fried VME modules

why not just get power supplies that don't suck?

How the hell does that happen???

Don't do that. Put a delay-on-break relay in line with the mains. It won't let power be re-applied for the timeout etc...

I should add the delay-on-break will not interfere with normal operation. E.g., if the power has been off for the timeout duration, as when the crate has been off normally, it will allow the power to come right up without delay.

Seems like it would be easier to just bolt on a "switch smartenerupper" to ensure power never gets cycled in ways that upset the power supplies.

Yeah, I'm an amateur hobbyist know-nothing, but I would think an OVP should be inside the supply, not plugged into the bus. If you need four

"Time" is likely a second-order manifestation. You likely want to watch some (or all) of the supplies and ensure they have discharged to some "appropriate" level before allowing power to be reapplied.

Note that how quickly the supplies discharge will likely be reflective of the actual load they are PRESENTLY seeing. So, the "time" could change if the loading on the backplane changed (e.g., if one or more modules were removed).

Using the current state of the supplies is more consistent with <whatever> is causing them to misbehave in this short-cycled application.

That's not my call.

Looks like someone bought some switching supplies and hacked into them to add a low current pushbutton power switch on the front panel. Badly.

If I fix them, maybe for free, I'll make some friends.

It would be a major project to remove all the crates from a bunch of sites and add all that stuff. A plugin clamp would be an easy field addition.

Looks like 10 or so surface-mount dpak fets would be nice. We have FDD86367 in stock. Each will conduct about 100 amps with 5.5v on the gate.

Nobody in SED seems to want to actually D.

Yeah, seems like a bigger effort with more unknowns than simply addressing the (apparent) "cause" of the problem.

Like beefing up the bumpers on your car because your brakes aren't good...

Hack into the low power push-botton switch.

There's a bunch of POR detectors with delays in the second range.

PT7M6315 2000ms MCP130T 700ms STM6524 4000-7500ms SR2LA 4000-7500ms

Fighting the overshoot with an active clamp shouldn't be as power-intensive as you're thinking. a simple to247 doing its zener clamping to 4VGS + a couple of diode drops should do it.

Do both. Belt and braces.

RL

yeah, this entire project sounds stupid. It sounds like the repair fees for the blown cards is pretty low though, so everyone should be happy.

Here are a bunch of SCR crowbar circuits:

A crowbar would shut down the system. I guess that's better than blowing up modules, but just working would be even better.

Pulling the crates and reworking them would be a big deal.

I'm laying out a board now, with ten beefy DPAK fets with a bit of resistance in the drains to share the dissipation.

Since nobody here wants to discuss the design of a gate driver, I did it myself.

What's there to discuss? I use an ARM micro to monitor the (4S to 6S) backup battery voltages and shunt cells to a heavy load via a MOSFET with a PC123. People probably think it's overkill anyway.

My electronics run from batteries, with the main charging it occasionally.

Not for nothing. if you had wanted to subcontract the job, you'd have had to specify it in more detail.

Specifying the FDD86387 at the part you want to drive was a start, but saying that you think you need ten of them doesn't characterise the current you think you need to clamp in much detail. It certainly doesn't specify the length of time you'll need to keep it clamped.

I can't find any info on this FET. Just because you have it doesn't mean it's the right chip for the job. You are essentially building a 5V shunt regulator, using 5.5V gate drive might not make much sense.

I would pick a N-FET with 2.5V gate drive. Since most micros are 3.3V output.

And you are not limited to just using 10 of them.