Well I almost burnt the house down. Time to ask for some help....

ken morgan

Solar Addict
Get a BMS, hook them in series until one cell hits 3.5 to 3.65V. Then go to parallel charging to balance them. Much faster.
agreed, but my cabin is 95 miles from my house... Thats a three hour drive in japan, and even farther in the Philippines how do we do that in a place with no internet to monitor? not all of us have first world problems. The best bet is a parallel connected bank that I can check once every couple of days when i have time to go there. I would guess the same for Dave.
 

Sojourner1

Itinerant
why so much anger? which camp do you sit in???
If you like dead lead use them, baby sit them, coddle them.

Reading your other thread on issues you're having with them has you thinking about dipping your toe in a new pool though.

I'm in the camp of set it and forget it. ;)
 

Supervstech

Administrator
Staff member
Moderator
agreed, but my cabin is 95 miles from my house... Thats a three hour drive in japan, and even farther in the Philippines how do we do that in a place with no internet to monitor? not all of us have first world problems. The best bet is a parallel connected bank that I can check once every couple of days when i have time to go there. I would guess the same for Dave.
Certainly parallel the cells, and have a CV power supply provide charging voltage. It works.
On a large pack, it will take a LOT of time.

internet is not needed to balance charge a bank. The BMS will automatically disconnect the charging on high voltage at any cell...
just a bit faster to bring the pack into the knee...
THEN the near full cells can be paralleled and topped off much quicker.

no need to comment on social status or locale privileges or shortfalls, we are here to help everybody.
 

Dave Knapp

New Member
Personally I don't care for the step method. The power supply may not be able to put out the full amps it's capable of with the lower voltages even using good cables, and may not go into CC mode. I have experienced this for myself using a Riden 6012 with 12awg cables. After dealing with this when I started my top balance, I decided the heck with it and set the power supply to 3.65 volts.

I am attaching a photo of the Riden only putting out 5.84 amps with the voltage set at 3.4 volts. It is in CV mode. Once I set the voltage to 3.65 volts it put out close to 12 amps, switched to CC mode, and remained there until the voltage reached 3.65 volts. Once 3.65 volts was reached the Riden switched to CV mode and then the current began to taper off.

I also don't see anything wrong with charging each cell individually. Since each cell in the pack needs to be topped off I would disconnect the BMS if using this method.
I think that is the safest strategy, however time consuming it will be. The BMS is not connected yet, so no worries there. I'll just top off each cell to 3.65, then reassemble in 16s configuration, and hook up BMS. Thanks. There's a lot of info out there, some of it conflicting. I'll stay conservative.
 

Dave Knapp

New Member
Get a BMS, hook them in series until one cell hits 3.5 to 3.65V. Then go to parallel charging to balance them. Much faster.
Thanks for the reply. Since I'm a noob, I'm gonna stay conservative and charge each cell to 3.65 with a charger I'm buying on Aliexpress. It will take time, but there's virtually no risk of pilot error. Be safe.
 

A.Justice

Swears he didn't start that fire.
Thanks for the reply. Since I'm a noob, I'm gonna stay conservative and charge each cell to 3.65 with a charger I'm buying on Aliexpress. It will take time, but there's virtually no risk of pilot error. Be safe.
There is very little risk for error with the above method, it is a safe, and seriously time saving way to top balance. It only requires setting up a BMS, which you will need to learn to do anyway.

That being said, charging all the cells in parallel to 3.65 is a "set it and forget it" method that works great except for the amount of time. It took about a week to top balance my 4ish KW pack, and I was using two, 10 amp chargers.

I would suggest connecting ALL the cells positive (not just blocks of 4) terminals, and all the negative terminals together (parallel configuration). If done individually, the previously charged cells voltage will settle down over a week or so as you charge the next cell group, and in my experience, they can fall somewhat out of balance between the first charged cells, and the last, and prevent you from getting a full charge on your assembled pack.

I don't know what sort of charger you are ordering from AliX, but I would highly suggest getting a bench power supply also, the 3.65 volt charger really only has a 1 time use. You can set voltage (on most) between 0-30v and 0-10amps. I've seen 60v ones that would be better for a 48v system though. They run $50-100 for a decent model, and can be used to charge, or provide power, to anything. It's one of the MOST useful tools I have for testing the electronics (and my DIY hobby) that I fix for a living.
 

ken morgan

Solar Addict
There is very little risk for error with the above method, it is a safe, and seriously time saving way to top balance. It only requires setting up a BMS, which you will need to learn to do anyway.

