Yesa pack "modulation"

[BiGH]

okay so i've got 1-2 suspect cells in my yesa pack. Before sam will state that tehy are warrantable, he wants me to "modulate" them, in essence balancing the pack.

his reply was this:

"Charge the battery fully, then check the cell voltage with the other cells,
if the cell have too high voltage, use about 22?/5W resistance to discharge the
high voltage cell till similar to others . If the voltage is too low, you can use constant
power and modulate the voltage to 3.9V and 2A current to charge. Use the method to
modulate the cell to have the similar voltage with the other cells."

I thought it quite interesting to get the non bad cells to discharge down to the same level as the unhealthy cell and then charge the pack up.

I also noted that he suggests using a 3.9v 2a current to charge. I looked at the voltphreaks single cell charger and it says its for a 3.2v cell.... not sure what the go is here.

I need some help guys!. I was gonna pop down to the store and grab a 22? 5w resister and a breadboard to discharge the other cells, should i just grab a voltphreaks charger insted?

 

[Malcolm]

Sounds like it's worth a try. The 3.2V quoted for the Voltphreaks charger is the working voltage of the A123 cells. The charger will actually charge to 3.7, maybe 3.75V, but as soon as you put a load on the cells they will drop to around 3.2-3.3V.
3.9V is a bit higher than you'd normally use for A123 LiFe cells, but I guess the Yesa cells are a little different. I've been messing about with some A123 cells, charging them up in a single parallel string to 3.75V and then discharging them at around 2C in series. I've done this three times. At the start a couple of cells were about 0.15V lower than the rest, but now they're within 0.01V of each other after discharging to around 3V.

 

[Ypedal]

The VP chargers will bring the cells to a peak of 3.8v before going green !

fyi

 

[BiGH]

i'm gonna grab the resister tomorrow, and start discharging the good cells until the voltages are around teh same amount 3.20v and then do a full charge

this *should* be interesting. i just hope the pack was badly out of balance and not that the cells are buggered.

 

[fechter]

It sounds sort of like doing an equalizing charge on a lead-acid. Basically, you overcharge the crap out of it, but by 'modulating' or only intermittantly applying the overcharge, you hopefully prevent any damage.

I suspect that if the cells are manufactured, then sit around for a while, the cells self-discharge at different rates, resulting in unbalanced cells. Once you get them balanced, they should stay in balance with regular use. If you park the thing all winter or something, you could go back to an unbalanced conditon and need to repeat the excrecise.

 

[BiGH]

thanks fetcher

won't have a problem with being away for the winter - where i live is quite warm still.

i'll try the resister and if that doesn't work will invest in a lab power supply. $205AUD on ebay.

 

[Mark_A_W]

"quite warm still"???

Umm, summer is two weeks away...it's gunna get REALLY FRIGGIN HOT SOON


I hope your pack comes good.

 

[GGoodrum]

Discharging the high cells down to the level of the lowest is exactly how most of the RC balancers work. If you have a weak cell/cell block, the rest will only end up at the same capacity as the weak one. That's why I prefer individual cell chargers.

BTW, my 10 VoltPhreaks 2A CC/CV chargers have cutoff voltages that vary from a low of 3.78V to a high of 3.89V. The a123 cells seem quite happy with that.

-- Gary

 

[BiGH]

i've equalised the voltages to 3.33x v each +/- 0.01 v
doing a charge now, its taking a while, which is good, showing that i've drained a bit ouf othe cells.

tomorrow is going to be 35d celsius - good day to ebike and have a shower @ work lol.

 

[Mark_A_W]

Now they are saying 37 degrees..

Way too hot for November

I'm going to ebike to work and not have a shower...I'll be going pretty much on the motor today :lol:

 

[Freddyflatfoot]

Yep, did the same this morning. Chucked the uniform in my panniers and donned shorts and shirt for my ride to work!...................................And that was at 6AM!
Cheers!

 

[BiGH]

excellent work fellas!

yeah i have to ride down at 2pm - so i'll need a shower since i have to peddle along to amke teh distance. I'm still modulating my pack though :s taking ages to discharge the cells far enough. I've only got 4 cells out of ballance (too high).

I'm trying to find a cheap source for a single cell lifepo4 charger...

i've just enquired at voltphreaks, will wait for their reply when its daytime in the USA.