slime340

iTrader: (3)

I know everyone is really tired of the LiPo question but I am confused! My converted Hyper 7 uses 2 LiPos and up till a few weeks ago I used a matched pair of SMC 7.4v 28C 6000 LiPos, but then I added a 11.1v AcePow 30C 5200mAh LiPo to the mix and subsequently destroyed both 2cell LiPos on 2 differnt days. So for a replacement battery, should I A: match mAh e.i. capacity, B: Discharge rate or C: is brand matching most important? Someone let me know, Oh yeah, I still plan on using a 2cell LiPo with the 3cell.

20 SMOKE

iTrader: (103)

i would buy the same for both 2 and 3 cell,why dont you buy a 5 cell

jnyrcr

iTrader: (5)

did you mix different MA batteries together? like a 5000 with a 5200? and a 2s with a 3s?

Zachfeen

iTrader: (9)

If you are using two batteries they need to be the SAME EXACT battery. Not 2 different brands with the same specs. Same brand, same everything. And they should only be used together, never apart from each other. DO NOT use a 2s and 3s battery together because they will discharge at different rates.

slime340

iTrader: (3)

Well, I didn't buy the 3 cell battery, I got it for AcePow testing of they're new batteries. And I bought the RC Product Designs conversion kit for my Hyper 7 because of the battery trays being on each side of the buggy so that it offers better balance than having 1 large battery or 2 smaller batteries on one side. In theory and practice.

Duster_360

iTrader: (21)

A 2S and 3S run together in series works just fine as long as the lipos are the same capacity. I run this combo in my Sav Flux a few times a month. There's no sign of probs, the esc is warm, lipos are just barely warm and I get 20+ min run time easy. Been doing it for a while. Same as running a pair of 2S lipos.

If you do a little research on running with combined lipos, what you'll find is that to combine lipos in series, lipos have to be same capacity, but can be diff cell counts. If you combine lipos in parallel, the lipos have to be the same cell count, but can be diff capacities. All the other caveats apply - same C ratings and same history.

Plane guys have been running both kinds of combos for years.

jnyrcr

iTrader: (5)

So what happens when the smaller battery weather its MA or cell count runs low while the other still has juice? will that not damage the smaller battery and maybe even kill it if not worse, low voltage cutoff won't detect low voltage correctly if I'm not mistaken, it seems if you did it the way your talking about you would have to watch your batteries very carefully, that's kinda the way I was thinking, but I could be wrong.

Zachfeen

iTrader: (9)

I understand the concept or parallel vs series. The problem as I see it is if one dumps earlier than the other (which is bound to happen) that battery would still be used by the esc ruining the battery eventually.

Duster_360

iTrader: (21)

Like I said previously all the other requirements still have to be met for combining, same useage history (same number fo cycles) and same C rating. If you do that it eliminates the concern you just posted. I can run my Flux with a 2S 5000 25C and a 3S 25C wired in series forming a 5000mah 25C 5S equiv lipo to the lvc and guess what, when I re-charge them, I see about the same 3800-3900mah go back into each one regardless whether it's the 2 or 3S. To the esc, it's just a 5S 25C 5000mah lipo. If there was a big C rating diff (which you're not supposed to use to run in combination), then there could be probs. But this is something you don't do anyway.


Experience has shown that this is not an issue - again, you don't combine a 10C and a 50C lipo together and you don't combine a lipo with 250 cycles with a high IR with a brand new one with a low IR. You use lipos that are identical that have diff cell counts (in series) or diff capacities (in parallel).

Zerodefect

Each cell should be identical.

You can series a 3s and 2 s together as long as they are the same type, brand etc. That would give you a five cell pack. A good option to balence a Caster type setup. Put the 2s on the motor side.

When you use two diferent battery cell types the weakest cell is the weak link. Full current flows through each cell. I don't think this would really cause the weaker battery to die prematurely.

SMC batteries used to have a stinky rep for puffing, "unless babied". Even with proper care plenty puffed. Maybe you had the old wimpy batch?

jnyrcr

iTrader: (5)

Duster 360 and guess what, Like I said I could be wrong, it was just my way of thinking, that ok with you?

cbr74

iTrader: (14)

LiPo's, like any set of cells in series will seek to achieve equilibrium. It's why you don't mix old and new cells because the newer cells will charge the older cell(s), and in the case of non-rechargeables like alkalines, the weaker cells are destroyed.

In the case of LiPo's, the cells with the higher capacity will seek equilibrium with the cells of lower capacity which puts the lower cap. into an overcharge state and thus, they go *poof*.

You can run any number of cells in series provided they are the same capacity and at the same level of charge.

Duster_360

iTrader: (21)

cbr74 - parallel or series? Clarify please, there is a ton of misinformation out there in the surface rc on this kind of issue. You can run any number of lipos in parallel provided they are the same cell count and start pretty close to the same voltage.


http://www.youtube.com/watch?v=NczQwVTI2bY



What you can do charging, you can also do discharging (obviously with no balance wires).