DIY Stepper motor output reducer

[Tempy111]

Hi, Minor time DIYer mostly doing little fun projects, so my skill level is a bit limited.

well, I also have a 3d printer. Now, I know all electrical motors generate AC power when freely spinning. Problem is, when there is a need to manually move the head or the build plate, this, of course, spins the motor and generates a small amount of AC power, enough to go though into the motherboard which can lead to the screen flickering on. When the power is on, I don't think this is much of a problem, but when the power is off, this isn't really a great thing to have this electricity spike..

So I'm wondering about some way to deal with this and I guess some kind of switching method so when the power is off, the electricity generated by the motor moving is rerouted instead of going into the board... any ideas? i'm not 100% on how stepper motors work so I'm not sure if something simple like a resister setup would in fact create more problems of not allowing the power when it should.. any ideas?

thanks

 

[James]

This is going to be a low voltage dc system, assuming the stepper motor drive board is separate to the main motherboard, place a diode in the power supply to that board,
This should prevent back feed to the motherboard and hence the display.
You might find info on the web if you search online forums dedicated to that type of control.
Alternatively you need to find a friend that’s good at electronics.

 

[Tempy111]

ah yes.. I don't use diodes much as my stuff is very.. amateur but I got some.. pretty much everything is modular, (apart from, sadly since one blew, the chips for the thermocouples) so it's easy to customise bits. the Motors are connected to the board with a 4 pin connector, which then leads into the driver circuit which is connected ontop, so putting something (even making like a little extension) between the 4 pins and the connector isn't hard.

The stepper motors are up to 36V with up to 1.4Amps I believe. 4 wire bi-polar connector. like I said, I should have a few diodes around but any thing particular to look for? I know it's important to know which is the positive end and which is the negative but that's about it.. since the current is up to 1.4amps, I guess at least a 1.4 amp diode..

 

[James]

Without going in to too much detail, there should be +ve supply going to the stepper motor control board. You will need a diode capable of handeling the peak current the drive can take.
Diodes allow electricity to pass in 1 direction but block it from traveling in the other.
Google or an electronics forum are your best bet on this topic I expect.

 

[Tempy111]

ah.. yeah.. so the electricity the motor is generating is going Back up the Positive line to the driver and then to the board.. there is mm... the VDD pin.. I think that's a 5v power in to the driver chip.. I don't have too much luck with google ^_^
anyway, thanks, this has been useful. I'll have to double check the power line and see able a diode for that.

 

[StephenRowley]

Shouldn't be any need to spin the motors by hand anyway, use the 3d printer jog software. I would also expect that moving parts of the 3d printer by hand ain't going to do it any good.

 

[Tempy111]

If something happens and you need to manually move the build plate up or down a bit, or move the carridge with the head along the x or y axis, they are 5 main things controlled with stepper motors, so they lead to the motors spinning. There are times when such need is needed, though as much as possible, not often, but enough.

 

[Lucien Nunes]

What is happening is that the output bridge in the driver is rectifying the AC the motor is generating, and dumping it back into the DC rails. This in itself is not harmful provided it does not raise the rail beyond normal voltage, which should not happen unless the motor is turned faster than it would normally operate. If the motor is driven from an unregulated rail separate to the logic supply, even if the logic supply regulator is fed from it, no harm should arise.

The problem with putting a blocking diode in series with the driver DC input is that the less load using up the regenerated DC, the higher the voltage will rise at the parts that still see it. Also, the driver may rely on regenerating back into load during normal operation, just as an electric train regenerates back into the supply when braking and needs to dump power into a resistance if it cannot be returned to the grid. If you do add a blocking diode (use a generously sized Schottky for low Vf), I would also add a power zener or transistor equivalent to clamp the driver input a few volts above normal max working voltage.

 

[marconi]

Could you let me know the dc voltage which supplies the stepper motor driver board please? And measure the dc current to it when the printer is in operation.

I am thinking you could insert a 3 lead linear voltage regulator into the Vdd line to the motor driver board with a capacitor (say 500uF) across the output side of the regulator to absorb any generated current - the regulator would block reverse current. The ones I use don't have a large minimum input-output differential voltage.

eg:
linear voltage regulators | Rapid Online - https://www.rapidonline.com/Catalogue/Search?Query=linear%20voltage%20regulators

and here is a 36V 1.5A one since you mentioned these values:

LM317T-DG Adjustable Voltage Regulator 1.5A TO220 Dual Gauge - https://www.rapidonline.com/lm317t-dg-adjustable-voltage-regulator-1-5a-to220-dual-gauge-47-3321

Would need a heat sink which requires some a calculation of power dissipation before it can be sized.

 

[Lucien Nunes]

Wouldn't use a VR personally. Many types warn against applying voltage to the output and require a diode from output to input to prevent this. e.g. if the load has large bypass caps, the protection diode allows them to discharge into the unreg side at switch off without reverse-biasing the reg's pass transistor.

 

[marconi]

Temp111 - Section 6 and Figure 7 of:

https://static.rapidonline.com/pdf/47-3318.pdf

for the 'extras' around the linear voltage regulator I recommended.

 

[Tempy111]

I'll have to check the values for the power and get back to you ^_^

I got some lower voltage regulators (3.3volts and 5volts) and I might have some higher.. i'll have to check or look online (town with basically no electrical shops or anything around ¬_¬).
thanks

 

[Lucien Nunes]

Buuuuut...
If you put the protection diodes around the regulator, you defeat the original purpose which was to avoid backfeeding the MoBo as D1 in Fig.7 will do exactly that.

What's wrong with a diode? Something like an SB540?

 

[marconi]

My C3 (should have said in #12 but did in #9) is circa 500uF; and deltaQ=CdeltaV, so deltaV=deltaQ/C, where deltaQ is the charge fed back. C3 is discharged through R1 and R2 and if D1 is forward biased through it into the PSU smoothing capacitors, and again V=Q/C. My idea does not reduce feeding back of charge but reduces the voltage rise deltaV of Vdd when SM turns and generates deltaQ- (actually for Vdd read the rises of potential wrt ground of the input and output of the LVR) so that display does not activate. Or something like this. It is not being done on my bench so its a thought design which I think has legs.

 

[marconi]

And Temp111 might indeed try the simple diode first to see how it performs in practice.

I hope he lets us all know how he gets on.