Aha, so it is about protecting the reed switch itself and presumably increasing it's lifespan.
Reliability of LGB Track Contacts 17100 or Reed Switches and Best Practice for Use and Installation
- Thread starter fairflixt
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Here's a link to a discussion on this forum on the varistor from a couple years ago that I just came across. Some familiar faces in that thread. As for finding a specific part - it looks like if you set the max voltage to 25V, then the typical varistor on Digi-Key seems to have a peak current of 100A for one surge and 50A for two surges which would roughly be in line with the description in the image I posted earlier. Lots of options in that range.
Greg Elmassian
Guest
I might take exception to the use of schottky diodes... I think the faster recovery time is better, agreed, but the lower resistance allows more current to flow, not better, worse.
This is splitting hairs though, since the addition of a varistor is the key to helping handle high voltage/current spikes that are trying to kill the reed switch.
Greg
This is splitting hairs though, since the addition of a varistor is the key to helping handle high voltage/current spikes that are trying to kill the reed switch.
Greg