DC TRACTION MOTOR HELP?

Maybe you should look at the previous post in electrical engineering.

One pair of terminals are to the motor fields the other pair to the motor brushes.

The application that you are using the motor on would determine whether it could be used straight from a set of batteries.

Ozzie, thanks, are you saying then that both the armature and the field are energized with the 72volt battery power (rated at 72v 82amps 5kw 6.7hp)?

Is there any way to identify (perhaps with mutimeter which 2 are field connections and which 2 are brush (armature?) connections? Thanks,

Yes, you can identify them with a meter.

The field will have a high DC resistance if it is shunt wound. Expect 10-50 ohms. The shunt wound field electrical connections should be much smaller.

If it is a series field, the electrical connections should be the same size as the armature's. In this case, both will have a low resistance reading but the armature resistance will change when you turn the rotor slowly. This is caused by the brushes resistances making a variable contact on the commutators. You might also be able to read a small DC voltage at the armature connection when you turn the un-powered motor by hand as fast as you can.

Hi Marcot,

Thanks for response! We are wondering if anyone has ever been able to run a series connected motor with straight battery power. We know that ideally a pwm controller is best but they are expensive and this need is rudimentary. In other words would it run away or settle down to a top speed if full 72v were applied directly to the 4 contacts (thru field then armature). Small permanent magnet motors are run with full on off type power and so we are asking if it can be the same on series motor. Is there anyway to not have a controller or to have one that is basic switch etc. thanks!

FYI: The motor is rated at 72 volts and 82 amps. We would hope that it would not draw independently more than that in any case just as a 60watt light bulb or golf cart motor doesnt' draw too much more than rated .

Hi Ken

Have you checked this company out http://www.smhco.com

Wow... what a catalog! Thanks! In some of these huge catalogs you can find a production piece for $10 that would otherwise cost $200 to make.

They are some times marked A1, A2, S1, S2 check them. There are some other designations too these are the most common. On the type of DC motor you are talking about. There is usually a band type cover over the area of the brushes. remove it. Check continuity from the input terminals to the brushes to make identification.

While your there check the brushes and commutator.

Good answer!

Hello, 4 connection points would indicate that it is a series dc motor. What this means is that 2 of the connections are for the field windings and the other 2 for the armature. This would would normally be indicated by letters stamped into the housing near to the connection points.

So for example you are looking to see "F1" and "F2" for field, "A1" and "A2" for armature. Some motors have "S" instead of "A".

If there are no markings use a voltmeter set to 200 ohms and test for continuity across the terminals. You should be able to isolate them in pairs with continuity. the meter will beep or indicate a reading. Just mark each pair as "X1" and "X2" and "Y1" and "Y2". At this stage whether it is a field or armature doesn't matter.

The simplest way to get the motor to work is to use a short jumper to connect one of the terminals to an opposite one.

ie. A to F, or X to Y

Now connect the other two to a 12volt battery. If you reverse the connection to the battery it should rotate in the opposite direction.

Safety Note;

Never connect similar marked terminals to power supply that will short it out. Secure the motor as the torque reaction could cause the motor to roll away suddenly.