Rebuild 24VDC motors

[[email protected]]

I have 4 electric motors on a crane that sat in a field for 8 years. These are 24 Volts DC and they are not small. I have a local rebuilder that seems to get $500 or so to do this work. I think this is very pricy. Is there a place (anywhere is the lower 48) that would be more affordable? It seems there is always that old, hidden rebuild service that the older guys know. Where is that???

 

[MBfreak]

Hello.

Electric motor rebuild,as long as it is not replacing the coils in stator/rotor is not difficult.
You need a workbench, some handtools and maybe bearing pullers.

1 Make a precise drawing of the wires going into the motor, take down colors and markings. Note area on each.
2 Try spinning it by hand. Some resistance expected, since it is a DC unit with a commutator and brushes. Also some light squeks.
3 Open up the brush holder covers and inspect the commutator. If very worn, you need pro help, turning, maybe even repacing the commutator.
4 Mark the position of the end caps, remove the screws and pull off the caps. Bearings should slide out easily, from at least one end. Then lift out rotor and other endcap.
5 Clean out stator part from as much dust, grease and whatever you can by hand, do not damage the stator insulation. Put citric acid degreaser in a can, dilute to 30% and spray entire stator inside and out, brush all surfaces with a stiff brush. If possible remove the brush holders , be very careful to note exact place and connection on each. mm accuracy required.
Repeat several times. Hose down stator with VERY hot water, several times.
6 Do the same with the rotor after first having pulled off bearings. Then study the commutator closely. Since it is 24 VDC the brushes will be rather soft and I do not think the commutator should be undercut between the copper bars. Maybe resurface the commutator by hand with 120 grit paper
7 Heat stator and rotor in an oven at 75 Centigrade for several hours, after first having blown them as dry as you can with air.
8 Check condition of shaft and all "general" mechanical parts.
9 Reassemble, connect and try out on a 12 VDC source, put a 20 A fuse in series.

Unless the motors have been overloaded in service and/or drenched in water chances are pretty good that this will succeed. 24 VDC does not require the same insulation as ie 120 VAC, If you have, can borrow a 250 V megger, do that and test insulation before and after. Let the motor cool down after 7 before meggering, must be ambient.

Good luck, and some pics would be nice

Ola

 

[TractorJeff]

FWIW If the local rebuilder is a true Motor Repair shop which is going to re-dip bake the coils. $500 verses the cost of 4 replacement motors sounds reasonable.
If he is not going to re-dip/bake, then go with Post #2.

 

[nehog]

If it is $500 for four motors, go for that. Otherwise consider doing it yourself.

 

[EOC_Jason]

$500 to re-wind a motor is not unreasonable, depending on its size. That's about the bare minimum any shop will charge.

 

[BillK]

I have a local rebuilder that seems to get $500 or so to do this work.

If that is the price for all four then he is actually pretty cheap in my opinion. You know he is going to take at least an hour or so on each one. That ends up being $125 per hour, not much different than most good auto repair shops.

 

[matt_i]

Are you rock solid sure its a 24vdc and not a 240/250VDC motor? I recall a legacy higher DC voltage standard for bridge cranes before a VFD was invented.

A 24vdc motor would seem to have almost no torque unless a redonkulous amount of amps in huge wires were thrown at it...

 

[Dagny]

I heard it never rains in southern California I bet they will work. But if the brushes are stuck in their holders as they wear contact with the commutator weakens and arcing occurs.

 

[[email protected]]

$500 for EACH motor

 

[[email protected]]

They are on a crane that runs off 2 12V batteries (big ones). They are 24V

 

[[email protected]]

Maybe I will try. If it is too much, then I am back to the place I am now