Relay/Diode/Back EMF with a new twist

speakerguy79 said:

1.5KE18CA-E3/54 Vishay Semiconductors TVS Diodes - Transient Voltage Suppressors

That will handle 500W for a 10ms pulse. Should be all that you need. It is bidirectional, so you don't even need the normal diode, just this guy across the relay.

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speakerguy79 said:

Here's a good example. A little 3W standard zener in a surface mount package:

https://www.electro-tech-online.com/custompdfs/2009/09/1SMB5913BT3-DPDF-1.pdf

Look at Page 4, Figure 2. It will handle 50W for a 10ms rectangular pulse if the starting temp was 25 degrees C. That's the sort of info you need to pick a good diode. You also need to have an idea of how long the pulse is going to last from the relay spike, kind of hard to know without a scope though. I would think 10ms would be a totally fine guess.

Also, I would personally use a TVS zener. Hardly any price difference when you're buying single unit quantities, and better at pulse handling (and they will ALWAYS have a chart for pulse handling in the data sheet).

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