That being said, charging all the cells in parallel to 3.65 is a "set it and forget it" method that works great except for the amount of time. It took about a week to top balance my 4ish KW pack, and I was using two, 10 amp chargers.

I would suggest connecting ALL the cells positive (not just blocks of 4) terminals, and all the negative terminals together (parallel configuration). If done individually, the previously charged cells voltage will settle down over a week or so as you charge the next cell group, and in my experience, they can fall somewhat out of balance between the first charged cells, and the last, and prevent you from getting a full charge on your assembled pack.

I don't know what sort of charger you are ordering from AliX, but I would highly suggest getting a bench power supply also, the 3.65 volt charger really only has a 1 time use. You can set voltage (on most) between 0-30v and 0-10amps. I've seen 60v ones that would be better for a 48v system though. They run $50-100 for a decent model, and can be used to charge, or provide power, to anything. It's one of the MOST useful tools I have for testing the electronics (and my DIY hobby) that I fix for a living.
you forgot taxes... at least according to the us government ;)
 

Dave Knapp

New Member
you forgot taxes... at least according to the us government ;)
Well, after 2 weeks I'm back with an update and a plea for some guidance. I bought a bench power supply and 2 LifePO4 specific chargers. Since the batteries are physically bundled in a 12.8v bank of 4s, I used the chargers to bring them all to 13.5v. The theory was good, but the execution left some issues. Of the 8 bundles, 4 of them contain 1 "overcharged" cell, ranging from 3.47v to 3.72, and one bundle has 2 overcharged cells. There is virtually no guidance with the 2 daly 48v, 150A, 16s BMSs, but I get the feeling that a 0.4v disparity in one 4s bundle is more than the BMS can cope with. So, I see 2 possible fixes, and would love to hear of any others. My 2 approaches would be to either put the concerned bundle in 4p and let them equalize overnight, or use some kind of a load to drain down the high voltage cells, maybe a resistor? Any ideas? Thanks.
 

MisterSandals

Participation Medalist
I used the chargers to bring them all to 13.5v.
Your mistake was to do this without a BMS and without watching your cells carefully. You should try to drain the cells over 3.65v asap to minimize damage. You can use simple things light light bulbs or resistors or solder irons to drain energy. They don't need to function, just getting warm will drain the cell.

Why were you charging in packs of 4? Were you trying to top balance or something?

Hopefully you have your cells labeled and have taken notes. The cells that charged the highest will be your weaker cell(s) (of the 4 in a pack). This info will be useful down the road when managing your 16s battery.
 

Hedges

I See Electromagnetic Fields!
My 2 approaches would be to either put the concerned bundle in 4p and let them equalize overnight, or use some kind of a load to drain down the high voltage cells, maybe a resistor? Any ideas? Thanks.

I don't think cells in parallel balances them well. All should be pushed in the same direction to the same SoC, not pulled in opposite directions.
So after you've bled down the high cells like Mr. Sandals says, recharge all of the to some target voltage (e.g. 3.65V) and wait for tapered off charge current.
You can wire in parallel to do that, or leave it as a pack and use bench supply to top one cell at a time. They may show slightly different voltages due to settling for differing amounts of time, but should actually be a same SoC.

All charging should be voltage limited on a per-cell basis. Either single cell charging with voltage setting of power supply as the limit, or monitored by BMS when charging in series, with BMS shutting off charging.
 

Dave Knapp

New Member
Your mistake was to do this without a BMS and without watching your cells carefully. You should try to drain the cells over 3.65v asap to minimize damage. You can use simple things light light bulbs or resistors or solder irons to drain energy. They don't need to function, just getting warm will drain the cell.

Why were you charging in packs of 4? Were you trying to top balance or something?

Hopefully you have your cells labeled and have taken notes. The cells that charged the highest will be your weaker cell(s) (of the 4 in a pack). This info will be useful down the road when managing your 16s battery.
These "cells" came physically and electrically in a pack of 4s, with busbars attached. The bottom line, to me, is will the BMS accommodate 7 of 32 cells being as much as 0.4v higher than the rest? Right now, 25 of the cells are between 3.30v and 3.35v. The highest cell is 3.72, then 3.69, 3.68, 3.60, 3.58, 3.47, and 3.43. If I need to drain down the high voltage cells, what would be a convenient dc load? Maybe a DC light of some kind.
 

