Pulley size change 5HP ele. motor

[durfman99]

I have a air compressor that has a new head on and takes 4HP to run [spec sheet on it] I used the same ele. motor was on it that is cheap 5HP [SPL] 3600RPM which is like 3HP correct? has 4 inch pulley on ele motor, Is suppose to use 15AMP max but is drawing 18AMP and over heating at times. the new head has 10.5 inch pulley. The RPM is the max I can put on new head according to spec sheet,

So I found real Dayton 5HP for good price and is 1750RPM so I need an 8inch pulley [I found cheap] to come out with about same RPM on head. So Is this ok to use? I know I,ll loose some torque but with a real motor thought be ok?

Dayton motor draws 23AMPS with 1% service factor and both run 220 Volts.

 

[TRWham]

The 1750 rpm motor has twice the torque, so you lose nothing.

 

[BarryWells]

'sall good. Bolt'er up

 

[LS6 Tommy]

I have a air compressor that has a new head on and takes 4HP to run [spec sheet on it] I used the same ele. motor was on it that is cheap 5HP [SPL] 3600RPM which is like 3HP correct? has 4 inch pulley on ele motor, Is suppose to use 15AMP max but is drawing 18AMP and over heating at times. the new head has 10.5 inch pulley. The RPM is the max I can put on new head according to spec sheet,

So I found real Dayton 5HP for good price and is 1750RPM so I need an 8inch pulley [I found cheap] to come out with about same RPM on head. So Is this ok to use? I know I,ll loose some torque but with a real motor thought be ok?

Dayton motor draws 23AMPS with 1% service factor and both run 220 Volts.

It doesn't really work that way. When you decrease the the pump pulley diameter to increase the pump RPM, you'll draw more amperage on the motor. The only way to know for sure is to try it and check amperage draw.

The easiest thing would be to use a motor with the same RPM and HP specs as the original and run the same size pulleys.

Tommy

 

[larry_g]

Cheap way out is to change your drive pulley. So you pulling 18 amps on a 15a circuit. reduce your motor pulley by the percentage. 15/18=.833 .833x4" (drive pulley)=3.333

new pulley size. For margin go with a 3" drive pulley and check your current draw. It should be ~13.5a. You can also reduce your cutout pressure down a bit to reduce current.

lg
no neat sig line

 

[TRWham]

I interpreted this as he is overloading the existing motor and wants to upgrade to a larger motor to maintain maximum compressor capacity. As far as the pulleys, I interpreted that he wants to increase the motor pulley to get back to the compressor speed he is running now with the new, slower motor. He will also need to ensure the circuit is sufficient to carry the new load (a 5 hp motor will need a 40 amp circuit).

ETA: Regardless what the motor says for amperage, the branch circuit needs to be sized per Table 430.248

 

[bob15]

This calculator works really well and makes it easy to understand

https://www.blocklayer.com/pulley-belteng.aspx

As for getting pulleys: McMaster Carr is your friend.

Also how many belts? If more than one, make sure they are matched.

 

[TRWham]

Or banded. I have a B3 on my compressor. It’s absurdly over-specced by current standards, but is what it had originally.

 

[durfman99]

I interpreted this as he is overloading the existing motor and wants to upgrade to a larger motor to maintain maximum compressor capacity. As far as the pulleys, I interpreted that he wants to increase the motor pulley to get back to the compressor speed he is running now with the slower motor. He will also need to ensure the circuit is sufficient to carry the new load (a 5 hp motor will need a 40 amp circuit).

