the capacity? I have a load tester I can attach and hit it and see how it goes.. what would be the best procedure ?

These are lifepo4 50ah packs 3.2v

I want to see what the Ah is left in them per 12.6v pack
 

Re: Lithium experement

Reply #4 –

For battery testing and management I recommend an iCharger 4010Duo or better. See: Amazon.com: iCharger 4010Duo: Toys & Games

It will do three important things:

- Charge, Discharge while measuring Amp Hours.
- Balance all cells. Bottom balancing is preferred.
- Storage charge (Will set charge to around 50%) while rig is not in use.  This will prolong battery life.
- Show the voltage of each cell and the difference between high and low cells, a measure of battery health.

It will not:

- Initiate the above automatically.
  This is good because human intervention makes us actively involved.
- Display SOC (State of Charge).
  This is OK because BMSs are notoriously inaccurate.
    SOC must be derived by putting minimal or no load on the batteries and viewing the voltage. For LiFePO4, that's 3.35V=100% and 2.5V=0% SOC at no load.
- Needs a separate power supply. I have used 12V and 48V powered by 115VAC.
- Be easy to use. However, if you can solder and use a smartphone, you'll be fine.

No other BMS can do this.

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1997 U270 34FT Build 5140 Cummins 8.3 Allison 3060R
Solar 1920Watts, 14KWH lithium. Orion BMS.