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Registered Member #5323
Joined: Fri Jun 15 2012, 02:14PM
Location:
Posts: 104
I understand that Varistors are often used as HV protection for circuits. However, can a Varistor reliably substitute for a spark gap? Or... would the Varistor degrade rapidly and soon fail if used as a spark gap? Just curious.
Registered Member #62119
Joined: Sun Feb 04 2018, 04:59AM
Location: Cedar Rapids, Iowa
Posts: 136
There are many things wrong with this idea.
1. Varistors are sacrificial in nature. Some of the material is consumed during each over-voltage event. Eventually the varistor fails. Some fail as a short circuit, some fail as an open circuit. At hundreds of triggers per second, a varistor would quickly fail.
2. They will not handle the current repeatedly. SGTCs typically have 10s and sometimes 100s of amps of current in the primary circuit when the spark gap fires.
3. The resistance of a varistor is relatively high even when triggered. A varistor would quickly overheat and fail when being triggered hundreds of time per second.
4. A SGTC requires that the gap be fired at the peak, or shortly after, of the charging sine wave for maximum charge on the capacitor. The firing voltage must be consistently at the same voltage level. Varistors do not trigger at a predictable consistent voltage.
Registered Member #4362
Joined: Sat Jan 21 2012, 03:44AM
Location: Texas
Posts: 98
Hello, What circuit would you need a substitute for ? As mentioned the MOV is consumable. They work great for "Terry filter" circuits but are only needed for out of tune coils. I uses these across MOSFETS 1.5ke220 for protection.
Edit : I just noticed you mentioned SG coil. Sorry.
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Varistor Substitute for a SG?
