Hot end and stepper motor issue.

Have any of you guys encountered an issue where the stepper motors started acting underpowered when you heated the hotend. It seems they don't have enough torque once the hotend starts heating. This is my first printer, so I don't know what skipping steps sounds like, but if it's a pulsing jerky clicky noise coming from the motors when they try to move then that's what my motors are doing. And it's every single one. Also, the fan hooked up to the 5 amp rail also sounds significantly quieter when the hot end is heating. So it seems like everything is being underpowered. Any ideas or possible solutions to what might be going on? Thanks!

Also, I should mention:

RAMPS 1.4 board
Makerfarm i3v 12"
trim pots adjusted to 0.66v
DRV8825 stepper drivers
e3d v6 hotend

The motors work perfectly when the hot end isn't heating. At least they move smoothly and consistently.

I just compared the voltage on the stepper drivers with the hot end off and with it heating and when it's off they are at 0.66 mV but when it's heating the voltage increases to 0.8 mV. Is 0.8 too high? I heard 0.66 might even be too high but I don't know.

Also, the led for the D10 mofset for the hot end blinks rapidly immediatly when instert heating. I think this is supposed to happen. What interesting is the motors are clicking with the same frequency of the led.

One last thing. When the motors are clicking the voltage on the trim pot is actually 0.66 V. It's only 0.8V when the motors aren't clicking, which seems to happen if I wait a few minutes after telling one of the axes to move. No clue what's going on. Also I said mV in the above posts - I meant V. Sorry

When the heating is working the PSU may be over-stressed and this may effect the drivers/currents.

However, not all steppers and drivers are made equal.

First look up your specific stepper motor types and which current they actually need. Locate the type number on the steppers and google them. Different steppers require different max currents as the coil resistances differ. I have steppers that have a max current of 1.2A, 1.3A and even as high as 2.5A.

Once you know the max current your steppers need, then adjust the pots on the driver boards. Be aware that there are boards out there with different current adjusting resistors (100 and 200 milliOhm), best to locate them and measure to be sure.

Attachment 8307Thanks for the quick reply. I've attached a photo of my stepper motors. I wasn't able to find a data sheet for them but I did read that these ones are 0.5 amp motors. I'm in school right now so I can't do any diagnosis at the moment, but I will get on it when I get home. Any chance you could explain to me the affect of different current adjusting resistors on the driver boards. I'll look it up when I get home, but just thought I'd ask. Thanks! Hopefully I can get this sorted out soon.

The motors are produced by:
CHANGZHOU CHUANGWEI MOTOR ELECT APP


I can't find much info on the net, but they may be similar to the 150 sub-type which is rated at 1.5A.

As to the resistor, the current through the stepper coil also goes through a measring resistor and thus generates a voltage proportional to the current. This voltage is compared to what you set with the pot and defines the cutoff current. There are boards out there that use 100 milliOhms and also 200 milliOhms. You will need to verify which one is on your boards. The datasheet of the driver chip also provides more info on this.

Thanks for the reply Alibert. I appreciate the clear explanation. Learn something new everyday! Anyways you were right that the PSU was over-stressed. Well its actually an ATX PSU that can push 49 amps supposedly but I think my issue was that I did not have enough 12v and ground wires going from the PSU to the 5 amp rail on the RAMPS board. I thought 2 20AWG wires per 12v and ground would be enough, but I guess it wasn't. I'm using 4 20AWG wires now and am having no issues. Thank You for working through this with me! Quick question - what does the 11 amp rail power. Just the heat bed? If I am using a relay then can I expect that there will never be the whole 11 amps drawn from that rail? Thanks again!

Quote:

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Originally Posted by pjfossee

... what does the 11 amp rail power. Just the heat bed? If I am using a relay then can I expect that there will never be the whole 11 amps drawn from that rail?

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On RAMPS, the 11-amp input *only* sources power for whatever is connected to the D8 output, which is usually the heat bed. If you're using a heat bed relay, D8 would only need to supply a small amount of current to energize the relay. #20 wires would be more than fine for that, as would just adding short jumpers from the 11-amp input to the 5-amp input.