9v Battery pack Series and Parallel select switch and charge

[rezaf]

Hi,
I have a battery pack that contains 10x9v NiMH rechargeable batteries. the scenario : in the "use" mode all of this batteries connections are series but I want to make a small circuit to add "charge" mode and change all batteries connections to parallel with a switch and charge all batteries with a external charger.
do you have any idea to do this change between series and parallel easily from a switch without conflict between series and parallel modes?
if the charger has this specifications, can I use it for this work : output voltage : 15v - output current : 600mA (60mA for each battery - batteries are 200mAH) ?
Thanks,
Best Regards.

 

[chuckey]

If you have ten batteries then you need ten double pole double throw switches or relay contacts to switch them from series to parallel. I would build a small converter to provide 90+ to charge them all in series. This is a better charging system, because it makes sure that all the batteries get the same charge. If you try and charge them in parallel, then one battery might hog all the current and overheat while other batteries receive little or no charge.
Frank

 

[D.A.(Tony)Stewart]

You need 4 switches for each battery to use 2P2T transfer operation.
Whereas in a series charger , you need a Zener-like part to bypass each battery being charged on series with a boost SMPS, so only one power switch per battery.

The bypass switch however must dissipate more power in linear mode above 9V to match each cell within 1% State of Charge for longevity.

I might consider a more clever switched inductor mode for continuous bypass for series regulation.

batteries either in series or parallel must be matched <2% for ESR otherwise over current on shunting during serial to parallel switching or over charge on serial charging will degrade batteries faster.

 

[Audioguru]

I hope you have a low voltage cutoff for each battery to prevent the weakest battery going dead first then the remaining discharging batteries in series with it actually are charging it in reverse which is damaging it.

I agree that charging batteries in parallel will overcharge some of them and barely charge others.
Charging batteries in series is also bad since some will overcharge and others will undercharge.

When you charge and discharge a single 9V battery then you are relying that all the cells are identical, but you should still have a low voltage cutoff at 1V per cell (6V for a Ni-Cad or Ni-MH battery).