Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: guynamedbathgate on February 08, 2007, 10:21:10 PM

Title: temperature alarms for motors?
Post by: guynamedbathgate on February 08, 2007, 10:21:10 PM
so I just fried my first servo motor. maybe the gibs were to tight I dont know. but. regardless I overheated the dang thing and its toast. was wondering if anyone has fitted any of they'r motors with some sort of temperature alarm. something that would beep if the motors got to hot. so when I dont have to babysit my machine while its running. anyone know of a cheap way to rig one up?
Title: Re: temperature alarms for motors?
Post by: DAlgie on February 09, 2007, 01:39:02 AM
Or run a coolant jacket like I did on the Y axis motors on my router. I use the spindle coolant system, this probably halves the motor temps.
Title: Re: temperature alarms for motors?
Post by: guynamedbathgate on February 09, 2007, 11:24:48 AM
well my servo system is completely sealed for flood coolant. I suppose I could add some nozzles to point some coolant over the motor housings. but something about that seems to me to be risky. you know if the housings arent perfectly sealed.
Ill think about that.
Title: Re: temperature alarms for motors?
Post by: DAlgie on February 09, 2007, 12:43:23 PM
Yeah, I wouldn't actually spray coolant on the motors I don't think, recipie for disaster. Mine are fabricated aluminium jackets that cover three of the four sides as you see, and I added a small radiator and fan to the system as well.
Title: Re: temperature alarms for motors?
Post by: patmul on February 09, 2007, 01:42:26 PM
Well, here's a thought:

Buy as many Thermodisc (www.tod.com->Products->Bimetallic temp switches) "click-style" resettable temp sensors as you have motors.

Strap the sensors to the motors with tywraps. Wire them in series, and use a Mach 3 input pin...or wire them in series with the E-Stop pin.

If any motor gets too hot, it will open (or close...your choice at purchase) and trigger the condition.

When the motor(s) cool down, the Thermodisc will reset (re-click?).

Thermodiscs can be ordered for just about any useable temperature range, say open at 90C and close at 40C...etc.

BTW, I don't work for or have any interest in Thermodisc, Inc. My day job is EE, and I'm simply famiiliar with the product.

-Pat-
Title: Re: temperature alarms for motors?
Post by: guynamedbathgate on February 10, 2007, 06:05:19 PM
seems interesting. but the site doesnt give pricing or tell you where to find a supplier. for some reason they dont look cheap. I can buy a meat thermometer that beeps at a certain temperature for 20 bucks and convert that to beep if my motors get to hot. but Id like a more elegant solution than a meat thermometer sicking outa my motor. any more info on them and what anyone thinks is a safe operating range for a servo motor would be appreciated.
 :-\
Title: Re: temperature alarms for motors?
Post by: Chaoticone on February 10, 2007, 08:25:24 PM
Pat, you took the words right out of my mouth.

Bathgate, look an McMaster Carr. I would think they would have all kinds of ways, styles to read temp.


Brett
Title: Re: temperature alarms for motors?
Post by: watswood on February 11, 2007, 01:23:05 AM
Here are some surplus ones that should work:

http://www.allelectronics.com/cgi-bin/item/THSW-75/765/THERMAL_CIRCUIT_PROTECTOR,_75_C_.html

75C is a good trip temp. for most steppers.

Eugene
Title: Re: temperature alarms for motors?
Post by: guynamedbathgate on February 11, 2007, 12:51:44 PM
looks good. Im curiouse how water resistant they are. Im running full flood coolant also Im curiouse if there is any temp difference for running servo motors instead of steppers. I imagine its about the same.
Title: Re: temperature alarms for motors?
Post by: watswood on February 12, 2007, 12:19:44 AM
I would put heat-shrink tubbing completely over the leads and your wire joints, then tape the disc,with electrical tape,  to the hottest part of your motor.  Wrap the disc and wires several times so it's completely covered.  It's no guarantee, but its cheap and easy to try.  As for your motor temp., I would try to find some data on them.
Title: Re: temperature alarms for motors?
Post by: patmul on February 14, 2007, 10:11:59 PM
DigiKey has Cantherm R20 snap-disc thermostats in a wide variety of temps.

For instance, an 80C Normally-closed switch is DigiKey part no. 317-1086-ND,  $6.60 ea.

Not truly cheap, but not expensive either...when you consider the cost of a cooked motor!



Title: Re: temperature alarms for motors?
Post by: patmul on February 14, 2007, 10:21:22 PM
Oh, yes...I forgot to mention...

Thermal Protectors, such as referenced below, are a kind of fuse. Once tripped, they have to be replaced.

Snap-disc thermoswitches, on the other hand, reset themselves when cooled down.
Title: Re: temperature alarms for motors?
Post by: cybertek on February 16, 2007, 02:11:13 AM
This would be a good reason to use a cubloc!

You could display Motor Temp as well as program a  automatic Emergency Stop,
Or a G-Code Pause till the motors cool to a safe temp then start G-Code again.

http://cubloc.com/product/01_01.php
Title: Re: temperature alarms for motors?
Post by: chad on February 16, 2007, 03:23:10 PM
Hi guys,

Just a couple of comments. You didn't say if they were servos or steppers.  Steppers are designed to run hot, like hotter than you think they should be but if you are burning out coils than you need to back down the current to the motor. Cooling won't help with a over current coil open.
Now you might be saying if I turn down the current than the motor is not fast/strong enough. In this case you need to fit bigger motors. If you are  running them so hard as to burn them up/out to get the performance then you just need to get into a bigger motor and lower the safe operation area.
Same goes for servos.

One of the strange things with steppers is they pull pretty much the same amount of current at a stand still as they do at full speed. Knowing this a thermal alarm for mach won't do any good unless it actually cuts power to the stepper drivers. Again steppers do run HOT but if yo are burning them out you are just running them TOO hard!

.02c

Chad
 
Title: Re: temperature alarms for motors?
Post by: guynamedbathgate on February 16, 2007, 10:27:33 PM
well to answer alot of questions. Im running servo's. but turns out that my overheating was due to an overtightened bearing retainer. the feed screw was nearly binding so the motor burned up because of that. I loosened everything up and it should be running real cool as soon as I get the replacement motor. I guess Im still somewhere on the learning curve eh. ;).
shouldnt have any over heating problems now. so I guess an alarm is a bit uneccisary if everything is as it should be.