Tell me about lith... batteries!!!!

[leon_luxton]

Hey
I am in the process of making a new robot and was wondering a little about the lith batteries as i see many others now using them in there ant weights.
So can some1 give me a quick run down about lith batteries and all the important information i may need about then!
Also could some1 recomend me a good light rx to use in a ant weight?
Thanks
leon and stuart

[Andrew_Hibberd]

Hi,
Lithium polymer (lipo) are special high discharge batteries. This means they can give out power faster than NiMh or Nicad batteries.

http://www.indoor.flyer.co.uk/cells.htm

This link is to where i personally buy my lipos from there is a great deal of information about the cells and safety with them. They don't have the thick metal shell like NiMh/nicad batteries. I am using the 2 cell 145Mah pack. This gives 8.4V at fully charged, to 7.4V when discharged.

The major things that needs to be taken into account is that they require a special charger and most receivers and servos can't handle the voltage so a voltage regulator is required to a safer level.


I know of two good RX's the futaba R114 (?30), and the Hitec Feather (?17). It is possible to use a futaba TX (or similar) and a Hitec RX if the channels are the same, however it can cause problems on some frequencies.

EDIT: There is a thread about lithium chargers here:

http://robotwars101.org/phpBB/viewtopic ... adb1c70910

[Remote-Controlled Dave]

I just bought a Hitec feather from www.sussex-model-centre.co.uk for ?15. Comes highly recommended, very small, very light, very cheap.

[leon_luxton]

Hello..thanks for the good replys.
I will buy the hitec feather then as it seems like the best Rx at the moment.
One more thing.....voltage regulators,what one is needed? were do i get it from? any other info on voltage regulators is appricated.
thanks again!!!

[Andrew_Hibberd]

This is a quote from scott from team ultimatium

The ones most of us use are from www.maplin.co.uk, the 5v version has the product code L7805CV, and the 6v version is L7806CV

The wiring of these can be found here:
http://windisch.co.uk/electra/howto/vol ... ulator.htm

Simon that is a very useful how to

I hope that helps.

[BeligerAnt]

Probably the most important thing with lithium batteries is to ensure that they are charged correctly.
Buy a decent charger, treat them carefully and you should be OK.

There are pictures on the net of models going up in flames because of lithium batteries catching fire. This is most likely to occur when they are overcharged, from what I have heard this is what most of the pictures show.

The nominal voltage of lithium cells is 3.6V, but a fully-charged cell is 4.2V. This means that 2 cells will give a peak voltage of 8.4V and typically around 7.2V

Lithium cells should not be over-discharged otherwise they will be permanently damaged. This occurs around 2.5V per cell. Using a simple voltage regulator (like the ones mentioned above) should give some protection against this. Two cells would give 5V, but the regulator output will always be a volt or so below its input. So when your battery pack gets down to 5V, the receiver voltage will be below 4V and the robot will start to slow down and maybe misbehave - a sure sign of flat batteries!

[Andrew_Hibberd]

Just have a question, how much does a 3 cell 145Mah battery weigh

i know they are 4g each, but you need solder and wires etc.

Thanks

I think i can run anticipation on this, so the solanoid valve will switch faster, a lot faster 8)

[Andrew_Hibberd]

How much do the 3 cell 340mah packs weigh from indoor flyer-the ones with the PCB, and what are the dimentions.

Thanks,

[Rhys]

33g with wires, solder, plug and all that nonsense. But as I type this I remember that they have them on robotbirds with the exact dimensions and weight. At least I know my scales are accurate now

[Andrew_Hibberd]

going to have to save some more weight after having saved 12g from kwijebo