Is 1180(ish) RPM's OK for a 1.5 HP 2x72?

M

Mike Fennessy

Joined
Dec 19, 2005
Messages
326
I'm building a grinder and have a 3ph 1.5HP motor. It's only 1180 (or something like that)RPM's.

I just ordered a 2HP VFD for it which was about $225 and I know I can pick up 3ph 2HP 1725 RPM pretty cheap (about $50-70 shipped) so I'm wondering if I it's worth it to get the slightly faster motor for it or will I be slowing it down most of the time anyway?

Right now I'm using the delta 1x42 with a 1/3 HP 3450 RPM so anything's an improvement.

Thanks for any input,
Mike
 
Nevermind, in for a penny in for a pound. $65 for another 1/2 hp and faster, why not? I'll figure out a use for the other motor I'm sure.
Mike
 
With VFD you will have variable RPMs. A significant range from prolly 40% of speed and up, will have 90%+ of the torque, so you can really hog steel.

1180 is kind of low - you might have to use a larger driving pulley to get to the desired SFPM . Or , with most VFDs, you can program it to drive your motor at up to 120Hz,
as opposed to the typical 60Hz, doubling the top RPMs "free of charge".

You need to make sure the bearings and motor at large can take it and the torque is right.
 
"Where are you getting your motor?"

ebay. I just typed in 3ph 2hp and it was the first motor that came up. A used Dayton. It ended up being $66 shipped. The same place also has 1 1/2HP for $50 shipped. http://tinyurl.com/2oou9m Note:In case everyone doesn't know, these are 220V THREE PHASE motors. The 220V in most houses and shops is ONE PHASE. Hooking them up to a VFD (Variable Frequency Drive, $100-200) allows them to work on ONE PHASE and also gives them variable speed.

These are really small for a 3PH and there isn't a huge demand for them. I actually got stuck with my 1 1/2HP cause they didn't say it was 3PH in the auction.

I couldn't give it away and didn't want to mess with ebay. I was about to pull the wire out of it for copper before I learned about VFDs. Now from what I've researched I'm glad I ended up with a 3PH, lots of people like them better than DC for variable speed.
 
I have both DC and a VFD. I like the DC but LOVE the VFD. It has better torque at lower speed and is easier to adjust. Cost is much cheaper also. If you are hooking this to a belt grinder with pulleys then you could play with the ratios to get the speeds you want. If you go up to 2hp the VFD may lose some of it's power, up to 30%. You normally need to go 50% larger on the VFD than the largest motor you will be running. But then I run my mill (3hp on the tag) with my 3hp VFD. No problems... Good find.
 
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