Top balance grade A brand new cells that are all at exactly the same voltage?

[bordenov]

So I bought 4 280ah cells off aliexpress to build a 12v battery for my van conversion.

They all measure to 3.233v. Do I still need to top balance these?

Also, how often do cells generally need to be top balanced over their lifespan?

Thanks for any help.

I'm not sure if I should go through with buying a DC charger and a few other components and top balancing or if they're fine. Some people on reddit said it's fine, but I'd rather check here as well.

 

[GSXR1000]

I would say a must... but a 10amp power supply and make some 10guage wires.. put it on 3.6v (before you connect to the battery) and let it sit for a week... DO NOT adjust voltage while connected to the battery's

theses cells in the middle of the state of charge can contain 2 different amp hours at the same voltage

Thread 'Top balancing why proper wire' https://diysolarforum.com/threads/top-balancing-why-proper-wire.17168/

 

[bordenov]

I would say a must... but a 10amp power supply and make some 10guage wires.. put it on 3.6v (before you connect to the battery) and let it sit for a week... DO NOT adjust voltage while connected to the battery's

theses cells in the middle of the state of charge can contain 2 different amp hours at the same voltage

Thread 'Top balancing why proper wire' https://diysolarforum.com/threads/top-balancing-why-proper-wire.17168/

Okay thank you for your help, I think I’ll go ahead and order what I need to then. What is the reason for keeping the DC power supply on for a week at that voltage before balancing the cells with it?

 

[OnTheRoadAgain]

I would say a must... but a 10amp power supply and make some 10guage wires.. put it on 3.6v (before you connect to the battery) and let it sit for a week... DO NOT adjust voltage while connected to the battery's

theses cells in the middle of the state of charge can contain 2 different amp hours at the same voltage

Thread 'Top balancing why proper wire' https://diysolarforum.com/threads/top-balancing-why-proper-wire.17168/

Question......
As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason?

 

[OnTheRoadAgain]

Okay thank you for your help, I think I’ll go ahead and order what I need to then. What is the reason for keeping the DC power supply on for a week at that voltage before balancing the cells with it?

That's called top balancing. The cells are in parallel.
After you assemble the pack in series to get up to 12v, the BMS will keep them balanced....or is supposed to.

 

[GSXR1000]

Okay thank you for your help, I think I’ll go ahead and order what I need to then. What is the reason for keeping the DC power supply on for a week at that voltage before balancing the cells with it?

it will be more like 3 days... it will stay the same voltage for days and you will think it isn't working and some people mess with the voltage and ruin there batteries cuz the get in a hurry

remember 4x280ah=1120ah
1120ah charged at 10 amps will take 112 hours or 4-5 days

 

[bordenov]

That's called top balancing. The cells are in parallel.
After you assemble the pack in series to get up to 12v, the BMS will keep them balanced....or is supposed to.

Oh i misread what he said. I thought for some reason he was saying you need to set the DC to 3.6 for a week before connecting the battery lol.

 

[bordenov]

it will be more like 3 days... it will stay the same voltage for days and you will think it isn't working and some people mess with the voltage and ruin there batteries cuz the get in a hurry

remember 4x280ah=1120ah
1120ah charged at 10 amps will take 112 hours or 4-5 days

Oh the total amp hours are 280, so shouldn't it be 28 hours?

 

[bordenov]

Question......
As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason?

I saw that you should use a blocking diode to protect the power supply, so maybe another one in reverse direction?

 

[GSXR1000]

Oh the total amp hours are 280, so shouldn't it be 28 hours?

in series voltage goes up AH stays the same... IE 12v @ 280ah in parallel voltage stays the same and AH goes up ... IE 3v @ 1,120ah

so no not at all... now that being said your batteries will not be at 0% so more like 700ah worth of charging so 70 hours

 

[bordenov]

in series voltage goes up AH stays the same... IE 12v @ 280ah in parallel voltage stays the same and AH goes up ... IE 3v @ 1,120ah

so no not at all... now that being said your batteries will not be at 0% so more like 700ah worth of charging so 70 hours

Ah didn’t think about that haha. Sorry I’m new to this stuff, just wanted a cheap effective alternative to, say, a battleborn so I could have plenty of power in my van. Thanks again!

 

[GSXR1000]

Ah didn’t think about that haha. Sorry I’m new to this stuff, just wanted a cheap effective alternative to, say, a battleborn so I could have plenty of power in my van. Thanks again!

that's why I say do it right the 1st time and take your time... the savings is huge...
I spent right at $1000 for 560ah tested

Thread 'Just ordered Lifepo4 prismatic cell 3.2V 280Ah lithium lifepo4' https://diysolarforum.com/threads/j...smatic-cell-3-2v-280ah-lithium-lifepo4.14955/

 

[Deleted member 23531]

As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason?

Yes, and the solution is to use a better power supply which has compliance voltage settings you can trust!

 

[Deleted member 23531]

I saw that you should use a blocking diode to protect the power supply, so maybe another one in reverse direction?

I have not seen that. Can we really not trust a DC power supply these days? Seems unnecessary and could slow down the process if the voltage drop across the diode and the wire makes the power supply enter constant-voltage mode sooner than it would otherwise.

 

[GSXR1000]

Question......
As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason?

nope... I did disconnect every day or so and check the power supply with my meter...

 

[GSXR1000]

I saw that you should use a blocking diode to protect the power supply, so maybe another one in reverse direction?

what would a diode do? reverse polarity maybe but then you do not get an accurate voltage to the battery.
I did smoke one power supply connecting it backwards

 

[OnTheRoadAgain]

Yes, and the solution is to use a better power supply which has compliance voltage settings you can trust!

"As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason? "

"OTHER THAN" the settings on the power supply was actually my question

The question assumes a power supply failure no matter what you buy or who you trust

 

[GSXR1000]

"As they sit there for that week, other than the setting on the power supply, is there a way to have the cells protected from overharge in case the power supply acts stupid for any reason? "

"OTHER THAN" the settings on the power supply was actually my question

The question assumes a power supply failure no matter what you buy or who you trust

does anyone use a 1S 3.65v BMS?

 

[Deleted member 23531]

The question assumes a power supply failure no matter what you buy or who you trust

That's not true at all. The failure rate is a property of the power supply. I have *never* seen an Agilent, Keithley, or Rigol power supply "screw up" and change its own settings. The worst that can happen if they brown out or whatever, is they shut off. It's only the crap brands you can't trust, and even those seem pretty trustworthy based on all the people using them successfully to top balance their cells.

I think you're over thinking it. Just set the power supply correctly (with no load) and don't touch it. It isn't like its knob is going to "creep higher" in all likelihood. You should check on it periodically throughout the week or so of top balancing. If you're really nervous you can set it to 3.4V, wait for that to complete, then do the final quick march up the 3.4V -> 3.65V knee of the curve. Doing this, however, the first step to 3.4V will take a lot longer because it will switch to constant-voltage mode when the cells are still in the flat region of their charge curve. It's not until the very end that there is any risk of over-voltaging, and that would only happen from neglect: like not checking on it every few hours.

 

[GSXR1000]

does anyone use a 1S 3.65v BMS?

maybe need to install lightning protection... and yes tornado protection..... lol

there are 100s of us on here that use the $60 power supply.. no one has had a run away failures