# Constant Torque & Constant HP



## paulengr (Oct 8, 2017)

HP=torque x RPM / 5252



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## Helmut (May 7, 2014)

paulengr said:


> HP=torque x RPM / 5252
> 
> 
> 
> Sent from my iPhone using Tapatalk



I think the question I am asking, is what is the difference between the two?
When should this motor be wired as a wye, in the high torque mode, vs delta, in the horsepower mode? I think I get the difference in torque, but only in starting torque, not running torque. Horsepower is the energy needed to run the load?

Does this sound right?


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## paulengr (Oct 8, 2017)

With VFDs up to rates speed, torque is approximately constant. Above rated, HP is constant. This also applies to DC motors.


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## Helmut (May 7, 2014)

paulengr said:


> With VFDs up to rates speed, torque is approximately constant. Above rated, HP is constant. This also applies to DC motors.
> 
> 
> Sent from my iPhone using Tapatalk


Thanks, but no VFD in this issue. Standard full voltage contactor with heater overloads.


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## paulengr (Oct 8, 2017)

https://www.electricaltechnology.org/2014/09/comparison-between-star-and-delta-connections.html




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## Helmut (May 7, 2014)

I am thinking variable speed cordless drill.

Slow speed=high torque
High speed=low torque


If you have a high speed/high torque motor....wouldn't it have to use more KVA to obtain this?

Vs a high speed low toque motor?


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## TGGT (Oct 28, 2012)

Helmut said:


> I am thinking variable speed cordless drill.
> 
> Slow speed=high torque
> High speed=low torque
> ...


Drills have gears that change the torque, a motor does not so I don't think it's apples to apples.

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## paulengr (Oct 8, 2017)

Yes if speed and torque both go up Horsepower has to go up also. HP is approximately proportional to kva and HP x 0.746 = kw. The reason kw isn’t kva (kva x pf).


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## Wiresmith (Feb 9, 2013)

i don't know if this will help or hurt

power=forceXvelocity, 


torque=forceXradius





sidenote
(Velocity=distance/Time,)


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## sparkiez (Aug 1, 2015)

Here is an example:

Very large wash basin belt driven. OEM equipment had a delta-wye starter. The machine could be loaded with up to 2000 pounds of product at a time and often over-loaded with product. The motor started in a delta configuration, using torque, and then a timer swapped the motor from delta to wye to keep rotation for agitation.

In this case, the pump is needing a lot of torque to hold the negative pressure of the vacuum, so it is a delta pump, so that would be something to keep in mind. In the above example, we "simplified" that circuit by going to a 3-wire start-stop back to a standard starter in the MCC. Then, we wired the motor for wye. Then we started getting incessant calls during production that the washer was stopped, and had to reset the overloads. The overloads were then increased in size, and as of the time I left two years later, the overloads still tripped from time to time.

Also the motors started lasting less than a year. This was a pretty large motor, but I can't remember the size. Just be wary of that.


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## gpop (May 14, 2018)

most 6 lead motors would have a label showing dual voltage or start/run wiring unless its a specialist motor like a dual speed. A 3 lead motor would only show one voltage on the data plate.

You will come across all sorts of motor configurations like y, yy, delta, double delta, etc. Most of these are at higher horsepower simply due to the fact that a the T leads can only be so big and to give a option of reduced voltage starting.

voltage with out speed equals heat so reducing the voltage until the motor gains speed reduces temperature. In the days before VFDs you could not reduce voltage unless you increased the number of motor coils.

With Y/delta starting you are really connecting 2 coil packs in series on start up which means each coil pack sees half the voltage. When the motor is up to speed you switch the motor so each coil is seeing full voltage. 

If you have a 6 lead motor that shows start/run connection patterns and you are only using one contactor (3 wires from mcc) then the motor should be wire to run. If you wire it to the start pattern the voltage per coil is reduced so for the same amount of work the ampage will increase causing it to trip.

With out seeing the motor data plate its hard to really say what kind of motor you are dealing with.


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## Helmut (May 7, 2014)

gpop said:


> With out seeing the motor data plate its hard to really say what kind of motor you are dealing with.


see below



Helmut said:


> View attachment 125665


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## gpop (May 14, 2018)

ok it looks like a constant torque 2 speed motor as explained on your other post so lets take a step back and look at the basics

60 hp at 1780 rpm equals about 180 ft lbs

125 hp at 3525 rpm equals about 180 ft lbs

so the torque is the same (close enough)

all the motor is doing is giving you a option of wiring it as a 2 wye to give you a 3600 rpm motor that's rated at 125hp or wiring it as a single delta to give you a option of a 1800 rpm 60hp motor. 

Nothing is free in this world so 60hp will cost you 90 amps of 440v at 1800 rpm and 125hp at twice the speed will cost you 155 amps of 440v. 

On paper its easy to explain how the coils in a motor work but its way to hard to explain on the internet. You can google how motor coils work and get a good idea.

The 2 wye should then make sense as its like a wye motor except its 2 of them running in parallel. 

Now the real question is based on the motor that failed. 

its data plate showed it was a 125 hp 3560 rpm 480v motor rated at 140 amps. So you are good based on hp, torque, and speed but are you good on voltage (over loads would need to be adjusted or changed). 
The new motor is rated at 440v which ive never worked and I have no clue what voltage you are wired to.


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## Helmut (May 7, 2014)

gpop said:


> The 2 wye should then make sense as its like a wye motor except its 2 of them running in parallel.
> 
> Now the real question is based on the motor that failed.
> 
> ...


The reason it failed is because they were pulling about 200Hp out of the motor. The overloads in the contactor were by-passed.

According to John's document in another thread, I has 3 options with this motor. 
Constant torque connection
Variable torque connection
Constant Horsepower

I want constant horsepower I think, at high speed.

This shows me to connect in a delta arrangement, leaving leads 1,2,3 open.

Not sure why you say run it in a wye for high speed. That would be constant torque. and I think the application I have is for horsepower. I base that on the old motor I took out, which was a standard delta 125HP. 3 lead motor.

Does this sound right?


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## gpop (May 14, 2018)

Helmut said:


> The reason it failed is because they were pulling about 200Hp out of the motor. The overloads in the contactor were by-passed.
> 
> According to John's document in another thread, I has 3 options with this motor.
> Constant torque connection
> ...


 
I have to be honest.

Ive been doing this job for a while and I have no idea where you are getting your 3 options from. I think you may need to go back to the link john gave you. 

Only one diagram is the same as your motor. The other diagrams are for other motors. You do not have 3 options you have 1 option and that's the wiring diagram designed for your motor. 

Also the quote about bypassed over loads and it pulling 200hp kinda scares me.


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## Helmut (May 7, 2014)

gpop said:


> I have to be honest.
> 
> Ive been doing this job for a while and I have no idea where you are getting your 3 options from. I think you may need to go back to the link john gave you.
> 
> ...


 read this thread

Page 6 of the doc John posted


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## gpop (May 14, 2018)

page 6 has 3 different motors on it 


how many motors do you have


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## Helmut (May 7, 2014)

gpop said:


> page 6 has 3 different motors on it
> 
> 
> how many motors do you have


Page 6 shows the different configurations for a two speed, single winding, 3 phase motor.


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