LiPo charging question

[bledsoenc]

Hello all,

I'm trying to figure out if my Triton Jr. will work with a 8000 mAh 3S2P LiPo pack I just ordered. It's rated for 1-4 LiPo cells and the mAh selection on the charger only goes up to 5000.

My question is if the "cell rating" actually just means 3.7 - 14.8 V, or if it really means that it only does that number of cells. Also, could I run two cycles to charge to a full 8000 mAh -- the first I'd set to 5000 (the max), the next to 3000?

Thanks,
Neil

[Jason Maxamps.com]

The 8000 you have is an 11.1 volt pack. Set your charger to it's max setting's 5 amps. And charge it will only take longer to charge with the 5 amp rate but it will do it. If the charger stops at 5000 mAH simply start it again and it will finish the charge.

Jason

[bledsoenc]

Thanks for the quick reply, Jason. I'm also wondering if the charger's "cell rating" of 1-4 actually just means 3.7-14.8 volts, since the 3S2P is 11.1V but has 6 cells.

[Jason Maxamps.com]

Yup the 1-4 cell count does refer to the pack voltages. Even though the pack you have consists of 6 cells it is wired as a 3S pack and gets charged as such.

Jason

[bledsoenc]

It's a little odd that they sugar coat it like that -- "3 cells" really means 11.1V which could consist of 6 cells.

Thanks again Jason. Since it looks like my Triton Jr. will work I have a few followup questions. How does balancing typically work with packs that have cells in parallel? Are they balanced in series as well or as individual cells?

I saw the instruction manual for the "recommended" balancer for my charger and it explicitly states that it doesn't work with packs with cells in parallel. Is this typical of balancers, and can you recommend a good & cheap inline balancer that will work?

[BrianG]

When selecting cell count, always looks at the "S" part of the pack rating. The "P" part only tells you the number of parallel cells, but is not really important because this just affects capacity and that number is listed on the pack.

You could have a 3s200p pack, which is 600 cells, but still only charge at 3s. Capacity would be enormous, but that is irrelevant when selecting charge cell count.

I wonder if it would be a good idea for chargers to ask for the SERIES cell count instead of just the cell count? Might reduce confusion a little, but I dunno.

[Jason Maxamps.com]

It's a little odd that they sugar coat it like that -- "3 cells" really means 11.1V which could consist of 6 cells.

Thanks again Jason. Since it looks like my Triton Jr. will work I have a few followup questions. How does balancing typically work with packs that have cells in parallel? Are they balanced in series as well or as individual cells?

I saw the instruction manual for the "recommended" balancer for my charger and it explicitly states that it doesn't work with packs with cells in parallel. Is this typical of balancers, and can you recommend a good & cheap inline balancer that will work?


I'm assuming you were refering to the Equinox balancer and I find it strnge that it says that about Parallel packs. Our MaxAmps Method balancer works fine with packs like this. http://www.maxamps.com/MA-Method-Balancer.htm

Jason

[bledsoenc]

I'm a little suprised the Equinox wouldn't work with parallel as well. Here's the quote from the manual (emphasis theirs, not mine)...

For LiPo packs with 2 to 5 cells assembled in series (not parallel).

I wonder if the were trying to point out that you only need to consider the number of series, or if it really won't work with parallel.

[GSMnow]

The number in P really does not matter unless the charger has a low current limit and/or limits total charge to where it won't fully charge the pack. A 2S1P rated at 3000 mAh would be exactly the same to charge as a 2S4P made from 750 mAh cells. It would still total 3000 mAh. But if you had a 2S4P made out of 5000 mAh cells, it would have a total of 20,000 mAh (or 20 AMP hour) and would either take 20 amps or a very long time to charge. Due to the CC/CV charge profile though., it should still charge just fine up to 8.4 volts (4.2 per cell in SERIES).

The other possible limitation is the balancer capability. The Method Balancer can provide up to 300 milliamps to keep/bring the cells to balance. With 3000 mAh cells charging at 1C or 3 amps, that means it could keep the voltage balanced to a full charge with cells that are up to 10% out of balance. A 2800 and a 3100 cell for example. With a 20 amp hour pack, charging at 20 amps, that 300 ma balancing is now only good for a mis match of 1.5%. Those would need to be well matched to be safe. Though the Method Balancer will still safely cut off the charge current when any cell reaches full, but it is only rated at 6 amps, not 20.