Brushless permanent magnet motor troubleshooting 1

[Millwrongwelder]

Howdy,
I'm fabricator who doesn't know as much as he should about motors. Hope it's not too amateur of a question: I got a brushless permanent magnet dc motor that doesn't spin, when turned on in twitches one position and that's it. The controller board looks fine, nothing throws a flag. All components are potted with clear epoxy or some super hard coating that looks like epoxy. It's an expensive sprayer I'm hoping to fix for a friend. Any help us beyond appreciated!

 

[itsmoked]

A brushless DC motor is actually an AC motor that needs a special controller to run it. The motors are pretty robust, usually more robust than the electronics. It sounds like the electronics are having an issue. One twitch can mean the controller jazzes the motor just enough to have the position sensor show which way it's going and to provide the required timing information needed to drive the motor in a coordinated manner. Seems like either a position sensor, its wiring, or the control board circuitry could be screwed up and not providing useful control info.

Not easy to fix... Unless you can find an obviously bad connector.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[benta]

Question is, if it's a motor with sensors or it's a sensorless design.
In the first case it should spin up with no problems.
In the second case, you need a startup control strategy, as you'll have no feedback until the motor is actually spinning.
There are several ways of doing this, none of them foolproof. As an example, you can bring the rotor to a known position (one out of three), start commutation very slowly and then increasing the commutation speed until you start getting feedback (BEMF) - all in the hope that the rotor will follow your commutation (which it won't if it's heavily loaded).

 

[MikeHalloran]

Check the pump (and hoses?) (and spray head?) to make sure there's no hardened (paint?) (epoxy?) in it.
Which probably means disassembling the spraying system and blowing compressed air or smoke through all the passages.

If the entire spraying circuit is found not clogged, and the motor still won't start, _then_ suspect the motor.


One of my past employers had a crew in on a Saturday, using his expensive airless sprayer to apply epoxy paint to a bridge crane, when they decided to quit, and just turned off the sprayer and left, without flushing the (catalyzed) paint out of it. It took a lot of work, and nasty solvents, to get the hardened paint out on Monday morning. Actually, we bought another sprayer to complete the job, and spent days cleaning the clogged one.




Mike Halloran
Pembroke Pines, FL, USA

 

[Millwrongwelder]

Howdy again,
didn't want to be that asshat that gets good advice from good people and never gets back to say thank you! As MikeHalloran suggested there's was some stupidity involved here but on an industrial scale. I'm in New Orleans where as you might know there are issues with flooding of all kinds. My friends shop is just a block away from a big ol pump station with brand new giant pumps designed to help with heavy rain flooding we get on the regular. Well the damn thing wasn't installed/tested correctly, failed and the neighborhood flooded including my buddies shop and his tools and the said sprayer, which he failed to mention before he brought it to me. Everything seemed to point to a controller issue, there were no smoking guns so I sat it aside to maybe salvage presumably usable motor.
Best
Arthur

 

[WGJ]

I think I am asking benta this question ---

Are there any good sources you could recommend for teaching myself the electrical basics of brushless motors?
I'm basically a mech eng, and partly (very partly) educated in electrical, so other readers - please don't shoot me for not knowing.

I'm trying to specify/design a slotless, brushless motor. Off-the-shelf designs for the application don't exist.

I think I am going to be using a four-pole armature with six field windings. I see youtube vids with 'diamond' windings that look like they'd keep the diameter of the motor to a minimum but I don't know what other advantages there's be with this winding technique.
It looks like it would be a sensored design as there would be a variable load applied.

Any and all sensible advice would be welcomed. To other viewers, I said I am not an electrical eng, so go snipe elsewhere, thankyou.

Bill

 

[itsmoked]

You want info? Wade around in the vast Texas Instruments marsh-of-knowledge.

They have many many motor driver chips that have extensive brushless and brushed instruction in them.

[URL unfurl="true"]http://www.ti.com/product/drv3201-q1[/url]

Same with Microchip:
Microchip AN1292

Keith Cress
kcress -

http://www.flaminsystems.com

 

[WGJ]

Thanks for that it smoked, however, it's the mechanical arrangement of the windings that I'm trying to get a grip on. I'll have a trawl through the Texas docs to see whether there are any references. I've been there before but it was a while ago.

Bill