Re: Motor for A/C – Can you drive a 5HP VAC from 140VDC?
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.