I just discovered that a drill motor that works at 110 VAC on one of my machines has been causing a controller's MCU to spontaneously reset. I've checked all the wiring and ground and everything, and now I'm pretty sure that's what's causing it. Funny thing, is that the machine has two identical drill motors, and only when one of them in particular is on the problems show up. I'm guessing it has to do with the brushes' commutation, but it's just a guess.

The machine in question works using 110 VAC and 220 VAC. So it has two live lines, and a neutral one, plus ground. I've tried feeding the drills from a separate live wire to no avail. That is, if all the 110 VAC electronics is being fed by L1 and N, and the drills by L2 and N, the problem remains.

I have little experience dealing with this sort of thing. Last year I built an H-bridge driver for a DC motor working with fully-rectified AC that suffered from a very similar problem, and it wasn't until I installed an EMI filter at the AC input (which is fully isolated from the control circuit) that things got fixed.

Question, will a similar strategy work for this? Or does it have to be solved as a trial-and-error thing?

If I connect one EMI filter between the power line and the motor of each drill, does this situation have any chance of getting better?

@MaxHeadRoom

 

f I connect one EMI filter between the power line and the motor of each drill, does this situation have any chance of getting better?

Yes, I would try the filter and see if it works.
If not, you might try cutting the cords and moving the filter as close to the drill motor as possible.
It could be radiating from the cord.

 

... moving the filter as close to the drill motor as possible.

My thought exactly... I've been looking for a commercially available inline filter that could be plugged between the drill motor's chord plug and the ac contact feeding it. But they don't seem to exist.

 

If I connect one EMI filter between the power line and the motor of each drill, does this situation have any chance of getting better?
@MaxHeadRoom

I would say there is a good chance of curing it, one decent manufacturer of R/C/L line filters is Corcom.
What is the nature of the controller/MCU?
You also could use a filter on this.
Max.

 

I would say there is a good chance of curing it, one decent manufacturer of R/C/L line filters is Corcom.
What is the nature of the controller/MCU?
You also could use a filter on this.
Max.

The MCU is a board that I designed myself, and that I've been successfully using on other machines with no problem. It's being fed by a regulated 12 VDC wall wart that has an inline ferrite on its output cable. I've used those wall warts before and they're decently clean.

 

You may want to also look at grounding of the relative machines, including adopting a star point ground system
There used to be a very good PDF on it on the Siemens site until they revamped the site, I did manage to download it before they did but it is too large to post.
It also covers shielding and equi-potential bonding to prevent ground loops.
If your MCU has any contact to the outside world it might pay to bond it to earth ground.
Low voltage electronics systems are very vulnerable out in the industrial world.
Even your desk top PC has its P.S. L.V. earth grounded.
Max.

 

including adopting a star point ground system

Already implemented

equi-potential bonding

Dunno about that... gonna have to look it up

If your MCU has any contact to the outside world it might pay to bond it to earth ground.

Haven't done that, but it's definitely worth a try.

 

Can you post that pdf....Max?

 

OK Here it is.
Max.

 

Thank you kindly.

 

Already implemented


Dunno about that... gonna have to look it up


Haven't done that, but it's definitely worth a try.

PICs have an MCLR pin (active low - "master clear" (reset) ). It must be pulled high. It can also be disabled in software so the pin can be used as GPIO. Do you have a floating MCLR (or equivalent?) causing troubles? It has caused lots of headaches for noobies to PIC.

Even a bad solder joint or faulty tactile switch on the MCLR can cause headaches.

 

Another little 'nugget' from the EPRI.
Max.

 

PICs have an MCLR pin (active low - "master clear" (reset) ). It must be pulled high. It can also be disabled in software so the pin can be used as GPIO. Do you have a floating MCLR (or equivalent?) causing troubles? It has caused lots of headaches for noobies to PIC.

Even a bad solder joint or faulty tactile switch on the MCLR can cause headaches.

Thanks Gopher, I'm a noob when it comes to analog electronics. But I do have significant experience with digital circuits, so that detail was dealt with from the beginning.

Still, it's always wise to triple-check everything before venturing into other possibilities.

Thanks again.

 

If your MCU has any contact to the outside world it might pay to bond it to earth ground.

Yesterday I connected the board's ground to the machine's central ground node as you suggested, and it seems that I've hit paydirt... It's been working just fine for a day now, without any incidents whatsoever... then again, it was working fine too for months before this problem suddenly popped up. So maybe it's been definitely fixed, or not ... we're just gonna have to wait and see.

Why is that? Why was the machine working fine for so long, and then all of a sudden it decided to go testy on me? Was it a latent problem waiting for the right conditions to show up? Are all control circuits in a machine supposed to share ground with the rest of the components?

I'm going to give a thorough read to the two documents you've just posted... see if I can get a clearer understanding of what just happened.

 

This is where equi-potential bonding comes in, the idea is to prevent ground loops which is essentially is if there is a potential difference between one grounded point of a machine and another, and to eliminate it.
There is basically two methods of choice out there, to isolate all distinct/individual parts of the machine power, the other to bond all or most commons to earth ground.
I have always followed the latter.
'Noise' can also be transmitted from one part to another by either inductive or capacitive means, so in this case, isolation may not help.
I'm some time amused by the suppliers of intermediate equipment to the DIY CNC community, their mantra on the whole is total isolation, so you have a PC which has a grounded P.S. and is fed to one of their BOB's (Break out Boards) and there a signal is isolated via a SSR for e.g. and they use it to turn on a VFD.
But the VFD power is referenced to earth ground via the grounded neutral and so is the PC, so essentially, no isolation occurs..
Hope your fix hangs in, otherwise it is go to plan B!
Max.

 

Hope your fix hangs in, otherwise it is go to plan B!

I hope so too ... I wasn't looking forward to assembling a couple of in-line EMI filters and have them sent to my client just to see if they worked. Fortunately, I was able to work this problem remotely with one of their technicians. You see, the machine in question is in Central America, and I was trying to spare my costumer the expense of having me flown down there just to solve this problem. I wouldn't have minded charging him for this service after a couple of years had passed, but in this case the machine has been operational for only a few months... an expense like that one wouldn't have looked good on me, especially since they're (apparently) planning on acquiring a couple more machines this year.

Many thanks to you, and Gopher and Crutschow ... you've helped me out with a very serious issue here ... I only hope I can somehow return the favor one of these days... or at least pay it forward in the near future. Cheers!