Wiring Lipo's in parallel Question
 

If I want to wire two lipo's in parallel, I understand that obviously, they have to have the same voltage, same C rating etc. However, do they have to have the same capacity? I want to wire two 6S Flightpower packs (a 2550 and a 3250) in parallel, both are 20C continuous, both are (obviously) Flightpowers, both are the same Voltage etc.

Is this Ok? I would have though that it would be, but I'm after some more opinions.

Thanks

No it won't be ok - They can sustain different amp draws and will discharge at different rates...

The 2550 will dump quicker and the cutoff won't notice... This is a bad idea...

Righto, thanks for the quick reply.

I was only wondering as two 3250s in parallel is heavy, and gives me 'too much' runtime, whilst two 2550s don't give me quite enough but are far lighter.

Hmmm, a 2900 would be great, but I can't find anyone selling the right capacity with about the right dimensions.

Damn...

I wouldn't suggest doing it, but it would be interesting to see what it actually would do in the real world. As the 2550's start losing voltage the 3250's should charge the 2550's back up a bit, since voltage between parallel cells should be even. Could have an unhappy ending though.

I have seen strange lipo setups used before with no issues though. 6 cell nimh (I think IB4200's) in series with 4900 mah 2s lipo. 4900 mah 2s in series with 4000 mah 3s of diferent C rating and brand. 25c 5000 2s venom pack with venom 4000mah 20c 3s pack, and a couple of others similar to that. I think the main thing is not to discharge the packs to far, 5 min races didn't hurt them.
Still don't recommend it though, especially when going for maximum runtime.

Do the packs need have certain dimensions? Can you fit 2x 3s 5000 - 6000mah packs in series.

No, not really, they need to be quite short, and most large capacity packs are long. Also, I would like to stick to Flightpower, as they are the best manufacturer at the cheapest price in England. (Polyquests and stuff would end up being more for the same cells, just because of the distributors).

Admittedly, there are the Trakpower 5400mAh 'Traxxas' packs, which are 11.1V, but they are only 16C, so I think I may be pushing it there.

I've looked at different set-ups, and two 5S 3250mAh packs in parallel should give me about the run time I need, but still aren't too heavy.
Besides I don't have to risk the MMM on 6S (though most don't suffer from this, but I'd still like to stay on the safe side).

What length do you want?

Enerland 2s 5k hardcases are nice...

I'm looking at about 135-145mm long.

I like Flightpowers (Enerlands), but to get actual Enerlands will cost me loads, as we can only get limited Lipos in the UK. Really it's Flightpower, Tornado, and any RC Car related manufacturers (Orion, LRP etc).

http://www.allerc.com/product_info.p...oducts_id=4530

http://media.hyperion.hk/dn/g3lipo/G3-Specs-EN.pdf

Can be arranged to be posted from with the UK... I have vistors going back to UK next week.

The 25C Flightpower 4900's are just under 145mm. http://www.flightpower.co.uk/index.a...m=EVO25-49003S

It's a good point, but that range is now discontinued, the new range is the "EON" range. I doubt I'll be able to get them anymore in the UK. It doesn't matter now anyway, as Arct1k has ordered some Hyperion Lipos for me which he's bringing over to the UK next week.

Thanks anyway Patrick

Oh ok. The price of the hyperions does look a bit better.

Yes you can do this, just connect them in parallel and go. Just confirm both packs are fresh off the charger to ensure they have same voltage.

Actually I run three 6S pack in parallel to run my boat, a 4500mAh35C, a 2600mAh25C, and a 2200mAh25C. run them together and charge them together for months, no issue found.
(When charging, the balance tabs are also connected in paralell to ensure every cell is under supervision of the chareger)