LiFePo4 Round Two

[bdosborn]

I found a great deal on eBay and bought another four 180 a-hr CALB cells. $600, including shipping. I ordered them on February 19 so it took awhile to get here. Cell voltages tested at 3.287, 3.288, 3.288 and 3.289 volts, which is great. Hopefully that means they're closely matched. I've got all the busbars made and the cells are now connected in parallel till I'm ready to charge them.


Next step is to make the plywood case, similar to the first one:


I'll connect them in 2P4S arrangement with the first four cells for a total of 360 a-hrs of capacity, with 288 a-hr usable at 80% discharge.
Bruce

[MtnDon]

[John61CT]

Sweet deal, assuming at least 170 capacity.

Can make a harness to let both packs get charged / balanced and/or protected by the same set of devices, run them as one bank most of the time but still be able to use separately for a portable need.

Only in parallel of course

[bdosborn]

Nope, I thought about it but decided to go with the 2p4s and not parallel strings. Mostly because I don't have a good solution for a BMS, certainly not one for two separate batteries.
Bruce

[John61CT]

Actually even with 4S2P the balance leads can be paralleled independently of the serial wiring.

So no difference from 2P4S,

either way, only one BMS is needed.

Just FYI not pushing anything

[bdosborn]

The new battery passed the 80% discharge test, phwew what a relief! That's the problem with ordering from China, you can't afford to ship them back if they're bad.





I learned something new and I'm glad I discovered in the garage and not in the field. Don't run the battery down so low that the battery meter alarm opens the relay to the charger. I'm going to print out the following and stick it on the battery:

If Low discharge or SOC alarms activate: The relay to the charger is opened. When the now unconnected charger is plugged into shore power, the charger output voltage goes to 14.7V and it's locked out on high voltage. No power to the battery. Perform the following steps:

- Unplug charger
- Edit relay alarm values till reconnect points clear voltage and SOC alarms.
- Wait 1 minute for relay to closes back in (or edit delay to 0).
- Plug in charger.

I also learned that I forgot to connect the battery meter alarm relay to the battery load disconnect.While it would disconnect on low voltage on its own, I'd like it to disconnect on 20% charge level so I need to connect it to the alarm relay.

The cells where within 0.001V of each other at 80% discharge, despite the midpoint deviation of 0.4% reported by the battery meter. We'll see what happens to the cell voltages at 100% charged. But so far everything looks good, I think these are good cells.

Bruce

[bdosborn]

Here are all the cells in parallel for top balancing:



Bruce

[bdosborn]

I got the batteries installed in the camper, its tight as Dick's hatband. The balance and meter leads look pretty messy, I need to clean that up somehow. I have a couple of cables to the inverter on order as they are stretched too tight. I didn't size the battery area for LiFePO4 batteries, heck they weren't available when I designed this thing.


Here's a screen shot of the first discharge, 65 amp-hrs and its not even breaking a sweat.


Here's what the golf cart batteries looked like, yuck!


So that wraps up the battery project, I'll post an update if anything goes wrong. Hopefully, ,these will last till I don't want to camp anymore.
Bruce