inverter to VFD

[thekman]

I need to run a 3HP ac motor with 24VDC. I figured inverting the 24VDC to 230vac, which will feed a 1ph - 3ph VFD, then 3phase ac motor. The input current rating of the VFD is 21 amps.

I found a pure sine inverter of 6000W w/ a surge rating of 18000W for 20s. I have not used an inverter this way, and want to get some input. I saw one post here that discussed a similar situation but cannot find it now.

I’m driving a transmission with the motor, so aside from starting, ramping and stopping, the load will be constant.

 

[itsmoked]

What you describe can work fine. That's a LOT of 24V current you're going to need and cheap high power inverters are.... cheap and failure prone, so do your homework on reviews of any models you're considering.

I'd try to find a 24VDC motor instead. You can control it with simple PWM.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

You will probably be drawing over 200 Amps. You will have losses at every stage of your conversion.
You may avoid some losses and save some money with a DC to DC convertor and feed the DC bus of the VFD directly.
If this was my project I would exhaust every avenue and means to develop the 3HP other than using 24 Volts.
Apologies if you have already done that.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Why only 24VDC? As mentioned, that's a LOT of current to come from a source only capable of that voltage. If its a battery bank, you might be better served by putting more of them in series to raise the voltage first.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[thekman]

Yes, finding a way to do this without building a power plant is going to be a challenge. Thanks for your replies, I'll update when I get a plan together.

 

[ScottyUK]

The old-fashioned solution for a transmission would be a series-wound or compound-wound motor. 3 HP is fairly large but certainly possible at 24V; your biggest problem will be volt-drop in the high current conductors which will easily become a significant fraction of your available supply voltage.

Anecdotal: a gas turbine design I was once very familiar with used an AC drive motor for its barring gear, and had provision to supply it from the 110V essential services battery when the main AC supply was unavailable. The concept was to invert the 110V DC to 415V AC 3-phase, then feed a VFD from the inverter. It did not work, ever, across the fleet of eight turbines in ten years of trying. I scrapped the entire ill-conceived installation and replaced it with a brutally simple and robust compound-wound motor with a series resistor starter. The new scheme never failed.