Is there a difference between a 7S and 8S charger?

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ebike11

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Hi guys
My friend has a 24v10Ah LiFEPO4 battery pack but he couldnt find his old charger so ordered one from china.
Its a 7S 3A charger but when plugged in, does nothing. The green power light is on but doesnt change to red to charge. However with the battery installed on the bike and the charger connected to the bike and wall socket, the bike does in fact turn on and the motor turns normally until you unplug the charger from the battery.
Would ordering an 8S 2A charger make it charge properly? Thanks in advance!
 
The charger doesn't care too much if the battery is 8s lifepo4, or 7s ncm/nca. Having the correct charge voltage for the battery, is the important thing. The charger doesn't know or care how many series cells, or their chemistry (within reason).

8s Lifepo4 requires a charge voltage of approx 8*3.65V = 29.2V. 7s for ncm/nca (most 18650 cells) requires 7*4.2V = 29.4V.

Basically, it's almost the same thing and should be pretty well interchangeable. Lifepo4 is less critical with regards to charge voltage, a little over 3.65V per cell, isn't normally an issue, but for 18650 cells and of course lipo, you need to be far more careful about overcharging them.
 
What is the charger voltage ? You always, always check charger voltage and polarity. Always. Do you have a multi meter ? Get one. Free with coupon at Harbor Freight and small purchase.
 
The 7S charger doesnt seem to work. The green light comes on but not the red charging light. The battery is pretty much dead now because it was sitting for awhile.
Would an 8S charger make it charge correctly? Im thinking he miscounted the cells.
 
It might refuse to start charging a very low voltage battery.
 
dogman dan said:
It might refuse to start charging a very low voltage battery.
Click to expand...

I see....would there be a way to jump start the boost from such low voltage since its been sitting for awhile
 
999zip999 said:
What is the charger voltage ? You always, always check charger voltage and polarity. Always. Do you have a multi meter ? Get one. Free with coupon at Harbor Freight and small purchase.
Click to expand...

Charger voltage is 29v when i tested it with a volt meter when the charger was plugged into the wall.
 
He said 24V LiFePo4, so 8S times 3.65V should be 29.2V full charged. I charge my 16S A123 pack with a 59.4V charger so that seems right.

I would recommend testing the voltage of each cell (or cell group) and make sure none of them are below 2.0V or above 4.0. These are extremes, really you shouldn't see anything below 2.5 or above 3.85 under normal conditions.

If there's a cell at high voltage, it might be trying to bleed down that cell before it starts charging. Depending on the BMSs bleed capacity, and the Ah of the cell(s) this could take a fair bit of time.

A really low cell might cause it to halt charging entirely for safety reasons. If you find a really low cell, let us know and we can come up with an idea on how to get it back into the working range.
 
ebike11 said:
Yes the battery is 24V 10Ah...however no charging starts when the charger is plugged in. Weird
Click to expand...
There's probably a very logical reason for that. As the charger seems to be fine the battery pack is probably the culprit.

Did you check the battery pack's voltage or check the voltage of the individual cells/groups, like pointed out by others?
 
TristanP said:
ebike11 said:
Yes the battery is 24V 10Ah...however no charging starts when the charger is plugged in. Weird
Click to expand...
There's probably a very logical reason for that. As the charger seems to be fine the battery pack is probably the culprit.

Did you check the battery pack's voltage or check the voltage of the individual cells/groups, like pointed out by others?
Click to expand...

Hi I was thinking that...I havent opened the pack to test cells however we did test the overall battery voltage and it read around 17 to 18V. So it definitely has no juice at the moment. Also when we pushed the battery indicator on the battery pack itself, no lights displayed
 
Ah yes...
It looks like the cells are REALLY low. I might need to charge each cell one by one to get them each up to bormal levels. Can you recommend a 1S charger or the proper equipment to do this?
Thanks a lot
 
Voltphecks has a single cell charger for lifepo4 that stops at 3.65v. You can use a cell phone charger, but they are at 4.4 or 5v or more 7v. Even thou 4.5v is printed on the sisideAlways check with meter. Just get it all to 3.0v all the cells the same. Must seat and watch. Seat. Then hook up the charger. The meat of lifepo4 is 2.8 - 3.35v under 2.8v is a fast race to zero as it's M T. And after 3.45v the race to the top and above very fast after 3.45v for lifepo4.
 
Si . lt will rise fast to 2.8 then a little time to 3.0v then a long time to 3.45 volts. It depends on the rate printed on the side of unit ( don't believe what printed on the phone charger check ). That's why you sit with it and learn to 3.0 or 2.8v. Maybe have two to keep your interest. But watch , because as soon as you ealk away or p things happen. Seat
 
I'm trying to get you to write down the voltages first . Then charge to 3.0v, then put it on the charger. It can charge to 3.6.

The meat of the charge for lifepo4 is 2.8 to 3.45v please do add anything to this.
 
999zip999 said:
I'm trying to get you to write down the voltages first . Then charge to 3.0v, then put it on the charger. It can charge to 3.6.

The meat of the charge for lifepo4 is 2.8 to 3.45v please do add anything to this.
Click to expand...

Yes will do!
Ill be back home on the weekend to test and check the cells thanks!!
 
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