FP ok to stall?

[Kevin Sevcik]

Originally Posted by Joe Johnson

I love data. Nice.

From the above two posts we learn:

1. The breaker is good, but when you have good airflow (due to high RPM of the motor) it is sort of a marginal protection device.
2. 1/3 to 1/4 full stall torque looks to be about the upper limit of high duty cycle applications.

One final clarification. From Kevin: "You can't beat them for sheer power." This is not exactly correct. The CIMs do actually beat them for sheer power (300+ W peak power vs. 200- peak power), but the CIMs are much heavier and much larger (even after you include an extra gear stage to slow down the speedy FPs).

What I intended say is that the FP motors are easily the top motor in the KOPs based on both power per unit volume and power per unit weight measurements.

Regards,
Joe J.

Actually, if you start looking at attainable power, thing get slightly more competitive. The CIM hits max power at 67 amps, which is going to trip a breaker or fault a jag eventually. Granted that's something like 10 seconds for the breaker, but still. If you look at the power at 40 amps, you're down to 280 W. Meanwhile, the FP can pull full power at about 35 amps. The CIM still wins, but it's a bit more competitive of a race.

But yes, even factoring in a 4:1 gearbox to get down to similar speeds, the FP blows the CIM out of the water in power density.

Important discovery pertinent to this discussion:
Our Snap Action breakers are only guaranteed to trip at 135% of rated current. This means if you're protecting a FP with a 40 amp breaker, it may be happily pulling 54 amps indefinitely. Even at 200% overload, the trip time is between 1.5 and 3.9 seconds. And I have a feeling our nice air conditioned environments will trend us toward longer trip times. As such, it's likely much much wiser to use a 30 amp breaker on FPs instead of the usual 40 amp. With a 30 amp, your FP can only pull 45 amps for up to 3.9 seconds, which should do a much better job of keeping it safe.