New motor feels like running too slow

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Forum topic by Tom22 posted 09-14-2013 12:35 PM 809 views 0 times favorited 7 replies Add to Favorites Watch
View Tom22's profile


3 posts in 1967 days

09-14-2013 12:35 PM

Topic tags/keywords: motor 3hp 2hp pulley slow motor fat motor

Hi guys! I just bought a new motor because the otherone burnt out. The new one has more HP I was hoping it would resist the daily hardships better, but it feel like its running slower than the one before it, which had less HP. I’ll write the details of each below.

Old Motor:
2HP 1725 RPM
Pulley: 7 in.

New Motor:
3HP 1725 RPM
Pulley: 3. in.

I am taking a wild guess it might be the pulley on the axis but wanted to run the question by more experienced peolple befor spending more money.

Thank beforehand for any help!


7 replies so far

View Shawn Masterson's profile

Shawn Masterson

1294 posts in 1368 days

#1 posted 09-14-2013 12:48 PM

I don’t understand why you changed the pulley size. HP makes no difference in speed. If the old one was 1725 with a 7” pulley then the new one also needs the 7” pulley. by going from a 7” to a 3” you cut the speed by more than 1/2. Put the 7” pulley on the new motor then it will be normal again.

View Clint Searl's profile

Clint Searl

1533 posts in 1780 days

#2 posted 09-14-2013 12:49 PM

Maybe the wire is kinked and not letting enough electrons through.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

View Don W's profile

Don W

17873 posts in 1987 days

#3 posted 09-14-2013 12:51 PM

I agree with Shawn.

-- Master hand plane hoarder. -

View ernie's profile


14 posts in 1426 days

#4 posted 09-14-2013 12:56 PM

Not a wild guess, it is right on.
Change that 3 inch back up to a 7 inch and your back to originals again.

-- Ernie, Etna, WA

View Picklehead's profile


991 posts in 1348 days

#5 posted 09-14-2013 01:12 PM

Running at the same RPM, the old motor with the 7 inch diameter pulley moves 2.34 times the amount of belt per revolution compared to the new 3 inch diameter pulley. (7 inch pulley circumference = 22 inches, 3 inch pulley circumference = 9.4 inches). But I bet you got some torque!

-- You've got to be smarter than the tree.

View Tom22's profile


3 posts in 1967 days

#6 posted 09-16-2013 03:11 PM

Thanks for your help everyone!

The new motor I bought has a diffrent axis size so I had to buy a diffrent pulley and that moment I tought the pulley we were using was smaller. It was a big mix up with the pulley size because I had two 2hp motors at the shop Booth burnt out I beleive because it’s not managing hte workload with 2hp so I got the 3hp. One of the 2hp motors is 1725rpm and the otherone at 3450rpm the 3450 has a smaller puller and the 1725 had the larger pulley when I went to the store to get the new motor I mixed up thinking one had the other.

Anyhow, the lesson: Check, compare and write down as many details before goint out for spare parts etc…

Thanks again!!!

View MrRon's profile


3891 posts in 2663 days

#7 posted 09-16-2013 05:48 PM

Problem solved.

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