My home built printer has been having issues running properly. The x/y/z motors will run freely with standard non build position commands but when they are suppose to start a raft layer and they freeze up and don't respond properly. When I put my hands on my x/y motors they're cold as if no power is getting through, yet they ran just a moment before. I currently have a variable PSU which allows from 0-48v power output. I started turning the supply up and as I reached about 34v I noticed the motors started to run properly but my board did not regulate the power and instead started pushing the power through all of the ouptuts activating the second empty extruder and causing the heat on my extruders to rise to an extreme 300°C vaporizing my PLA. Ever since this incident my board continues to attempt to push power through all outputs regardless of the power output settings (ie if I set the output on my PSU to 11v, the motherboard still activates all motors and heaters) I am curious if I were to use 2 24v PSUs in parallel (or a series) if that would allow my motors to get the power they need without putting strain on my motherboard.

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    $\begingroup$ 1) In case it isn't obvious yet, you need a new motherboard. 2) What does the "switch fuse" in the title of your question have to do with it? 3) It would be better to ask about your problem ("why do my motors not run without 34V") than about the proposed solution (which you do not seem to understand yourself either, given that you haven't decided between series or parallel) 4) Please include sufficient details! What (exact) power supply did you use before? What was its current rating? What is the part number for the motors? Which main board and motor drivers are you using? $\endgroup$ May 7, 2018 at 6:12

1 Answer 1


@TomvanderZanden's comment is right. You have probably damaged your motherboard and/or driver boards by applying 34 volts. You should never exceed rated voltages.

It might help to study stepper motor driver circuits a bit. Stepper drivers usually act as current sources, not as voltage sources. They typically have a high-frequency switch that applies pulses of voltage so that the current through the inductance of the motor matches the current needs for the desired step position. Motors generate torque from the strength of the magnetic fields, with is linearly related to the current through the coil. The voltage drives the current, but the current cannot change instantaneously in an inductive circuit. Unless the motors have an uncommonly high coil resistance, two to five average volts will be enough to provide the maximum current.

The motors are pretty insensitive to the voltage applied, as long as the current meets the specifications. The motor driver chips are sensitive to the applied voltage. They are sensitive because the internal switches and logic can only withstand certain voltages, and they are sensitive because the circuits assume that the current won't change too quickly. If the current gets so high that the magnetic material in motor saturates, the inductance suddenly becomes much lower, and the current can spike to very high levels. This current spike can destroy drivers.

Heaters also have a voltage spec. The heaters I've seen are specified for 12 or 24 volts. To avoid burning out, a heater must have a low enough thermal resistance to the object being heated that the inner heater temperature is not so high that the heating element is damaged. Powering a 12v heater from 34 volts would cause the current to increase by a factor of 34/12 = 2.83. The power would be that ratio squared because both the current and the voltage are higher. The heaters, whenever they were on, would be generating 8.02 times the power. This might not result in the good behavior of the heater control systems, and could damage the FETs which are driving the heaters.

As for changing the power supply, before doing that I would want to check that the power supply was not supplying the needed voltage and current.

When you've replaced the motherboard and drivers, and configured the drivers for the required operating current, attach a voltmeter to the power supply. Turn on all the heaters, power up the otors, and watch the supply voltage. If it remains true (say, within 15%), the power supply isn't the problem. If the voltage dips, or pulses, or does anything other than staying stable, I would consider a higher current (not higher voltage) supply. Connecting two supplies in series causes problems with the ground reference of one of the supplies. Connecting two supplies in parallel, unless they are designed for that use, often isn't any better than a single supply because they will not necessarily share the load well.

Good luck! I look forward to further questions.


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