Just installed the diodes in parallel with the resistors at the gates, and the fets are no longer warming up. But most importantly, the MCU is not resetting itself either, even with a duty cycle of up to 50% (I don't intend to use more than that)
I'll be installing those diodes on the high-side fets only, since they're the only ones being switched for PWM.

This tells me an important thing: the EMI responsible for MCU reset is produced only during switch-on. That is, the inrush current to the motor is the one affecting the circuit, and not its disconnection.

Might be worth some scoping around on the 5 volts to the micro. I would be real curious looking at the output of the regulator vs at the board.

 

I'm already using a couple of TVS-SA180CA (180 volt) at the PCB, one for power input, and the other one right where the motor's wires are connected. The snubber currrently installed at the motor consists of three 1k@1w resistors in parallel, connected in series to a 1uf@350 cap.
Today I'll be receiving a few 330Ω@3W resistors, which I'll use to substitute the 1k resistors.

The motor is connected through twisted, but unshielded #18 wire about 6 meters away from the PCB.

 

Might be worth some scoping around on the 5 volts to the micro. I would be real curious looking at the output of the regulator vs at the board.

I'll do that as soon as the isolators arrive and are mounted and tested. I don't think it'd be wise to connect my scope's ground clips to the PCB until then.

 

I'll do that as soon as the isolators arrive and are mounted and tested. I don't think it'd be wise to connect my scope's ground clips to the PCB until then.

Moving the TVS to the connection box might help. The scope will help. Then you can experiment and see results besides go no go.

 

Update:

I removed the RC and diode filter, and replaced it with a TVS. And the MCU is almost unaffected. That is, at 50% duty cycle it rarely resets itself, but it still happens. So what I'm going to do now is use both components. That is, the RC-diode filter (an arrangement of double 2 uF@350V electrolytic and 330 ohms@3W in series and a diode, as shown in post #170, plus the TVS across it.

As soon as I get the components, I'll be replacing this kludgy thing with something simpler:

​

 

I did a few more tests, Ron... and your intuition proved to be right. The placement and orientation of that ribbon cable made a difference as to if the MCU would reset itself or not. Fortunately, that cable will be real short in the final working version, and the AC and motor wires will be pointing directly outwards from the PCB. That will hopefully eliminate all possibility of any serious EMI.

 

Hello to everybody,

This thread really motivated me to start designing a simple 90VDC motor driver, since I have some of these motors lying around my bench. For one reason or another, I was delaying the designing and building of my own 90VDC driver, but your success and the wise comments and theory explained by the members pointed me in the right direction.

However, my design only requires forward direction of the motor (never reversal, so I do not really need a H-bridge), and to simplify I do not need variable speed also (I will add all these features later after reading and understanding well all the theory involved).

So I was thinking about using the follow scheme:

a) 120VAC mains to full-wave bridge rectifier (that would be the motor power supply).
b) The positive output of the bridge rectifier connected to one leg of the motor.
c) The remaining leg of the motor connected to the drain of a N-channel power mosfet.
d) The source of this mosfet to the negative output of the bridge rectifier.
e) To proper firing of the gate of the mosfet, I prefer to use a real gate driver (not discrete components), but to my understanding I can use the IR2XXX parts that only concern with the low-side, and I recall (maybe I am wrong), that the low-side do not even require some kind of switching since there is no bootstrap involved. Just feeding a static signal would be sufficient.
f) So that is all. I could use a simple microcontroller to start and stop the motor via an optocoupled signal to the IR2XXX.

What do you think about these approach? Am I missing something? (of course I will add snubber, varistors, reversal fast diodes, etc.)

Thank you in advance for any advise.

 

Hello to everybody,

This thread really motivated me to start designing a simple 90VDC motor driver, since I have some of these motors lying around my bench. For one reason or another, I was delaying the designing and building of my own 90VDC driver, but your success and the wise comments and theory explained by the members pointed me in the right direction.

