Lipo charge / discharge strategy's

[rodgah]

So in light of Jesters lipos puffing, and my previous scouring of the forums searching peoples efforts at maintaining lipos, Ive decided to make a thread in here about strictly Lipo and everybodys observations and ideas. I am a noob when it comes to balancing and charging, so anything I get wrong, please correct.

I know there is a Lipo thread in battery tech and it has been discussed alot deep in other build threads, but my guess is most people on this section of the forum are more from a hobby rc background and therefore approach this differently to the majority.

Since the Recumpence drives are based around astro motors and the meaty CC controllers, 48volt limit is what most of us aim at. Matt has mentioned before that he uses a 12s Hyperion charger, but I for one am still struggling to get my head around the methods everyone uses.

My idea is to get all cells to a common state of charge, link the discharge leads together to create your 12s Xp pack, parralell all balance wires together to create a single 12s 13wire connector (im guessing this is available i just cant find). Charging requires disconnection of main power from controllers, connecting them to the charge wires of the charger and balance connector to the balance port of charger(does this require a certain order of connection?).

(assuming a 4parralell pack of 5ah cells)I am guessing when all balance taps are paralell the charger see's each cell as 4 times the capacity(mega cell lol) of what a single cell would be but at the same voltage. If this is correct then would using a cell monitor likehttp://www.hobbycity.com/hobbyking/..._Cell_Voltage_Monitor_2-6S_Lipo_(New_Version) plug into the balance plug before and after charging to check that each 'mega cell' is within tollerances of eachother.

question is what is the bad effects of leaving all balances parralell together while discharging in bike/storage not in use. if a single cell dies, is this method enough to notice that the mega cells are out of balance and that further inspection is required. Is there a way to configure the discharge wires to limit the effect of a dead cell has on the rest of the pack. IE is it better to series 2 packs together then parralell each 12s block, or paralell first then series 2 blocks to make 12s.

correlation of alot of topics. thanks guys

 

[recumpence]

It is good to let cells ballance to each other. However, there is a possible issue storing them when paralelled at the cell level because if one cell is going bad, it will pull the other cells down it is connected to. So, in your scinerio, it is possible you could lose 4 cells rather than just the one.

Bear in mind, I have never had a cell or a pack go bad merely from sitting. I let my lipos (for RC stuff) sit more than a year sometimes and they work fine afterward.

Other than the obvious "do not exceed 4.2 volts per cell" rule, one major piece of advice I have is to be nice to your lipos. Try hard to never pull more than 50% of their rated "C" discharge capability, and always leave 40% or more in your pack (AH capacity) and lipos will keep going, and going, and going. If you pull them down to 20% SOC every run, and pull the max "C" from them repeatedly, they will wear out quickly.

Matt

 

[rodgah]

Matt could I please trouble you for a picture/diagram of how you wire up your 1210i and I gather 2 external balancers to your packs with 12s. As I have come to realise the 1210i doesnt accept a single 12s "input" but 2x6s but is still called a 12s charger because it can monitor and ballance 12s.....so obviously they arent parralelled somewhere inside of charger. my main interest is the discharge wires as each balancer board has a - an +, so do you have a "series Y" cable you remove for charging effectively turning your pack into 2 x 6s 50millionAH ........then replacing the Y cable for discharge, or is there some trickery of the balance boards to accept your pack that i havent figured out.

 

[recumpence]

Yes, the 1210i does accept 12S in series. It is the newer chargers that don't.

I do not use ballancers when I charge. I just occasionally ballance my packs with stand alone ballancers.

Matt

 

[rodgah]

Matt i forgot you said that somewhere else I read. I think I am worried too much and obviously trying to make things overly complicated. When you say if a cell goes bad in storage and wrecks 4 other cells, is this only when the balance tabs are paralelled and the discharge wires in 12s4p config or will this happen whether or not the balance tabs are connected. Thanks for your patience Matt, BTW I look forward to the unveiling of the V3 drives.

Rodger