Adding adjustable over current protection to large server SMPS units?

[Chris Wilson]

I use a few 52V at 50 odd Amp computer server power supplies made by HP for my LF amplifiers for amateur radio. it would be very useful to have at least one with some form of external, adjustable, fast acting over current protection. If it could work from say 5 Amps to 40 Amps that would be ideal. Is it viable and what would be the best way of achieving this without internally modding the SMPS? Thanks.

[Kalin]

Would an online fuse on the output be fast enough action for what you need?

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[max_torque]

52V at 50A is getting tricky to break, and you'd need to use semi-conductor switches to get any kind of sensible reaction time (<1ms)  A parallel array of charge pumped N-FETs will probably be required, with suitable current sensing and either analogue comparator based triggering or a small micro etc.

That's assuming you want a simple "when the current exceeds this value, turn off" type arrangement.  If you want a constant current control, then the task gets really hard, because the potential power dissipation in the 'switches' becomes large.

[Chris Wilson]

This is what I feared, it needs to be fast otherwise I might as well use a simple fuse. Any idea how many devices I would need to parallel to safely switch that sort of current and voltage? Thanks for all the replies.

[bingo600]

Maybe have a look @some of the large HP LABSUPPLY's  schematics , ie. the 60xx series.

I think they use a "Crowbar or SCR" to pull output down , if a condition is exceeded

/Bingo