bilge pump

I have a diaphgram bilge pump, it is 12V and it is protected by a 10A fuse on the panel.
Because of some rust on the body of the electric motor, I decided to open it, clean it and paint the body, I also checked the inside to make sure there was no corrosion and checked the brushes.
The brushes are in very good conditions (the pump is only 2 years old).

I put the motor back together and tried it and it works fine.

I put the motor back on the pump and it works, but when it starts sucking water it blows the fuse …

I already opened it like 10 times checking for shorts or other problems .. checked the hoses, and tried with wires coming direct from the battery (with a 10A fuse in between) ..but still the problem is there, …..

Any idea????



We had a problem with one, because of rust the bearing of the electric motor (where the sahft exits the case) got frozen.
The fuse on the panel was blown.

We dissembled the motor and changed the bearing, put back together the motor and the pump, changed the blown fuse and connected with the switches.
The pump runs but blows the fuse.
We tried the motor without the pump and it runs ok…. but when the pump is attached to the motor, then the fuse blows.

To make things worst..., we dissembled the other one (that was working fine) cleaned and sprayed it with WD40 (to prevent rust) and put it back together… and now the two pumps are blowing the fuses ….


When connected to the pump the pump runs freely…. actually the weird thing is that it sounds like the motor is spinning faster than before…..

Any idea on what could be the problem??

 

Difficult to diagnose without pictures, but I see two possibilities:

If the pump output is restricted, the motor will draw more than 10 Amps and blows the fuse.

Or, there is a short in the rotor winding. Without load it passes that point quickly, so the motor runs. With load, the short circuit causes excessive current drain and blows the fuse.

 

ok the output is fine, just to make sure, i took the pump out of the boat and tried it with a bucket and a new piece of hose as output, same result …
I'm going to take pictures of the motor …

 

i found the problem ….
the wire attached to the brush was not letting the spring push the brush all the way …
I moved it a little with a small screwdriver while assembling the body and now it works fine...