mobert

Please tell me if I'm doing my math right. I am currently using 14-cells GP3300 NiMh cells, which work out to 32oz. in weight. I need approx. 35 amps, and 40 in short bursts. If I were to use the new Kokam 2100 20C discharge Lipo's, I would need a 5s1p to get the voltage and the amperage. This weighs just under 16 oz. given the FMADirect weight specs. Although this is a 16oz savings in weight, I am going down from 3300 mah to 2100mah capacity. So, it's probably better to look for another 5s2p type combo with smaller capacity cells that saves me approx. 12 oz. in weight but gains me much more capacity, correct?

hexonxonx

My Feedback: (2)

by cutting battery weight in half and increasing volyage a few volts(18.5 lipo---16.8nimh) you could keep up with less throttle and not notice much flight time loss.a fully charged 5s lipo is closer to 20v. from what i understand each cell fully charged is close to or is 4v.
that much weight saving and increased voltage sounds sweet.im not forsure but kokam might have 3270 mah @ 20c, fmadirect.com should have that info.65+amps of moto-vation----hizzah.

mobert

Thanks Hexonxonx, maybe the improved weight will indeed allow me to get almost the same flight times. I checked fmadirect and the do have a 3270mah, but it's only 3C!! Actually, I found some Polyquest Lipo's at aircraft-world.com that will give me a 12oz weight saving, and be 4400mah - these are 2200mah cells which I would make up as 5s2p, and they have a 10C continuous rating.

Peter Khor

My Feedback: (4)

TP4200C-2S2P + TP4200C-3S2P; 430g or <16oz.

or

TP4000-5S2P, also <16oz.

The Kokams are HEAVY.

mobert

Thanks Peter, didn't know TP4000s were available. If they are less than 16 oz, wow, that would take away a lot of the weight! I guess I'll do some net searching tonight.

Matt Kirsch

My Feedback: (21)

The Kokams have to be heavy to withstand 42 Amps continuous draw. There's still no getting around the laws of physics, specifically thermodynamics in this case. Mass to absorb heat, surface area to dissipate it.

A while back I went 12 rounds with a chap who started in about "LiPo math." NOWHERE has anybody said that 2100mAh will give you longer flights than 3300mAh given the same current draw (throttle levels). NOWHERE! That's just plain foolish.

There are two ways that LiPolys can improve your flying experience:

1. Decreased weight. Saving a pound on a 6lb airplane is a MAJOR improvement. You need less power to overcome lift induced drag.
2. Increased capacity for the same weight as NiCd/NiMH. You can pack a lot more mAh into the same amount of weight and space.

Normally, we work with a combination of the two. We get some weight savings, and some additional capacity. On smaller park fliers, it's easy to increase pack capacity by factors of 5 or more. When you get 5 minutes on 150mAh NiCds, you're going to get 30+ from a 1020mAh LiPoly.

BTW, you only need 4S1P to equal 14 cells. That saves you even MORE weight, and you can still double up on the Kokams and save about half a pound over the GP3300 NiMHs.