Varistor Substitute for a SG?
GammaRay, Tue Sept 21 2021, 08:31PMI 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.
Re: Varistor Substitute for a SG?
MRMILSTAR, Sat Sept 25 2021, 03:07AM
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.
MRMILSTAR, Sat Sept 25 2021, 03:07AM
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.
Re: Varistor Substitute for a SG?
E.TexasTesla, Wed Nov 03 2021, 01:47PM
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.
E.TexasTesla, Wed Nov 03 2021, 01:47PM
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.
Print this page