I have been testing my new machine out and was successfully cutting a 1/2" plate of T6 6061 aluminum at 6mm DOC, 42 mm/s, with 0.5mm stepover. All was great until I realized I had not actually checked the VREF on the Chinese clone 8825’s and they were set to 1.6V. Went back and tuned them 0.5V, and now I don’t have anywhere near the holding torque that I need for the heavy cuts I am trying to achieve. The holding torque seems to be much lower than I am used to when tuned to 0.5V. Did I burn up my steppers (they still work fine and still hold great if I turn the VREF back up), or did I burn up the drivers (they still work too).
One note, I am using the wiring harnesses that I purchased about a year ago from here. I think they are wired in series, but not really sure.
I ordered 5 TB6600’s that should be in tomorrow, and I am going to re-wire and give each stepper their own upgraded driver this weekend and see if there is a noticeable difference.
Is the wiring harness in series or parallel? In the parallel one, the current is split between the two motors, so you should go up to 1.4V. If it’s series, it should be at 0.7V. series will be stronger, so it might be worth wiring it up that way, or buying a new harness from the shop.
I’ll take a look tomorrow and see if they are series or parallel. At 1.6V the drivers were overheating after only a few minutes. I am going to try pushing the motors with some larger TB6600 drivers this weekend, but I’ll probably save the electronics for another build. Appreciate the clarification on the voltages though!
Your steppers have a number that they can handle. The number is found on the spec sheet and I can tell you even that number is usually too high. For our purpose of having the steppers always energized running at above 90% or rated amps usually is too much. (I ship at 70-80% rated max). If your drivers or steppers get too hot the setting is incorrect.
If you have any nema 17’s the standard drivers are enough by far if you are wired in series.
1.5A on a drv8825 is 3A to the motor, and the drv8825 can not sustain more than 1A and that is with amazing cooling.
70% of your rated (generously rated) capacity is .7A that is why we all start there. If everything goes okay and you have driver cooling you can move up to about .8A and at that point your steppers should be getting pretty warm.
These parts are a little to sensitive to just wildly guess and check, something will give.
I ended up rewiring today. Ran dir and pulse signals from the prontoneer cnc shield 3.5 over to five independent tb6600’s set to 1.5a. Added 16 gauge wiring throughout the machine up until a couple of inches from the steppers to hopefully reduce power loss due to thin wiring. The steppers seemed to stay cool, and the new drivers will not need a turbofan to keep them from overheating. I was physically unable to stop the machine from moving after this change, so heres to hoping i get some improvements in the cuts. Wiring is ugly, i couldnt fit the new drivers in my previous box.