Heat build up???? Need suggestion.

with a 5 volt regulator to power the ttl logic, I'd suspect.

ah.. no, that's not how it works.

there are two kinds of drive, chopper and direct. Chopper drives measure the current in the motor coils, then turn off the driver so that the current stays within limits. The higher voltage (than the motor) recommended for these supplies decreases the rise time for the current in the motors, and increases the high speed torque. For these kinds of drivers, you do want a higher voltage.

If you have a simple saturating transistor driver, you have at most

1.0 volts in the transistor in saturation (probably less than 0.5 volts), the motor voltage itself, and that's it. for a 6 volt motor, you would run at no more than 7 volts. 13.8 volts is way too much, if you have this kind of driver.

current limiter, but that depends on the kind of driver that's running the motors.

6.5 to 7, roughly, but not much more.

Possibly when everything is hot.

Harvey

The below item is what I'm using to driver my motors, the specs say from 0- to 24 vdc. That was the reason for the middle of the road use of 12 vdc. Also would a resistor setup work or should I use a series of diodes to step down my voltage say to 7 volts from 13.8?

(S3ROC) Stepper3 Rev OC - 3 Axis 3 Amp Unipolar Stepper Motor Driver

Really TIA Neil

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This turns out to be the maximum voltage that the board will tolerate.

Ok, reading page 9 of the manual:

1) the power supply used for the stepper motors shall be selected at approximately one volt higher than the rating shown on the stepper motor.

I'd use a power supply rated at 7 volts. You'd do well to find a power supply rated at that voltage, or step the voltage down with diodes. Figure about 0.6 volts/diode and experiment with them, and they either have to be rated for the full current of the motors combined, or you need a string for each motor rated at the full current of what the motor will draw. Figure either the phase current for full step, or 2x that for the half step mode. I'd go with at least 2 1/2 to 3 times the maximum current just to be conservative.

NOTE: you do have this kind of driver.. so 13.8 volts is too much.

This is a very simple kind of driver. In hindsight, a xylotex board would have worked better, giving you more torque, if the phases of your motor were not common. (6 wire unipolar rather than 5 wire unipolar).

I am not sure what the overcurrent will do to the steppers.

Harvey

Thanks Harvey, Now for a new question, I have a couple of AT power supplies. Could I put in series a resistor as a current limiter? And achieve the same results. The below link has the same motors I'm using. The SP3/HT is the complete setup. It shows an AT ppower supply being used.??

The mechanics I've gotten worked out, but as you can tell know very little about the electronics end of things. Your help is greatly appreciated.

Neil

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For unipolar driving A 6V motor needs a 6V power supply (say 7V for cable volt drops). Keep the 13.8V supply and feed the motor coils via resistors mounted on heatsinks (maybe a 20W 2.2ohms resistor per each coil pair). The motors get their 6V when they are on, so don't burn out but you will now have some extra performance out of them due to the initially higher supply voltage being able to get the motor coils moving faster. regards john

in

I believe the standard way for home builders to drive stepper motors is to use a high voltage supply and dropping resistors. I'm not sure this is any better than using the correct voltage but that seems to be what people do.

If your motors are rated 6 V @ 3Amp and you have a 12 V supply the calculations you need are:

Resistor value = (12-6)/3 = 2 Ohms

Power rating = (12-6)*3 = 18W

It might be cheaper to use multiple resistors in parallel if 18 W isn't available or is too expensive.

Colin

The problem with a stepper is that you are switching a voltage through the inductive coils on and off. Current lags and builds up slowly. If the pulse is fast enough (rapid stepping, high RPM), then current does not approach the nominal drive current... Result: low torque at high RPM.

By running the motors at a higher voltage, but limiting the current with an external resistor, you get the advantage that the current will rise faster in the coils, thus giving better performance at higher RPMS.

The real solution, if possible, is to use a chopper driver with current limiting, which switches the motor coil to full supply voltage (often 10 times the rated voltage) yielding a rapid rise time (switches have a very low impedance), but turning off the switch when the current has reached the nominal rating in the coil.

Gives you better torque at higher rpms as well.. this can be done with two ICs for motor supply voltages to 35 volts and currents less than 2 amps.

Harvey

I didn't realise they were inductive enough and/or stepped fast enough for this to be a problem. Thanks for putting me straight.

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