Grinder motor horsepower

scott.livesey said:
I hate to tell you, but your 1.5Hp draws 4.5amps, if it drew more amps than that it would be a 1.75 or 2hp motor. if a motor draws 8 amps it is 3hp. basic electricity.
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Only took you 6 years to tell me that.

Thanks LOL
 
First, this is an old thread. However, there seems to be some disagreement on the subject of the new poster.

Robert, most grinders have 1.5 to 3HP motors. 1.5HP is more than enough for most all knife making work.




"I hate to tell you, but your 1.5Hp draws 4.5amps, if it drew more amps than that it would be a 1.75 or 2hp motor. if a motor draws 8 amps it is 3hp. basic electricity."
Scott Livesey

Scott, not sure what you're saying? One electric Hp is 746 watts. A 3HP motor uses 2238 watts. That is theoretical, and the actual use will vary depending on the motor efficiency rating. If it is an 85% rating ( normal), then it will draw 2984 watts to deliver 3Hp. At 220VAC, that would be 13.56 amps. Even the theoretical draw would be over 10 amps at 220VAC.
1.5Hp motors normally draw 9.3 amps at 120VAC and 4.65 amps at 220VAC. Either way they use 1120 watts ... theoretically. Actual draw is usually around 10-12 amps at 120 and 5-6 amps at 220.
 
Robert01 said:
I'm going to build a 2×72 grinder and was wondering if a 5 hp motor with a vfd would be too much.
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I guess my first question would be "why"? 2hp is more than enough power for 95% of makers, with 3hp being more than enough for the remaining 5%. Even if I already had a 5hp motor and vfd, and the power and setup to run it, I still probably wouldn't go past 2 to 3 hp, especially for a direct drive setup (which would also become problematic for a larger framed motor.)
 
Well I can get a 5 hp motor and vfd for less than $100. and my electrician friend owe me a favor so material and build cost is pretty cheap. The 5 hp motor is the cheapest motor I can find near me.
 
Robert01 said:
Well I can get a 5 hp motor and vfd for less than $100. and my electrician friend owe me a favor so material and build cost is pretty cheap. The 5 hp motor is the cheapest motor I can find near me.
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Just make sure the VFD you're looking at is 220 single phase in, and not a 3 phase to 3 phase VFD.
 
Robert01 said:
What's the issue with 3 phase?
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I'm assuming you have only single phase in your shop? If you have 3 phase (or a phase converter, 5hp or above), then you can use whichever you like. That said, many VFDs, especially when you get above, say, 3 horsepower, are 3 phase in, 3 phase out. These also tend to be the VFDs that you'll find for less than $100 from surplus shops and the like. Most residential shops/garages are single phase only, unless you have a phase converter.

Just to be clear, if you're running a VFD, you'll typically use a 3 phase motor, but you'll be looking for a single phase input unless you have 3 phase supply.
 
Lets simplify things here:
Robert -
What power do you have available? voltage, phase, amperage?
 
If one understands how VFDs work, one should realise a ”3Ø VFD”, its input does not need to be 3Ø.

But just be aware to derate its maximum output.
For example, if ten amps is normally upon each input conductor of 3Ø, fifteen amps will be upon each input conductor of singlephase.
”Rule of Thumb” for this example is 50%. So, 2.5 hp motor is maximum if singlephase power is supplied to a 5hp 3Ø VFD.

Some VFDs monitor input voltage on all three phases, & will display an error code if supplied only singlephase. Thats easily remedied by a simple jumper wire between the unused phase input and either singlephase input conductor.

knife to a gunfight said:
I'm assuming you have only single phase in your shop? If you have 3 phase (or a phase converter, 5hp or above), then you can use whichever you like. That said, many VFDs, especially when you get above, say, 3 horsepower, are 3 phase in, 3 phase out. These also tend to be the VFDs that you'll find for less than $100 from surplus shops and the like. Most residential shops/garages are single phase only, unless you have a phase converter.

Just to be clear, if you're running a VFD, you'll typically use a 3 phase motor, but you'll be looking for a single phase input unless you have 3 phase supply.
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Thanks for clearing up the confusion.
knife to a gunfight said:
I'm assuming you have only single phase in your shop? If you have 3 phase (or a phase converter, 5hp or above), then you can use whichever you like. That said, many VFDs, especially when you get above, say, 3 horsepower, are 3 phase in, 3 phase out. These also tend to be the VFDs that you'll find for less than $100 from surplus shops and the like. Most residential shops/garages are single phase only, unless you have a phase converter.

