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Blowing diodes across forward reverse switch?

COMachinist

Active User
H-M Platinum Supporter
Joined
Sep 10, 2013
Messages
352
I am blowing the 1n4001 diode across the forward and reverse switch on my PM932m with the three wire set up.I was thinking of using a stronger diode. it only happens once in awhile but I go into the electrical box to change it. Any suggestions is appreciated. Yes I have good grounds to earth, whole shop surge protection at the pole. There has not been any storms, fairly nice weather in fact. Kind of puzzled. Thinking maybe a 1n4007 a little more meat in the junction.
CH
 

mksj

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Jun 12, 2014
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2,630
The 1n4001 diode is only rated to 50V, if you have any voltage spikes like a relay/contactor snapping open you see peaks of 200V. This will quickly kill a 1N4001. I would replace it with a 1N4007 which is rated to 1000V. I typically use 1N4007 or UF4007 or similar (800-1000V) in my builds across the relay contacts and for logic. Do not see any reason to have a higher amperage unless the diode will see the full current of say a power supply, I also use them to prevent damage to wiring/components if someone hooks up the power supply polarity backwards, it short circuits through a diode. When this occurs the diode needs to be rated higher then the power supply current.
 

Bi11Hudson

Artificer00
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Feb 13, 2017
Messages
637
Just a reminder, diodes are usually applied in reverse across any inductive load, especially relays, as they can produce several times their rated voltage when they drop out. In the 1N4000 series, the last digit indicates the rated voltage. With inductive loads, the higher the better. The 1N4007 suggested is the best choice for anything 480 or less. I will suggest you read http://www.hudsontelcom.com/uploads/ShopElex.pdf as I have some tales of large inductors. A lot to wade through to get to them though.

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markba633csi

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Registered
Joined
Apr 30, 2015
Messages
4,684
I'm guessing it won't run without the diode, although I don't know what the circuit looks like. But yes you should use a higher voltage part like Mark says for anything powered off the line
M
 
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