Gertbot (Heatsinks) and Stepper Motors getting very hot

[nike357]

Hi Guys,

I have a Gertbot running two Stepper Motors and the Gertbot and the Motors are getting very hot after running app. 2000Steps.
I use 12V from an old ATX PSU to supply the Gertbot.

The Steppers are this kind:
SHINANO KENSHI STP-42D204-01
3.15 V
0.7 Amp
4.5 Ohms/phase
1.8 deg/step

I have the same motors running on a Ramps Board with a 3DPrinter at 12Volts and there they are not getting this hot.
(Using same ATX PSU)

Any ideas what I can improve?

[mikronauts]

That's an easy one.

You are drawing WAY too much current!

A quick google for the specs of the motor shows

12VDC @ 1.7A max

http://www.jameco.com/z/STP-42D201-37-S ... 58531.html

So by trying to run it at 3.3V you are trying to draw potentially 6.2A (stall condition) from 3.3V!!!!

I am surprised you have not fried your gert board yet.

You can't just hook up a random motor without finding its specs and making sure the driver (and power supply) you are trying to use can handle it.

Hi Guys,

I have a Gertbot running two Stepper Motors and the Gertbot and the Motors are getting very hot after running app. 2000Steps.
I use 12V from an old ATX PSU to supply the Gertbot.

The Steppers are this kind:
SHINANO KENSHI STP-42D204-01
3.15 V
0.7 Amp
4.5 Ohms/phase
1.8 deg/step

I have the same motors running on a Ramps Board with a 3DPrinter at 12Volts and there they are not getting this hot.
(Using same ATX PSU)

Any ideas what I can improve?

[nike357]

Thanks, I was afraid of this, I just don't understand why this is an issue with the Gertbot while the same motors are running fine on my 3D Printer.

I have another Stepper Motor Model:
MINEBEA
Type 17PM-K018-G22ST
3V at 1.2A per Phase

I am not good in electronics and therefore don't know how to calculate the max current.
Reading the Gertbot Manual it says that the board has a over current protection, so when you say i am drawing too much current, why didn't it trip the protection? Or does the over current protection only work with DC motors?

[nike357]

That's an easy one.

A quick google for the specs of the motor shows
12VDC @ 1.7A max
[...]
So by trying to run it at 3.3V you are trying to draw potentially 6.2A (stall condition) from 3.3V!!!!

I just read your lines a second time, how do you come to 6.2A at 3.3Volts when the motor specs show 12VDC @ 1.7A max?
How can I calculate which Stepper should run fine at 12VDC Input without damaging my gertbot?

[Burngate]

... 12VDC @ 1.7A max ...

I just read your lines a second time, how do you come to 6.2A at 3.3Volts when the motor specs show 12VDC @ 1.7A max?

This is one of those occasions where he's misread something ... you have specified SHINANO KENSHI STP-42D204-01, he's found STP-42D201-37 - a different beast! (Google does that to you)

Yours should be driven with no more than 3.17v, at which it takes 0.7A because its windings are each 4.5Ω (Ohm's Law)
Putting almost four times the voltage on them means almost four times as much current (Ohm's Law again) and sixteen times as much power (V x A) so they get hot!

Choose a different motor, with spec to match what you have

[mikronauts]

For electronics, you have to REALLY memorize two basic formulas:

1) V = I * R

Where V is voltage, I is current (amps), R is resistance.

Using algebra, if you know two of the values, it is easy to calculate the third.

2) P = V * I

Where P is power (in watts), I is current (in amps), and V is voltage

Again, algebra can be used to calculate any third value if you know two of the values.

While there are obvious cable loss & other efficiency issues, then:

12V * 1.7A = 20.4W

So at 3.3V to get the same power (P = V * I)

20.4W / 3.3V = 6.18A

Whenever you have a motor, google for the actual data sheet if at all possible.

That's an easy one.

A quick google for the specs of the motor shows
12VDC @ 1.7A max
[...]
So by trying to run it at 3.3V you are trying to draw potentially 6.2A (stall condition) from 3.3V!!!!

I just read your lines a second time, how do you come to 6.2A at 3.3Volts when the motor specs show 12VDC @ 1.7A max?
How can I calculate which Stepper should run fine at 12VDC Input without damaging my gertbot?

[mikronauts]

OOOPS! Sorry, my bad. Did not notice the different suffix. I googled to verify the OP's specs.

This is one of those occasions where he's misread something ... you have specified SHINANO KENSHI STP-42D204-01, he's found STP-42D201-37 - a different beast! (Google does that to you)

[stderr]

I have the same motors running on a Ramps Board with a 3DPrinter at 12Volts and there they are not getting this hot. (Using same ATX PSU)

I don't have the board so I'm just looking this up, it looks like there isn't support in the board for chopping, see page 16 http://www.gertbot.com/gbdownload/man/Gertbot.pdf , "The controller needs a minimum of 8V to work. If your stepper motor requires less voltage you must add series resistor". If your Ramps Board for your 3DPrinter supports chopping, then the behaviour will be entirely different.

You cannot just hook up a stepper motor to voltage and go to the party, you have to fight the fact that the motor is going to have a lower resistance in the windings than you can allow current through. This getting hot business is the first lesson of stepper motors, well, after the lesson of how you plug in all those crazy wires. So like an LED, that means a current limiting resistor, a big one (or more than one if designed in a parallel configuration to deal with the heat), unless you can live with the low torque you get from running the stepper directly at the rated voltage, which in your case is pretty low.

If you are running an ATX power supply without a normal ATX motherboard load, remember that you need to provide a minimum current draw on at least some of the voltages, look up the specs, in order to get correct functioning, unless the manufacturer is doing this internally somehow. I think usually this means that you need a load on the 5 volt and the 12 volt rails, the 3.3 volt might share with the 5 volt, it all depends.

