Help with over heating

[gary-cook]

Heres the story.
Im building JGRO's cnc router.

I bought 3 bipolar steppers from ebay with the following details
23LM-C064-03v
Rated Voltage 4.4v
Rated Current 1.5a/phase
Max input 13.2w
Winding Resistance 2.95 ohms

I then bought these controllers (3 of them) http://www.quasarelectronics.com/3158.htm which are rated for 5 to 50v at 5 amps.

At the moment i want to use a computer psu rated at 12v 15a 250w.

The problem is i ran the steppers and the controllers got so hot they actually melted the solder on the mosfet's within a minute.

Any suggestions on what i can do to resolve this problem.

Also when i can afford it, a few months down the road, i will build a power supply. Any recomendations on what voltage and amperage i should use. We are on 240v av mains here.

Many thanks

[coherent]

something sounds wrong... your board shoudn't be getting that hot unless you're running way to much power. I'd reduce it and work your way up. If your board doesn't have adjustable power pots for each axis, you're going to have to use power resistors to reduce the stepper voltage. I suppose it could be a bad board, but definately shut things down if it starts overheating. Don't wait until solder starts melting because you're way past too hot at that point and something is wrong. At that temp/power, you may have damaged on board part, wiring or your motors.
-Marc

[gary-cook]

Thanks for the response.

All the boards are the same. They all get hot.

If the psu is 15 amps, would i have to step it down for the 5 amps which the board can take?

Can i put power resistors before the controller or do they have to go between the controller and steppers?

What size of power resistor should i go for? i get confused with all the working out.

Cheers

[ViperTX]

Is this a Kit that you built? Did you add heatsinks? Did you add a current limiting resistor for each driver (2 per board unless the VCC is common...which it doesn't appear to be)?

[gary-cook]

Yes this is a kit i have built. And I know all the components are the right way round etc because i used to work soldering up PCB's. There is no heatsinks, there wasnt any supplied, and there were no heatsinks recommended in the literature which came with the kit.

This is the setup i have

PSU
(12v 15a) --------- Controller ------------ Stepper
I
I
5v from psu

Other than whats on the controller I have added no resistors or anything.

Would heatsinks make that much difference if the mosfets are getting that hot?

[fyffe555]

Gary,

How hot are the motors getting??? Anything moving? Anything changed colour? Have you checked you haven't got a short across anything and that the motors are wired correctly?

To drive your motors those mosfets shouldn't need heatsinks. The fact that they're getting hot enough to melt solder is a problem! Sounds like the mosfets are passing more than their rated 5a - I'm surprised it hasn't damaged the motor too.

You've got a 12v supply feeding a 4.4v motor and there's nothing to limit the current through the motor. You need resistors between the driver and the motors to limit the current to the motors rated 1.5a. 12v supply, 4.4v 1.5a motor needs something in the order of 5 ohms and 12watts for a single resistor? Anyone check that for me?

FYI these kits are similar to the open source drivers Phil (pmimno) put up in the open source forum here. There's some good info there.

hth

Andrew

[H500]

You need to put 5 ohm, 15 watt resistors in series with each coil. Otherwise, you'll burn up your motors also.

By the way, you won't get much speed out of those motors with this circuit & 12 volts. You should just scrap it and build a chopper drive.

[joecnc2006]

Originally Posted by gary-cook Yes this is a kit i have built. And I know all the components are the right way round etc because i used to work soldering up PCB's. There is no heatsinks, there wasnt any supplied, and there were no heatsinks recommended in the literature which came with the kit. This is the setup i have PSU (12v 15a) --------- Controller ------------ Stepper I I 5v from psu Other than whats on the controller I have added no resistors or anything. Would heatsinks make that much difference if the mosfets are getting that hot?

What kit is it? I have the bobby cnc board and use no heatsinks, it works fine with a fan blowing on the chips. i feed 32v through it and have the pots set correctly as per my motors.

[gary-cook]

The kits are from here
http://www.quasarelectronics.com/3158.htm

I plan to when i know everything works to build a 30v variable powersupply possibly at 15amps if i can get this psu working.

Do you know where i can find circuit diagrams for good chopper drivers?

Ill try putting the resistors between the controllers and motors, but why put them there and not reduce the current before it goes into the controller?

[H500]

Steppers have inductance. Using the a low volt supply, the current would never have enough time to reach 1.5 amps when the motor is turning at a decent speed. The resistors limit the current when the motor is near standstill.

Here's a link to good & simple open source design:
http://www.cnczone.com/forums/showth...9991#post79991

[solarchimesam]

I am running 12 light bulbs inline with the stepper motor and when the motor is idle the bulb takes the heat (light comes on).
This solved my over heating steppers.
All I did was run a standard car bulb (1157) with a socket from an old tail gate I had. 1 wire into controller and the other to the stepper motor.

Hey it works for me :-

[gary-cook]

Got the resistors today. Ill give them a try over the weekend and let you know how i get on.

Thanks for the support guys.