Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 21,398
I don't think the transformer after the inverter helps with split-phase motors.
I do see "motor starting transformers" which seem to be auto-transformers, reducing voltage and increasing current, for 3-phase motors. But 3-phase motors have good starting torque. Split phase motors have poor torque.
Modern LF sine wave inverters use HF switching. But they use LF transformer to step up from something like 40V peak to 170V peak. There is heating of the transistors during switching transitions, so both could be subject to the same aging. Better power transistors today, so maybe can be as reliable as the old LF inverters.
I've had SMPS die just being used. Transformer type power supplies only due to overload - some are "impedance protected", supposed to be able to handle shorted output.
The difference is probably quality, of parts and design. My 24 year old Honda still runs fine, with ECU driving ignition coil and injectors. A large inverter of course is carrying much more current; maybe if designed with transistors sufficiently oversize they are reliable. Then there is the effect of various loads which present short circuit (motor starting) and voltage spikes from inductive kick.
We don't know how reliable Rosie will be, but Midnight should have a fair idea. Right now we're hearing about test of heavy loads that might be within its specs, but without measurement can't know for sure. This was a 5 HP induction motor. Midnight had demoed starting 4x 1.5 HP air compressors, but those were brush-type motors so easier.
An induction motor with full-load current near inverter spec'd output is something we wouldn't have expected an inverter to start at all.
The 5 HP motor is likely 6.4kVA under load, and I expect starting current 5x as great or 30 kVA. That is twice Rosie's specs.
I do see "motor starting transformers" which seem to be auto-transformers, reducing voltage and increasing current, for 3-phase motors. But 3-phase motors have good starting torque. Split phase motors have poor torque.
Modern LF sine wave inverters use HF switching. But they use LF transformer to step up from something like 40V peak to 170V peak. There is heating of the transistors during switching transitions, so both could be subject to the same aging. Better power transistors today, so maybe can be as reliable as the old LF inverters.
I've had SMPS die just being used. Transformer type power supplies only due to overload - some are "impedance protected", supposed to be able to handle shorted output.
The difference is probably quality, of parts and design. My 24 year old Honda still runs fine, with ECU driving ignition coil and injectors. A large inverter of course is carrying much more current; maybe if designed with transistors sufficiently oversize they are reliable. Then there is the effect of various loads which present short circuit (motor starting) and voltage spikes from inductive kick.
We don't know how reliable Rosie will be, but Midnight should have a fair idea. Right now we're hearing about test of heavy loads that might be within its specs, but without measurement can't know for sure. This was a 5 HP induction motor. Midnight had demoed starting 4x 1.5 HP air compressors, but those were brush-type motors so easier.
An induction motor with full-load current near inverter spec'd output is something we wouldn't have expected an inverter to start at all.
The 5 HP motor is likely 6.4kVA under load, and I expect starting current 5x as great or 30 kVA. That is twice Rosie's specs.