Fireball

by John Thompson

‘Fireball’

Rechargeable Lithium batteries are here to stay, and if used properly, with the correct equipment, comparatively safe. The above picture shows all that was left of a large, scale, aerobatic model when the ‘expert’ modeller did not heed the manufacturers instructions.

At the recent Blackpool electric event, this modeller had been bragging about the 32 cells in his model, and that it was safe as long as you used the best charger. However he was charging with the batteries inside the model against all the safety suggestions, and suffered the consequences. Over £1,000 went up in smoke and what you see is all that was left, and he was lucky his car did not go the same way, not to mention anyone nearby!!

Thirty two cells equates to a potential of about 130 volts

He stated that there was about 4 Kilowatts of power

With these cells in close proximity you only need one to overheat and the rest will quickly follow. I have been using "Li-Poly" and "Li-Ion" cells (in small numbers) for 6 months now without any problems. I use a "Prodigy" Charger which costs £50 and does up to 10 nicad (nickel cadmium) or NiMh (nickel metal hydride) cells as well as up to 3 Lithiums. The cells are always charged out of the model in a well ventilated area, and not left unattended.

An ordinary nicad charger is no good at all with Lithiums. Also the ordinary speed controller for Nicad or NiMh cells is not suitable and in fact will destroy your batteries if the motor is left running too long. I won’t bother you with the technicalities but it is true. Most new controllers can be programmed to either pack, and I have a reasonably priced "Jeti" Brushless which automatically detects what the batteries are.

The only difference between "Li-Poly" and "Li-Ion" are the plastic and metal casings, so the former are a bit lighter, and resist overheating better. The main advantages of this technology is they are a fraction of the weight of normal can cells, and that you can charge them up today and they are still full next week. If you have any reservations about using them, don’t.

If I can be of any help my number is 01924 515595

John Thompson