Demagnetized...

[electric]

How do you reliably test whether a motor has been demagnetized? I am told mine may have done this and caused my esc to blow up. I want to ensure the motor is good before I invest in another esc.

One person told me if it spins freely. However, the motor always spun pretty well to begin with. The motor is a feigo 580 12

[sailr]

You can't go by the 'spin freely' logic! Brand new Feigao and most other 2 pole motors spin freely when brand new. If you had a motor that 'cogged' (had hard spots when you turned it) and now spins freely, then yes, you have lost the magnetization.

Running motor WAY too hot will demagnetize it. High quality (more expensive) motors like NEU, use high temp magnets that can withstand temps over 200 degrees fahrenheit before they are damaged. Most of the cheaper motors start getting demagnetized around 150 degrees.

IF your motor has lost its magnetization, it simply won't have any power. It may also draw outrageous amps trying to make up for it!

In the case of the Feigao 580, I have heard they have a problem with magnets cracking. You might want to ask Steven at OSE about this.

Finally, what are the exact symptoms? I had a couple of boats that just wouldn't GO fast anymore. I thought it was motors too. Then I discovered it was my batteries! Installed brand new batts and Zooooom. Wasn't the motors after all. Although my old batteries checked out perfect, they should would not put out the power anymore.

[Steven Vaccaro]

There were a few magnets that got cracked on motor that were spun at 35,000rpm-40,000rpm. They was a total of 5 motors that failed out of over 100 sold. Thats not to bad a failure rate, but still sucks for the user. So they carbon wrapped the rotors. There haven't been any mags cracked since.

The 580 is easy to test for demag. Unscrew the screws on the endbell. Remove the endbell. Remove the rotor. the rotor should be hard to remove from the casing. If it comes out easy its lost strength. If its hard then put it up to a piece of metal the magnetic attracting should be very strong. Not the most scientific way, but it works.

[calcagno45]

In the case of the Feigao 580, I have heard they have a problem with magnets cracking. You might want to ask Steven at OSE about this.

Yes, the motors are now made with kevlar wrapped rotors to prevent this.

Also, does the motor still work? Does it heat up extremely fast?

[m4a1usr]

How do you reliably test whether a motor has been demagnetized?

Theres only one way I know how to test a BL motor for us garage types. You can put the motor shaft in the chuck of a drill press and spin it at a known rpm, then read the voltage across any of the motor leads. Since we know the Kv and your drill press should have a known rpm range or setting you can do the math and calculate what the reading should be. But you should do it with the help of another person for safety sake. If the calculation doesnt work chances are the motor magnets are bad.


John

[sailr]

I have had my 580 for about two months. I HOPE mine is wrapped! Will run the boat seriously for the first time tomorrow. If the magnets crack, the motor can lock up and take out the esc too! Can't afford that!

Yes, the motors are now made with kevlar wrapped rotors to prevent this.

Also, does the motor still work? Does it heat up extremely fast?

[Steven Vaccaro]

I have had my 580 for about two months. I HOPE mine is wrapped! Will run the boat seriously for the first time tomorrow. If the magnets crack, the motor can lock up and take out the esc too! Can't afford that!

Why hope???
Sort of like "assuming". It hardly ever works. Take it apart and look.
Most likely its wrapped. And like I said before. MANY people are running these UNWRAPPED and have had great results.

[Rumdog]

I didn't mean to put fear in anyone. The problem I had with mine was a freak thing in my opinion. And like Steven said, I bought it "new" on rumrunner, so who knows if it really was. I did appear as new to me though. Never had been soldered by the looks of it and no marks at all on the shaft. I wouldn't hesitate to get another. My replacement ran great the one time I used it!

[Rumdog]

Also, when I say the shaft will spin freely, it was only the case in my demag. It spun VERY freely as if it was just a shaft with bearings.

[Brushless55]

is there any way to remagnatize a rotor?

[Steven Vaccaro]

Also, when I say the shaft will spin freely, it was only the case in my demag. It spun VERY freely as if it was just a shaft with bearings.

Yours was the worst I've seen to date. Absolutely no magnetic effect. :-)

[Steven Vaccaro]

is there any way to remagnatize a rotor?

Not that I know of. Its best to warranty it.

[electric]

Just got home from the river and am catching up. Steven, I read your suggestion and that seems to be a reasonable way to try the best I can to figure out whether the motor is bad or not. If the magnets are pulling strong, then I will go ahead and get another ESC and give it another try.
The background on all of this is described in the thread from yesterday(Poof!). Blew up my esc on what I believe to be about 60 or 70amps of pull. I have all the measurments in that thread up to the point it failed.

RPMS are...28.8 * 1051 = 30268 I know the voltage is somewhat higher, but certainly the rpms should have been ok...

I will pull the back off this evening and let everyone know what I found...

[electric]

Yes, the motors are now made with kevlar wrapped rotors to prevent this.

Also, does the motor still work? Does it heat up extremely fast?

Hard to know if it still works since the ESC exploded! I measured the temps, in the 130's range (see other thread POOF!) I think it was, and then re-taped it. Dropped it in the water went about 50 yards and POOF!. Can't imagine the motor got too hot at that moment...

I did wonder though, why I was getting even that much heat on the motor since I had propped down to test out getting a longer run time. I had no heat issues before that with the motor and the esc was cool at all times...

[electric]

Steven,
I pulled the back of the motor off and it slid out with some resistance, but not much at all. I did have the magnet attach to a wrench and it will stay attached even if I shake it a bit. I can take it off with very little pull. Hard to describe it accurately. I would say it comes off with maybe a very gentle pull.

What do you think? Anyone?