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Top Balancing "How to"

For current best practices on top balancing cells, please watch the video and download the PDF at the following page:

Top Balancing Cells Using a Low Cost Benchtop Power Supply

If you are interested in a more general tutorial of what balancing is about and *Why* to balance, check this out:

Explanation for Beginners of Top and Bottom Balance

If you're asking yourself if you should top balance your cells, the answer is almost always: "YES!" If you don't, it's almost certain that even a small imbalance in the cell SoC will cause "runners" at near full charge and will be VERY frustrating. However, if you follow the guide, you may discover that you may not need to top balance.
This is a good guide for any beginner, but i would add that it's important to double check the power supply voltage with a decent quality multimeter.
Don't trust your power supply unless it's a high quality brand!

In my case, my power supply was putting out 3.9V when set to 3.65V and ended up top balancing my cells somewhere slightly above 3.7V according to my BMS.
Thankfully I should be OK, as after doing some research here, anything under 4.2V won't kill the cells, but its not recommended to go above 3.65V
 
This is a good guide for any beginner, but i would add that it's important to double check the power supply voltage with a decent quality multimeter.
Don't trust your power supply unless it's a high quality brand!

In my case, my power supply was putting out 3.9V when set to 3.65V and ended up top balancing my cells somewhere slightly above 3.7V according to my BMS.
Thankfully I should be OK, as after doing some research here, anything under 4.2V won't kill the cells, but its not recommended to go above 3.65V

Did you set it to 3.65V when the PS was disconnected from the battery? That's very critical. If you set it under load, you will overshoot.
 
Did you set it to 3.65V when the PS was disconnected from the battery? That's very critical. If you set it under load, you will overshoot.
Yes i adjusted while disconnected from the cells.
I got 3.9V on my multimeter when I checked afterwards.
It's just a chinese unit, looks decent enough in quality with a fancy OLED display, but I.now question the accuracy.
 
This is a good guide for any beginner, but i would add that it's important to double check the power supply voltage with a decent quality multimeter.
Don't trust your power supply unless it's a high quality brand!

In my case, my power supply was putting out 3.9V when set to 3.65V and ended up top balancing my cells somewhere slightly above 3.7V according to my BMS.
Thankfully I should be OK, as after doing some research here, anything under 4.2V won't kill the cells, but its not recommended to go above 3.65V
It seems like power supplies are fairly cheap. Can you and/or anyone else here suggest a high quality brand? Last thing I'd like to do is damage cells.
 
I searched all over for that Binford Tools 28000 wire crimper and came up empty. Even their site, Binfordtool.com, Made in USA, didn't have a crimper.
Oh. THAT is funny. Binford Tools was a fictitious company from the sit-com "Tool Time" that aired in the early 90s.

The main character (Played by Tim Allen) would always talk about his Binford tool being the biggest, most powerful, best, etc on the market. He would say something like "The Binford 5000 is the best saw you can buy". It is hilarious that someone actually formed a Binford Tools company.

My comment above was a joking nod to that show. Sorry I sent you on a wild goose chase.
 
Oh. THAT is funny. Binford Tools was a fictitious company from the sit-com "Tool Time" that aired in the early 90s.

The main character (Played by Tim Allen) would always talk about his Binford tool being the biggest, most powerful, best, etc on the market. He would say something like "The Binford 5000 is the best saw you can buy". It is hilarious that someone actually formed a Binford Tools company.

My comment above was a joking nod to that show. Sorry I sent you on a wild goose chase.
Haha! Yea I remember tool time, but didn't watch it much ;) !! No worries, It was only about a 45 second snipe hunt, so I didn't go too far off the beaten path. I've spoken (here) with you on a few topics, and coincidentally I'm looking on the forum for a HD smart BMS, a good crimper for large wires as well as a good power supply for the work bench. Can you make any suggestions?
 
You can't go wrong with a TEMco hydraulic crimper.

I'm partial to JBD contractor based BMS but that's all I've ran and they have been excellent.
Others have had great success with the OG JK w/ 2A balancer.
Batrium would be the Cadillac.

My generic amazon special bench power supply has worked fine. I always verify the voltage with a trusted meter if I'm doing anything I want precision on.

Battery Hookup had some beefier bench supplies a while back, not sure if they are still in stock.
 
I was leaning towards the 60V 20A for my next one. Both would be really useful.

Looks like a decent power supply at a reasonable price compared to other sources, though BatteryHookup is higher. I looked for reviews on YT but didn't find any for that specific model. There are videos of other Maisheng models.
 
