Noob struggling with extruder motor, please have mercy!

[urbantuckerman]

Help!! I have just assembled a ctc prusa i3 copy, thanks to some excellent youtube vids since the instructions are garbage. However the extruder motor is not working and despite hours and hours of research I cannot make it work. The motor works fine if you plug it into the x axis cable, but not on it's own cable, and the voltage readings are radically different between the two cables when tested. the x asis motor, working perfectly gives the follwing readings when working: negative probe on meter on black wire, red and green fluctuate between 0 and just over 1 volt the blue wire fluctuates also between 0.2ish to 1.8v, However the wire to the extruder motor gives a much higher reading between the black and blue wires is 11.3v This doesn't seem right, and I think it may be the cause of the problem, but I a newbie at this and do not know what to try next. If you have any info that could help me out, or links to any pages that have, I would be mega grateful!!

[urbantuckerman]

Aaaah, I think it is the a4998 motor driver. If you swap it into another socket, the problem migrates with it. I have ordered half a dozen spares. Mine don't even have heat sinks so despite the cheapness of the replacement parts I am calling it an upgrade

[Kmxsoft]

It is very important that you power off the 3d printer before swapping the motor cables. If you don't power off there is a high chance that you will blow up the driver circuitry.

The reason for this is that the motor is an inductive load and it can produce high voltage powerful spikes. These spikes are a death sentence for electronic circuitry.

[iDig3Dprinting]

Glad you solved it urbantuckerman.

The driver is the usual cause for this type of issue. Always best to swap the connections around to identify which part is causing the issue.

[Kmxsoft]

Always best to swap the connections around to identify which part is causing the issue.

AFTER powering down the printer.

Sorry to be pedantic, but swapping cables on stepper motors whilst the power is up is known to be a cause of electronics failure. If you are lucky it blows the easily replaceable driver board, however it can fry the whole control board (and with some boards the driver circuits are built into the control boards so you are guaranteed an expensive repair).

[iDig3Dprinting]

Always best to swap the connections around to identify which part is causing the issue.

AFTER powering down the printer.

Sorry to be pedantic, but swapping cables on stepper motors whilst the power is up is known to be a cause of electronics failure. If you are lucky it blows the easily replaceable driver board, however it can fry the whole control board (and with some boards the driver circuits are built into the control boards so you are guaranteed an expensive repair).

NOT whilst the power is on
Pedantry is acceptable.

[urbantuckerman]

Hey. thanks everyne for getting back to me. sorry, I don"t check back more often! Yeah the stepper drivers seem to be a weak point, I ordered half a dozen from china, and a couple from the uk as quicker. I have gone through about three, but the latest incumbents seem stable. It looks like you can swap ut the a4998 for a higher quality unit, doeas anyone have any advice? I am just mounting an extra fan over the board also, which should help. Thanks again peple!

[Kmxsoft]

Hey. thanks everyne for getting back to me. sorry, I don"t check back more often! Yeah the stepper drivers seem to be a weak point, I ordered half a dozen from china, and a couple from the uk as quicker. I have gone through about three, but the latest incumbents seem stable. It looks like you can swap ut the a4998 for a higher quality unit, doeas anyone have any advice? I am just mounting an extra fan over the board also, which should help. Thanks again peple!

Wow, losing 3 is serious.

The extra fan probably won't help - I doubt this issue is due to overload and heating of driver technology. I'm more inclined to believe the circuits are getting zapped by the high voltage spikes which will occur when you physically disconnect and reconnect motors which are powered up.

Take a look at the following article. A stepper motor IS an inductor - voltages are generated and consumed by windings around the motor and it isn't impossible that a voltage spike measuring hundreds of volts and significant current is generated when an inductor is shocked thru interruption of its power source. These spikes might only last a nanosecond, however that's enough to destroy driver circuitry.

https://en.wikipedia.org/wiki/Flyback_diode

You do not need flyback diodes. You simply need to make sure you only disconnect and reconnect when the power is off.

However if you do want flyback diodes then check out the TL-Smoother:

https://www.aliexpress.com/snapshot/0.h ... 2813449421
https://groups.google.com/forum/#!topic ... HJEQG_wR9Q

I don't have personal experience of the TL-Smoother, but it looks like it does the job.

[urbantuckerman]

Hi, I seem to have given the impression that I keep plugging and unplugging my stepper motors. I don't though The motor drivers seem to be fine now, the originals didn't have heat sinks and the replacements seem better. thanks for the advice though!

The new reliability of the stepper motors has allowed me to address the second problem, from day one my heated bed has not worked. My electronics diagnostic skills are about as good as an intelligent rabbit"s, however I have learned the following; There is no 12v at the power socket on the board, there is 5v to the thermistor. The original themistor had a resistance of 150 ohm, I replaced this as according to various things I read online that was too high. The bed heats if you connect it directly to 12v, and the display reads the increasing temp. I checked the resistance across the various connections of the mosfets on the board, they are all identical, so I assume that they are all ok (?!). The temp at the display reads 0 for the board temp, not ambient temp like the extruder. I also checked the fuses on the (gt2560) board, they check out fine.

But I can't suss out why the bed isn't heating, does anyone have any ideas?

Thanks again.

[Kmxsoft]

Possibly a silly suggestion, but make sure the connectors to the stepper motors are firmly engaged at both ends. If they had any possibility of making an interrmitent connection that could feasibly lead to motor driver circuitry being blown.

Losing botsteps (a4998) is pretty rare, so losing 3 has to be unusual.