12v DC motor question

[C08]

My outboard engine power tilt motor (a small 12v dc motor drives a hydraulic pump) has started to intermittently fail to work. It is not the solenoids or wiring and is now removed where I can "hot wire it" to test it. This involves just connecting to a 12v battery directly and the motor should then drive up or down depending on which way the leads are connected. Sometimes it works sometimes not. The unit is only 4 years old. On stripping down the motor the commutator looked black and shiny but soon cleaned up, there is no visible wear and the segments are undercut ok. There was some carbon dust in the housing. Checking the commutator to ground with a multimeter does not reveal anything amiss.
In the normal course of events I would just replace the motor brushes which are one small plain brush and one with a small thermal breaker in the base fitting but the money I have been quoted is insane by any measure, even boat part standards,
So my questions are :-
How sensitive to length of the brushes are DC motors (these units are made by SHOWA, Japan and I have failed so far to ascertain the length of the new brushes.
Does the appearance of the commutator suggest worn brushes i.e. should it look shiny and coppery if the brushes are making proper contact.
An other thoughts about DC motors welcomed!

 

[RichardS]

My outboard engine power tilt motor (a small 12v dc motor drives a hydraulic pump) has started to intermittently fail to work. It is not the solenoids or wiring and is now removed where I can "hot wire it" to test it. This involves just connecting to a 12v battery directly and the motor should then drive up or down depending on which way the leads are connected. Sometimes it works sometimes not. The unit is only 4 years old. On stripping down the motor the commutator looked black and shiny but soon cleaned up, there is no visible wear and the segments are undercut ok. There was some carbon dust in the housing. Checking the commutator to ground with a multimeter does not reveal anything amiss.
In the normal course of events I would just replace the motor brushes which are one small plain brush and one with a small thermal breaker in the base fitting but the money I have been quoted is insane by any measure, even boat part standards,
So my questions are :-
How sensitive to length of the brushes are DC motors (these units are made by SHOWA, Japan and I have failed so far to ascertain the length of the new brushes.
Does the appearance of the commutator suggest worn brushes i.e. should it look shiny and coppery if the brushes are making proper contact.
An other thoughts about DC motors welcomed!

I would say coppery as the brushes normally keep it polished if everything is working well. How long are the brushes compared to their holder and how tight are they being held against the communtator? Try stretching/bending the springs a little if they are weak just to see if that solves the problem.

Richard

 

[VicS]

My outboard engine power tilt motor (a small 12v dc motor drives a hydraulic pump) has started to intermittently fail to work.
An other thoughts about DC motors welcomed!

It should not be black. Suggests arcing. Intermittent nature of problem suggest bad contact between brushes and commutator rather than winding fault

Check bush length allow good spring pressure. If so clean up ad try again.

If not try an auto electrician for replacement brushes. I guess the one with the thermal breaker will cost a bit! ... several x £10

Lucky though that the brushes are available. A complete new motor would cost several x £100.

 

[C08]

Thanks for ideas-the replacement brushes are quoted at £120 for the plain brush and strangely £118 for the one with the thermal breaker. The breaker is just a little bi-metallic strip that bends away from the contact with heat from continuous use, nothing fancy. If this was a vacuum cleaner, car or other bit of kit the cost would be more like £10-15.

 

[prv]

Thanks for ideas-the replacement brushes are quoted at £120 for the plain brush and strangely £118 for the one with the thermal breaker. The breaker is just a little bi-metallic strip that bends away from the contact with heat from continuous use. If this was a vacuum cleaner, car or other bit of kit the cost would be more like £10-15.

It seems highly unlikely that the motor was created specifically for use as an outboard hydraulic pump and nothing else. You just need to find the "vacuum cleaner, car, or other bit of kit" that it's also used in (or just the generic part number of the motor).

Pete

 

[LadyInBed]

Is it intermittent in both directions or just one?
If stretching or padding springs doesn't fix it try shorting the thermal cutout to eliminate that as the cause.

 

[VicS]

Thanks for ideas-the replacement brushes are quoted at £120 for the plain brush and strangely £118 for the one with the thermal breaker. The breaker is just a little bi-metallic strip that bends away from the contact with heat from continuous use, nothing fancy. If this was a vacuum cleaner, car or other bit of kit the cost would be more like £10-15.

Heck whatever outboard is that for?

At least the solution is simple... just do as Pete suggests find another piece of equipment that uses the same motor and buy the brushes for that.

 

[William_H]

As said it is the actual pressure of the brush on the commutator that is important. Obviously as the brush wears down the spring pressure gets less. You may be able to increase the pressure a bit. Certainly worth trying that by refitting. If I had to replace the brushes I would not refit a thermal overload. i would just get any sort of brush. They can be filed down to correct dimensions to fit the holder. good luck olewill

 

[C08]

It seems highly unlikely that the motor was created specifically for use as an outboard hydraulic pump and nothing else. You just need to find the "vacuum cleaner, car, or other bit of kit" that it's also used in (or just the generic part number of the motor).

Pete

Thanks for the suggestion, a good idea except that there are no markings at all on the motor and the SHOWA corporation do not seem to sell spares for these. New motors come in around £400 but may take several months to land.

