# What is the correct way to 'bench test' a DC motor?



## rillip3 (Jun 19, 2009)

if you don't have a dyno (most don't) to create a load on the motor, you must be careful to only put low voltage through it so that it does not over-rev and tear itself appart. Connect a voltage source, 12v is a convenient, low, safe voltage, and see if it turns. If it does, you win. If it doesn't, get a refund. You just hook it up positive terminal to the positive input line, negative terminal to the negitive line, nothing fancy for this.


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## DavidP (Jun 9, 2010)

I don't know which is the + and which is the - connection ... 
The closest information I found so far are the rough drawings here :- 

For *Shunt, Separately Excited, REGEN, DCS, PDS, IQ Type Cars *(my motor)

http://www.empinc.biz/tech_support.php?page=low_voltage_no_controller_shunt 

&

For *series wound motor *

http://www.empinc.biz/tech_support.php?page=low_voltage_no_controller_series

I guess it will get it moving in one direction?? 
But not sure how to check for the reverse direction ??

I'm more mechanically inclined ... but a complete NOOBY for anything to do with DC wiring ... I'll have to learn as I go ...


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## major (Apr 4, 2008)

DavidP said:


> I'm sure its been mentioned before ... as I'm sure I read it here myself ...
> 
> I just can't find the thread again ...
> 
> ...


Hi Dav,

First off, for series motors, you need to wire the field in series with the armature. Usually like A1 to B+, A2 to S1, & S2 to B-. Then careful to use a low voltage for B+ and B-. 12 Volts max.

You have a SepEx motor. So don't connect it up like a series motor. And all SepEx motors are not the same as far as field strength and resistance. But if you are careful and watch it, like be there if things start to get hot and smell ripe, you can test it with a single 12 volt battery. I have some nice power supplies available, so use those, one supply on the armature and one on the field and can adjust them separately. If you have this available, do it. Adjust the field to about 6 to 8 amps and bring the armature voltage up slowly. Watch RPM and raise the armature voltage such that you see about 2000 RPM. You can then adjust the field voltage while leaving the armature voltage alone. And you can see the effects of field weakening. But keep an eye on the RPM and keep it under 4000, to be safe. The lower the field current, the higher the RPM. And you may find that you trip the armature power supply if you increase the field current too fast because it regenerates into the power supply.

So, you probably don't have 2 power supplies. Just use a 12 volt battery. Hook the field up first and disconnect the field last. Remember this. O.K. So connect F1 to B+ and F2 to B-. You'll see a little spark. Endure it. It won't hurt. Use like #16 wire for the field to battery. Should be at most 10 to 12 amps. If the wires get hot, better shut down. 

Now you have the field excited. You can use the same battery for the armature or a different one. You probably want a little heavier wire, like jumper cables. Connect A1 to B+ and A2 to B-. Again you'll get a spark. And the motor will rotate. It will accelerate quickly and tend to rotate on the bench. You should have nothing connected to the shaft, maybe those pulleys are o.k. You can strap it down or block it so it does fall off onto your foot.

So now you have 12V to the field and 12V to the armature. Should be rotating smoothly, maybe 700 to 1000 RPM. Should be no big sparks anywhere, or smoke, or bad smells. If so, shunt down, ARMATURE FIRST, then the field. If you disconnect the field first, you might get a speed up of the armature and then a real high current in the armature and could damage stuff. Same on start up. FIELD FIRST, then connect the armature.

Now, I cannot tell what that field is rated for. So 12 volts to a 1 ohm field will be 12 amps. That might be over the field coils' rated current. So don't run it there for hours. Maybe 20 minutes if you watch it. 

With an empty output shaft, you're running at no-load. So the armature current will be low, but higher than the field. Maybe 30 to 50 amps. So it will draw down the battery pretty fast. At no-load current, the armature and brushes should not overheat for hours. So you can run the motor for a while and break it in. You can even hook up a battery charger to the battery and use it to run longer, or run the battery down, charge overnight and run it again tomorrow.

If you have a separate battery on the field, make sure it does not run down while you have the armature excited. It will speed up. I doubt it will overspeed with 12 volts on the armature, but it will draw excessive current and can damage the comm and brushes. Without field current, the armature is basically a short circuit across the battery.

There you go, but don't blame me if things go wrong  Just kidding. But do be safe. 12 volts is not going to electrocute anybody, but it can draw a big arc which will melt a wrench and send a molten spitball into your eye. So wear safety glasses. Use your head (and brain) and good luck.

major


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## major (Apr 4, 2008)

DavidP said:


> I've just roughed out the new bearing end cap ... and like to make sure everything is working ... hopefully forward and reverse as well ..


Oh yeah,

You have to have the Drive End (DE) bearing solidly in place when excited or the field will pull the armature into the poles and it will rub.

And to reverse rotation, switch polarity of either the field or armature, but not both.


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## DavidP (Jun 9, 2010)

Thank you eek:maybe) for taking the time to 'explain' that ... 

As a complete ""NEWBY"" (NOOBY) doing any wiring for a DC motor ... I have no idea what you just said ... 

I suspect there could be a few others that don't fully understand what you said either ... 

Using the "KISS" principle (keep-it-simple-stupid) ... is the simple drawing in the url below showing fig A & fig B correct for my SepEx motor or will I blow something up using 12V source for a quick test ? 

http://www.empinc.biz/tech_support.p...ntroller_shunt 

This is just for a quick test prior to the working out the permanent wiring and controls ...

I'm going to go take a couple of aspirin (acetylsalicylic acid) after reading that reply ...


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## major (Apr 4, 2008)

DavidP said:


> Using the "KISS" principle (keep-it-simple-stupid) ... is the simple drawing in the url below showing fig A & fig B correct for my SepEx motor or will I blow something up using 12V source for a quick test ?
> 
> http://www.empinc.biz/tech_support.p...ntroller_shunt


 
Why not? Basically that is what I told you to do


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## major (Apr 4, 2008)

DavidP said:


> As a complete ""NEWBY"" (NOOBY) doing any wiring for a DC motor ... I have no idea what you just said ...


Just wondering what you have in mind for a control system? I suggest you get that figured out on the bench before you go through all the effort to install the motor into a vehicle. It will make things a lot easier in the long run.

Hey, I'm just trying to give advice, not headaches 

major


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