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Batteries in Parallel

jeff77789

Feb 23, 2013
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If I want to use 2 9v batteries for my circuit, what happens when i run them in parallel?

what i want is increased capacity or mAh rating

now, if these batteries are different, one might drop in voltage faster than the other battery. for example, i might have one 8v battery and the other still might be at 9v. What voltage will the power unit (with the two batteries in parallel) show?

if i still have those two batteries and i wanted to replace one of them, can i take the 8v battery out while the circuit is still on and replace it with a new battery on the fly?

thanks
 

john monks

Mar 9, 2012
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If both batteries are of the same make and date code and are new you should have no problem running two 9 volt batteries in parallel. Using different voltage batteries is a crap shoot,
To replace batteries in parallel one at a time would probably be ok if you did it very quickly. Ideally they should be replaced in pairs.
 

GreenGiant

Feb 9, 2012
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Depending on what the circuit is like you should be fine swapping one and then the other out, just do it quickly like john monks said.

If you want to be careful you can set up some circuitry so that there are voltage regulator circuits, and things so that the voltage is always the same to the components
You should also be able to set it up so that both battery is isolated, in parallel but isolated from each other, that way you can easily and safely swap one and then the other.
 

jeff77789

Feb 23, 2013
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Depending on what the circuit is like you should be fine swapping one and then the other out, just do it quickly like john monks said.

If you want to be careful you can set up some circuitry so that there are voltage regulator circuits, and things so that the voltage is always the same to the components
You should also be able to set it up so that both battery is isolated, in parallel but isolated from each other, that way you can easily and safely swap one and then the other.

the voltage is going to be through a 5v regulator
 

davenn

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Sep 5, 2009
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the voltage is going to be through a 5v regulator

Thats going to be very wasteful of the low level of power you have available if you used a standard 7805 reg.
of you really wanna do a regulation to 5V, then look at buck converters on the www
They are plentiful and very cheap on eBay

Dave
 

jeff77789

Feb 23, 2013
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Thats going to be very wasteful of the low level of power you have available if you used a standard 7805 reg.
of you really wanna do a regulation to 5V, then look at buck converters on the www
They are plentiful and very cheap on eBay

Dave

how you go about using a buck converter? especially setting the output voltage.....

i found pictures but i did not find any datasheets...
 

davenn

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Sep 5, 2009
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how you go about using a buck converter? especially setting the output voltage.....

i found pictures but i did not find any datasheets...


http://www.amazon.com/Retailstore-LM.../ref=pd_cp_e_0

like i said, no datasheets..

you didnt look hard enough ;)

see the trim pot on the board ... the blue thing with the brass screwdriver slot.
You use that to set the voltage
And if you look down the left side of the main image of the site you linked to you will see the datasheet !! :)

Dave
 
Last edited:

davenn

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Sep 5, 2009
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That buck converter will still have losses
It just wont be as bad as a standard 78xx series regulator

After a bit of use, you will have to decide if you need to revise your style of power source

cheers
Dave
 
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