Got me a new lipo and need answers

[crazyjr]

I just got a Polyquest Twenty LIPO 3s 3700mah with a Polyquest 3s cpu balancer. I need to know if i can charge at 1c with the balancer, if not, what amp do i use? Also, what should i set the cut-off voltage on my Mamba 5700 esc, 9.3v (3.1v per cell), or 9.6v (3.2v per cell). I know that it used to be 2.7v, then 3.0v, now i'm not sure what to set it to. If nobody has any idea i'll set it for 9.6 and work down to a good level between 9.0 to 9.6.
Thanks in advance for any info

[neweuser]

Not sure about the balancer, but you should be fine at 3.1 cut off. If you want to play it safe, go 3.2

[BrianG]

I agree. From what I've read, the idea is to set the cutoff such that when the battery is disconnected from any load, the voltage will rise to ~3.6-3.7v again after 15-20 minutes.

That said, I would set the cutoff to 3.2v and then run it until the ESC stops. Let the battery sit disconnected for a while, then hook it to the charger and see what the standing voltage is. If it's 3.7v or higher, maybe reduce the cutoff to 3.1v.

3.2v is a safe cutoff to extend the life of the pack, but of course the runtime will be slightly less than if you set it to say, 3.0v. I say slightly because at that point of the packs cycle, the voltage drops quite rapidly so any runtime gains would be minimal.

What is the max amp rating of the balancer? Does it actually charge through the taps, or does it charge through the main power leads and just monitor/balance through the taps? I think MetalMan mentioned somewhere that the taps are good for 2-3A max, but that's just from memory.

[neweuser]

See Brain, you taught me something!

[crazyjr]

Ok i just looked at the paper that came with it and it says max current charge is 5A/h, so, would that be 5Amps? If so then i could charge at 3.7 with no troubles. I forgot to mention that i'll be charging with Triton and triton2 chargers and this will be put in either the T4 or a traxxas SRT with the mamba 5700 system (pack will barely fit the T4 but looks like it will fit easily in the SRT. I want to see 60MPH in a stadium truck.:028:

[neweuser]

Is that charging thru taps? You should be fine then.

[MetalMan]

Does the balancer go between the battery and charger? If it does, does the balancer have an extra set of wires coming from it that attach to the battery's output wires? If it doesn't have the extra wires, and does to between the charger and battery, then 3amps is the max. you should do. Otherwise, charge as high as you want! (1C max. recommended, of course).

[crazyjr]

Yes it goes between the battery and charger. The only wires on it are the red and black for the charger and in the plug there are 4 black and one red wire. I was only aiming for 1C, which on this pack is 3.7amps, so 3 amps will do.
Thanks a lot for the info guys

[MetalMan]

Yeah, in this case 3amps is the max. you should do. You can charge at 3.7amps if you connect the battery to the charger, and the balancer to the battery (not between the battery and charger).

[Serum]

From what I've read, the idea is to set the cutoff such that when the battery is disconnected from any load, the voltage will rise to ~3.6-3.7v again after 15-20 minutes.

This makes no sense in RC IMO.

With RC the loads are not constant. i use a 3V cutoff. you don't drawn them entirely till 3V, it are just peaks less than 3V, that make your car stutter.

When my pack reaches the point where the car starts to show this stutter, you quit running it. about .1 second after the pack dropped till 3V it's above 3.6V again.

[crazyjr]

Thank you Very Much guys, I had most of the knowledge from here. Just needed a few specifics. Thank you. So 3 amp charging and 3V per cell cutoff will be good

Edit: Got a couple more Questions:
1, Can i charge, then balance later seperate of the charger?
2, Do i need to balance everytime or can i skip every so often?

[Serum]

I personally ballance them every single time. I know Mike doesn't do this though.. But eversince it doesn't take much more time, (at least, my balancer can do up to 10A)i am more comfortable with balancing them every charge.. And there is quite some imbalance with every charge..

I don't quite get your first Q though? i would balance them during charging.

[crazyjr]

Just a question, I like to know wether things can be done even if i don't plan on doing it, you never know.

Thanks Serum and everyone who answered my questions. I have learned a lot in the year and a half i have been here and still come here first when i have questions

[neweuser]

I also balance everytime, it makes me more comfortable with the life of the battery. I charge then balance. Sometimes I check the balance of the packs before charge though too.

[BrianG]

The only downside to balancing after charging is that the balancer does its job by discharging the higher cells until they all reach the same voltage. Consider this: You have a 4s pack and and decide to charge without the balancer. At the end of the charge 3 of the cells are at 4.15v and last cell is at 4.35v. This will still look like 16.8v to the charger (4.2v X 4 cells). So, three cells aren't getting the full charge and one is getting too much. If you hook the balancer up after the charge, it will discharge the high cell until it reaches the same level as the others, which will further reduce the total capacity of the pack when you come to use it since it will be at only 16.6v. No, it doesn't sound like much, but is when you consider that the constant voltage portion of the charge is roughly 1/4 to 1/3 of the charge cycle.

Also, if you balance after the charge, it's a good idea to balance before charging as well. After a pack is depleted, each cell might not be at the same voltage. So, the charger is starting with an unbalanced pack. It is possible they could even themselves out during the charge process, but not guaranteed. Balancing before charging equalizes all the cells from the get go, which minimizes the chance of an out of balance condition by the end of the charge. The only exception to this that I can think of is if you are using an LVC that monitors each individual cell instead of the total pack voltage.

If you balance while charging, all the cells will reach an even 4.2v by the end of the charge so you have full pack capacity.