Post by thread:Pic lock up with motor

Hi All, I have a little problem that my Pic that is switching on a motor via a relay is locking up :( The relay has a diode across it, and if I run it with no motor there is no problem. Only when the motor runs (12v windscreen washer motor) for over 2 - 3 seconds things lock up. Putting a diode across the motor seems to solve it, but have I only just solved the problem? What else should I look at doing? Thanks Regards Peter Mcalpine

At 10:07 AM 5/10/00 +1000, you wrote: >Hi All, >I have a little problem that my Pic that is switching on a motor >via a relay is locking up :( >The relay has a diode across it, and if I run it with no motor >there is no problem. Only when the motor runs (12v windscreen >washer motor) for over 2 - 3 seconds things lock up. > >Putting a diode across the motor seems to solve it, It's a DC motor with a commutator, so it produces a lot of electrical noise that gets coupled back through the relay. The diode will kill some of the noise, especially if you put it right at the motor. > but have I only just solved the problem? Determining the margin you have is not easy. It's possible it could act up with slightly higher voltage or with a worn commutator. Maybe you could improve the grounding and relay circuit so it works *without* the diode, then add the diode. Operating the relay with an optoisolator is one way to (potentially) improve things. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" spam_OUTspeffTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Hi Peter If this is a ongoing project you could try a few things separate power supply for motor. Filter to the pic and loads of caps low value 1n to 100n as well as 5u to 100u. A trick I have seen done was to have a large cap 4700u , I think it was this supplied the controller for the time it was activated.this was a few seconds. regards Art {Original Message removed}

> Hi All, > I have a little problem that my Pic that is switching on a motor > via a relay is locking up :( > The relay has a diode across it, and if I run it with no motor > there is no problem. Only when the motor runs (12v windscreen > washer motor) for over 2 - 3 seconds things lock up. > > Putting a diode across the motor seems to solve it, but have > I only just solved the problem? What else should I look at > doing? > > Thanks > Regards > Peter Mcalpine Impulsive noise from the motor is coupling to the PIC. Most likely the supply lines. You have to either separate or de-couple the power supplies. I take it you have a regulator driving the PIC and the motor is run off the input side to that regulator. Then a large electrolytic capacitor is a good start say 2200uF or more. AFAIR wiper motors are very thirsty motors, like 5 to 8 amps at 12 volts. Then there could be a problem the your common wire developing serious potential across it(since it is unlikely to be a superconductor), enough to upset the PIC if the PIC is sharing that wire back to the power source. So run one common wire for the motor and another common to the controller and as much as possible the same for the +12 volts. More intensive measures would be a diode before the 5 volt regulator and 2200uF on the input to the regulator. That stops the motor using the cap. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________

Right. Seen this one before. The motor represents a somewhat inductive load. The relay contacts, when they break, generate a hefty arc across the contacts. Of course, this has little to do with your flyback diode on the coil. The powerful EMI from the contacts couples through any means necessary and corrupts your PIC circuit. I had one unit that would generate upwards of 60VPP hash surges on the PIC side of the relay. The dead giveaway is when you put the scope ground on PIC ground, and the probe to the same ground point. (bear with me on this one). If you see hash on your scope, then it is EMI events. The scope chassis ground cannot keep up with the high frequency events, and you see a false image on the scope screen. The easiest solution is to put a 0.1uF capacitor across the contacts to supress the arc and subsequent EMI/EMC. If you want to get sophisticated, you can go further and try to design a snubber of some fashion that suits your load very closely. BOL Chris Eddy Peter McAlpine wrote: {Quote hidden}> Hi All, > I have a little problem that my Pic that is switching on a motor > via a relay is locking up :( > The relay has a diode across it, and if I run it with no motor > there is no problem. Only when the motor runs (12v windscreen > washer motor) for over 2 - 3 seconds things lock up. > > Putting a diode across the motor seems to solve it, but have > I only just solved the problem? What else should I look at > doing? > > Thanks > Regards > Peter Mcalpine

On Wed, 10 May 2000 10:07:15 +1000 Peter McAlpine <.....mcalpineKILLspam@spam@GME.NET.AU> writes: > Hi All, > I have a little problem that my Pic that is switching on a motor > via a relay is locking up :( > The relay has a diode across it, and if I run it with no motor > there is no problem. Only when the motor runs (12v windscreen > washer motor) for over 2 - 3 seconds things lock up. > > Putting a diode across the motor seems to solve it, but have > I only just solved the problem? What else should I look at > doing? > > For a DC inductive load, I think the diode across it is fine. I recently had a problem where a PIC was driving a FET driving a 12VDC relay (with a diode across the coil). All worked fine until the 120VAC vacuum pump the thing controls was connected. The arcing of the relay contacts crashed the PIC. A snubber (I used 10 ohms and 10 nF in series) across the contacts solved the problem. It's fun trying to get this stuff out of PIC circuits. I had another project a year ago where we were firing up a big xenon lamp right next to the PIC. Ended up putting a steel plate between the two to keep the PIC from crashing. Harold ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: dl.http://www.juno.com/get/tagj.