That's tricky. Some user might slam a capacitive load or a motor a lot of times.
Here's a Riedon ceramic DPAK 50 ohm resistor. It could absorb at least
50j, 100 with two in parallel. That would work. They will need a mosfet to switch them on when the 48v supply gets over-driven to 58 maybe.
Ok, thanks. Looks like it proves your idea. (-: Ed
Unh.
Cute, even in pairs. If two, would stepped response (two MOSFETs) be worthwhile?
For the record, VFD (Variable Frequency Drive) for three-phase motors also have the backdrive problem when stopping. The 2 HP motor and lathe chuck being driven have considerable rotational inertia, and can store much energy. The objective is to stop in maybe five seconds (too fast stresses the motor windings). I have a 100 watt power resistor in a ventilated housing above the VFD, which is on the wall behind the lathe being powered. It is possible to get that resistor to a red glow.
Joe Gwinn
I think there is damage at higher pulse energies, as few as a single pulse.
Just like a car in hill country. Power up a slope and fry the brakes coming down.
We have runaway truck lanes here, a side road filled with gravel. A big loaded semi doesn't have much engine braking and then smokes the brakes.
We have one a few miles away. It is at the bottom of a series of zigzag bends and on the *inside* of the last bend. Any runaway lorry would have to negotiate the bends in order to to reach it and then turn through two sharp 90-degree bends to enter it.
It seems to be mostly used by picnickers who have reasoned that the chance of any runaway reaching them is minimal.
From the crest near Truckee to Auburn CA, there's a downslope of about
6200 feet over about 50 miles. Trucks tend to smoke their brakes going down the steeper parts of that. The runaway truck ramps are tangent sidings off the right side of the highway that still slope down but are filled with deep gravel, terminated by a big pile of dirt. Youtube has some great stop videos.A loaded semi must store a lot of joules.
Some power supplies have enough output capacitance to blow a fuse in a DVM on its current range, even if the power suppy is set to a low current limit. That's good to know.
I've ordered fuses for the two DMMs that my old HP6212A just blew up. I was testing some MOVs and it was set for 20 mA current limit and zapped a couple of 600 mA fuses.
The quick test is to short a supply and see how loud the spark is.
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