The main character (Played by Tim Allen) would always talk about his Binford tool being the biggest, most powerful, best, etc on the market. He would say something like "The Binford 5000 is the best saw you can buy". It is hilarious that someone actually formed a Binford Tools company.
 
I've read many resources on Top Balancing, including Nordkyn Design series and the Marinehowto article.
(mind you my mind is exploding with the LiFePO4 learning curve I'm on at present !). I'm just about to order 52 x 3.2V 272AH Lishen cells from Basen for 2 sets of 24 cells (3 x 8 Cells each with BMS) for 2 boats. My questions seem to multiply as I digest more information !

If we assume 280AH cells, 50% charged initially

WARNING: Top each cell up, to a similar SoC level, prior to wiring them in parallel.

Q1. What voltage difference is it safe between cells to connect them parallel ? What surge currents can be expected ? for how long ?

(eg in extreme, if one plugged a 90% SOC cell in parallel with a 10% cell (about a 300mv difference ? ) then approx 224AH would flow over tens of hours, but what would flow in the first seconds ? minutes ?

Q2. Whats the best way to safely connect such batteries together. Separately charge the lower till within X mv diff ?

Similarly if one had 3 strings of 8 cells usually connected in parallel but one taken off line for repair and wanted to connect back to the others.
Q3 how close should their voltages be and what current flows might be expected/tolerated initially. If one has BMS systems on each string, what risk of blowing one with initial surge current ? Perhaps disconnect the BMS' initially till the 3 are settled ?

Specific questions re the Parallel Step-Method Top Balance:
assume 8x 280AH cells, 50% SOC initially, 20A 30V DC supply..

1- Wire the cells in parallel
2- Set the power supply to 3.400V and 80% or less of the rated amperage (80% to not burn it out)
3- Turn on power supply and charge cells to 3.400V

Q4 if initially at 50% SOC, expect to take 120AH?/16amps * 8 Cells = 60hrs ?
4- When current has dropped to 0.0A at 3.400V turn off the power supply & set it to 3.500V
Q5 how close to 0A ? How long to take 8 x 280AH from 3.4 to 3.5V ?
5- Turn on power supply and charge cells to 3.500V
6- When current has dropped to 0.0A at 3.500V turn off the power supply & set to 3.600V
7- Allow current to drop to 0.0A (or very close) at 3.60V

Q6 How long to take 8 x 280AH from 3.5 to 3.6V ?
8- Done, pack is balanced.
Q7. Is 3.5 as a reasonable more conservative value to top balance too ?
Top Balance works wonderfully but how do you do it on welded cells in a pack?
 
Top Balance works wonderfully but how do you do it on welded cells in a pack?
1) Clip leads to the cell and charge each cell to 3.65V individually
2) hook up an external active balancer and let it work, but only turn it on at the end of the charge cycle when the cell voltages are ~3.4V.
(lower than 3.4V is in the flat part of the curve and relative voltages are not good indicators of SOC.... it is possible to make things worse by using a balllencer below 3.4V)
 
You can't go wrong with a TEMco hydraulic crimper.

I'm partial to JBD contractor based BMS but that's all I've ran and they have been excellent.
Others have had great success with the OG JK w/ 2A balancer.
Batrium would be the Cadillac.

My generic amazon special bench power supply has worked fine. I always verify the voltage with a trusted meter if I'm doing anything I want precision on.

Battery Hookup had some beefier bench supplies a while back, not sure if they are still in stock.
Thanks 420 ;) !! I'll check out those bms. What happened to JK? Did they stop development? Looks like batteryhookup still has a few, and I'll for sure test voltage, disconnected, before using...
 
Thanks 420 ;) !!
You're welcome.
I'll check out those bms. What happened to JK? Did they stop development? Looks like batteryhookup still has a few, and I'll for sure test voltage, disconnected, before using...
As far as I know they are still making the original and people are still happy with it. The newer smart model has some bugs so I wouldn't recommend it, there is a massive thread about that model.
 
You're welcome.

As far as I know they are still making the original and people are still happy with it. The newer smart model has some bugs so I wouldn't recommend it, there is a massive thread about that model.
You're welcome.

As far as I know they are still making the original and people are still happy with it. The newer smart model has some bugs so I wouldn't recommend it, there is a massive thread about that model.
Overkill is saying the og JK bms is no longer being produced: https://overkillsolar.com/product/4s-bms-120a-lifepo4-24/

I'll read that Smart JK thread from beginning to end while I wait for Overkill to actually deliver the Pathfinder/Nomad smart bms :) !!
 

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