Unglued magnets in 1hp DC permanent magnet brush motor.

Hello all, new member, avid DIYer but no specific electric motor knowledge other than what Google has provided thus far. Please forgive me if my terminology is not up to par. I have a 1hp DC permanent magnet brush motor off a Robert Brent/CXC (brand/model) potter's wheel that I cracked apart. It definitely needs brushes but I'm not going to bother with that till I solve the greater issue. 6 of the 8 permanent magnets have become unglued from the casing. They have shifted around and I don't know where to reglue them. Also, I read, too late, that I probably should not have taken the motor apart with out a magnet "keeper". Not sure how that works but the magnets have mainly stayed within the case. My questions are, is exact placement necessary or is it fine as long as one polarity is on one side and the other polarity on the opposite side? My guess is that pretty close to exact placement is required, if so, how do I now determine their placement? Did I damage my motor by taking the armature out? A couple magnets where completely out of the case briefly but most were left in the case. If damaged, what will be the effects? If the adverse effect is merely a bit of weakening I could be almost as happy with a 1/2 hp motor since many wheels are supplied by a 1/2 or even 1/3 hp motor. This is $1500 wheel new, 600 to 900 used, and I got it for $100. A new replacement motor is $450, this would still put it in the "good deal" category but I simply don't have 450 to spend on this right now. I'll take any advice and tips anyone has even if seemingly not directly related to solving my problem. Thanks in advance!
-Cory

We had same issue with a blower motor except magnets on armature.

They should bee still in correct orientation so get masking tape and make labels on the inside.

Next remove them and clean everything.

There should be marks where they were so look close for a fingerprint or other mark like uneven gluing so you can identify where any one magnet goes.

Once you know that the rest are easy since you marked them...I 2 3 4 or whatever...

There are basic epoxy but get good stuff.

There is some hvac epoxy that does wide temp range and it is about 30 bucks far a small package.

Clean with acetone then slather on epoxy and place inside.

Holding will be difficult, maybe a small inner tube from a hand truck tire.

Once the first one is in the rest could be glued in at same time.

Make sure the shaft goes in before gluing in next ones just to check

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Polarity of magnets should be the same on either side of the case, if you have N at 0 degrees there should be a N at 180 degrees. You may have to figure out and make the appropriate width spacer for the magnets while re-gluing them.

Why would you think removing armature would damage motor? Why do you think removing magnets would weaken them?

Some types of magnets DO lose "power" if the magnetic circuit is broken. Mostly old type magnets, but some others will ahow an effect.

Motors have an air gap that adds "reluctance"* in the circuit, so the effect is generally less, you cannot KEEP the strongest magnetization in a magnet without an uninterrupted magnetic circuit. So the motor magnets are already weaker than they could be, if of a susceptible type.

I have removed and re-glued magnets in small DC motors, in cases where the motor was just not available. Worked out fine. Epoxy and polyurethane glues may be best.


* reluctance" is like resistance in an electric circuit.

dalmatiangirl61 said:

Polarity of magnets should be the same on either side of the case, if you have N at 0 degrees there should be a N at 180 degrees.

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This makes sense to me, especially since there are four sets of magnets. However, the two magnets that are still very much glued in place are side by side, touching each other (evenly spaced magnets would have a gap as you suggested), and are of the same polarity. Since there are two magnets in each set (a double ring of magnets basically, one larger than the other), I wonder if there is an offset between the two rings, which would put like poles 180 degrees from each other but from top to bottom, not directly across. Does this make sense? Is it simply not possible that they would align all North polarity magnets on one side and all South polarity on the other? Every diagram I see shows magnets aligned in this manner but I assume that could be an over simplification to help understand how they work.
The weakening was just something I read on several google results, AFTER I had removed the armature of course! My guess is that this did not cause much, if any, damage. Thanks for the response, I learn a little bit with each one!

They should bee still in correct orientation so get masking tape and make labels on the inside.

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Unfortunately, and I'm embarrassed to say, I believe I have gotten these out of sequence before taking any notes. I was kinda eager beaver with it. I knew the brushes were seized and I thought I just needed to crack it open, get the brushes out, clean it up, add new brushes and good to go. Magnets sliding out stuck to the armature was not in my plans, lol! I do need to get a really good light on it and see if there is any way to line up magnets with clues provided in the casing as you suggest. Thanks for your suggestions!

JST said:

I have removed and re-glued magnets in small DC motors, in cases where the motor was just not available.