ETA: Regardless what the motor says for amperage, the branch circuit needs to be sized per Table 430.248

I, It is a V belt and heres the Head Name;NorthStar Air Compressor Pump — 1-Stage, 2-Cylinder, 13.7 CFM @ 90 PSI---https://www.northerntool.com/shop/tools/product_200596491_200596491?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Air%20Tools%2 0%2B%20Compressors%20%3E%20Air%20Compressor%20Part s%20%2B%20Maintenance%20%3E%20Air%20Compressor%20P ump&utm_campaign=NorthStar&utm_content=4592900&gcl id=CjwKCAjwkqPrBRA3EiwAKdtwk2b5Ja6fwL69P8cHPewjeaI h4ICNSxajV-7Q5CQQw16cDZCDllJyihoCba0QAvD_BwE
I just checked it tonight with a new belt 1/2inch and pulling 20AMPS now? It,s colder out?? So am going to go get that motor tomarrow and work on a pulley to fit it--8inch I can make about any fit have a lathe and Tig welder--Says max RPm is 1396 so guess I,ll try the 5HP? It is a good price for that motor New there over $800 and 3 to 400 used
I think? this will work if I put smaller pulley on motor I have now and lower preasure [only 130LB] max now I won,t have enough air for what I need?
Don,t know why it,s drawing even more AMPS now compared to last week? Maybe thought it,s colder out and oil might be thicker? By colder it only 68 out? The motor heats up fast now also? If other motor draws 23 amps would a 30amp line be ok even at start up draw?? Bunch of work for just smaller unit. That northen tool head is rated at 100% duty so should not hurt it running at high end of rated specs??

 

[Bert_]

With an 8" pulley on a 1750 rpm motor and the 10 1/2" pulley on the pump it will spin 1330 rpm. Northern tool says 4hp at 1396 rpm so the new 5hp motor should work well. At only 15A calling the old motor 3hp is even being optimistic.

The new 5hp motor needs a minimum of a 40A breaker. 50A is a better size and will pretty much guarantee you don't have nuisance trips. Code actually allows for up to a 70A breaker.

Wire needs to be #10 THHN or #8 romex.

 

[durfman99]

Cheap way out is to change your drive pulley. So you pulling 18 amps on a 15a circuit. reduce your motor pulley by the percentage. 15/18=.833 .833x4" (drive pulley)=3.333

new pulley size. For margin go with a 3" drive pulley and check your current draw. It should be ~13.5a. You can also reduce your cutout pressure down a bit to reduce current.

lg
no neat sig line

Well just got home with motor I bought and ran it checks out good but will take apart to check switch inside make sure all is good--Bearings sound ok, As far as the other motor like I said it was drawing 18 AMP then other day checked it was drawing 20 to 21AMP?? [suppose to draw 15 Max] Now just went out tried run it with No belt on and Nothing? Just Hum and blew over load--So will take it apart later see what fried?? One I just bought came with a 6inch pulley on it so would turn pump at 1000RPM guess be better to use that I guess? Don,t know how much it would affect CFM out-put?
Darn thing is so big might be job to mount, will last longer I guess?
Maybe might sell it and buy a GOOD 5hp motor run 3600rpm would mount easier? Only paid 160 for this one there 6 to 800 NEW and seem to sell for 3 to 400?

 

[MattT]

One I just bought came with a 6inch pulley on it so would turn pump at 1000RPM guess be better to use that I guess? Don,t know how much it would affect CFM out-put?

It'll drop you to about 10 CFM, which is better than no air. Run it for now until you can get the correct pulley.

Maybe might sell it and buy a GOOD 5hp motor run 3600rpm would mount easier?

I'd rather make the 4 pole motor work personally. Regards a 2 pole being easier to mount it'll depend on the motor frame sizes. If you can find one the same frame size as the old motor it'll be a bolt in replacement. Post up the frame sizes, or pics of the motor nameplates, if you need any help figuring that out.

 

[durfman99]

It'll drop you to about 10 CFM, which is better than no air. Run it for now until you can get the correct pulley.



I'd rather make the 4 pole motor work personally. Regards a 2 pole being easier to mount it'll depend on the motor frame sizes. If you can find one the same frame size as the old motor it'll be a bolt in replacement. Post up the frame sizes, or pics of the motor nameplates, if you need any help figuring that out.

