3600 rpm motors

[Mark Williams]

Do the 3600 rpm motors generally have less torque than the 1450

 

[insanity]

ok lets see if i remember this correctly. If the two motors have the same horsepower rating then the 3600 rpm motor would have half the torque as the 1750 motor. Though I think that if you are useing step pullies or something similar then the torque of the final shaft would be the same at the same rpm.

 

[rfrink]

Wayne is exactly right. HP=T X RPM . When comparing 2 motors with the same HP...but different speeds, the faster motor has proportionally less torque. (ie: 2x speed----1/2 torque). Pulley ratios can "gear down" a fast speed to make more torque...if you gear down to 1/2 fast...you'll get 2X torque. Viola! a 3450rpm motor geared down 1/2 fast will have the same torque as a 1725rpm motor....both with the same HP. This also works the other way... over drive a 3450 to say 6900rpm...and you'll drop the torque by 1/2.

 

[Dan Gray]

Wayne is exactly right. HP=T X RPM . When comparing 2 motors with the same HP...but different speeds, the faster motor has proportionally less torque. (ie: 2x speed----1/2 torque). Pulley ratios can "gear down" a fast speed to make more torque...if you gear down to 1/2 fast...you'll get 2X torque. Viola! a 3450rpm motor geared down 1/2 fast will have the same torque as a 1725rpm motor....both with the same HP. This also works the other way... over drive a 3450 to say 6900rpm...and you'll drop the torque by 1/2.

rob if the 3450 motor is rated at 1 hp,, at that speed won't it double the hp
geared down by 1/2 to 1750?

1750 rpm rated at 1 Hp, using a 2" sheaved pulley =? hp
3450 rpm rated at 1 hp, using a 1" sheaved pulley =? hp
would not the 3450 motor have
double the HP of the 1750 motor at the belt...?
not talking torque here ,, I'm talking HP...

you're going to tell me that torque is worth more than HP right

 

[rlinger]

If you step it down with pulleys I doubt you will notice. At low voltage and the pulley is 1:1 yes, you may. I got my torque up by stepping the motor down with a pulley and using the DC drive to get to the low end RPMs. It works well for me. At 1:1 mine would bogg at real slow speed.

RL

 

[J-dogg]

Just like with cars. HP is braggin' rights. Torque is what gets you down the road.

 

[T Blade]

Going back to old motor head days. I'd rather have a set of 4:56-1 gears than 3:23-1 gears for those 1/4 mile races, in my 67 GTX, that's what help give me mid 12 second times through the quarter, (engine not quite stock) .

Just as my MMG grinder using a 1 1/2 HP treadmill motor with 4000RPM, I put a 2 5/8 " on the motor with a 5 1/4" pulley on the grinder drive shaft, which cuts the RPM at the grinder to 2000 RPM. I believe I don't need such high SFPM at the platen, I'd much rather have the torque at the belt produced by "gearing down".

Larry T

Member of NECKA & NCCA

 

[Dan Gray]

rob if the 3450 motor is rated at 1 hp,, at that speed won't it double the hp
geared down by 1/2 to 1750?

1750 rpm rated at 1 Hp, using a 2" sheaved pulley =? hp
3450 rpm rated at 1 hp, using a 1" sheaved pulley =? hp
would not the 3450 motor have
double the HP of the 1750 motor at the belt...?
not talking torque here ,, I'm talking HP...

you're going to tell me that torque is worth more than HP right

OK I've been around the block a few times.. I listed this just for clarifacation guys..
there's a method to my madness

that's why the
you're going to tell me that torque is worth more than HP right

apples to apples ... no veri this or veri that

 

[rfrink]

Dan, HP and torque are completely different entities. HP is a measure of energy...torque is a measure of force.

Energy is the product of Force and Speed. Or HP=TorqueXRPM

It boils down to the "basic energy in = energy out concept"

HP is the energy put out by the motor...it is directly related to the energy taken in by the motor measured in WATTS of electricity. So for a given system...if you put 1HP into the system...at best you'll only get 1 hp out. You cannot get more out than what you put in.