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Thanks for your response! Do you have any insight in regards to placement of polarities (see my response to dalmationgirl)

I have seen mention of removing magnets or armature causing serious degradation of motor power on some forums, but they were made by people with non-technical backgrounds, so I never gave them much merit. In my mind, it was assembled from individual parts, so it can come apart, leaving it apart for extended periods might be different.

How are you testing polarity of the 2 magnets that are still glued in place? In my experience, the magnets are always alternate polarity, but have not seen it all yet. Any chance it is just magnetism holding one of those magnets in place?

Demag on removal Only applies to alnico magnets which have a permiability of 10 iirc, which means the magnet itself can concentrate its own field above the coersion strength.

Ferrite and neodymium cant do this.


Usually thr number of poles is set by the number of brushes.

Angular offset will cause problems but +/- 10 degrees is probably good enough. Grinding off the aalignment tab on the endbell that fits into a notch cut on the motor housing will usually permit some brush angle adjustment

dalmatiangirl61 said:

How are you testing polarity of the 2 magnets that are still glued in place? In my experience, the magnets are always alternate polarity, but have not seen it all yet. Any chance it is just magnetism holding one of those magnets in place?

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I held the same magnet in front of each, they both repelled strongly. They are definitely glued. I was able to get a look in the bright sunlight (which we finally got briefly today). I can see where each size of magnet had previously been so that is a huge step. I am starting to feel pretty strongly that one polarity is on one side and the opposite polarity are all across on the other side (i.e. not alternating), unless some one can confirm that this is not a thing. I will add some pictures that show the magnet layout, you can also see the brush positions in relation to the magnets if you note the brush holders at the bottom.

johansen said:

Usually thr number of poles is set by the number of brushes.

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There are two brushes (you can see where they align in the photos below). Would this indicate that all North on one side and all South on the other?

johansen said:

Angular offset will cause problems but +/- 10 degrees is probably good enough. Grinding off the aalignment tab on the endbell that fits into a notch cut on the motor housing will usually permit some brush angle adjustment

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Not sure I follow this part. Are you saying that as long as they are within 10 degrees of where they ought to be that it will still run ok? Because I was able to locate exact placement based on size of magnet. Just need to make sure I have the correct polarities in the correct spots. I think I am on my way to getting this resolved! Below are some pictures with the correct magnet arrangement (based on size only) as indicated by glue markings on the case. It is important to remember that one pair of the shorter magnets (seen nearer top of case) are still factory glued right next to each other and have the same polarity.

looks good to me, and yes that is a 2 pole motor, N on one side and S on the other. looks like they just used the same magnets for 2 pole as they did 4 pole motors for that size motor.

you can't align the brushes in your case by rotating the end bells, but you can on a lot of motors. if all the magnets came out and you had to reglue all of them then it would be a concern that they be radially aligned correctly, but it doesn't matter in this case as you're only re-gluing some of them.

I agree.

Brush count sets the number of poles, or vice-versa. You have two.

The alignment can be fairly approximate without messing too much up, but in your case, what is shown appears correct.

As for the assembly, magnets are normally assembled in the non-magnetized condition. They would be totally unmanageable in production if magnetized when installed. They would stick to tools and each other, and as they were installed, they would pinch fingers, "jump" to surfaces and maybe be cracked by the impact, etc. It CAN be done with magnetized parts, but it's a lot more hassle if there is a way to magnetize after iassembly. Speakers have been done after assembly, for instance.

After assembly, the whole part is subjected to a very strong magnetic field by a "pulse magnetizer, that has such a strong field (made by a very high current pulse) that it saturates all the iron, and magnetizes the magnets in place.

You magnetixe a magnet by forcing all the "magnetic domains" (tiny areas that act as a unit) to align. If the surrounding structure allows the magnet to maintain sufficient magnetic field, it can stay as strong as when magnetized, which holds all the domains aligned, maintaining strength. (yes, it is a bit of "chicken and egg")

But if the structure cannot carry the field, then the magnet, if of certain types, can have some "domains" drift out of alignment, and it loses strength.

A "keeper" is a substitute that carries the field just like the original structure, so that the magnet does not lose field strength.

A motor is unlikely to lose much, for two reasons. The air gap does not carry a field well, so it is already a problem for maintaining ultimate strength.

Also, the rotor (armature) is not solid steel... there is a lot of volume used for copper, and so the ability to carry the field is far less than for solid steel. So there also, the capacity for "keeping" the magnet is poor.

That's why it is not always very damaging to pull out the armature.