However, my design only requires forward direction of the motor (never reversal, so I do not really need a H-bridge), and to simplify I do not need variable speed also (I will add all these features later after reading and understanding well all the theory involved).

So I was thinking about using the follow scheme:

a) 120VAC mains to full-wave bridge rectifier (that would be the motor power supply).
b) The positive output of the bridge rectifier connected to one leg of the motor.
c) The remaining leg of the motor connected to the drain of a N-channel power mosfet.
d) The source of this mosfet to the negative output of the bridge rectifier.
e) To proper firing of the gate of the mosfet, I prefer to use a real gate driver (not discrete components), but to my understanding I can use the IR2XXX parts that only concern with the low-side, and I recall (maybe I am wrong), that the low-side do not even require some kind of switching since there is no bootstrap involved. Just feeding a static signal would be sufficient.
f) So that is all. I could use a simple microcontroller to start and stop the motor via an optocoupled signal to the IR2XXX.

What do you think about these approach? Am I missing something? (of course I will add snubber, varistors, reversal fast diodes, etc.)

Thank you in advance for any advise.

Hello Anselmo.

A couple of observations:

• The terms of service (TOS) of this site prohibits the discussion and design of any circuit connected directly to mains. You will have to use an isolation transformer.
• The circuit that you need to accomplish what you want is far simpler than the one being discussed here. You don't even need a mosfet for that. You could use a triac (which is far less delicate than a mosfet) with its proper driver, an opto-isolator, and a full wave bridge rectifier plus a few resistors and caps here and there, and you'd be all set.

Since what you want is different than what's being discussed here, I suggest you open a new thread. Once that is done, just tag me and I'll be more than happy to assist you.

 

CM, just an idle thought on your predicament. What do they use in the so called "motor shield" circuits that are used with micro controllers? They don't seem to have the reset problems you are having, says the guy who avoids micros like the plague. Or look at how they do it on a treadmill speed control, since many of them are working at the voltage your motors are.

Another thought, have you tried dropping the gate resistor value since going to the two input driver IC? I've never seen anyone using that high of a value in any schematics. I know you needed it to get around the original drivers problem, but it could be causing you problems now slowing down the turn on speed of the mosfet. Just thinking out loud.

Edit. I just remembered this site, a lot of good stuff on motor control and related things.
http://www.4qdtec.com/

 

CM, just an idle thought on your predicament. What do they use in the so called "motor shield" circuits that are used with micro controllers? They don't seem to have the reset problems you are having, says the guy who avoids micros like the plague. Or look at how they do it on a treadmill speed control, since many of them are working at the voltage your motors are.
.

The main reason I use isolation is that in many cases the drive is used to interface with other equipment, I know T.M. and KB controllers use non isolated supply, by virtue of a simple zener dropped supply for logic.
But in the case of T.M., the board is part of a dedicated system, and KB do offer a isolated add-on board if it is required.
Max.

 

Hello Anselmo.

A couple of observations:

• The terms of service (TOS) of this site prohibits the discussion and design of any circuit connected directly to mains. You will have to use an isolation transformer.
• The circuit that you need to accomplish what you want is far simpler than the one being discussed here. You don't even need a mosfet for that. You could use a triac (which is far less delicate than a mosfet) with its proper driver, an opto-isolator, and a full wave bridge rectifier plus a few resistors and caps here and there, and you'd be all set.

Since what you want is different than what's being discussed here, I suggest you open a new thread. Once that is done, just tag me and I'll be more than happy to assist you.

Oh, I did know that!. I am sorry.

Yes, I will open a new thread.

I understand the motivations regarding safety issues of the terms of service (TOS).

However, I know that none of the manufacturers of 90VDC drives in the market include any kind of isolation. The inclusion of that would incrementet in a prohibitive manner their pricing (I had opened and repairing dozens -if not hundreds- of 90VDC drives in the last years, from the small brands to the full featured brands).

