Dan Friedrichs
06-11-2020, 7:09 PM
Maybe a dumb question, but I'm unclear on why motors are rated for currents that would seem to generate well more power than their nameplate says they're good for.
For instance, I have a 2HP dust collector motor rated 220V, 12A. Even assuming 80% efficiency, that's 2.8HP, isn't it?
I have access to some fun tools: a clamp-on current meter and a battery-powered (floating) oscilloscope. For fun, I hooked them up to said motor while it was running (with no restriction on the dust collector input). I measured 238V, 8.6A, and 1454W (calculated by the oscilloscope as a point-by-point multiplication of V*I, then averaged, so it correctly reports real power accounting for power factor).
434806
1454W is 1.95HP, which seems right, since it's a 2HP dust collector and I removed the restrictions on the inlet (assuming the manufacturer built a more generous safety margin than 0.05HP in, originally...).
So why is that 8.6A, and not the 12A on the nameplate?
In another vein, I have a motor I thought was 5HP (no nameplate). But using the same measurement equipment, I find it draws 6.2HP under load (power washer), and I've used it like this for years. Would a 5HP motor survive driving a 6.2HP load for long periods?
For instance, I have a 2HP dust collector motor rated 220V, 12A. Even assuming 80% efficiency, that's 2.8HP, isn't it?
I have access to some fun tools: a clamp-on current meter and a battery-powered (floating) oscilloscope. For fun, I hooked them up to said motor while it was running (with no restriction on the dust collector input). I measured 238V, 8.6A, and 1454W (calculated by the oscilloscope as a point-by-point multiplication of V*I, then averaged, so it correctly reports real power accounting for power factor).
434806
1454W is 1.95HP, which seems right, since it's a 2HP dust collector and I removed the restrictions on the inlet (assuming the manufacturer built a more generous safety margin than 0.05HP in, originally...).
So why is that 8.6A, and not the 12A on the nameplate?
In another vein, I have a motor I thought was 5HP (no nameplate). But using the same measurement equipment, I find it draws 6.2HP under load (power washer), and I've used it like this for years. Would a 5HP motor survive driving a 6.2HP load for long periods?