Efficiency gain DC to AC motor?

[jdfs]

Hello,

I have 6 DC direct drive motors on a production line that are aging and will be replaced with AC motors. Are there any rules of thumb I can use to determine efficiency gain? The existing DC motors are between 1.5 to 5 HP, and are using 240V single phase, amps measured on the AC side are 2A to 11.5A depending on HP.

I don't have the specs for the new motors, but they should be AC and probably the same HP rating. Any help would be appreciated, thanks.

 

[DickDV]

As a general rule, an AC VFD/motor system will come in around 6% more efficient than a similarly rated DC drive/motor system. There are exceptions, of course, but that's a pretty safe number for estimating purposes.

 

[jdfs]

Thanks for bringing up the VFD since i forgot to mention it. Do you have a reference document that you can point me to for the 6% efficiency gain?

 

[DickDV]

I don't have a particular white paper to reference on this but, look first at the motor. There are published efficiencies on both AC and DC motors. You will see that the differences are around 7%.

Since the AC drive is double conversion and a DC drive is single conversion, I would estimate the difference in losses to be around 1% with the DC being better than the AC.

Maybe someone else on here has some reference material. If so, please volunteer.