Substitution of NiMh for lipo for flight battery

[trev]

Hello all. been looking around the threads for an answer to this one but just ended up confusing myself.

 

I have just got an Electracam for a bit of fun ( thanks galaxy models - great delivery and price ). It uses a 8.4v 900 Mah 7 cell flight pack / 380 brushed motor and I want to install a li poly instead. Questions are:

 

1. will the esc still run ok on it with no problems

 

2. what would be the best lipo be, a 2 or 3 cell and again what effect will it have on the esc / motor if any.

 

I have some spare 2300 3s lipos and was considering using them but figure that a 2s 1500 would be better. This will of course only give a nominal voltage of 7.4v as opposed to the 8.4 in the NiMh pack, so will pull a little more current, wheras a 3s 1500 would run at 11.1v ( too high perhaps ?).

 

Any input gratefully received.

thanks

Trev

[Lee Smalley]

you have already raised the main points, i think you need to find out some details of the ESC fitted to answer them

[Tim Mackey]

1) Yes....but you have to time your flights to prevent the lipos getting too low on voltage.

2) 2s

 

A 3s lipo under load, will show around 10.5V or so...and will possibly be too high, pushing the current up considerably - you could prop right down, but that may not suit the model.

Also, the brushed motor will soon burn out at 3s levels.

[trev]

Thanks chaps, most helpful. looks like a 2s 1500 it is then.

 

Figured that if I keep the flights to 15 - 20 mins max then that should cover the voltage drop from going too far.

 

cheers

 

Trev

[Steve Hargreaves - Moderator]

Or fit a cheap LiPo screamer so you know when the voltage is getting critical.....you'd probably hear it in flight unless you were too far away....

 

Remember if the voltage of your Lipo drops too far it can kill it....be a shame to have to fit a new battery every flight....expensive too!!!

[PatMc]

The LVC on an ESC meant for nickel cells will be around the lowest setting for some lipo friendly ESCs on 2 cells. If you only allow it to drop to LVC occasionally there shouldn't be any problem.

However you can always set a time limit on the first few flights to say 10 mins, see what a re-charge takes & increment the time from there.

 

PS avoid running at low throttle towards the end of the time limit. Low current draw will allow the battery to become more deeply discharged before LVC is detected. 

Edited By PatMc on 22/11/2011 16:11:20

[trev]

Hmmm, the lipo screamer is definitely food for thought, never come across them. Now on my list for next order from GC.

 

Thanks again for all the advice.