Battery question - two 7.2 V packs to get 14.4 V

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Sharp - 23 Nov 2005 20:03 GMT

Hello

Can anyone tell me can I connect two 7.2 V Ni-MH packs in series to get
14.4V, use it for powering 20 W halogen lamp, and after power runs down
disassemble it and charge 7.2 V packs separately, first one and then
another.
Is it possible to do this and not damage the batteries?

I own smart battery charger that can charge only 10 cells (MW 7168 omni) and
I need 14.4 V battery.

Thank you

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Jonathan Hodgson - 23 Nov 2005 20:33 GMT

> Can anyone tell me can I connect two 7.2 V Ni-MH packs in series to get
> 14.4V, use it for powering 20 W halogen lamp, and after power runs down
> disassemble it and charge 7.2 V packs separately, first one and then
> another.
> Is it possible to do this and not damage the batteries?

Yes.

My only bit of advice would be to avoid running the pair of batteries
flat, since if one discharges before the other it is likely to be
reversed, and damaged. Make sure you charge them (both) before they're
close to flat.

You might also want to discharge each pack occasionally (say, every six
charges) but I'll wait for others to add their advice.

HTH,
Jonny

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Stephan Brunet - 24 Nov 2005 03:07 GMT

>>Can anyone tell me can I connect two 7.2 V Ni-MH packs in series to get
>>14.4V, use it for powering 20 W halogen lamp, and after power runs down
[quoted text clipped - 14 lines]
> HTH,
> Jonny

Is the Halogen a 12 volt light? If so, I think Running it at 14.4 volts
will shorten it's life (unless it's of the automotive grade). Also if
you put 10 cells together you will have 12 volts and be able to charge
it on your Omni.

If you do run the 2 packs it may be a good idea to have them as closely
matched as possible to avoid one discharging before the other as
mentioned by Jonny. You can also set up a relay to auto cut the circuit
so they will never completely drain. You may have to play with some
resistors to find the right cutoff voltage.

Steph.........

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Sharp - 24 Nov 2005 08:45 GMT

> Is the Halogen a 12 volt light? If so, I think Running it at 14.4 volts
> will shorten it's life (unless it's of the automotive grade).

According to the lamp manufacturers when you overvolt about 20%,
12V--->14.4V, you get 15% increase in power consumption BUT about 40% more
light output.
Drawback is that you get only 5% of lamps life, but from 4000 hours down to
200 is acceptable because halogen MR16 dichroic lamps are cheap, and 200
hours is still at least 6 months of use or more.
And I will always have a spare with me ;-)

You can also set up a relay to auto cut the circuit

> so they will never completely drain. You may have to play with some
> resistors to find the right cutoff voltage.

Can anyone point me to a webpage with schematics for a such circuit?

Thanks

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Stephan Brunet - 24 Nov 2005 23:09 GMT

>>Is the Halogen a 12 volt light? If so, I think Running it at 14.4 volts
>>will shorten it's life (unless it's of the automotive grade).
[quoted text clipped - 15 lines]
>
> Thanks

I will try to drum up a bit of time to draw one out for you unless
someone has a page with that type of circuit..

Later
Steph

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Stephan Brunet - 26 Nov 2005 18:57 GMT

> I will try to drum up a bit of time to draw one out for you unless
> someone has a page with that type of circuit..
>
> Later
> Steph

Here is the diagram as promised
http://clod.macphreak.com/helpfull.html

should take about 30 min to put together once you have all the parts.

let me know how it goes.

Steph

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Sharp - 26 Nov 2005 20:05 GMT

> Here is the diagram as promised
> http://clod.macphreak.com/helpfull.html
[quoted text clipped - 4 lines]
>
> Steph

Thanks ! I'll try it.

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Model Forum / Radio Controlled / Land Models / November 2005

Battery question - two 7.2 V packs to get 14.4 V