If a 3450 motor is rated at 1hp....then it is always 1 hp. ... gear it up or down or sideways...it is still 1 hp. It still takes in 1hp worth of electricity and still puts out 1 hp worth of energy.

Imagine, if you took the 1hp motor and geared it down...1/2 speed...no say 1/20,000...this won't make it a 20,000 hp motor... it is still 1 hp. But due to the gearing, you will increase the torque 20,000X and it will turn very very slow...and will take forever to move anything.

HP is Energy. In engineering, energy is never gained or loss...it simply changes and can always be accounted for. For example, a piece of coal has a given amount of chemical energy(calories)...the coal is burned...producing heat (thermal energy BTU's) ..heat is used in the power plant to make electricity(watts)...which runs the motor....which is used to raise a weight...which is dropped to forge a part...etc....

So..if we are talkng HP...we are talking Energy. Which can be BTU's, calories, watts, joules...there are many different units to describe the quantity...and HP is just one of them.

For your given machine...if you need a lot of enegy output....you need a lot of energy input.

Heck I'm not sure if this made any sense...but have fun with it.

-Rob

 

[fitzo]

So lemme see if I understand this:

if I pack the coal directly around the motor and light it the heat will produce "contact watts" and thus more HP without all the resistance loss from those transmission lines, right?

 

[indian george]

So lemme see if I understand this:

if I pack the coal directly around the motor and light it the heat will produce "contact watts" and thus more HP without all the resistance loss from those transmission lines, right?

Fatzo!!! Now you are sounding as thick headed as Dan.

 

[ysforge]

Alright, for those wondering, a simple explaination is that a 1725 rpm motor rated at one hp is putting out 750 watts of energy, and a 3450 rpm motor rated at 1 hp is putting out 750 watts energy.

As for the 1 hp 3450 rpm motor being geared down; If we where to assume that there where no mechanical losses, then the motors speed cut in half would provide twice the torque, which would be exactly the same as the torque provided by a 1 hp 1725 rpm motor.

The calculation goes something like this:

Horsepower = rpm x torque / 5252

A one horsepower motor running at 3450 rpm with a one pound load produces 18.268 in/lb of torque.

A one horsepower motor turning at 1725 rpm with a one pound load produces 36.536 in/lb of torque.

So the answer is, no a 1 horse motor geared down will not give more power at the belt than a 1 horse motor that isn't geared down.

Then there are the mechanical losses to consider, I've yet to find a bearing that was 100% efficient, and when I do, I'm buying all of 'em just to resell at a profit. so, ideally, the motor you should be running would be as close as possible to the final output speed you need.

Tony

 

[Dan Gray]

anyone else want to exsplain that again OK
now who thought it was the way I said it first come on fess up..
who now knows how it is..

see it's the shock efect that makes the ole farts learn and retain it hahaha
except IG they didn't have motors when dirt was new and he was kicking it around.. no need for brains back then hehehe

 

[Dan Gray]

Dan, HP and torque are completely different entities. HP is a measure of energy...torque is a measure of force.

Energy is the product of Force and Speed. Or HP=TorqueXRPM

It boils down to the "basic energy in = energy out concept"

HP is the energy put out by the motor...it is directly related to the energy taken in by the motor measured in WATTS of electricity. So for a given system...if you put 1HP into the system...at best you'll only get 1 hp out. You cannot get more out than what you put in.

If a 3450 motor is rated at 1hp....then it is always 1 hp. ... gear it up or down or sideways...it is still 1 hp. It still takes in 1hp worth of electricity and still puts out 1 hp worth of energy.

Imagine, if you took the 1hp motor and geared it down...1/2 speed...no say 1/20,000...this won't make it a 20,000 hp motor... it is still 1 hp. But due to the gearing, you will increase the torque 20,000X and it will turn very very slow...and will take forever to move anything.

