# 9V batteries in series question



## Cougar Rock Rail (Jan 2, 2008)

Hello all you battery powered dogs!

I'm working on a little project that requires at least 10V, low current (for 4 incandescent bulbs--say


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## dbodnar (Jan 2, 2008)

Keith - you should not have any problems - keep in mind that most rechargeable 9 volt batteries don't put out 9 volts - either 7.2 or 8.4 is more likely.

dave


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## Greg Elmassian (Jan 3, 2008)

Doing some quick searches, not only are these usually 8.4 or 7.2 volts, the mah rating is often 200 mah, and the "high capacity" ones are 250 mah. 

So there's not nearly enough current for 1/2 amp. Normally you want to stay at 1/2 C or better, that would be a 100-125 milliampere load. 

I'd either look at putting a number of leds in series, so your load is higher voltage, but only 20 milliamperes (that would worrk). 

I'm only guessing here, but if you are considering 10v minimum, then there's no way you can put the incandescent bulbs in series to minimize the current draw. 

Regards, Greg


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## dbodnar (Jan 2, 2008)

Keith - I missed your comment about drawing 1/2 amp - I would agree with Greg - go with LEDs or find space for more power!

dave


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## Cougar Rock Rail (Jan 2, 2008)

Thanks for the info, guys. I know from trial and error with my project that a single 9V gives more than enough current for just the lights, so my actual draw is probably closer to 250mA. I'm trying to remember now but I think I actually did the wiring for the lights in parallel because I wanted each of them to get the exact same voltage. As far as voltage goes, anything over 10V gives me enough power to run the sound plus the lights, and I can dim down the light output as needed to keep it at around 8V which is what the bulbs were rated for. As long as it's OK to put them in series I should be OK. Once I get it all done I'll post some pictures...I think you guys will get a kick out of it. 

Keith


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## Dan Pierce (Jan 2, 2008)

For 2 9 volt batteries in series, put your lights in series so the 8 volt units become 16 volts. 


This will cut your bulb current in half making the batteries last much longer!!!!! 

Add diodes in series to the lights and each diode can reduce the voltage by .7 volts. 

So, a rechargeable at 8.4 times 2 gives 16.8 and add a diode to 2 lights in series to give the lights 16.1 volts. Or add more diodes to reduce the light voltage and brightness.


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## Cougar Rock Rail (Jan 2, 2008)

Thanks for that good advice Dan, but unfortunately I've already built the light unit so changing it now isn't an option at this point. This unit won't be running for extended periods...only for a few short periods here and there. 

Keith


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