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View Full Version : Need Help! VFD for vacuum blowers



adfergusson
12-08-2013, 12:53 PM
Hi,

I'm looking at a number of vac holding fixtures and a few vac hold down devices (e.g. for holding parts for routing or for a cutting table to hold down textiles). It seems for, whatever reason, that really high power and flow pumps come up on the likes of eBay at very tempting prices quite regularly, along with VFDs capable of driving the motor. Pumps pushing the 5-10kW range have far more 'suck' than I'm likely to need, most of the time. I was thinking that wiring one high power up to a VFD may be an elegant way of adapting the flow I need to the task I have. However, I've got an idea of how I might do this, but am not sure if it possible, or safe. Here's what I'm planning (I'd appreciate any advice):

Get a really over specc'ed pump with loads of flow capability
Put together a steel, or Al extrusion, 'trolley' to push it about
Mount a suitable VFD to the trolley and program it to drive the motor
Wire some 32A flex cable to the VFD and put a commando plug on the other end
Stick a thermocouple wired up to an arduino on the ports of the pump and program it to activate a relay for an estop or send a 'stop' command to the VFD in case temps rise too much (concerned about cooling at low rpms).
Push the pump around the workshop to where its needed, plug it in, and adjust the speed of the motor to suit the need/sound I can tolerate

Decent or dumb idea?! I like the idea of lower power consumption, but am even keener on the idea that the pump will run a lot quieter at lower speeds, so I won't need to wear ear defenders/will be less likely to upset the neighbours. I'm aware that there are problems with switching a conventional asynch motor designed for constant speed operation to VFD. However, many inverters/VFDs from the likes of ABB, Jaguar, etc... have chokes/du/dt filters/powerline reacotors/whatever you want to call them, and sometimes even sine wave filters, built in and I'm hoping that by sticking the VFD right next to the motor I'll be available to avoid a number of problems like voltage overshoots anyway.

I think that I've covered most of the potential problems that I might encounter in switching a conventional motor from a star delta or DOL starter to a VFD, but would keen for any insight and experience that anyone might be willing to share?

Also, would this be safe?! I'm guessing that if I earth everything on the trolley to the VFD, and the VFD is earthed via the 32A cable to a commando socket, I'm good to go?

Cheers,

Alex