Printable Version of Topic

Posted by: bbrock Nov 28 2017, 10:17 AM

While replacing the diodes on my Hobart Handler MIG last week, one of the leads popped off of one of the little capacitors attached to diodes for protection. Googling, I found advice saying the exact value of those capacitors is not important and to just get "something close." But no indication of what close enough would be. The factory part is 0.01uF, 100v. Digging through my spare components, I found, and installed a 0.3uF, 100v capacitor (I do have 0.01 uF but only 25v). After the repair, the welder is working like new.

But I'm wondering if that substitute capacitor is sufficiently protecting the diode. Getting the correct capacitor is easy enough, but digging into the welder to replace it is not. I'd like to call the repair done, but don't want to burn up my new diode. Thoughts?

Posted by: Spoke Nov 28 2017, 11:17 AM

Not sure a 0.3 is close to a 0.01 since it is 30x larger.

You can order one of the correct value from Digikey.

Posted by: bbrock Nov 28 2017, 11:29 AM

Thanks, That's kind of what I suspected. Although I understand the basics of how capacitors work, it is a bit of a mystery to me how they work to protect circuits in this type of application. So I wasn't sure if 30X would be significant. Do these capacitors smooth the current running through the diode? Better safe than sorry I guess. I'll check the local Radio Shack tomorrow, and if they don't have it, I'll order from Digikey or Jameco.

Posted by: Spoke Nov 28 2017, 12:15 PM

Capacitors are often used in circuits as "snubbers". That is it snubs or knocks down transient voltages across components like diodes. A real high transient voltage on a diode can destroy it in microseconds.

Posted by: bbrock Nov 28 2017, 12:28 PM

Ah! Makes sense. Thanks! Gotta protect my $24 apiece diodes!!!!