[subcooledheatpump]

Well yes, it's whatever you want. A smaller pulley which could mean more friction since a certain part of the belt is moving faster, or a motor with more poles which is a little bigger. Either way really.

[dillond666]

I have only seen an air conditioning compressor once in my life (Not often required in Scotland!) and it was on a Range Rover. It had a belt drive and an electromagnetic clutch to enable or disable the drive. Couldn't it just be driven from the motor tailshaft? The clutch could even be wired to the brake light to give A/C on braking, could be a useful way to capture some of the wasted braking energy?

Derek

[jaspersk]

Attached is a picture of what a 3.8 CHP treadmill motor commutator looks like after trying to run an A/C compressor.

[subcooledheatpump]

Thats why I only use brushless motors....

Yeah I'd say a little more power is required, something obviously went wrong

[johntrhodes81]

Any more thoughts about using a 5 HP motor? Could a generic industrial AC motor work running off an inverter?

John R.

[PStechPaul]

I would think a 5 HP industrial three phase motor would work fine, but you would need about 300VDC for a 240 VAC VFD. Mine drops out below 200 VDC. It may be difficult to get an inverter rated at 5HP or 3kW, and they are not generally rated for driving motors. But I did rig up a 2kW inverter with a 12V battery and was able to run a sump pump with something like a 3/4 HP single phase motor.

Most inverters are not isolated from the battery, so you must be careful. You might be able to use two inverters and batteries, and rectify the outputs and run them in series to get about 320 VDC. Internally they have a 150-170 VDC supply which is then "modified" to appear as an equivalent sine wave. So if you can tap into that source you won't need to rectify it and you will have two DC sources you can connect in series. But the batteries will be floating well above ground, so you will have essentially an ungrounded system, or you can connect the DC link (-) or one of the batteries to ground.

But in your case, starting from 140 VDC, you would need to build a special inverter or doubler to use a standard VFD, or modify a VFD to work at a lower voltage. In that case you would only be able to run the motor at about 100 VAC, which would be half the rated voltage. You might be able to rewire the existing windings from star to delta and get 138 VAC nominal. Or you could use a 10HP motor and run at half voltage and half speed.

In any case, using the proper motor controller with internal overcurrent protection, and perhaps temperature sensors in the motor windings, should eliminate catastrophic failure as shown in the treadmill motor.

[jaspersk]

Thanks for the reply. I do have a working system now. I found that the A/C compressor required a 5HP motor to work at the rated speed without overloading. I currently have an industrial 180VDC permanent magnet motor running on 144V pack. I used a starting resistor (ceramic heating coil which doubles as heater) and a time delay relay to bring it up to speed before putting it directly across the full battery voltage and another second after that, I engage the A/C clutch. It has been running for 3 months now with no issues and I am very pleased with how it is functioning.