Rednroll - thank you so much for posting!
Back-EMF with motors I am more familiar with and is a serious concern, After further thought, the 12V relay coil winding is more substantial than at first glance (duh) so I realize now it could store enough energy to cause an issue. So the diode/fuse I mentioned will protect the system from the relay:
- diode, "inverse parallel" connected to the coil pins to absorb the reverse voltage energy on the relay coil when power is pulse/switched off. (NOTE: diode inverse parallel - i.e. the negative/cathode/line side of the diode is connected to the positive 12V supply side of relay coil terminal and the positive/anode side of the diode is connected to the ground side of the relay coil.)
- fuse, series connected to coil positive supply pin (in case of any bizarre relay short scenario).
Some are getting chattering which I assume is partly caused by using a relay that needs very little voltage to activate combined with having a fast drop out. My Radio Shack relays don't have any problem.
Aside from building stuff, in a previous life so long ago I've forgotten everything - I rep'd Aromat (Panasonic) relays and they have a guide at: http://pewa.panasonic.com/pcsd/tech_info/pdf/rti.pdf
Given the inverse parallel diode method increases relay release time - isn't that going to fix the PWM issue?
The way of handling the PWM chattering is described here:
The diode is in series with the relay coil positive line and the capacitor goes across the coil pins in parallel. The inline diode is suppose to stop the back EMF, however, I read induction can still cause voltage spikes in adjacent wires.
DSY's diagram says "220pf electrolytic capacitor" but it is 220uf (microfarad not picofarad). Others use 100uf instead. I am wondering - how high is the voltage/current on the back EMF and is it degrading the electrolytic over time - I've seen photographs of spikes blowing holes in aluminum-paper electrolytics. I am not a fan of putting something that will eventually fail shorted there - need to at least add a fuse to that line or risk wiring damage. Electrolytics fail short and catastrophically if voltage is reversed (good firecrackers - I've seen many a PC board with a hole blow clear through it from tantalum electrolytics - also ceramic bypass capacitor failure does it)
I think there is something wrong in your O'Scope setup.
Very good - you caught my laziness with the scope interface software! You have the eye for detail, natural curiousness, combined with the ability to explain to lay people - not as common abilities as you may think.
The probe that comes with the scope is a manually switched 1X-10x-ref probe I had in 10x. The software also can autoswitch the probe but I had that tuned off. I should of photochopped off the text since I was just using it for the waveforms and didn't change the headings for my manual messing around - in "Auto" mode it updates everything for you - my bad, just takes a second to fix.
"connected to the CAN Bus" - now you'll hate me. I do research mostly in IP litigation, electronics patents. When an engineer speaks - you spent a lot of time and money learning the language of precision. When legal speaks - precision is a myth.
So, courts have ruled in electronic patent claims "connected to" means "directly or indirectly". Doesn't matter if it is electrically isolated through 20 semiconductor components. Engineers that make it into patent litigation as an expert witness get paid $300/hr to $800/hour - a lot of money but few can do it - requires rewiring the brain into mush or another way of looking at it, an exceptional intelligence to learn the fine art of throwing pearls to swine. In your second post you say "directly connected" which works for most people (including me) but of course there is another patent claim legal argument about what that means. In my world, the spark plug is connected to the tires and even "directly connected" is still open to legal argument. Sad.
This had a side effect of introducing a delay when turning my highbeams off, so I tested with progressively smaller capacitors until I found one with an almost imperceptible delay.
What value did you settle on?