Braking a motor not on a vfd - Page 2 - Electrician Talk - Professional Electrical Contractors Forum
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Unread 11-29-2019, 01:43 PM   #21
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My old man found these, and the pricing is cheaper than a vfd/brake setup. Anyone have experience with these?

460 Delta, that is a great idea. I'm gonna remember that for a crushing plant we do work for.

Paul, like I said, I haven't setup braking through a VFD before other than setting a ramp down speed (which I know isn't the same). I did some quick googling and saw automation direct had some braking modules tied for specific VFDs, so that's what I was going by. I don't claim to be an expert, which is why I reached out here for a situation I haven't run in to yet.
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Unread 12-02-2019, 03:02 PM   #22
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Ambitech are DC injection brakes, they've been around a long time and are of decent quality, albeit a bit light on options that can come in handy. For a long time in the 80s and 90s they had the only UL listed DCIB unit on the market, so they sold a lot of them. I don't know where they stand now however, I haven't used one in a long long time.

As I had said in the other referenced thread, the big problem with DCIB in general is that of motor thermal stress. Every motor has a limted number of starts-per-hour it can handle, and when you add DCIB each start implies a stop where the thermal effects are the same as starting, so your starts-per-hour capability is not only cut in half, but the "minimum time between starts" is doubled. On a 10HP motor, the basic starts-per-hour is likely somewhere around 20 with evenly spaced rest times between them, so that's running every 90 seconds, with 90 second rest times. So if you add DCIB, that's 10 starts, with 3 minute rest times minimum. If your auger operators will not conform to those limits, you will be smoking motors rapidly.

You can get stand-alone Dynamic Braking modules (i.e. braking resistor), but they are expensive and as previously mentioned, buying a simple 10HP VFD with DB will likely cost you less.

You can't just hook up resistors to a contactor and expect that yo stop a standard AC induction motor. Whne the running contactor is opened, you are removing power from the windings. No power = no flux = no ability to generate energy to go into the resistor = no braking.
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Last edited by JRaef; 12-02-2019 at 03:04 PM.
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