 

[C08]

Update:-
the commutator shows zero resistance between all segments so I guess it is burnt out. Any ideas how much rewinding small armatures should cost. although I guess I will find out in the morning when I take it to a rewind shop.

 

[ExcaliburII]

Update:-
the commutator shows zero resistance . . .

Are you sure it really is zero? The windings will probably only be one or two ohms, so if you are trying to read it on too high a range it will look like zero.

Also, if the thing was completely burnt out, the motor would have just stopped and never worked again. Also smelled horrible. My money would be on the poor contact theory as others have said, which would give the intermittent fail symptoms.

 

[GEB]

As stated above, it is difficult to determine if an armature winding is shorted using an ohmmeter.

A device called a Growler is often used - http://www.tpub.com/basae/28.htm

 

[C08]

Not got a Growler but on the 200 ohm range on my DVM it reads 0.2 ohms between any 2 segments on the commutator. There is no connection to ground between the commutator and the armature shaft itself or the armature. 0.2 ohms is the same as the meter reads with the DVM leads shorted together on this range. I guess the armature rewind guy will tell me what is going on.
I have no idea what the cost may be to rewind the armature? I was asking what cost I should expect to do this in order to just leave it to be done or shop around for a better price.

 

[ExcaliburII]

Still worth another trial with increased brush spring pressure by whatever means IMHO, even a temporary bodge just to test it. If it runs without lots of heat/smoke the armature is definitely not the problem. If it won't go at all or there is a 'dead spot' from which it won't start, the armature may be the problem.

 

[Alex_Blackwood]

If you are getting a reading between all segments of the commutator then the armature is OK. The reading will be virtually zero very low resistance The armature depends on "Back EMF" for resistance when running. With intermittent operation I would suspect an open circuit in the armature. Start with one lead on one segment and and go round the other segments with the other lead. Repeat this for all the segments in turn and see if any one shows an open circuit. Tedious task but not too bad on a small motor. I assume that you did get it to run on test with a battery? If so did the commutator and brushes show any sign of sparking, That is an indication of an open circuit. If not sure then as others suggest a visit to an auto electrician or do you have a tool repair shop any where near.

 

[C08]

If you are getting a reading between all segments of the commutator then the armature is OK. The reading will be virtually zero very low resistance The armature depends on "Back EMF" for resistance when running. With intermittent operation I would suspect an open circuit in the armature. Start with one lead on one segment and and go round the other segments with the other lead. Repeat this for all the segments in turn and see if any one shows an open circuit. Tedious task but not too bad on a small motor. I assume that you did get it to run on test with a battery? If so did the commutator and brushes show any sign of sparking, That is an indication of an open circuit. If not sure then as others suggest a visit to an auto electrician or do you have a tool repair shop any where near.

Thanks for that info but if the resistance is 0.1 ohms that means the initial start up current will be say 120 amps at 12v. I appreciate what you say about the back emf limiting current when it is going but how does the engine fusing cope with such a big power drain momentarily? When trying to test the motor disconnected from the pump is there any risk of the motor exceeding its rpm limit under no load?

 

[VicS]

but if the resistance is 0.1 ohms that means the initial start up current will be say 120 amps at 12v

I think you will find that because its an inductive load the initial current will not be as high as your simple calculation suggests

how does the engine fusing cope

Time delay fuse perhaps

Your engine is not unique. There are probably thousands with the same T&T motor

 

[Heckler]

My outboard engine power tilt motor (a small 12v dc motor drives a hydraulic pump) has started to intermittently fail to work. It is not the solenoids or wiring and is now removed where I can "hot wire it" to test it. This involves just connecting to a 12v battery directly and the motor should then drive up or down depending on which way the leads are connected. Sometimes it works sometimes not. The unit is only 4 years old. On stripping down the motor the commutator looked black and shiny but soon cleaned up, there is no visible wear and the segments are undercut ok. There was some carbon dust in the housing. Checking the commutator to ground with a multimeter does not reveal anything amiss.
In the normal course of events I would just replace the motor brushes which are one small plain brush and one with a small thermal breaker in the base fitting but the money I have been quoted is insane by any measure, even boat part standards,
So my questions are :-
How sensitive to length of the brushes are DC motors (these units are made by SHOWA, Japan and I have failed so far to ascertain the length of the new brushes.
Does the appearance of the commutator suggest worn brushes i.e. should it look shiny and coppery if the brushes are making proper contact.
An other thoughts about DC motors welcomed!

I agree with others, typical symptoms of worn brushes and black comm confirms, it shoukd be shiny. I have filed new brushes to suit before when I havent been able to get the exact ones, easy to do. Is the thermal breaker acting as the limit switch? Or is it just a safety device?
S

 

[Playtime]

Have you checked the contacts on the thermal cut-out?

 

[DownWest]

Def sounds like brushes to me. Happened a week or so ago to my angle grinder. Looked in the box of a recently bought sander and filed down one of the spare brushes supplied. Works fine. As for rewinding, I doubt that you will find that easy for the armature of a DC brushed motor. More common on AC ones with only stator windings.