DC motor wiring questions

[HOPOIL]

Hi
I couldn't figure out how to attach a PDF or Image,,, so I'll do my best to describe in words.


I have a G.E. Series-wound, 7 HP, DC motor. the specs go like this: 48 volts, 100 amps, 4200 rpm.
Has 4 posts: A1, A2, S1, S2 arrayed at 90 degrees around the motor.
The wiring info goes like this: for CCW rotation connect A2 & S1 and power across A1 & S2. It also says that A1 is the "terminal screw".

My first question is can I bench test this thing by hooking wires straight to a 12-volt battery?

Second question: Which post (in the CCW scenerio) becomes Positive, A1 or S2? or does it matter?

third question: What does "terminal screw" really mean?

thanks
Jeff

 

[frodus]

to bench test it with a 12V you can wire A2 and S1 together with a short cable..... then take some longer cables and briefly touch A1 to + and S2 to - and it should spin CCW. If you want it to spin the other way (CW), connect A2 and S2 together and briefly touch A1 to + and S1 to -. Don't leave it on for very long because you're essentially shorting the battery.... just put it on for a few seconds.

You can connect either terminal to + and it will spin according to how you wire it up. Wiring determines direction on the motor, not the polarity of the battery connection.

Terminal screw means that A1 should always be connected to the source. A2 should always be connected to either S1 or S2 (depending on direction). The leftover "terminal" should be connected to the source. They're just saying to always connect A1 to the output of the controller.

 

[HOPOIL]

thanks Frodus.
I'll try it out this evening.

 

[frodus]

its better to use a controller, just be careful... and use a BIG battery.... smaller ones might pop an internal cell.... remember, there's no current limiting.

Don't load the motor and it should be fine to test.

 

[HOPOIL]

Frodus:
I talked with the electrician here at work yesterday and when I asked him whether I'd be able to spin this motor, on the bench, with a 12volt (motorcycle) battery, he said probably not. At the lower voltage (12v) the motor would need many more amps than at its recommended voltage (48v).

this sound correct?

I guess I'll bring it to a Motor Repair shop to test, as I have to invest in other stuff (like gears - like Frank did on his Suzuki) for this bike before I'll buy batteries. I think I'll get (4) 20 amp/hour AGM's from B&B battery. I have a Curtis controller, but not a Magura twist grip yet. nor a contactor. so i'm a ways off still from testing this bike. It would to reassuring to know the motor was good, though.

thanks, HOPOIL

 

[frodus]

Volts determines speed, amps determine torque... and since you're not loading the motor, it won't be drawing a TON of amps. I've done it on my series wound ADC K91-4003 motor.... worked just fine.

Its not something you should do over and over, but to test that the motor works, and rotate for 5sec or so, it should be fine. Just make sure its a stout battery.

Its not mounted on the bike is it? Just make sure the shaft has no load on it.

 

[Link]

Since nobody's pointed this out, series motors don't have a no-load speed. Because the field current is linked to the armature's current, the field gets weaker and weaker as the armature speeds up. And since a weaker field equates to a higher RPM, the armature just keeps accelerating until it balances out with friction or something goes very, very wrong. Be careful.

Dunno what your electrician was thinking, but it should move on 12V. I'd even try it on 6V first just to be safe. That should be enough to get it to at least turn over, IMO, and wouldn't be too damaging to the batteries since it won't be drawing a load of amps at that low voltage.

Or, if you have a small brushed controller, hook that up to it and go easy on the throttle.

 

[frodus]

Forgot about series motor "runaway"

the back-emf weakens the field windings and cause the motor to speed up quite a bit.... one of the problems when designing the controller... and a good reason to have a controller with a tach input.

 

[fechter]

I think it should run fine on 12v. With no load, it could overspeed but not very likely with 12v.
Just watch the motor rpm and disconnect if it sounds like a phaser on overload. It will take a while to build up enough speed to self-destruct, and it may never get going that fast because there is always some load from brush and bearing friction, windage, core losses, etc.

My electric saw is series wound and it does not blow up with no load.

I did blow up a vacuum cleaner motor with the rotor removed one time. It must have been doing well over 20,000 rpm. Shot across the room when the windings flew off and jammed the armature.