PV Gap

Cassandra Said:

horse power to Power ratings?

We Answered:

Here is another approach:

Starting at http://www.reliance.com/mtr/prfchr.htm I selected a 5Hp, 1750RPM, 230/460V, 3ph, 60Hz motor in a totally enclosed fan cooled enclosure. The data sheet indicated that the full load current is 13.2A for the 230V connection. The efficiency is 89.5% at full load. The locked rotor current is 92 amps.

The full load input power required by the motor would be 5Hp X 745.7 / 0.895 = 4166 watts.

The 92 amp locked rotor current is not unusually high for a 5Hp 230V motor. Since an inverter is needed to convert the DC output from the PV panels to AC, you should consider using a variable frequency drive (VFD). That would allow you to limit the VFD input current to very little more than the current required to deliver the power to the motor at full load and full speed. The VFD efficiency should be about 95%, so you will need to supply 4166 / 0.95 = 4385 watts. For 230V VFD output, you will need to provide 230 X sqrt2 = 325V DC input from the PV panels. For 4385 watts, you will need 4385 / 325 = 13.5 amps.

VFDs have an internal rectifier to provide an intermediate DC power stage. Some VFDs provide terminals to allow DC to be supplied directly to the intermediate DC supply. The intermediate DC supply has a large capacitor that filters the AC input. With DC input, that capacitor is still required to supply reactive current to the motor. When DC is applied on power-up, a resistor needs to be inserted for a short time to limit the charging current.

For use with a VFD, the motor needs to be rated for VFD duty. I didn’t find a VFD rated motor with published efficiency, but a VFD motor similar to the motor above should be available.

For a DC motor, you would probably need about the same watts from the PV panels. You would need to be concerned limiting the current when the motor is started. That might mean using an electronic controller, but timed insertion of a series resistor could probably be used. If you will be using batteries with a PV charger, the batteries can probably tolerate the starting current.

Christy Said:

What would happen if you were to circuit-wise "stack" weak solar panels?

We Answered:

If you wired them in parallel, the current would increase (by N, the number of panels) and the voltage would stay the same. Wattage would be N times the original wattage.

If you wired them in series, the voltage would increase (by N, the number of panels) and the current would stay the same. Wattage would be N times the original wattage.


But several problems. If you put them in parallel, and they don't all get equal amounts of sun, the ones in the shade would shunt down the ones in the sun. You would need to put in series diodes, but these waste power.

In series, similar problems can occur.

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Mae Said:

Solar Panels to run a motor.?

We Answered:

These guys have helped me many times and it only takes a minute or two.
http://www.electroniccity.com/
"They have a lot of experience"
(and they answer every question you can have)