How do I keep the wires from getting to hot when I connect a motor to batteries?will a fuse help?

Question

this is a 48v 100a motor connected to 4 12v batteries. I do not need to control the speed I want it to run at full speed. speed on motor is controlled by volts but specs say it needs 100amps batteries can give more and the wires are overheating

Answer 1

Basic electronics. Heat = resistance.  The only thing a fuse will do is prevent a fire from overheating. (if proper amperage of fuse is selected) It means that you have too small a gauge of wire connecting the batteries to the motor.  Typically it's not a bad idea to have some sort of voltage regulator between the two.  I would need either a diagram or description on how everything is setup.  I assumed batt pos directly to motor pos and batt neg directly to motor neg. No neutral, floating or closed grounds.  IF that's the case then you may want to introduce a common ground by coupling the batt neg to a ground or earthed pole. Then couple the motor neg to the same ground/pole.  This will actually increase the efficiency.  Still though you need to beef up your gauge.  Wire gauge (AWG) is smaller # larger diameter.  14~16AWG is like a brown extention chord.  6~8AWG is like a car battery terminal cable.  Hope this helps a little.

Answer 2

The current needed by a motor will change based on the speed of the motor. Your 100A spec is probably what's known as "stall current".. when the motor isn't moving, it'll be at maximum torque and maximum current, which would be that 100A.

Now, assuming you're feeding it 48V @ 100A, that's 4800Watts... pretty serious power. Think of the heat in a typical 100W lightbulb. A lightbulb is built with an intentionally lossy (resistive) element -- the filament -- which is a resistor that, oh-by-the-way, gives off light.. but mostly heat. The effective resistance of your wires will result in some of that 4800W of power being converted to heat, due to their inherent resistance.

Of course, once the motor's up and running, the current will drop. If you're talking about something like a fan, it's pretty much going to stay dropped, and so heating in the startup surge isn't critical. If your motor's in a vehicle, it may ensure prolonged low speed/high current operation, and you probably want to keep that heat (and loss) down.

And that's is relative to wire gauge. It's not the voltage per se in the wire cauing the heat, but only the bit of voltage lost in the wire, which is <resistance> * <current>... thus, the power lost in the wires is <current>^2 * resistance. This is why big motors get higher voltages (like the 300-500V used in hybrid cars, etc)... less worry about the wiring.

Here's a calculator that may help:

http://www.denningelectronics.com/wirega...

In truth, there's no single right answer for gauge vs. distance vs. current, because what you're really calculating is loss, and thus heat, in the wiring. Some of that's perfectly acceptable, and the simple answer is, of course, if the wires are too hot, get thicker wire (or double/triple/quadruple the leads you're using now). Filling in some numbers, the calculator here suggests something in the 8-12ga range, assuming less than 4ft of wiring.

Answer 3

You did not mention the wire gauge you are using ?

But, I would increase the gauge of your wire.

The bottom of the web page I provided has a wire capacity chart.