Protect DC to DC solid state relay from inductive kick back - Page 1
Forum section: electronics / projects

author: ruko
author_rank: Newbie
timestamp: October 09, 2024, 05:41:50 pm
content: HelloI'm trying to power an automobile coil using a 12 volt DC supply and a DC to DC SSR with a square wave pulse generator to turn it on and off. So far two 25 amp SSRs have been toasted because, I think, of an apparently very high kick back. Apparently these SSRs use TRIACs or MOSFETs or just plain transistors. It's hard to tell. Anyone have an idea how to protect an SSR when you're not sure what drives it?Thanks,R

author: Zero999
author_rank: Super Contributor
timestamp: October 09, 2024, 06:38:21 pm
content: You need an SSR with a MOSFET output. A TRIAC output will just latch on and smoke.What's the voltage rating of the SSR?Presumably you can't add a freewheeling diode because you need the kick-back for the spark.Add a zener diode, with a value the same as the SSR's voltage rating in reverse parallel with the SSR.

author: Manul
author_rank: Super Contributor
timestamp: October 09, 2024, 06:45:04 pm
content: Which SSR, part number? Generally, many SSRs are simply too slow for such job. They might cook just because of that, not from kickback. Normally you would use single IGBT or MOSFET. What is your pulse length?

author: inse
author_rank: Super Contributor
timestamp: October 10, 2024, 05:33:12 am
content: Why would you need a SSR anyway?In an automotive 12V surrounding there’s usually no need for galvanic isolation.If you can’t add freewheeling, take an ignition rated IGBT, it will handle the kickback at ease and is extremely simple to interface.I did tests on 100s of those components…

author: jonpaul
author_rank: Super Contributor
timestamp: October 10, 2024, 05:48:52 am
content: SSR + inductive load....Use special type or it cant workj

author: CaptDon
author_rank: Super Contributor
timestamp: October 10, 2024, 01:25:48 pm
content: Why not just use an automotive ignition module?? The GM H.E.I. modules and coils can be pulled from any junk yard GM distributor. Or buy a used MSD ignition module designed for use with the standard Kettering ignition coil. Some of these systems are hot enough to send your heart into fibrillation!! The spark energy is hot enough to erode craters into the body electrode (the one you bend to change the gap).

author: Seekonk
author_rank: Super Contributor
timestamp: October 10, 2024, 01:34:21 pm
content: I've been testing a number of DC to DC SSR and it is a real grab bag of shit. Some take well over 8ms to turn off and the fastest turn in will be about 1.2ms. That isn't fast enough to run a hit and miss engine. Another interesting thing is these can not be driven with an analog signal. If control voltage slowly drops below minimum turn on the fast turn off electronics does not work. Gate drive can go below 1.5V causing internal FET to overheat from low drive.

author: Randy222
author_rank: Frequent Contributor
timestamp: October 10, 2024, 03:50:29 pm
content: 1) avalanche rated is spec to look at on the silicon2) you can quench the induced voltage with a 1-2-5 watt zener to gnd3) because the whole thing is a Z, zener with a proper snubber to stop the ringing when switch goes offYou can put a diode backwards across the inductive load, but this freewheels energy through the load, which may cause the load to "operate" longer than desired. Not sure what you load it, the small time in freewheel probably does not matter for you.

author: Seekonk
author_rank: Super Contributor
timestamp: October 10, 2024, 05:02:33 pm
content: Just a couple images of response times. The fuzzy drive is transformer coupled the other is opto