electric motor problem

[White_Lady]

I have just reurned from the boat after spending 4 days trying to fix the passarelle motor.Iwas with a good pal who is a top spark,but no joy!
The motor had stopped working. We found a faulty solenoid bit and replaced.
The motor now goes but sooooo slowly.About i revolution in 90seconds.At that speed it would take an hour to lower the gangplank So any ideas.The battery are fine.The brushes look perfect.The motor is two directional.It is marked as 24 volts,but is running on a 12v battery.No that isn't the problem because it has worked fine for 5 years.The gearing all appears fine.Why so slow.PS it goes in both directions.

Any thoughts gratefully recieved! /forums/images/graemlins/confused.gif

 

[Poignard]

Bad connection = high resistance = less voltage at the motor??

 

[White_Lady]

Connections good.Even took motor and connected direct to battery. /forums/images/graemlins/confused.gif

 

[Poignard]

Some things I would want to know.
1. What is the voltage at the motor terminals when running?
2. When you connected it directly to the battery did you bypass the solenoid?
3. Are you absolutely sure that battery is ok? Just measuring the terminal voltage off load is not sufficient; you can get 12 volts from eight torch batteries but they wouldn't drive your motor.
4. Does the motor get hot? Does it smell?
5. Is there any mechanical problem with the motor and gearbox and what it's driving? e.g worn bearings, mangled gears, lack of lubrication, dirt etc.

 

[andy_wilson]

If it is marked 24V there is a good chance that it is 24V.

Any chance wires could have been replaced incorrectly at the battery end when the batteries were changed?

 

[kandoma]

solenoid gone.... is it possible, that the switch operating the solenoid got stuck in the up position for an extended period of time, the motor stalled without making any noise, the motor got hot because you operate the 24 volt motor with 12 volt and the motor just stalled in the endposition, finally damaging one or more wire inside the motor, doing so also blew up the solenoid. After repairing the solenoid, the wire(s) inside the motor are still damaged and you may get only a small magnetic field.

You may have to open the motor and check with a very good ohmmeter all windings. One or more may be burnt and will have a short, but you will not see it. The damage is usually inside the windings, where it is much hotter then on the outside.

If the motor is burnt and you are good with your hands, rewind it by yourself. Cost: 100 meter copper wire, a couple of broken fingernails and nothing else.

Peter

 

[Robin2]

Rewind it in a room by yourself so nobody is offended by the bad language. /forums/images/graemlins/smile.gif That is not a simple DIY task.

 

[nedmin]

we need to know more about type of motor, Has it got wound field coils? Or is the field a permanent magnet type?You need to strip the motor down,put the motor in a vice,place 2 bare wires in series with a stop lamp bulb and 12v supply opposite one another held in place with an elastic band.the lamp will light.place your multi meter set on volts(start at 12v) on 2 adjacent commutator bars and read and note the volt drop,across the 2 bars.move to next,and note until you have been all way round,obviously you will have to move the wires under the elastic band round as you move the multi meter test leads.the volt drop you get should be approx the same if not you have shorted turns,which means armature u/s.Its very difficult to test just going to each comm. bar on ohms as 12v motors have low resistance windings.Have you got an electric motor rewind shop nearby as they will have an electronic tester for shorted windings.which is much easier.You could wind it yourself but its not easy,you need to find size of wire and number of turns per coil,then you have to bake with varnish to stop it flying apart.

 

[William_H]

Yes shorted turns on the armature are very difficult to identify. They will cause the motor to draw very high current with very slow rotation and can be caused by overheating causing the enamel insulation to fail.
Obviously make doubly sure everything else is OK first. ie free to turn and full voltage under load at the motor.

Overhaul shops use what is called a growler to test for shorted turns of the armature. It is an electromagnet with pole pieces extended to match the poles of the armature. The growler is powered by 50 cycle AC. As each pair of poles are fed by the magnetic field they are themselves activated like a transformer. If it is applied to a pair of poles with a shorted winding then the load on the growler increases causing it to vibrate and go berserk.

You need to replace or rewind the armature. Usually all windings.

Often just removeal of the armature from the motor will show by the smell and colour that there has been burning. good luck olewill

 

[pampas]

gear box tight ?

 

[White_Lady]

Motor does get hot
no smell tho
have tried on other new batteries
gearing all running smoothly /forums/images/graemlins/confused.gif