Just to be clear, if you're running a VFD, you'll typically use a 3 phase motor, but you'll be looking for a single phase input unless you have 3 phase supply.
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A house will have only 220VAC single phase input. Unless the house already has a workshop in the garage with power for welders and such, you will likely have to run a sub-panel or install a larger 220VAC circuit and breaker to the shop to run a 5HP motor.

The VFD would be like this one:
https://www.ebay.com/itm/4KW-220V-5...117199?hash=item41aa2f8ccf:g:jpoAAOSwEzxYeYz4

You plug the VFD into the 220 volt circuit and hook the VFD output to the motor. Obviously, you have to configure the VFD jumpers for the right input.
You will need a 30 amp double breaker and dedicated circuit ( one socket only) to run the VFD and motor on. This all should be done by someone familiar with wiring and VFDs.
 
Kentucky said:
Folks must realize that not all motors are really what they say they are either..Lots of guys end up with take off motors that say 1 1/2-2 hp but only draw 8 amps(WHich means it aint 2hp)..We had a thread a while back where some of us did the math on amps drawn vs rated HP and such..Heres a post I made about it a while back..
--------------------------------------------------

.
I think that some newer motors are rated on "peak" power, not continuous. It takes "x" ammount of amps to get "x" ammount of watts to matter what you do.No motor can do otherwise.Volts*Amps=Watts, Watts/Volts=Amps
Heres a formula I found..
voltage x amps x efficancy
hp=----------------------------
746
Meaning if you have a motor that has a 70% efficancy rating, uses 125v and draws 9 maps its hp would be 1.0 hp..
.
Baldor uses the formula voltage x amps x efficancy x power factor= output watts..baldor does list thier efficancy and power factor on the nameplate, or they did anyway..
heres a link I found about air compressor motor ratings...
http://www.asedeals.com/air_compressor_faq.pdf
.
Most every website I found uses a loose guideline of 10 amps per HP on 115v and 5 amps per hp on 220v..
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^^^ What he said about all motor HP ratings not being equal .. I have a 1 1/2 hp Baldor motor on my Hardcore Grinder! Works great! I I wanted to grind 12” x 3” x 3/8” thick Bowie knives etc I would consider going to a 3 Hp & bringing in 220v.. Quality Ceramic belts are very important too!
 
Rhinoknives1 said:
^^^ What he said about all motor HP ratings not being equal .. I have a 1 1/2 hp Baldor motor on my Hardcore Grinder! Works great! I I wanted to grind 12” x 3” x 3/8” thick Bowie knives etc I would consider going to a 3 Hp & bringing in 220v.. Quality Ceramic belts are very important too!
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Grinder configuration also makes a significant impact. Direct drive vs belts and pulleys, 2 wheel vs 3 or 4 wheel, platen size and shape, etc....
 
scott.livesey said:
I hate to tell you, but your 1.5Hp draws 4.5amps, if it drew more amps than that it would be a 1.75 or 2hp motor. if a motor draws 8 amps it is 3hp. basic electricity.
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My 1hp 1725rpm grizzly draws 14A... is that just on start up? It has a capacitor assist.
 
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Rick Marchand said:
My 1hp 1725rpm grizzly draws 14A... is that just on start up? It has a capacitor assist.
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must be. a 1hp motor uses 750 watts. formula is watts = volts x amps. so 120 volts is 6.25 amps. 240 volts is 3.125 amps. these numbers are a good ball park for actual amps drawn
 
I have found that adding 25% to the theoretical draw will be more like the real world draw for most motors. A 1Hp will generally draw between 7.5 and 9 amps once running. It can draw considerably more when starting ... especially if the motor is already loaded to the work at start ( no clutch, unloaded lever, or transmission). A motor under heavy load in use ( hogging) can also draw a good bit more current. When designing circuits for motors, it is wise to use a 50% over-current as the rating. Thus a 1 Hp motor will run on a 15 amp breaker, 1.5 on 20 amp breaker, 2 Hp on 30 amp breaker, etc. I can tell you from experience that you may still pop a breaker using those numbers if really hogging hard. Also consider that all wiring runs more than 15 feet will add to the load rating issues. On a 20 amp breaker circuit - 15 feet will use 10 gauge; 20 feet needs 8 gauge; 30 feet needs 6 gauge; 50 feet needs 4 gauge.
 
A 20 amp load on #10 wire will only drop 2 volts with a 50 ft run, that's only around 1/2% voltage drop. NEC allows 5% for a branch circuit, but 3% is better. Shucks, a 30 amp load would only give 2.7% volt drop at 100 ft on a #10 AWC cord.

Here's a good volt drop calculator: https://goo.gl/QARP6H
 
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