argh! Trying to fix/diagnose dc motor from sprayer pump. Help!

[HoosierBuddy]

Hey guys...

My Northern Tool towable orchard sprayer was DOA for this spring's tree spraying. When plugged into 12V, the pump/motor assembly made a pathatic tap tap tap noise and that was all. I also noted the 14 gauge power wire was noticably warm.

I disassembled the (Shurflo) pump and 12 Volt motor assembly and found the motor had water/rust/crud in it. On to NorthernTool to order a replacement pump/motor. They quoted $202 plus shipping. YIKES! The whole sprayer assembly is only $400, pump/tank/wheels/and hitch!

So...I figured I'd better do a little more work on the original pump/motor assembly and see if I can get another year out of it.

The rotating coil assembly cleaned up OK and looks good. The bearings feel good. The "brushes" had some gunk on them and the copper tabs they ride on looked a little carboned up. I cleaned them. So, with everything clean I started going back together but I'm stymied.

One of the permanent magnet halves came out of the metal housing during disassembly.

1. Does the permanent magnet half have a right and wrong way to go back in? In other words, does it have a polarity that must match the other half?

2. Should it have come out in the first place. It looks like it might have been attached to the metal motor housing via adhesive at some point?

3. If "it was glued and needs to be reglued" is the answer to 2. Does it have to be electrically isolated from the metal housing? There seemed to be some sort of paper backing stuck to the housing where the magnet should go.

What got me woried was when I reassembled the motor and noticed the magnet was pulling away from the motor housing and sticking to the rotor assembly. That doesn't seem like it would work UNLESS when the coil energizes maybe it pushes the magnet back out.

Guys...I really appreciate any help you can give. The bag worms are starting in on my apple trees and honestly I don't have the $202 laying around right now due to some unforseen bills cleaning up after the recent storms.

THANKS!

Phil

 

[justsam]

Difficult to visualize exactly what you have there, however the armature should be close but not touching the fixed magnet halves. Sounds like you have cleaned up the commutator and brushes so I would just try a quick reassembly to determine optimum magnetic field. There will be no harm if you get it wrong, it just will not perform well. Make sure you get the 12V polarity correct or the motor will run backwards. Again, no harm, just reverse the wires. One brush holder may just go to the case, if so, that is ground, or negative.

 

[A_Pmech]

1) It is my recollection that in a two-pole permanent magnet motor the magnets should have alternating poles. When installed in the motor frame the magnets should attempt to attract each other and a nail placed between the magnets should stand up. They should be glued to the motor frame diametrically opposite from each other. Be careful not to dislodge the other magnet as the timing between the magnets and brushes is somewhat critical.

2) Probably not. They should be glued in place. It is possible the chemicals you use act as a solvent. Clean and reinstall with 30-minute epoxy.

3) I do not believe the magnet needs to be insulated from the motor frame. However, an evenly spread layer of epoxy gluing the magnet to the frame will insulate it anyway.

 

[HoosierBuddy]

Thanks for the responses!

I tried repeatedly to figure out any difference in polarity between the magnet halves. It will only fit into the housing 2 ways and I couldn't discern any difference between one way and the other in terms of how the magnets interacted (they attracted regardless of how the 2nd half was installed) or how a piece of metal between them reacted OR in how my magnetic pick up tool reacted to them. It's almost like the OD of the magnet is one pole and the ID is the other pole. In which case they can't be installed backwards.

So...I epoxied the loose half in place exactly opposite of the other one. I'll try reassembly tonight.

BTW...I'm now convinced the loose magnet half is the reason the thing wouldn't run. It was stuck to the rotor and wouldn't let it spin. It probably happened during our last big storm when a rather large maple tree branch (300 pounds or so...fell about 40-feet) struck the sprayer cart a glancing blow when it fell out of the tree.

It didn't hit the pump directly, but the shock likely was enough to break the old adhesive that held the magnet to the housing.

Maybe.

Phil

 

[HoosierBuddy]

Hey guys,

Just wanted to follow up and let you know the motor is back together and runs. In fact, the sprayer is back together and working as good as new.

The only things required were some cleanup, some JB Weld, a lot of fiddling around, and a little help from friends at the Garage Journal.

THANKS!

 

[mrbreezeet1]

Hey guys,

Just wanted to follow up and let you know the motor is back together and runs. In fact, the sprayer is back together and working as good as new.

The only things required were some cleanup, some JB Weld, a lot of fiddling around, and a little help from friends at the Garage Journal.

THANKS!

 

[A_Pmech]

Glad to hear you got it running.