18v dc cordless drill battery converted to 12V or 9V or lower

[officework13]

i have several old rechargable batteries from corless drills, the drill is broken but the batteries are in perfect order. to assist in my hobbies if I can use these batteries then it woudl save me some $$$$$ on buying separate batteries.

what is the easiest way for me to reduce the voltage from the 18 volts down to either the 12 volts, 9volts or any other voltage.

i know i can buy a 12 volt converter to get to lower voltage, but what about when starting at 18volts. plus i have lots of old 12 volt converters/chargers will these work for anything.

also, i suspect the amperage rating of the device will be an issue, which i do not totally understand, but if my research on the other forums serves me correctly, then as long as the output amperage is greater than the device requirement, then i should be ok, and as long as i have an in line fuse with an amperage rating roughly equal to but greater than the device requirement, say a 1 amp draw device i use a 1.5 amp fuse, it should be fine and i should not have to regulate the amperge. however if this is not correct, how would i regulate the amperage.

thanks.
i can see that this may not be totally clear, but after you comment or question me on anything for clarity, we should be in better shape.

thanks

 

[Nigel Goodwin]

Take the cells out and just use as many as you need for the voltage you want - they are full of 1.2V cells in series (so ten for 12V, five for 6V etc.).

 

[officework13]

thanks,
something so simple, which i did not think about.
however, will the charger still work when i reduce the voltage of the battery, say from 18v down to 6v.

the other issue with using the method you indicate is that by reducing the number of batteries in the battery pack it will also reduce the duration that the battery pack will last, which is what i would like to keep.

any other ideas. thanks.

 

[Nigel Goodwin]

thanks,
something so simple, which i did not think about.
however, will the charger still work when i reduce the voltage of the battery, say from 18v down to 6v.

No, you will have to make a different charger.

the other issue with using the method you indicate is that by reducing the number of batteries in the battery pack it will also reduce the duration that the battery pack will last, which is what i would like to keep.

No, they will last just as long at the same current - any linear method of dropping the voltage will just waste energy, and any switchmode method will still waste some, and be greatly more complicated.

 

[officework13]

Thanks for the clarity.
that solved my problem.

 

[Noggin]

If you have plenty of 18v batteries, I'd say use a 7809 to get 9v from it, 7805 to get 5v, a 7812 to get 12v etc, or use an LM317 to make a variable supply. This way you can still use the same charger.

I wouldn't separate the cells from the battery pack. If you do that, then you could run into problems when trying to charge them. If you took 6 of em out, use them on a project, and then put them back into the battery pack to recharge them then you could damage the 6 that were unused by overcharging them. Lets also say that you took out 6 of them for a project and then took out 2 more later to use with those 6. The original 6 would have less charge and could go into a negative charge state long before the additional 2 are drained of their charge.

Because of reasons such as those I'd suggest using 78xx devices or an LM317. Use a TO220 package and heat sink it.