Big Battery 24v A123

[Rmeadomavic]

I went with this
Voltage Range: 20V – 28.8V -- https://bigbattery.com/product/24v-a123-lfp-battery-free-shipping/
That means 2.5 volts per.
If dead empty is actually 2.0 volts then I would want to see the discharge curve to find out where the knee is.

I don't disagree with 3v, but I'm just making sure I understand why. More importantly, I want to make sure none of these other settings in the BMS are interfering with what I expect to happen. BTW, thank you all for taking the time to help. This stuff is so damn cool.

 

[John Frum]

Considering that graph and the application I think I would stick with 3.0 for the in service cutoff.
Also I would not do a discharge test to <2.5 volts per cell until big battery changes their doco and/or test procedure.

 

[Rmeadomavic]

I've set to 3.0 as well. Will's video (and manufacturer)says to set cell overvoltage to 3.6v. Why 3.65v?

 

[MrNatural22]

I've set to 3.0 as well. Will's video (and manufacturer)says to set cell overvoltage to 3.6v. Why 3.65v?

That’s what it says for max charge voltage on the label. 8x 3.6 = 28.8
Not sure why the max. Different chemistry.
LiFePo variant Nono phosphate ?

 

[John Frum]

I've set to 3.0 as well. Will's video (and manufacturer)says to set cell overvoltage to 3.6v. Why 3.65v?

A bunch of reasons.
The pack is top balanced.
The charger should be acurately set to 3.6 volts per.
It should charge at ~.2c and will be in constant voltage mode before it gets there.
Lifepo4 chemistry is more tolerant to slight over charge then the explody lithium chemistries.
The bms should be balancing at the top.

 

[John Frum]

I wonder if I will need to explain cc/cv charging.
The short version is that current approaches 0 as the voltage differential between the charge source and the battery approaches 0.
On the other hand their is not such breaking mechanism for discharge.

 

[Rmeadomavic]

That’s what it says for max charge voltage on the label. 8x 3.6 = 28.8
Not sure why the max. Different chemistry.
LiFePo variant Nono phosphate ?

So, I'm right in setting it to 3.6? Or should I change it to 3.65v like yours?

 

[Rmeadomavic]

Next on my list is nominal capacity and cycle capacity. What are those about?

 

[MrNatural22]

So, I'm right in setting it to 3.6? Or should I change it to 3.65v like yours?

Yeah I set mine back to 3.6 on the protection menu. My oops. ?

 

[John Frum]

So, I'm right in setting it to 3.6? Or should I change it to 3.65v like yours?

I can't advise you but personally I would trigger at 3.625 and release at 3.575

 

[John Frum]

Next on my list is nominal capacity and cycle capacity. What are those about?

Not sure what the distinction is.
Maybe some context will help.

 

[MrNatural22]

Joey I’m using a switched bench power supply to charge. Set voltage at 28.8v 10a so the current will taper near the top but voltage should remain constant?

 

[Rmeadomavic]

I think things are looking pretty good

 

[John Frum]

Joey I’m using a switched bench power supply to charge. Set voltage at 28.8v 10a so the current will taper near the top but voltage should remain constant?

see this post for a description of cc/cv

RJ Energy 271 AH LIFEPO4 Lithium Batteries – detailed Top Balancing using the Parallel Step Method procedure

My second Video documenting my project step by step configuring Cheap high quality Lifepo4 cells. I did my best to follow the advice of a trusted expert with several years of experience and who is a marine electrician. Charger settings are detailed. RJ Energy Lifepo4 cells are balanced. The...

diysolarforum.com

 

[John Frum]

I think things are looking pretty good

Have you top balanced your pack yet?

 

[Rmeadomavic]

Have you top balanced your pack yet?

Not yet. Still considering how. (I have no access to alternate power)

 

[MrNatural22]

A123 24v #2 with a cleaner BMS install using the existing balance wires soldered to the 8s Overkill leads and eliminated the plug and Installed temp sensors and wires. I had to extend one of the Overkill’s temp sensor wires to reach opposite end of the battery.
I will be redoing the first A123 like this ASAP.

 

[softdown]

I'm looking at their 48V units. Posters have said the featured 24V units have new cells. Appears a great deal indeed. But I see no mention of new vs used cells in the ads I have seen.

 

[Off grid Colorado]

Hey soft down here from wind and sun?

 

[softdown]

Hey soft down here from wind and sun?

Yep - didn't know we had another member from Colorado there.