Grounding on grblShield

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Boston
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Grounding on grblShield

Post by Boston » Tue Apr 15, 2014 1:46 am

I want to power a small cooling fan from the grblShield v5 board.

I have a 12VDC, 0.12A fan to mount on the Arduino/grblShield enclosure, and an NTE966 (3-terminal positive; Vin, GND, Vout) voltage regulator to step the grblShield 24VDC power down to 12 VDC.

Where on the grblShield board should I ground the voltage regulator?

Thanks.

cvoinescu
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Re: Grounding on grblShield

Post by cvoinescu » Tue Apr 15, 2014 1:40 pm

I assume you're powering it from the motor power supply, so it would seem reasonable to ground it at the negative pole of the motor power supply too.
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Boston
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Re: Grounding on grblShield

Post by Boston » Tue Apr 15, 2014 3:17 pm

Thank you for your reply, cvoinescu. I wondered if the grblShield v5 board has a preferred approach.

E.g., use the "GND/Vmot" 2-point terminal, or use one of the three 4-point terminals for the motors (probably Z, since it does little except sit there and get hot).

Speaking of the Z motor, it gets quite hot, hotter than the X and Y motors, even without Z activity, although it drives up and down OK.

Does this indicate a problem? Should I consider attaching a thermoelectric cooler to it, mounting a small fan to it, or mounting a vaned heat sink atop it?

edwardrford
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Re: Grounding on grblShield

Post by edwardrford » Tue Apr 15, 2014 3:45 pm

The z-axis tends to get the warmest due to it's (relative) inactivity compared to X and Y. But, is probably only slightly warmer than X. The Y axis doesn't seem hot at all because it's sharing the current between two motors (so they are getting effectively half the amperage per motor compared to X and Z) (but the total amperage is the same across the gantry, just split between two motors)

It's a little counter-intuitive, because we think of things getting hot when they are 'working' and not sitting still. However, a stepper motor draws the most current when it's sitting still (to lock it into place). So technically, it's 'working' the hardest when it's not moving. It will get quite warm, but isn't a concern (unless you touch it). One thing you could do (but is not necessary) is adjust the pot on the z-axis driver to reduce the current, which will also reduce the temperature. However, you will be reducing the z-axis's torque at the same time, so some testing will be required to find the optimal position.

-Edward
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Boston
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Re: Grounding on grblShield

Post by Boston » Tue Apr 15, 2014 4:22 pm

Thank you, Edward -- Excellent explanation. I hadn't considered that, even though I've designed devices using stepper motors. Actually, even with the ShapeOko 2 powered up but all motors idling, the Z motor is much warmer than the X and Y motors, the three of which seem to be about the same temperature. I'll measure the temperature of each one the next time I power up the ShapeOko 2 and let it idle, and again after using it.

edwardrford
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Re: Grounding on grblShield

Post by edwardrford » Tue Apr 15, 2014 4:37 pm

One thing that I failed to mention, regarding heat: The z-axis is also hotter because it's not mounted to what is essentially a giant heat sink!

The Y and X-motors' heat gets dissipated through the motor mount plate they are attached to. Where as the z is just floating with 3 little brass standoffs trying to pull heat away from the tiny surface area they are touching.

-Edward
Shapeoko 1 #0 - a couple of upgrades.
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MeanderBolt
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Re: Grounding on grblShield

Post by MeanderBolt » Wed Apr 16, 2014 12:31 am

That is the best explanation I have heard. Yeah, I was shocked how hot it was when I first got going.

@ Boston, You can find 24v motors, then you could wire direct. I pulled mine from a computer a few years ago.
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Current tool chain > Draftsight > CamBam > ChiliPeppr
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Boston
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Re: Grounding on grblShield

Post by Boston » Wed Apr 16, 2014 3:52 am

Hi, MeanderBolt -

> "You can find 24v motors,"

(I'm sure you meant fans.) 24V fans were out of stock for 2-3 weeks at my relatively local electronics retailer and still on order, and the ones on order were physically larger than I wanted, so I got a 24V (1.5"x1.5"x3/8"), and a small voltage regulator (up to 35V in, 12V out). I expect the combination to work; I'll wire it up this week and try it, and report the result here. Thanks for posting.

MeanderBolt
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Re: Grounding on grblShield

Post by MeanderBolt » Wed Apr 16, 2014 9:10 pm

Yes, fans. Sorry. I get in here and it's all motors this and motors that... (until it isn't). ;)
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Current tool chain > Draftsight > CamBam > ChiliPeppr
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