Heres what I did today--The one I just bought I took apart and wow--It looks like it just was built yesterday--really. Even the contacts look like it never been run? I never seen a older motor so clean--checked all out ran it Amps good about 6-7. Now the older one I took apart and had a bad Run Capacitor and it is 15uf so put a 25uf in cleaned it all up greased bearings back together ran good about 5-6Amps so am going to see if it runs compressor and what the amps are when running it?

It does unload the air ok it built into the switch, Old motor ran at 3450rpm with SF at 1.0

So--Do I put this big 5hp in?--OR put that other back on? Most likely I could sell other for 3 to 350 make couple bucks BUT I don,t want problems in the future either?? The one I took off suppose to run at 15AMPS? so is only 3hp correct? The air head takes 4HP to run it. If my money was not so tight would not bother with all this but is way it i

 

[larry_g]

The air head takes 4HP to run it. i

I think that you MAY find that it takes 4hp to run it at its max rated RPM's. So if you slow it by using a smaller motor pulley you may be golden. I showed you the math in a previous post. Hopefully it will run as is now that the motor is cleaned up.

lg
no neat sig line

 

[The Cobbler]

..... bad Run Capacitor and it is 15uf so put a 25uf in....

you should keep the uf the same, voltage can be higher than the original however.

 

[Citation]

durfman, I'm going to try to rewind things a bit to understand your questions and where you are.

So first, am I right in thinking you have a motor that is a 204V, 15A motor (what most compressors would call a 3hp). This is your original motor?

Next you have a pump that is rated for 4hp? Can you find the model number?

Finally, you want to use a 5hp, 1750RPM motor but the original was a 3600 rpm motor.


So, assuming you don't have a bad motor, you should be able to make either motro work with the pump. If you look up the pump model you may find a table of pump RPM and motor power. Absent any other information I would just assume if the pump needs to spin at say 1000RPM with a 4hp motor then a 3 hp motor would want to spin it at 1000rpm/4hp*3hp=750rpm. Size the motor pulley for 750rpm and it will be fine. The pump will produce less flow vs at 1000 rpm but that's it.

Alternatively, with the 5hp, 1750 rpm motor you again need to find the correct pulley to spin the motor at 1000 rpm with a 1750 rpm motor. Just keep the pump pulley the same size and find the larger motor pulley.

As for the current testing on the motor. Don't exceed the current limit. You could also buy a wireless/optical tach off Amazon for $20 or so. With that you can check to make sure the motor isn't slowing too much. A drop too far below rated RPM means the motor is overloaded. Induction motors can be a bit deceiving with regards to current draw. At light load the your current draw may be much higher than you expect. Remember due to a phase shift associated with an induction motor, the actual power consumed by the motor won't be line voltage (120V ac) * motor power wire current (15A).

 

[durfman99]

Heres what I did today--The one I just bought I took apart and wow--It looks like it just was built yesterday--really. Even the contacts look like it never been run? I never seen a older motor so clean--checked all out ran it Amps good about 6-7. Now the older one I took apart and had a bad Run Capacitor and it is 15uf so put a 25uf in cleaned it all up greased bearings back together ran good about 5-6Amps so am going to see if it runs compressor and what the amps are when running it?

It does unload the air ok it built into the switch, Old motor ran at 3450rpm with SF at 1.0

So--Do I put this big 5hp in?--OR put that other back on? Most likely I could sell other for 3 to 350 make couple bucks BUT I don,t want problems in the future either?? The one I took off suppose to run at 15AMPS? so is only 3hp correct? The air head takes 4HP to run it. If my money was not so tight would not bother with all this but is way it i

Well Did NOT put the 25uf capacitor in went back to the 15 like suppose to be in it. I,m far from an expert on these things just know enough [at times] to get by

 

[durfman99]

durfman, I'm going to try to rewind things a bit to understand your questions and where you are.

