Water Puppy pump fell to bits - help please

[Cliveshep]

Hi everyone,

The magnets fell off our shower pump, a 12v Water Puppy 2000. Its got 2 each side, stacked one above the other bonded to the inside of the cylindrical steel casing. One pair fell off, i.e. one each side and the pump decided not to work. (Can't think why!)

Simple thinks I, clean 'em up, clean the inside of the casing, a bit of blue Loctite Epoxy and stick em back. However, in one position the buggers repel each other, in the other they don't.

Naturally with me, if there's a way of doing it wrong I'm often your man, and this time was no exception. I stuck 'em on so they attracted each other and stayed put and didn't slide up the steel casing away from each other. There seemed to be a sort of logic to that at the time. I'm not now sure that the reaoning was correct.

However, Loctite Blue is pretty quick setting and one of the buggers set slightly proud and the armature now grinds on it, the pump won't run, in fact it needs a wrench to turn it over!

Ok - I'll chisel them off and do it again but before I do, can some electrical genius please confirm that these permanent field magnets (is that the right term?) should be stacked so they attract or repel each other? If the latter I'll have to clamp them whilst the epoxy sets.

The best way I can describe the arrangement is take a piece of tube and cut it into three bits down it's length and throw one bit away. Now cut the 1/3rd tube lengths in half across the middle., and glue the two bits back together into another tube (the pump casing) opposite each other. That's how they fit together inside the pump. The armature is then supposed to spin freely inside them in an ideal world! Chances are they were once machined to give the right clearance and I've got the two opposite bits stuck on the wrong sides anyway which is why they foul the armature, but I'm also worried about the magnetic polarity as well.

Before I hit the thing with an even bigger hammer can someone please explain which way is up with the two magnets each side before I wind up destroying a £90 pump?
Many thanks in advance.

 

[ccscott49]

I reckon, it's time to raid the piggy bank, and, or buy a cheaper pump.

 

[Cliveshep]

Well, I would rather fix it as it's not burnt out. I've heated the outer casing and softened the epoxy and got the magnets back off without using my trusty hammer, so the first question remains - which way up?

 

[billskip]

TRY one way with a temp fixing then try the other..

If things dont change..........................

.......................................................

They'l stay the same

 

[Cliveshep]

Unfortunately that's not a serious option as the magnets have to be epoxied into place and once there the only way I've found to get them off is heat the whole thing up with a seriously large blowtorch. I'm sure I read somewhere that heat destroys magnets???? Or perhaps it was hammering?

I suppose all the electrical geniuses are out on their boats with the sunshine we've had this weekend, I just hope one drops by soon as it's clouding over and looks like rain again.

 

[DaveS]

I'm not familiar with the insides of this motor, so this is taking it from first principles; also sticking purely to the magnetic arrangements, ignoring gluing, skimming, etc...

The first thing to establish is how the magnetic field is oriented in your magnets. Is it radial, i.e. at right angles to the inside / outside curved surfaces, or circumferential, i.e. end to end, following the curve. (The third possibility, axial, i.e. at right angles to the flat faces is pretty unlikely.) With two magnets already loose to play with this should be fairly easy to establish.

Let's assume the field is radial (the most likely arrangement IMHO). This makes it fairly easy because each magnet can go in either way round. The important thing is that the polarities should alternate. Identify 2 magnets whose inside surfaces repel each other but attract the inside surfaces of each of the other two and mark them with a pencil. Place the marked magnets diametrically opposite each other, and arrange the other two equally spaced between.

If the field is circumferential it's a bit more complicated, but you want to end up with each gap between magnets being repulsive, i.e. any two pushed closer together will resist. In this case start with one magnet and mark one end with a pencil. Use this to test the others and also mark the end of each which your original marked end repels. Arrange them evenly so that ends facing each other across each gap are either both marked or both not marked.

 

[billskip]

I am an electrical genius..I just pretend not to be so i dont get bombarded with questions! /forums/images/graemlins/laugh.gif

 

[Cliveshep]

Hi Dave, thanks for that although I'll have to put my thinking cap on to understand it all. The magnets are not arranged around the housing, i.e. not four bits around the circle, but are in two sets opposite each other, i.e. two less-than-half circle sets opposite each other. Does that make sense? In other words, two bits end to end, and two bits end to end opposite them. Two opposites are still fixed at one end of the housing, it's the other two opposites that have come unstuck. They clearly have to pretty much touch together end to end or the brush holder and end caps won't locate given the housing length vs the total length of the two 1/3 circle magnets each side of the housing..

Are you saying that I had it right the first time, i.e. so the 1/3 circle magnet slid down the tube onto the fixed one should attract to it and be bonded in that position, or that I should force it against a repelling force and clamp it? Sorry to sound thick, (I probably am on this subject).

I could send you a sketch but I don't have any way to mail it to you

 

[VicS]

If I understand you correctly you have one magnet on each side still in position and that you have two magnets loose which have to be glued back up close to them.

If that is right then they have to go in in the position in which they are trying to repell each other.

If you put them in in the position in which they attract each other they will virtually cancel out each others magnetic field.

BTW hitting with a hammer and heating can both cause loss of magnetism.

 

[Cliveshep]

Absolutely the situation. OK then, I'll try and glue them back in repelling each other.

Don't hold your breath tho, it'll be later this week. Thanks for the advice.

 

[DaveS]

Ah, that's different...

It sounds from this description that the motor has 2 magnetic poles. I had assumed that the magnets were arranged symmetrically which would have meant 4 poles.

OK, the first step is still to play with the loose magnets to determine the orientation of the magnetic field. I would expect to find that it is radial. I would also expect their polarities to be opposite, i.e. the inside curves should strongly attract each other, the outside curves should also attract, but an inside should repel an outside. Check that this is the case.

If so, mark one of them (doesn't matter which). Hold the inside curve of your marked magnet against the inside curve of each of the still attached magnets. It should be repelled by one and attracted by the other. Mark the one that repels it.

Refix the loose magnets in place with the two marked ones together on the same side. They may want to repel each other, so some sort of clamping might be needed.

 

[Cliveshep]

Dave and Vic, thanks a lot for that info, I think there’s a good chance of getting it all back working now.

 

[Cliveshep]

Ok, magnets identified, bonded back in, pump now runs sweetly again. Thanks again guys.