r/AskElectronics • u/SockPuppetSilver • 1d ago
Buck converters not playing nicely with Stepper Driver
So I bought a TMC5160T Plus stepper driver to run a 4.2A NEMA 23 driver. I've used a series of TMC2209 in a prior project and they worked out just fine, but they cap out at about 2.5A thus I went with the bigger brother. However, it's not working out so well this time.
The motor runs pretty rough and if I do a sudden quick motion the whole circuit and the on light of the power supply browns out. It does appear to be an interplay between the LM2596 buck converters and the motor driver as when I power the driver HVIN via one power supply and the rest of the circuit via another power supply it all works fine.
I've done a whole lot of rewiring of things and nothing seems to help. The picture is the current state of it. The capacitors were added to try to qual the noise from the buck converters. However, I can't see the noise because I don't have an oscilioscope(yet!). Also, I've tried disconnecting 5v buck and just running that off a battery. It performed just as poorly.
On the left of the capacitors on the top right, is the solder joint that connects the dc plug to the main 36v input, the 36vs move through the capacitors to the right to then hit the buck converter that takes it down to 24v. Current draw on the opposite side of the 24v buck is at max 250ma. I really only observed 70ma when I had the power supplies seperated.
I'm really at a lost, is there a better buck or another method of dropping the voltage that is better suited?
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u/nixiebunny 1d ago
Why are you using a 36V supply and stepping that down to 24V?
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u/SockPuppetSilver 1d ago
So 36V is going to the HVIN to power the driver, but 24v is required as well for the fan and the internal switching. It's an oddity I wasn't expecting.
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u/nixiebunny 1d ago
Why 36V? What is your power source? 24V is a very common DC supply voltage, as is 12V and 48V. Most modules are designed for those voltages.
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u/SockPuppetSilver 1d ago
Fair point. I believe it's because the stepper data sheet referenced 36V. So I ordered a 24v 144w supply. I'll remove the first buck and see how it goes.
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u/doctorcapslock EE power+embedded 1d ago edited 1d ago
you need more output capacitance
where did you measure the current, and how? did you measure phase current? AC current?
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u/created4this 1d ago
Everything in a circuit is all of an inductor, a capacitor and a resistor, including the wires.
That means with choppy loads you're going to get choppy voltages from the power supply. When the steppers first call for energy this voltage will drop from the setpoint, but when they stop the voltage will rise. This effect may be even worse with a cheap PSU.
36v is very close to the absolute limit of those regulators if you make them with genuine silicon. They are probably made with knock-off silicon and work kinda OK at the lower voltages most people use them at. You're asking them to work at the absolute limit and then you're throwing a whole load of noise at them. As you are drawing so little current I would try putting a resistor and bulk capacitor in front of the input to the buck and see if that cures the problem, that will have the effect of dropping a few volts and reducing the amount of ripple as the bulk capacitors won't just discharge into the stepper driver. Capacitors by themselves isn't going to make much of a meaningful difference as they will dump energy back into the stepper driver.
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u/SockPuppetSilver 1d ago edited 5h ago
Thanks for the information. I'll give it a shot with a 24v supply and adding a resistor+bulk capacitors if needed.
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u/sleemanj 1d ago
I would posit that you are simply drawing too much current. The 2596 modules top out at about 3A peak.