[nike357]

thanks, now I understand.

So if I'd like to run my current stepper motor i'll need to add a resistor to each coil,online calculator gave me a 2Ohm resistor to achive 3,3Volts with burning app. 50Watt something, that's just to much power loss. I guess i'll search for another motor.

Just thought I'd could use the ones I have left. And yes checking my Ramps board, it has choping....

Just one more question, could I wire more motors in series to split the load or would that be even worse?
e.g. 3 Motors and run the Gertbot with 10Volts? (3.3 x 3 = 9.9?)
http://www.instructables.com/id/Wiring- ... in-Series/
http://i.imgur.com/tSbm2ob.png
(according to this the motors will act like a bigger one)

[stderr]

could I wire more motors in series to split the load or would that be even worse? e.g. 3 Motors and run the Gertbot with 10Volts? (3.3 x 3 = 9.9?)

Do you want to run both or three motors at the same exact rates? In any case, the reason for the higher voltage is to deal with the inductance of the windings that counters changes in current and thus in the magnetic field. If you increase the inductance by having more than one motor in series by adding the rated voltages to equal the voltage you are feeding the motors, I think that will be little different than having the one running at its rated voltage. I think this because I think the change is linear because it is operating on a conserved quantity.

There seems to be a dearth of information on google on this idea, however. I did find the following thread and it does actually discuss what you are talking about although it doesn't really have an answer for the idea of directly running steppers in series, most folks seem to have chopper type circuits:

http://www.cnczone.com/forums/stepper-m ... forum.html

This is an interesting question which would be nice to test but I don't currently have a test bed of this sort set up, a good thing to think about though. So have you tested it?

[nike357]

Thanks for your thought's, haven't tested running three motors in series.
Just wanted to get some feedback and not putting too much load on the board again.

If running three motors in series with 10Volts is okay for the board then I'd give it a try, i just don't want to fry my gertbot.

Basically what I'd like to achive is using the gertbot to power a 6x6 rover, initially i thought of running each side with one motor but as discussed earlier one stepper is drawing to much power. So if three stepper per side, one per wheel would be fine with the load, then i have something to test.

There's just one more thing I am not sure about the gertbot, in the manual it says in the DC motor section something about " over current protection", but I am not sure if this only applies to running DC motors.

[ewaller]

...
A quick google for the specs of the motor shows

12VDC @ 1.7A max

http://www.jameco.com/z/STP-42D201-37-S ... 58531.html

So by trying to run it at 3.3V you are trying to draw potentially 6.2A (stall condition) from 3.3V!!!!

Um, it does not quite work that way. The motor is not a constant power device. Unlike a switching power supply which can draw more average current when the voltage drops in order to maintain a constant power level, a motor (at least when stalled) is purely dissipative. Just like a resistor. You can drive it at up to 1.7A. It is not clear from the specification what the current draw would be if the winding were placed across 12V, it might exceed 1.7A. Regardless, at 3.3V, the current would be 0.275 x the steady state current at 12V. And the power would be 0.075 the stalled power at 12V.


Edit: I missed that the phase resistance is 1.55 Ω. That would be 7.7A at 12V. Way, way over spec. At 3.3V it is 2.12A -- Also over spec. To drive it from a 3.3V supply, put 1Ω (2W min) in series with the winding. Better yet, drive it from a constant current source.Pardon the noise here. I was working with the wrong motor The part referenced in the OP can almost be run from 3.3V. The current at 3.3V would be 0.733A (slightly overspec). I have lost the bubble at what voltage we are actually trying to drive these parts with.

Edit: Note that the Ramps Board apparently uses a stepper motor driver chip, the A4988
https://www.pololu.com/file/download/a4 ... e_id=0J450

[stderr]

I have lost the bubble at what voltage we are actually trying to drive these parts with.

The board requires a minimum of 8 volts and it's not a chopper type device. Supposedly the motor is rated at 3.3 volts. The poster doesn't want to use a resistor to limit current.

[stderr]

If running three motors in series with 10Volts is okay for the board

If you wire up the three motors in series, what is the resistance? I think it will be three times what it is with a single motor. What does Ohm's law say the DC current is going to be? Is that within what the board can deal with? I don't think the motors will behave better than they would if driven with their rated voltage, which is 3.3 volts, right? Have you tested them at 3.3 volts? You can't use the board because it requires 8 volts.

Other people talking about doing this worried about stalling one motor and this causing some sort of trouble, twisting and heaven knows what else, but that might not be a problem in your case because the other motors would just push the stalled motor, again I think.

[nike357]

Thank you everyone, I didn't thought that it would be that big difference to running the Stepper Motors on a Ramps with A4988.
So far I only had experience with chopper type devices and those run practically every Stepper without any issues.

Maybe i rethink my plans and switch to DC Motors.

Regards

[nike357]

Hi

Just found time to test running three Stepper Motors in Serial. IT WORKS!!!

It just needs a bit trial and error selecting the correct frequency and step count but now they're running smooth without any heat generated. The motors as well as the gertbot are staying perfectly cool, at least below body temperatur, I couldn't feel any heat generated by touching the motors or the heatsink on the gertbot.

Guess that's my solution, as I have more than enough motors lying around i'll just go with two tripplet configurations.

Unfortunately another topic popped up but that's for another post.

[nike357]

Hi Guys,

It's been a while since I had time to play around with my GertBoard.
I've just received a couple of new Stepper Motors and I think they are better suited.

They are Shinano Kenshi
STP-42D3019-01

according to the web they should be 24Volts at 2Ohms
unfortunately I do not find the fully spec sheet so I don't know how much Amps they are pulling. Will give it a try soon.