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Old Mar 31, 2006, 11:46 PM
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Joined Mar 2006
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why do I get told not to use Li-Poly on mt trainer

I have a fairly good background in electricity. And I am totaly puzzled that when ever I suggest using a 7.4V Li-poly battery in my Firebird Commander 2 with a brush motor, I get told it will damage the electronics. Would the different ri of a poly make any difference? As best I can tell that is what some are trying to tell me. To my knowledge any DC source, running a fixed voltage, should react the same as any other against the fixed resistance of any circuit. I would not think it would matter if it where coming from a NiMH, a Li-Poly, or a nuclear power plant. I talked to my Hobby Shop owner, he said Ii should not do it. He didnt know why but he had heard it was bad. I called tech support at my manufacturer and got a nice young fellow that said I should not do it because the li-poly had a higher maH so it would burn out the electronics, he said they had never tried it though. HUH? How does having a bigger gas tank burn up your planes circuitry. Well, I feel I have had to waste money on Nickle Metals 25.00 a pop, and a 40.00 charger when I should have been able to just go straight to the higher technology. Can someone give me the straight scoop here? Thanks so much for any help.

Larry
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Old Mar 31, 2006, 11:56 PM
It's been a while.
Daniel G's Avatar
Irvine, CA
Joined Jan 2005
2,690 Posts
It's the fact the your lipo will have a higher voltage than the regular flight battery and that the firebirds electronics will not shutdown the motor when the battery runs low.
If your firebird can handel a 6 cell nimh, then your lipo should work just fine, but when it runs out of juice, the electronics will not protect it so you will most likely end up destroying the battery.
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Old Apr 01, 2006, 06:06 AM
turn, turn, turn.
Athol, Massachusetts
Joined Oct 2005
10,392 Posts
The main reason is that lipos don't handle crashes as well as nimh. If you don't crash hard or often, who cares about the brushed motor in the Commander? Just don't wring it out too often, and when the power drops off, land. Simple as that.

I've used lipos in the Challenger when they first came out. Main thing is not to let the battery get too low. The motor will burn up eventually.
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Old Apr 01, 2006, 07:09 AM
Sussex, UK
RobinBennett's Avatar
Crawley, West Sussex, UK
Joined Jun 2004
7,373 Posts
1) lipos can be damaged by discharging below 3v per cell, and planes that were designed for lipos have speed controllers that cut off at this point, the firebird does not. You can fit a 'liposaver' that will warn you when you reach this point, or calculate and time your flights.

2) lipos are easily damaged, people expect trainers to crash a lot and the firebird has the battery right up the front where it'll take the worst of any crash.

3) damaged lipos can explode, either imediately or the next time you charge them. People have lost their cars or houses.
Check out the 'lipo fires' videos here: http://www.utahflyers.org/
(In the 'video' box, at the bottom of the list, there are two)

Basically, there's no technical reason not use a lipo in that plane IF you understand the risks and are sensible enough to plan accordingly, but many people expect a beginner to crash too often and not to know enough about batteries and electronics to care about the risks.
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Old Apr 01, 2006, 01:10 PM
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Mentor, OH
Joined Dec 2004
8,426 Posts
i went right to lipo's on my SS. the one thing i did learn was anything under a S400 does not like 3 cells.
did i ruin a few batteries...um, yes (one). did it cause any fires? um, no. was i safe when i noticed the big dent in the battery? you becha ya.
if your careful and don't abuse the lipo (i.e. dent, rip, mangle) and don't take it under LVC, then you should be fine.
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Old Apr 02, 2006, 01:35 AM
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Joined Mar 2006
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Thank you all Guys. I appreciate the insight.
Larry
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