commander Bob

Morning All

I've recently got into the electric flight thing.. great fun!

I have a GWS tigermoth and an e-starter. Both great planes.

However I have a question.

It's about batteries. Everyone seems to use nicad's of one description or another. They have a short duration and large mass compared with that of the liPo batteries. So why oh why don't people use them.

Example. In the tiger moth a 7.2v 300mah cell will last around 10mins and cost about £15, compare that to the LiPo 7.2v 1200mah that weighs the same and you'll get about 40mins flight time and it cost about the same £19.

Is the world crazy? or have I missed a very important fact.

Bob

3DFanatic

My Feedback: (5)

The fact is that LiPoly cells are, by far, more expensive then NiCds. For instance, I just purchased a 1200 3-cell pack and it came out to $60. Worth it to me for the performance..but not everyone.

Also, for most people it would require buying an additional charger capable of charging LiPoly cells.

blvdbuzzard

Plus I would like to add, if you have been flying before the lipo's came out, you will have a good stock of nicds, nimhs and chargers to go with them. Should I through all of that away to use the lipo's?? There are some high current setups that the lipos can not be used for. My two cents worth.

Dru.

Mike Taylor

My Feedback: (1)

About the higher current requirements, see Greg's thread on the 340SHC's: http://www.rcuniverse.com/showthread...70&forumid=269
Not only can you get the higher draws you need, but you can shed 1/4 or 1/2 pound from the AUW. I know that new technology is expensive, but lighter airplanes are worth the expense (at least, to me they are)..

slacsteve

My Feedback: (3)

In my view ten minutes IS a long time. Forty minutes could get boring . I bring sereral planes for variety when I fly and fly them all.

commander Bob

As do I..

The tiger moth will last 40 mins but the e-starter will chomp through the same battery in about 10 mins if it's at full power

By the way, I played around gliding the e-starter last night and it's pretty good at it... probably better than the moth!

And to top the evening off I managed to bring the e-starter home without a scratch.. this is something of a suprise as I've only flown it 5 times now and this is only the second time it's come home it the same state it went out in... it seems to be attracked to big solid things... tree's, houses and the earth!

Matt Kirsch

My Feedback: (21)

This is untrue. From almost the start, multiple LiPoly packs could be ganged together to combine their capacities for high-current situations. The result was a pack that weighed about the same as a NiCd, but had five times the capacity. However, the cost of building such a large back was and is prohibitive for most people. Twenty 1200mAh Etec cells at $15 each to make up a 5S4P (5 cells in series per pack, four packs in parallel) pack with the same current capacity as a 16-cell, 2400mAh NiCd is $300. The NiCd is only about $60.

It's getting better, but I question the usefulness of a super-duper-high-current LiPoly cell. If you blow through a 300mAh NiMH in a few minutes, and complain about short flight times, having a 340mAh LiPoly that can produce 6A won't gain you a whole lot. You'll lose a little weight, but unless your pack's right on the CG, you'll have to add ballast. Most people's goal for electric flight is performance comparable with glow-powered planes, no weight penalty, and no duration penalty.

3DFanatic

My Feedback: (5)

Also , Nickel-based batteries are mmore ruggin in teh sense of charge/discharge rates.

LiPoly cells shouldn't be charged at more then 1c or discharged at more then 2.

You can relly abuse Nickel-based packs charging them at 3c and discharging them at ..............

Mike Taylor

My Feedback: (1)

Sorry, Aaron, but that is not true. It may have been once, but not now. See this thread for a discussion of a 20C LiPoly: http://www.rcuniverse.com/showthread...70&forumid=269]

commander Bob

but the Lipo's have no memory, unlike the cadmium based batterys.

And the e-starter I have drains about 9amps off a 1200mah lipo cell thats higher than 2c.

Matt Kirsch

My Feedback: (21)

Memory is a myth these days. It may have been an issue several years ago with NiCd, but in the time between then and now, the manufacturers have improved the technology.

Etec 1200mAh LiPoly cells are good up to about 7C, which is 8.4A for a lone pack. Old metal-cased LiIon batteries were limited to 2C. First-generation LiPolys could handle 3C. Second-generation LiPolys are good for 5C to 7C. The latest cells are good for 20C.

If your Estarter is drawing 9A+ on 7.2V, there is something wrong. The stall current of a Speed 300 motor is 8A.

commander Bob

I was just going off the info provided by gws... have i got it wrong?

I think the manual states a max drain of 9.6v with a 1080 gws prop at 8.4...

I could be wrong I'm working off memory... (not always reliable)

3DFanatic

My Feedback: (5)

Mike - thanks for that link... That defies everything I've ever heard so I guess the old phrase aout learning something new every day is true!

Memory can occur and contrary to popular belief NiMH cells CAN develop memory.

Dr Kiwi

Hi Matt - I may have misunderstood your comment, but I'm puzzled by your indication that a Speed 300 should not be able to draw more than 8A. I've done a bunch of static tests and often got amp draws (measured with my Whattmeter) in excess of 10A. Though the motor certainly didn't like it, in one "momentary peak-power" test with a 5:1 g/box and a 10x7 Aeronaut prop on 8 cell 1700NiMH, I measured my Graupner Speed 300 sucking 11.6A, 8.8V, 102W, >7000 rpm and producing 14.1oz (400g) static thrust.

By the way, among the half dozen props I tried in the series, the best (most efficient) peak power test was with an 8x4 Slim prop, with readings of 8.4A, 9.3V, 81W, 8850rpm, 13.6oz (386g) static thrust. [With 8x6 APC E and 9x5 Slim props it needed >10A to reach this thrust figure.]

Cheers, Phil