And yes, of course, it would be simpler with a TRIAC. I was not considering it because I was thinking about rectifying first and then feeding to the switching device (a TRIAC will not shut off itself with DC). But as you explained it is like "switching device first, then rectifiying at last". I can get even power controlling in your approach, since I could use a triac dimmer and then rectifying the output with full-bridge.

Thank you.

Regards.





Just to

 

Oh, and CM, just to add about last comments of shortbus and MaxHeadRoom, and your issues about resseting the microcontroller.

For the many, many commercial 90VDC units that I had chance to repair, the designers considerations about isolating the power section (including the driving to the mosfets) to the control electronics is minimal (or none an all). On units with some optoisolation, the main reason is for interfacing to other units as Max comments.

Your desing seems identical like many of the commercial hundreds-of-dollars of brand units. (even better!). However, I just want to point out that your PCB it could be the cause of all of your problems, mainly microcontroller resetting. I think that you can even compress more tighted-space your layout (yes! power section closer to microcontroller!) but with a double-sided PCB layout with careful considerations about the tracks of the mosfet drivers section, your problems would disappear.

Remember that commercial units have high-speed micro (even low-end DSP or FPGA) located at only 1 or 2 inches of the power mosfets (without shielding!) and they work without resetting. And most of times with shared ground from logic to power.

Regards.

 

The HCPL-9030 digital isolators have arrived... and I've installed and tested them already... and they're working to perfection! They are in no way interfering with the PWM duty cycle that I programmed into the MCU, unlike the optos were doing.

Now my circuit has a perfectly isolated ground and everything's complete.

​

This circuit is more than adequate for the kind of mechanism that I intend to actuate with that motor. That mechanism in question has an overload slip clutch that that protects the motor, mechanically disengaging it if it goes beyond certain torque.

But what I intend to do now, is add one of those amploc sensor babies and a few more components to detect an electrical overload when it happens, and have the MCU stop all motion and raise an alarm. And since I already have experience with said sensor, and with the necessary circuitry to produce that signal, it should be a piece of cake.

So stay tuned, because I intend to continue this thread and report my progress adding that feature. In the meantime, many, many thanks to all of you who've helped me along with this. When I'm done, I intend to post everything in the completed projects collection. After all the help I got, the least I can do is give something back to the community. Cheers!

 

This is amazing! ... ever since I've included the digital isolators, the MCU has not reset itself a single time! ... zero, zip, zilch, NADA!

I couldn't be more pleased with the results... and to think that I was so discouraged only a couple of days ago...

 

But what I intend to do now, is add one of those amploc sensor babies

Glad to see it work!. Do those amploc's work to measure any voltage? The link didn't really say, Is you 90V going to be a problem for them?

 

But what I intend to do now, is add one of those amploc sensor babies

Do they have a N.A. distributor?
Max.

 

Glad to see it work!. Do those amploc's work to measure any voltage? The link didn't really say, Is you 90V going to be a problem for them?

They're not designed to measure voltage, but just current. If you were to measure steady DC using them is pretty straight forward. But if the current isn't steady, or you use them for AC, then you need to convert their output to an RMS value. You can do that with an AD536AJQ. I have those installed on an automated drilling machine. The drilling process stops for a moment, and slightly retracts the tool when the drill motor goes past consuming a predetermined amount of current (which can be adjusted with a trimpot), and then it resumes operation.

Do they have a N.A. distributor?
Max.

Their webpage doesn't mention where they're located. But it shows a U.S.-based phone number.

 

Looks like the factory is Here:
Address: 615 La Buena Tierra, Santa Barbara, CA 93111, USA
Phone: +1 805-259-7659
Max.

 

They're not designed to measure voltage, but just current.

Yeah I understood that, just didn't know if putting a high voltage wire through the hole would make a difference. They're like a hall effect current transformer correct?

 

Yeah I understood that, just didn't know if putting a high voltage wire through the hole would make a difference. They're like a hall effect current transformer correct?

I think so. I've used them with 120/220 AC, and also 24VDC. I have several of them with me, and are extremely simple to use.