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Blow oscilloscope measuring coil Back EMF

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T3sl4co1l:

--- Quote from: ptluis on August 24, 2023, 10:34:05 pm ---What I'm trying to do is to design a portable module to protect the output of power supplies when I connect inductive loads like relays, contactors, electric egr solenoid, etc for testing purposes. When using digital power supplies sometimes the flyback diode isn't enough to stop the PS or the display from shutdown. No problems with analog PS with analog displays. The flyback approach isn't enough and that's one of the reasons I want to see how high back EMF goes. But I won't do it anymore I'm going to save the scope, I already see what's going on  :) Like you write "Simply don't let that voltage appear" and  that's what I'm going to do.  :-+

--- End quote ---

That sounds like a wholly different problem, and one that you cannot in general assist: highly susceptible (presumbly, cheap) power supplies.

Tim

Fungus:

--- Quote from: ptluis on August 24, 2023, 10:34:05 pm ---What I'm trying to do is to design a portable module to protect the output of power supplies when I connect inductive loads like relays, contactors, electric egr solenoid, etc for testing purposes.

--- End quote ---

Power supplies will have a big capacitor across their output which will absorb EMF spikes, no problem.

ptluis:

--- Quote from: Fungus on August 25, 2023, 06:37:46 am ---
--- Quote from: ptluis on August 24, 2023, 10:34:05 pm ---What I'm trying to do is to design a portable module to protect the output of power supplies when I connect inductive loads like relays, contactors, electric egr solenoid, etc for testing purposes.

--- End quote ---

Power supplies will have a big capacitor across their output which will absorb EMF spikes, no problem.

--- End quote ---

It should, but the point is digital ps or displays shutdown randomly, and i want to prevent that. it doesn't matter how cheap or expensive the power supply is, I used to own a Rigol Dp832 and it happened sometimes, i sold it, and it was to heavy to carry arround. I normally test around 30-40 solenoids per day. I'm using an homemade ps with transformer and an old L200 regulator, analog voltmeter/ammeter. no problems. It only happens with digital ps supplies/displays.

joeqsmith:

--- Quote from: Fungus on August 25, 2023, 06:37:46 am ---
--- Quote from: ptluis on August 24, 2023, 10:34:05 pm ---What I'm trying to do is to design a portable module to protect the output of power supplies when I connect inductive loads like relays, contactors, electric egr solenoid, etc for testing purposes.

--- End quote ---

Power supplies will have a big capacitor across their output which will absorb EMF spikes, no problem.

--- End quote ---

I built a homemade linear supply years ago which I damaged a few times from transients.    Later I added a MOV to the output. 

I've also damaged both of my vintage linear HP supplies from transients as well.   These both have a large TVS installed now across the connectors.   Cheap insurance.  The TO3 transistors cost a lot more.   

Grandchuck:
Joe, why a MOV in one and a TVS in the other?  Just curious.

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