12V electric motor advice needed

[gman1001]

The trim tilt motor for my Yamaha outboard failed. OEM replacement is $700!

Bitting the bullet on a new one but also wanting to repair the broken one.

The motor appears to be a ‘permanent magnet’ motor. Motors appears to have had its 4 magnets glued to the stater/armature. Magnets are now loose and removed for cleaning.

Question is, should I glue the magnets back in? If so what type of glue?

Tx!

 

[engineer2]

I think a high-temperature epoxy would work.

 

[gman1001]

Thanks! Good idea. I should have also asked. Is gluing the magnets in place the right thing to do!?

 

[engineer2]

Many of the small motors I run across have glued-in magnets. Polarity, spacing and armature clearance are important.
There are likely motor experts here on GJ who can offer specific advice.

 

[Noltz]

Those magnets need to go back in in their exact place so the armature winding produce magnetic fields in the correct orientation. I tried to recover a transfer case motor that the magnets detached. They were slightly off and the motor became very weak. Rotating the housing slightly restored the strength but of course the bolt holes didn't line up anymore. Oh and I used JB weld 5 minute stuff to reattach the magnets.

TLR - Magnets must go back in the exact spot.

 

[gman1001]

That was my suspicion. The armature has four small tabs that the magnets rest on. Polarity/placement of each magnet etc is my challenge!

 

[gman1001]

I think a high-temperature epoxy would work.

Just found this online. https://www.permabond.com/resource-center/magnet-bonding-adhesive-solutions/

 

[Firebrick43]

make some aluminum bars to hole the magnet in the right place while the glue sets

 

[pancho400cid]

Not an expert on small DC motors... but a couple of comments:

1 - It's not a permanent magnet motor. It's a DC motor with permanent magnets for the field winding.

2 - You have 4 magnets apparently - two "Norths" ( Flux into the air gap) and two "Souths" (Flux out of the air gap). As said, they have to be correct polarity (alternating around the stator bore) and located as close to "exact" as possible.

3 - Each magnet has to bear one fourth of the motor torque... so strong glue is needed as said.

4 - Minor point - The term "armature" usually means the most powerful electrical winding. On DC motors, the rotor is the armature.

5 - Carefully look over the windings on the rotor and look for signs of arcing/shorting. Take uninsulated wire and wrap a couple of laps around the commutator. Then measure ohms from the wire to the rotor punchings. Should be Kilo or Mega-Ohms. If very low that would show the winding is shorted to ground.

Good luck!

 

[gman1001]

Solid advice! Thank you. Thought, you open to tackling this one!? For a fee of course.

 

[RPH]

Magnet bonding is a specialized motor manufacturing business. The magnets need to be placed correctly and taper must be correct. The cans are heated to 450*f. The magnets are fixtured inside the can while heating takes place. Heat to quick and magnets crack. The biggest problem I see is the magnet are magnetized after cooling. Heat kills magnetism is the alloy used.
Good luck! Seen too many cans go through the process!

 

[gman1001]

@RPH Tx for this. Makes sense. I may try to put this back together. If anything its a backup.

I'll fiddle with the magnets tonight to see if the polarity and positioning make sense.

 

[Innovate1]

It's obviously a permanent magnet motor as it has permanent magnets. It's not a brushless PM motor so maybe that's why some are saying its not a PM motor. Lots of terms get thrown around which get confusing.
https://en.wikipedia.org/wiki/Brushed_DC_electric_motor
Note the paragraph titled "Permanent magnet motors" about half way down the page.

The OPs motor is like the first shown "Simple two-pole DC motor".

The magnet flux polarity does not alternate on every magnet on this motor. It looks like two magnets are used for each pole with a generous space between them. The two loose magnets go opposite the ones still attached. The magnets alternate on a brushless PM motor (also called synchronous PM motor) but this isn't that type. And sometimes the magnet pole breaks are not all on the material breaks - sometimes each block has two poles just as an example but that is less common and doesn't apply to these. The two still attached are one polarity and the two detached are the other polarity so no way you can get polarity wrong. You can check that by trying to put the two loose magnets together with the concave faces together. Put a sheet of plastic or wood between them in case they attract so they don't smash into each other but if things are as I think they should repel each other.

Not all magnets are heat bonded. You should be able to find an adhesive that works well with room temp cure.

 

[gman1001]

Many thanks @Innovate1 The picture with the magnets in place is misleading. I placed them in there like that. As you state there is to be a space between them.

I'm going to test the polarity as you suggest and report back. THANK YOU

 

[Innovate1]

If they are all loose you need to get the magnets in the right place. If you reverse the north and south poles the motor will rotate in the opposite direction.