8i20 brake resistor sizing

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3 years 7 months ago #267869 by M4MazakUser
Any idea how to size a brake resistor?

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3 years 7 months ago #267870 by M4MazakUser
I'm right up at the 30a limit.

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3 years 7 months ago #267877 by blazini36
Brake resistor sizing has always alluded me. Not sure what has a 30a limit (the 8i20?), but you don't have to dump full current to the brake resistor, that depends on the mass you're trying to stop. If that's bad advice someone can chime in

I haven't used an 8i20 in like 2 years but be careful with the brake resistor settings. I can't recall exactly what got me in trouble but if the brake resistor output was activated like for a fast stop, there isĀ  case where the output can continue to dump current straight to the resistor. Twice I walked away from the mill after it shutdown to find my brake resistor completely melted

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3 years 7 months ago #267882 by PCW
Replied by PCW on topic 8i20 brake resistor sizing
150 Ohms would be fairly high (2.6 A braking current @360V)

15A current, (24 ohms would be more appropriate)

To prevent latchup you need to make sure that:

1. The brake-on voltage is higher than the brake-off voltage
2. The brake-off voltage is higher than the nominal open circuit voltage

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3 years 7 months ago #267907 by blazini36
Looking back at the thread I made about it, it looks like the brakeon/brakeoff need to have a a safety margin applied. When I set it up the stock settings looked fine @ 36000/34000 but the 8i20 read the bus voltage 10v higher than any of my DMMs. So it should have been more like 38000/37000.

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