This may be a bit offtopic, but I have a situation where only DC power is available, and i want to run an AC motor off a VSD (for a Crane Hoist). I am worried about the performance of the VSD when using an Inverter due to poor power waverforms.
Has anyone had any experience in doing this? Any recommendations on what to do/not to do?
I have done a little bit of research, and found that Seimens drives allow you to bypass the rectifier stage and power it directly from DC, which sounds pretty good for the application.
What size (HP or Kw) is crane motor? What is voltage of motor?
Want to drive vehicle using AC 3 phase motor. Vehicle is 56 Chev pickup and motor is Leeson 50 HP.
Have researched using "low DC" voltage (< 96 VDC) equipment to drive AC motors - stuff is out there most typically forklifts. Big stopper there is most forklift makers will not give software to change paramaters in VFD to allow modification to adapted need.
Gave up on this option and researched using off shelf industrial VFD to drive vehicles.
Basically tie DC source to DC bus in VFD. Main drawback is "high voltage DC". DC bus voltage will be 1.4 times that of motor ie for 230 volt motor DC bus voltage will be about 325.
Second drawback is how to bypass the AC input and recitifiers and connect to DC bus.
Common bus is the term to search for.
Two options I have found are
Hitachi SJ 300 - this can be modified for driving from DC source. You will have to retain the capacitors (per manual) thus will have to build a precharge protection circuit in DC line to protect the capacitors.
Allen Bradley Power flex 700 has option for direct DC supply. Advantage to me is it is all in one package ie hook up DC, hook up motor and turn on.
Both of these units are vector drive which depending on the demands of your hoist will be a good feature to have. I believe either will allow you to do vector sensorless (no encoder) or with an encoder to sense motor shaft speed - if you can do this I believe it to be the better option.
If you are driving from a battery you may not need braking resistor - dynamic braking will charge the battery which will act as a braking resistor. You will still need some method to charge the battery you can only count on dynamic braking to supply 15 to maybe 20% recharge.
If you are driving VFD from a DC source ie generator or rectifier you will need the brake resistor.
Allen Bradley unit is about 6,000 and Hitachi is about 4,400 US $. I will probably go with Hitachi mostly because of better local support and lower cost even though from technical standpoint I prefer AB.
Another issue with DC at 325 or more is that it is difficult to find equipment disconnect switches, fuses etc with proper ampere AND voltage ratings. Major fuse makers Little Fuse etc make the fuses but you may need to call them. I found Little fuse most helpful and knowledgable and they have a watts line.
Dan Bentler