So first, am I right in thinking you have a motor that is a 204V, 15A motor (what most compressors would call a 3hp). This is your original motor?

Next you have a pump that is rated for 4hp? Can you find the model number?

Finally, you want to use a 5hp, 1750RPM motor but the original was a 3600 rpm motor.


So, assuming you don't have a bad motor, you should be able to make either motro work with the pump. If you look up the pump model you may find a table of pump RPM and motor power. Absent any other information I would just assume if the pump needs to spin at say 1000RPM with a 4hp motor then a 3 hp motor would want to spin it at 1000rpm/4hp*3hp=750rpm. Size the motor pulley for 750rpm and it will be fine. The pump will produce less flow vs at 1000 rpm but that's it.

Alternatively, with the 5hp, 1750 rpm motor you again need to find the correct pulley to spin the motor at 1000 rpm with a 1750 rpm motor. Just keep the pump pulley the same size and find the larger motor pulley.

As for the current testing on the motor. Don't exceed the current limit. You could also buy a wireless/optical tach off Amazon for $20 or so. With that you can check to make sure the motor isn't slowing too much. A drop too far below rated RPM means the motor is overloaded. Induction motors can be a bit deceiving with regards to current draw. At light load the your current draw may be much higher than you expect. Remember due to a phase shift associated with an induction motor, the actual power consumed by the motor won't be line voltage (120V ac) * motor power wire current (15A).

Heres what I just did today--I put the older motor back on with new 15uf capacitor and ran it--It pulls from 17.2 AMPS at low air pressure then 18.2 at the 130lb cut off. So with money like it is and alot work [which I could do] to mount the bigger 5hp I think am going to run this and try sell the other and make enough to but a new 5hp 3600rpm motor which will work. This ran about 1 1/2 years since I put the new head on so it took a while to have trouble?

And it is running at 1314RPM I double checked the pulleys size and calculated them again. The old motor runs at 3450rpm not 3600. And the motor sets in a shed attached to garage [insulated] and I have a small fan puts heat out there in winter and I left it on once when I was painting and alot of over spray got into the cooling fines and did not help anything so now those are all cleaned up also.

I,m in Michigan if anyone would need a GOOD Dayton 5hp motor I am listing it today on craigs list. I want to Thank everyone who helped me with this.

 

[Citation]

I think 3450 is considered the correct speed. However, the high current draw, assuming the motor is rated for 15A, means it's getting over loaded. A smaller pulley on the motor would solve the problem. I assume the motor and pump weren't sold together.

 

[durfman99]

I think 3450 is considered the correct speed. However, the high current draw, assuming the motor is rated for 15A, means it's getting over loaded. A smaller pulley on the motor would solve the problem. I assume the motor and pump weren't sold together.

Yep your right not sold together--- I think i,ll check into a different pulley if I use that motor--That other motor is so nice and over kill for what I got just thought I could sell it make enough to buy a new 3600 5hp GOOD motor that would work without a bunch of work to mount it is all.

It did take over a year for it to fry the capacitor so maybe?--I have some time to sell this other?

 

[durfman99]

I think 3450 is considered the correct speed. However, the high current draw, assuming the motor is rated for 15A, means it's getting over loaded. A smaller pulley on the motor would solve the problem. I assume the motor and pump weren't sold together.

Well I solved this one now---I found a 2013 curtis CT-55 80gal air compressor for good price and comes with water separator and regulator AND w unit for water dryer I checked it all out looks like new so took it home ALL for $350--Yep thats right heck that water unit sells for $ 524 by itself. So this comes with balder motor 5hp which will fit good on my 60gal and I can put the 5hp dayton I have on this one and sell my 60gal and sell the water dryer AND even come out even or make few bucks--WOW I could not believe this guy sold this so cheap?? Thanks for all info

One more thing that dayton should be ok for air compressor? Heres photo