First Post - Great Information here - Top Balancing

[teckersley]

Wanted to drop a quick note and say hello to everyone. I have been lurking a long time reading a ton of material. It's great to have such an informative forum to get information and share idea.

I am top balancing 24 EVE 105h LiFePO4 cells for a 72v pack. All I can say is wow. Everyone talks about how long it will take but I never imagined it would be this long. I have had them all connected in parallel with an Amazon bought 0-30v 0-10amp DC power supply. It's has been on there since this morning and the watts are still reading 34.5 so there is a LONG way to go. It's fine, I am in no hurry.

* Note to anyone using these machines.. https://www.amazon.com/dp/B08HYK2ZW3?ref=ppx_yo2ov_dt_b_product_details&th=1

Ditch the crappy small wire and alligator clips and make some good leads. I was only getting about 4 amps with the supplied connections. I made some ring terminals with 14g wire and it was able to finally get to 10amps output.

Thanks everyone. Happy to join the community.

 

[MisterSandals]

Welcome!

24x 105Ah x 3.2V = 8064Wh

8064Wh / 34.5W = 233.7h charging from empty
233.7 x 1day/24h = 9.74 days

 

[teckersley]

Welcome!

24x 105Ah x 3.2V = 8064Wh

8064Wh / 34.5W = 233.7h charging from empty
233.7 x 1day/24h = 9.74 days

I tested a few and they were all 3.28v when i started. Yes, PAINFULLY slow.

Great point though and I am now curious. If someone was doing a very large ah pack like a 48v 16s x 304ah pack, how would you speed up this process properly?

 

[MisterSandals]

You could do 4 at a time or 8 at a time to make it seem like you are making better progress. But bottom line is that you are pumping a lot of energy in at a modest rate.

3.28V is roughly 65% based on this chart.
233.7h x .35 = 81.8h to go.

What some folks do is build a 4S battery (with BMS, either silicon or carbon (human) based) and charge until full.
If you have a charger that works at any battery voltage at a faster rate you can top up before the parallel top balance.

Happen to have a pic of your setup?

 

[42OhmsPA]

* Note to anyone using these machines.. https://www.amazon.com/dp/B08HYK2ZW3?ref=ppx_yo2ov_dt_b_product_details&th=1

Ditch the crappy small wire and alligator clips and make some good leads. I was only getting about 4 amps with the supplied connections. I made some ring terminals with 14g wire and it was able to finally get to 10amps output.

Yes, yes, yes. If only everyone would listen and do this from the get go.
Welcome aboard.

 

[teckersley]

Great Chart. Does anyone have a larger file format of this same chart that also includes the 74v?

Thanks

 

[MisterSandals]

You will get a better dispersion of charging putting negative lead on one end and positive on the other. You are charging the middle cells a LOT more than the end cells (most of your cells).

And actual ring terminals rather than alligator clips will help quite a bit too.

 

[time2roll]

9.9 amps out of a 10 amp rated supply is as fast as that buggy can haul. Need 20 to 50+ amp rating to really move faster.

 

[teckersley]

You will get a better dispersion of charging putting negative lead on one end and positive on the other. You are charging the middle cells a LOT more than the end cells (most of your cells).

And actual ring terminals rather than alligator clips will help quite a bit too.

no the multimeter is just in the middle. Look closer. The + and - ring terminals are on opposite ends already.

 

[teckersley]

9.9 amps out of a 10 amp rated supply is as fast as that buggy can haul. Need 20 to 50+ amp rating to really move faster.

I am in it already but if/when I do this again, I would highly consider the extra $ for the TeKPower 1560 version. That outta make much shorter work of this process.

 

[MisterSandals]

Great Chart. Does anyone have a larger file format of this same chart that also includes the 74v?

Large file format but not 74V. You might be able to talk Steve_S into adding a 74V curve.

(Click the orange download button)

General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V

I've looked at several places for a simple, easy to read at a glance "chart document" for LFP. I could not find anything comprehensive. I discovered an XLS Worksheet in my stored file and took parts of that to create this chart, I did not...

diysolarforum.com

 

[toms]

This topic has been done to death, but it is never a good idea to parallel connect cells of significantly different states of charge.

To speed up the process, assemble your pack in its final configuration, and either manually adjust the cell state of charge for cells that are out of range (resistive load for high cells is easiest), or connect an active balancer and let that complete the top balance.