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I'm attempting to replace my DRV8825's with TMC2130's on a Prusa i3 rework clone, 12 V RAMPS1.4, motor currents have been accounted for. Since they don't work as well with 12 V than with higher voltages, I bought a 10-50V 10A DC-DC converter to power the drivers (and steppers ofc). On the RAMPS this is done simply by taking the VM pin out and soldering it on the other side to draw power from an external source.

It is stated everywhere that VM should be powered BEFORE VIO. Would it be valid to switch on a relay with the DC-DC converter and connect the VIO pin to RAMPS 5 V through it? Is it enough having both sources turn on at roughly the same time? I haven't found any indication on how much time there should be in between (or if there needs to be any).

Please tell me your own experience if you have attempted something similar, or any alternatives (aside from buying a new board, because I'll eventually build a CoreXY or something else) that may be valid.

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  • $\begingroup$ I think it's more of an issue for when you have the board powered from USB, firmware and drivers active, and then consider turning on the power supply. I used pretty much the same setup for a while - a MKS Gen 1.4 board at 12V, a 12-36V boost converter to 24V, which then went onto the driver ICs. I did solder a 100µF capacitor to each driver though. $\endgroup$ – towe Jun 14 '19 at 13:06
  • $\begingroup$ @towe well, i did this almost a month ago, and yes, if you connect usb before turning the supply on then the drivers misbehave. But I'm happy enough, because I use a makeshift 6m USB cable that I didn't put the 5v line to anyways, so i only have this problem when I forget to turn the supply on and use another cable. I have it with the 50v 10a boost converter set at 36v (i could actually go higher, but my drivers are the high current type so it's nonsense) and a 2200uf electrolytic paired with a 1uf polyester for all of the steppers. $\endgroup$ – Matias Gonzalez Jun 14 '19 at 13:42
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First of all, I'm not talking on a first-hand experience: I don't own a RAMPS based printer. If I were you and wish to be 100 % sure the setup you are describing doesn't blow up in my face I would use a spare pin on the Mega to drive the relay which, in turn, drive the 24 V source line. In terms of delay I would use a couple of seconds after power on: enough time to have the bootscreen completes and all the pins being set as per firmware configuration.

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  • $\begingroup$ It's the other way around, the 24V have to be switched on first, but it's the same since I could switch the 5v with a relay. I'll consider doing this $\endgroup$ – Matias Gonzalez May 14 '19 at 22:33

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