DC Motor not working

Hello all

I have a "Dyna-Might Hydralic Pump" (very similar to the picture in the link) that operates a hydraulic cylinder which lifts a snow plow.

Dyna-Mite hydraulic motor

The DC motor that runs it stopped working a few days ago and I have not been able to fix it. Hopefully someone here will be able to point me in the correct direction.

The first thing I checked were the two batteries that run it. They are fully charged and when put under a load are still putting out enough juice to crank the engine and run accessories.
The next thing I checked were the brushes. They seemed to be fairly long and making good contact with the commutator.
I cleaned the whole armature well and buffed it back to a clean surface.
I blew everything out inside the motor with our air compressor and cleaned all wire contacts.... battery to solenoid cable and solenoid to motor cable.
When I engage the motor, I hear the solenoid click.
I have checked that its getting power to the positive post on the motor (after the solenoid) - Positive lead from the multimeter to the positive post on the motor, negative lead of the mulitmeter to the body of the motor (ground). The multimeter reads 0V when the motor is disingaged and around 12.6V when engaged.

Here's my Question:

When I put the multimeter on ohms and touch the positive lead to the positive post on the motor and the negative lead to the body of the motor, it completes the circuit - I thought it was supposed to be an open circuit? If so, could the motor be short circuiting?
Checking this further I made sure that the positive post on the motor is not contacting the motor housing in any way....sure enough its well insulated with its nylon(?) washer and two non conductive washers on either side.

This is where I left off. I would be happy to give any further details if needed.

Hi Gerry;
Electrical is definitely not my best department but...here's an experience I had.

Two years ago my Makita sliding compound saw went from running fine to not running at all. That quick !  We were using it , made a cut , came back and nothing ! I checked everything I could. Finally talked with the mechanic at Coeur D' Alene tools.   Told me to remove the armature and bring it in for a test. Sure enough it was dead.  No warning , no way to test at home.  New armature and I was back up and running.


Kinda sucks for your snowplow motor to pick now to go gunny bag.

Thanks for the info Thomas.  

It lead me to this YouTube video on how to test an armature.  Armature test   We'll see how it goes... and hopefully no snow in the immediate forecast!

I used to work for Douglas Dynamics who makes the snowplow brands, Fisher, Western and Blizzard. This is just a common problem with these brands of snowplows and any distributor has the parts for these plows. It is not uncommon to have motors go out several times a year.

Travis Johnson wrote:I used to work for Douglas Dynamics who makes the snowplow brands, Fisher, Western and Blizzard. This is just a common problem with these brands of snowplows and any distributor has the parts for these plows. It is not uncommon to have motors go out several times a year.

Yikes! Do you recall what the problems were that they were having? Until I perform the armature test (when it warms up this afternoon so my hands don't freeze to the motor while taking it out!) I really don't know what to replace.

Performing the 3 tests given in the video, I can now confirm it is the armature that is bad. There is definitely a short in some of the windings.
Tomorrow I will begin the search for hopefully an inexpensive used one.  Thanks again Thomas for the insight!

When I put the multimeter on ohms and touch the positive lead to the positive post on the motor and the negative lead to the body of the motor, it completes the circuit - I thought it was supposed to be an open circuit?  

Check the range selector switch of the ohmmeter. The higher scale will read through your body if you're touching the wrong places & look very similar to a complete short. It does sound like that motor is fried but if it was a complete short (to ground via the motor case) it would be loading the battery down hard when you did the voltage check. Or popping fuses. Or burning something.

Mike Barkley wrote:Check the range selector switch of the ohmmeter. The higher scale will read through your body if you're touching the wrong places & look very similar to a complete short. It does sound like that motor is fried but if it was a complete short (to ground via the motor case) it would be loading the battery down hard when you did the voltage check. Or popping fuses. Or burning something.

I used the lowest ohm setting on my multimeter which was 200. Also, when I tested, I made sure I was not touching the armature or the tip of the multimeter probe with my fingers.
Tesing the rest of the motor to be sure its OK as well would be a good idea. Any suggestions for doing this?
Here is the motor with the armature removed.

There is continuity between the + post and the motor casing. I double checked that the + post is grounded from the casing with a nylon insert so I'm assuming this is an indication that there is a short in the windings? If so, then if this part of the motor is also having issues then I'd be better off looking for a whole new motor rather than trying to fix it.

Gerry;  Use an unconnected  car battery, with jumper cables.  Connect ground to your case and touch positive  to your post.  Big spark its bad … no spark might be just fine.

Have you looked at ebay? might be someone selling that model, buy the whole thing mix parts till one works.

There is continuity between the + post and the motor casing.

With the armature removed? Check that wire carefully. Probably a tiny pinhole in the insulation which could explain why it's not popping breakers. Hard to tell from the pix but it appears the shielding around the positive lead is deformed. Maybe it's poking into the wire???

thomas rubino wrote:Gerry;  Use an unconnected  car battery, with jumper cables.  Connect ground to your case and touch positive  to your post.  Big spark its bad … no spark might be just fine.

Have you looked at ebay? might be someone selling that model, buy the whole thing mix parts till one works.

I'll try that battery trick.
The picture I included in my original post was for the whole pump assembly from ebay so I know it exists. Didn't look any further but may need to.

Mike Barkley wrote:With the armature removed? Check that wire carefully. Probably a tiny pinhole in the insulation which could explain why it's not popping breakers. Hard to tell from the pix but it appears the shielding around the positive lead is deformed. Maybe it's poking into the wire???

Yes, the test was done with the armature removed. That's a good eye you have! - the shielding on the inside is only deformed because its a piece of rubber from on old inner tube that I cut out to replace the existing one (some sort of compressed cardboard looking washer) that fell apart and was not reusable.

I removed the post originally to verify that it was not making contact with the case and checked its continuity with the case before hooking up the two leads back to it again. The result was no continuity (a good thing). I then hooked up one other lead and checked again (no continuity), then hooked up the final lead (the black wire with the eyelet seen in picture 2) and this caused it to have continuity (not a good thing). This black wire is what goes to one of the coils.
On the side of the motor casing there is a bolt that I think you can remove which holds the coil in place. I've tried to remove it but it won't budge - My thinking is that if the coil is grounding to the case due to a pin hole or insulation deterioration, maybe I can put something non conductive between the coil and case it would solve this problem?