Tamiya multiple 7.2V battery charging.

Hi Mark,

You are looking for a "peak detect charger". The one I have is made by Hitec and it's model number is 335, price in the UK is around £65. There are many other makes and models, things to check are the maximum charge current and the maximum cell count supported which vary between models.

The ones available from the hobby trade are typically designed to run off of a car battery but it's possible to use a 13.8V PSU instead of the car battery or to modify an old PC PSU (cheaper option).

Hth,

I think they need to be charged in series, it's bad form to parallel connect batteries. So the charger will need to be capable of more than 16x

7.2volts and be peak detect capable for what you want.

The charging technique depends on the battery type. The 7.2volt packs I have are Ni-CAD and I charge them using the cheap and nasty charges provided with the gadgets, which no doubt reduces the life of the batteries.

Standard charging arrangements for NiCAD used to be constant current at 1/10 the battery rated capacity eg 500mAh NiCADS are charged at 50mA the voltage at this rate would be about 1.5volts. It is the current that is set, the voltage floats. THis suggests the charger will have be capable of producing voltages of at least 150volts to charge the batteries correctly.

Once you get into fast charging it gets complicated to do properly.

Somebody will no doubt tell me I'm out of touch with latest thinking!

Steve

Um, I think I must've misread your original post - you want to charge

16 off 7.2V batteries simultaneously, not a single 16 cell battery ? That puts a different complexion on it to say the least.

If you can be sure that all the battery packs are in the same condition (age, capacity etc) and if they are all discharged to the same level then it is possible to charge several packs in series but the average hobby charger will only charge 24 or 32 cells at a time. This equates to 4 or 5 packs so you'd need 3 or 4 chargers to do ahat you want. Also be worth being careful of how much current you'd be taking out of the power supply or car battery at those cell counts.

You are basically correct, C/10 (capacity in milliampere-hours divided by 10 = milliamperes charge rate)

Series charging from one source can be fraught with various problems, particularly if some cells in the string are over discharged or reversed.

The best way to charge for full capacity is to cycle charge them as individual packs That means discharging down to 1V per cell and then recharging for a known period at a suitable constant current.

As the start of charge is a known point, the charge can be accelerated somewhat, typically a rate up to 3 or 4 times the C/10 rate can be used, but only if it is a timed charge and there is a temperature cut-off in the cell pack.

We used to cycle 25-cell packs of F cells (7AH) with a charge rate of 1A after discharging.

The C/10 rate is chosen so that you can start the charge at any state of charge of the cells, and the charge can be left on past the nominal 14 hours without too much harm to the cells.

Peter