To any of you Electrical savvy people out there, I am wondering if I can run wires from my 12-volt rechargeable battery drill to a 12-volt car battery or other 12-volt power source?
Many times I’m working away from AC power and my drill batteries go dead (I have 4 when I start) and I have to take the time to drive somewhere to recharge them.
What I don’t know is while the volts are the same will AMPS be a problem?
A Carpenter in the woods
A car battery can easily supply way more amps than what your little drill motor will draw, so that should be safe so long as you get the polarity right and do a competent job of wiring it up.
Why not buy on of the inexpensive DC to AC inverters and use your battery charger in the car?
Look on the charger and see how many watts it requires and buy an inverter of that capacity or higher.
Or, if you are always that close to the car, get a 115v AC inverter, and use a line-powered drill - better torque, and the power loss due to the inverter will be minimal.
Either way: look out for battery drain.
Be warned that 12v lead acid batteries have different internal resistance and discharge curves than NiCad or NiMH in your battery powered drill. I serously doubt if you’ll damage anything but you could easily find yourself without enough juice to start your engine when it’s time to go home.
Dcurt - You need something in the line otherwise your drill will be gone in no time. The DC commutator brushes will be the first to get destroyed. Been there and done that as a kid.
Drill DC Motors have nearly ZERO startup resistance: so essentially the startup current is the result of short circuiting the circuit. As the motor starts rotating it generates a back emf which reduces the amperage.
So I suggest you do this:
1> Short the current drill battery and find the current (Dangerous so do it only momentarily)
2> Use a current limiter to limit the current to this value. (A fuse will not work here because it is not fast acting. And if you use fast acting fuses, it will always fuse).
dcurt: I’ve done this. It works. The drill that I was using, however, had built-in socket that you used to connect a cable to the cigarette lighter.
You would need to do a bit more wiring work. The main thing you must remember is not to connect the car battery across the terminals of the drill battery. If you do, it’s goodbye drill battery. Remove the drill battery, and connect small alligator clips from the car battery to the inside of the drill where its battery contacts are.
That said, I can think of less painful ways to achieve the same effect.
GaryM suggested you get a small inverter, and use that to power your battery charger. Have one of your 3 spares charging at all times. That frees you from having a cable attached to the car.
Better yet, get an in-car charger for the drill battery. These are available from some specialty electronics stores here, and probably where you are as well, it just takes a bit of looking. If you can’t find one, go with GaryM’s suggestion.
Several posters have cautioned about flattening the car battery. You do need to watch this. The car battery is bigger than the drill battery, but probably only about 40 times bigger in terms of its electrical storage capacity. You may find that you have to start the car ocassionally and idle it for while to recharge the car battery. I’d suggest that for the first day at least, try starting the car engine every time you swap drill batteries. If the car is getting sluggish to start, let it idle for a while.
I agree. Car batteries are not designed for deep cycle use. So care must be taken not to discharge the battery to any significant extent.
Another thing: A battery pack containing ten NiCAD cells in series has a nominal V[sub]OC[/sub] of 12.0 volts. There’s also a fair amount of source impedance; this helps to limit the current, especially at startup when the load impedance is extremely low (as noted by andy_fl). If you power the drill from an automobile battery and run the engine, the voltage will increase to at least 13.2 volts. This represents a 20% increase in power dissipation (assuming a “flat” load impedance curve for the drill). Furthermore, the source impedance is essentially nil, which further increases the risk. So I would not recommend powering the drill from an automobile with the engine running…
Thank you everyone for the advice.
I’m going to try this out this weekend.
What I’m doing is using a boat battery which has a handle and does not leave me stranded when it runs down, 20 foot cables from an emergency light that already have clamps for the battery, and a alligator clips to the back of the drill I will see how much longer I can work after my drill batteries run down.
but NiCd (most drill batts are NiCd) have much lower internal resistance then Pb-acid. Because of the size difference I would wag that they would be about the same in terms of starting surge. remember your starter motor is a dc motor too and much more powerful then the drill motor.
IMHO your best option would be get an inverter to recharge your batts.
k2dave: Don’t sweat it about the internal resistance. andy_fl’s claim is: “danger - 12 V motors can’t run on 12 V, I did something with a motor when I was a kid and it blew up!”
dcurt: Let us all know how it went.
I highly doubt this is true. A lead-acid car battery must have a much lower source impedance than twelve small NiCADs in series, or else you’d be able to start a car with the NiCAD battery pack.
Crafter_Man: Again, don’t sweat it, it’s irrelevant to the OP, and only entered the thread as a WAG from someone that didn’t know any better.