Thread: choosing a bleed resistor
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12-07-2018 #16
I watched those videos - the first one was quite entertaining. But did no-one spot the value of the capacitor he was using? 2600F! Farad, not microfarad. That's about 3,000,000 times bigger than the usual smoothing capacitors we are talking about! Yup, quite a lot of stored energy. Not entirely relevant, though. My machine is wired according to good practice with separate feeds to each stepper driver from the PSU. In effect, I have four separate permanently-connected bleed devices connected. A bleed resistor in this situation is a waste of energy, quite literally. Those capacitors will not hold charge after switch-off except in an extraordinarily unlikely combination of faults. The only time, in practice, that a bleed resistor might be useful is when testing off-load, and in this case you just need to be aware of the possible problems. The mains input connections are a much bigger danger if you poke around with a finger or have loose trailing wires.
And as several people have said, certainly up to about 625VA toroidal transformers, a 16A B-curve or 10A C-curve MCB is perfectly happy without any inrush limiter.
The engineer says, if you don't need it, don't put it in!
You are more likely to get problems with things like the RFI filter on the VFD. These can cause out-of-balance live-neutral currents that trip RCDs.
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