Supervstech

Administrator
Staff member
Moderator
ANYTHING resistive will drain the cell.
If you have a roll of heavy wire, you can connect CAREFULLY the spool directly to the high cell... for a few seconds at a time.
gotta have over 20’ of wire in the spool, not a short wire...
 

Sabre36

Solar Enthusiast
Personally I don't care for the step method. The power supply may not be able to put out the full amps it's capable of with the lower voltages even using good cables, and may not go into CC mode. I have experienced this for myself using a Riden 6012 with 12awg cables. After dealing with this when I started my top balance, I decided the heck with it and set the power supply to 3.65 volts.

This is simply due to voltage drop between the PS and the cells. Once in CV mode it will be limiting current, just how CC/CV works.. If you set it to 3.4V it will hit a perceived CV (PS end measures 3.4V on output end but cell end is lower). Once the cells get full enough, so the accepted current drops below the PS end measured CV), the voltage will eventually rise to 3.4V at the cell end too and current will eventually go to 0A at 3.4V. At 3.4V the cells are very near 100%. This means the time spent at high voltage, once you move to 3.5V or 3.65V is shorter. Yes, it takes a bit more time, but 3.4V means less risk during the long part of the top balance and will not degrade your cells as bad as trying to achieve 3.65V in one step, if you're not there to watch it.

I am attaching a photo of the Riden only putting out 5.84 amps with the voltage set at 3.4 volts. It is in CV mode. Once I set the voltage to 3.65 volts it put out close to 12 amps, switched to CC mode, and remained there until the voltage reached 3.65 volts. Once 3.65 volts was reached the Riden switched to CV mode and then the current began to taper off.

The voltage drop between the PS and cells has not changed and by increasing the CV, and thus putting the PS back into CC / bulk mode, the 12A will create even more voltage drop. Also keep in mind that you don't want to run these small supplies at more than about 80% for continuous use.

Higher quality power supplies utilize a dedicated voltage sensing circuit, but these are significantly more expensive. We have a few small PS in our shop. One is a 5A linear (no v-sensing) and we use 6AWG wire on it to have an extremely low drop between the PS and cells. Most of our larger models, 60A etc., have built in voltage sensing making this sort of thing a non-issue..
 
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Sojourner1

Itinerant
ANYTHING resistive will drain the cell.
If you have a roll of heavy wire, you can connect CAREFULLY the spool directly to the high cell... for a few seconds at a time.
gotta have over 20’ of wire in the spool, not a short wire...

How is this done? Is it as simple as just taking the one end of the exposed wire and briefly holding it to the positive post, only to the cell that is higher in voltage? If this is the case then does it have to be disconnected so the cells aren't connect in series to form a 12/24/48v battery?
 

Sojourner1

Itinerant
Then, the cell need to be disconnected from the pack and then you take the one end of the long wire spool and briefly touch to the + & - posts? Is this correct?
 

NOLA_Castle

Learning Everyday....
First of all, I'm new to this. I'm posting in the the beginners area hoping not to be overrun with messages about how dumb I am.

I watched dozens of Will's videos and thought I knew enough. I put up the solar panels and bought a very expensive brand new 32 cell 48v lifepo4 battery and a good solar charger.

The cells came certified fully balanced and since they were brand new all I did was check the voltage and they were all the same. Also I thought if everything is new and balanced you don't need a bms. So hooked up the charger and everything looked good.

I left it for a while and came back an hour later to find one cell with HUGE bulges on both sides and was so hot I couldn't touch it. My kids were home so thank God it didn't explode.

Obviously I shut everything down and took it outside with a pair of gloves. Now the other cells are reading different voltages too.

I'm devastated. I don't know what to do, how to fix this, or even what I did wrong and I think i ruined my $4000 battery.

I don't know what happened or what to do now. Any help would be sooo appreciated.
My recommendation is: Please check your other solar system components, such as your solar panels to ensure proper fuses are utilized, check on the proper wiring size, etc. Battery is one of the components. SAFETY First!!
 

ken morgan

Solar Addict
if you have a dedicated 3.65 volt charger attach its leads to the positive and negative terminal and allow that cell to come up to 3.65. let it float for an hour or so and done. if you need to remove either the positive or negative lead this will disconnect the pack as a whole and allow you to concentrate on one cell at a time. for the ones that are over, a standard headlamp from any car with alligator clips will serve to bring that cell down...once again unhook one of the main leads so that you are using only the cell you are attached to.
 
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