HP is Energy. In engineering, energy is never gained or loss...it simply changes and can always be accounted for. For example, a piece of coal has a given amount of chemical energy(calories)...the coal is burned...producing heat (thermal energy BTU's) ..heat is used in the power plant to make electricity(watts)...which runs the motor....which is used to raise a weight...which is dropped to forge a part...etc....

So..if we are talkng HP...we are talking Energy. Which can be BTU's, calories, watts, joules...there are many different units to describe the quantity...and HP is just one of them.

For your given machine...if you need a lot of enegy output....you need a lot of energy input.

Heck I'm not sure if this made any sense...but have fun with it.

-Rob

Rob there's a point here..
throw that text book out for a min..
I understand in and out..but
if a motor at 3600 rpm's is rated at 1 hp at the shaft at 3600 rpm's
and a motor at 1750 rpm's is rated at 1 hp at the shaft 1750 rpm's
and you gear the 3600 motor down to 1750 , by the use of a smaller pulley compared to the 1750 Motor pulley..
causing it to run now at 1750
( something has to double from the reduction, newtons law.. )
you now have 2X what out of the 3600 motor,
if it = 2x nothing
what would the advantage be to the
3600 motor, if it's used in conjunction with belts and pulleys to run at 1750.
the reduction of 1/2" speed has to be converted to a posative energy, lost from the speed to something?..at the work end..
I call it 2x the power of the 1750 1 hp motor, if both motors are true 1 hp at their rated speeds.
tell me why this don't make sense...

 

[pso]

Dan

If I have remembered my physics courses correctly, the power rating is defined as the rate at which the motor does some work. Work is defined as movement against a force. Torque is a rotational (twisting) force.

The 3600 rpm motor is capable of turning at 3600 rpm with a certain torque load (T) on it's shaft. The 1750 rpm motor would be capable of turning at 1750 rpm with double the torque load (2T) on it's shaft.

Multiplying 3600 rpm by T gives the power rating of the motor. One gets the same power rating by multiplying 1750 rpm by 2T.

The different applications for motors require the motors to work against different torque levels and to move at different speeds. Thus, the manufacturers offer motors made to run at different speeds as a convenience to their users, reducing the need for them to use mechanisms, like gears and pullies, to increase or decrease the shaft speed.

I hope this made sense and was correct.

Phil

 

[ysforge]

so, ideally, the motor you should be running would be as close as possible to the final output speed you need.

Jeez, I don't know why I bother

In reality a motor geared down through some mechanical means, will always lose some power to the gearing, this is mechanical loss. it's usually negligable, but not always.

That said, a 3450 rpm motor geared in half,(1725 rpm) will have twice the torque of the 3450 rpm motor at full speed, or the same torque of the 1725 rpm motor at the same HP rating. one horsepower is one horspower, no mater how fast it's turning.

Tony

 

[rfrink]

Dan,

rated at 1hp...comparing 2 motors. a 3600rpm motor and 1800...

the 3600rpm motor has 1/2 the torque of the 1800rpm motor...but delivers it twice as fast.

When you gear down the 3600 to 1800...something does double....the torque doubles and the speed drops...now it has the same torque as the 1800rpm motor...and now it also has the same speed.

same torque-same speed=same hp.

It is important to recognize that the 3600rpm motor does not have the same torque at the shaft as the 1800rpm motor with the same HP rating.

 

[Dan Gray]

It is important to recognize that the 3600rpm motor does not have the same torque at the shaft as the 1800rpm motor with the same HP rating.


well that would have explained it



why not???

Do the 3600 rpm motors generally have less torque than the 1450

that would be a yes Mark anyone getting anything out of this.

 

[Mark Williams]

So does this mean that rated horsepower for a given motor is at max rated rpm ? Jsu to add to Dan's confusion.

 

[Dan Gray]

yes but don't turn the motor,
on it will use eletricity thus making your ele bill higher..but not twice as much as the other one if that one isn't used either .