2p charging
 

I plan on running 2 zippy 5000 mah packs in parallel in my maxx, and also want to charge them in parallel. Can I just wire them in parallel and only balance one pack, and switch which pack I balance every other time? Is there any way to balance both packs when charging 2p? Since I will run them 2p I want to keep the two packs at the same voltage at all times.

I do it with 2500mAh Zippy-R 4s packs, I made custom parallel balancer wire and charge it as 5000mah unit. Just sometimes split them and check voltage, and balance them sepparatly to get same voltages in cell safety reasons

You will have to have a custom harness made to balance the packs in parallel with one balance. Check out briang's sig, he has some diagrams there that you can play with. Oh, forgot to say "BALLS"

man, everyone's bustin my..... Ooooh! something shiny........

so if I just hardwire the pack leads and balancer leads from each pack together in parallel they'll always be balanced to each other, just like a purchased 2p pack, correct?

Yes, but I would make harnesses. Mainly cause I like to. Will you stack the packs and tape/shrink them together?

nope, riding on either side of the center diff on my e-maxx, motor mounted above diff for perfect balance, due to the placement harnesses would work better and look cleaner while the batteries are on the truck, I haven't done any wiring in some time, good excuse to buy a stripper. Oh, something to take the insulation off the wire might be a good purchase too..............

Hmm, I just pay the stripper per dance...

Wire strippers are great, I have dozens. I like to buy stuff...

you're right, renting sounds like a much better option, then I don't have to feed it.

i'm unclear how to wire the balance wires in parallel. i built 2 5s packs that are wired in parallel by connecting to 1 plug. looking at brian g's diagrams it looks as though I would have to have a 10 cell balance plug to make the balance wires in parallel. is this the case or am i missing something?

You need to do Y-balancer harness and Y-main wire

I just bought 2 these wires on 4s setup http://www.hobbycity.com/hobbycity/s...idProduct=5099
cut it in middle took every wire from two female and one male connector and soldered to Y. Made that with every wire, be sure that you paralleling exactly same wire do not twist them.
Same with main leads with Deans connectors.

Before charge be sure that every pack is discharged (i mean discharged to safe LiPo voltage which is close to 3V per cell but not less) and every cell on same voltage, balanced. If difference 0,01V its ok not terrible. Ideally every cell must be same voltage. Connect to your harness and charde as One big unit. Thas all.
Sometimes check voltage difference in every pack and balance (not charge) it sometimes separate.

I just spent about 10mins thinking about this (trying to determine what could go wrong with it, but it should work). You would make a harness for the two 5s packs such that all of the corresponding wires are in parallel, and are outputted to a single 5s balance connector. I drew up a quick thing to help demonstrate this:

If one pack is a weaker pack, won't this be dangerous ? I would charge the two packs together through the main charge leads to 90%, and then finish them individually on the balancer.

Actually, with the cells in parallel, each set (1 cell from each pack) of paralleled cells will try and stabilize at a voltage that equalizes them. Essentially, the balancer then will balance each set of paralleled cells as a single cell since the voltage will be equal in the cells.

However, while it should work fine, it would really be easier to just use 2 balancers and parallel the charging input into the balancers instead.

I cant confirm that actualy. Usualy after couple cycles I balance cells on every pack separately becouse notices that cells no not stabilize each other. If one cell is 3,5V and second paralel cell is 3,7V on avaraege shows 3,6V if both batteries connected parallel. Whats why i do it.
And if packs are same type and brand etc parallel using should do OK.
If they are not equal I am not recommend to doi it because difference in cells will rise and avarage can be OK but for example one weak cell will be over discharged.

Ideally, the higher voltage cell charges the lower voltage cell until they reach an equilibrium, but it must be such that Lipos would need to be paralleled for a long period of time to do so. TrueRC and MaxAmps both build packs with cells in parallel, but with the cells constantly connected, it should be much eaiser for them to maintain equilibrium.

Based on what you've personally experienced though, I can't help but recommend separate balancers for each pack.

If I was to parallel to seperate sets of packs:

• Charge and balance each pack seperately, but preferably at the same time on different chargers. If you charge one pack, then charge the other, the voltage on the first one might have fallen a little. Probably only ~.05v total. Measure with a voltmeter to be sure.
  
  
• Hook the main charge leads together + to + and - to -. If there's even a slight difference in pack voltages, you'll probably see a spark.
  
  
• At this point, each pack is the same voltage but the individual cells between each might be slightly off. So, then use a small value (~1ohm) resistor on the balance taps between each parallel cell to "soak up" any potential differences before hooking them permanently. Maybe even hook up a voltmeter across the resistor. When the voltage drops to 0, there is no current in the resistor then the two cells are equal. The voltmeter is simply to verify that there is no current from cell 1 trying to "charge" cell 2, or vice-versa.
  
  
• Once SURE each cell of pack 1 is exactly the same as the corresponding cell in pack 2, tie the balancer leads like MM has in his diagram.

Maybe I'm a bit over cautious, but that's what I'd do...

Once the cells arae permanently wired in parallel, each cell in the parallel pair will remain the same and never be different from each other. The balancer wire assures this.

The more I think of this, the more I don't like forcing the cells to equalize through a small balancer wire. They SHOULD stay equal, but if one is weaker than the other, there will most likely be current flow in the balancer wire. In a stock 2p pack, the cell tabs are tied together for a low resistance/high current connection.

So, to revise my previous statement, I would actually pull the packs apart, and make two seperate series-connected 2s2p packs instead. Or, balance each pack seperately as skyello said...

my packs are made up of cells from an A123 dewalt pack, brand new out the package, never charged, never run. This being the case is it safe to make up a harness like metalmans diagram or should I still go through the process above?

It's easy enough to check the voltage of each cell in the pack using a DVM (digital voltmeter). Of the maybe 6-8 Dewalt packs I've come across, I'd guess half of them have had a cell or cells of lower voltage than the rest. If that is the case, you can use the resistor charging method BrianG outlined above to charge up the low cell(s) using the other cells.