Increase Torque on 10 HP Motor Without RPM Change

[rickcjmac]

Howdy!

I have a 10 hp motor on a machine but it's only using 3 hp while it's running. The output shaft of the motor is connected to a bigger pulley to spin a wheel. Is there any way to increase the torque at the wheel while maintaining rpms? My first thought was to use more of the motor power by changing the pulley ratio, but that changes the rpms. Overall I am trying to get more torque at the wheel without changing the motor, but I'm not sure if that's actually possible. Thank you for your help!

 

[sophiecentaur]

I am not sure what you really mean by this question. If the motor is not actually stalling, then I reckon the mechanical load is less than the motor could cope with. Spinning a wheel shouldn't require a lot of power (unless the friction losses are very bad). You can only get torque out at a given speed if you increase the mechanical load and demand it.
But we'd need to know some more details for a good answer.

 

[meBigGuy]

The way to increase the torque at the load is to increase the load. Maybe you need to ask your question differently.

 

[sophiecentaur]

How are you measuring the 'Input Power' you think you are using? Measuring the I and V with separate meters won't give you the right answer because the phases will be nearly 90° apart.

 

[rickcjmac]

So I guess if I increase the load at the second pulley that will increase the load at the motor pulley. The motor will either maintain rpm meaning that it is drawing more power, or else the motor will stall meaning that it can't provide enough power for that load/rpm configuration. Does that sound right?

Sophiecentaur, the input power measurement was setup when I got here. I have to assume the guys before me did their work right setting up the measurement apparatus. From the looks of it they are measured simultaneously with a single meter.

Thank you for the help y'all!

 

[sophiecentaur]

Sophiecentaur, the input power measurement was setup when I got here. I have to assume the guys before me did their work right setting up the measurement apparatus. From the looks of it they are measured simultaneously with a single meter.

So you are saying (at least,implying, if you are just spinning a wheel) that the motor is consuming 3kW with no mechanical load? How are you cooling it (or the bearings of the wheel)?

 

[rickcjmac]

The wheel has a load but I want to increase the wheel's load and maintain its rpm. If I increase the load at the wheel will the motor maintain speed and draw more power? As far as cooling just natural convection cools the bearings.

 

[meBigGuy]

As you increase the load the motor will slow down a bit and as a result draw more current and output more power.

Do you understand how to model a motor in terms of the back-emf, and what determines the current.

 

[Windadct]

So "I have a 10 hp motor on a machine but it's only using 3 hp while it's running. " - again how do you know it is only using 3 HP? - What do you want ? To Increase the speed of the wheel? ( You wan to increase the Load? .. from the motor side this does not make sense - how are you adding load? )
What type of motor is this?

 

[meBigGuy]

You know, one would think that by now I would have learned to stay the heck out of motor threads except to ask questions.
It's probably AC and everything I know is wrong.

 

[sophiecentaur]

The wheel has a load

I think that would have been very relevant information for the OP. (??)
The way your motor responds to different loads is going to depend very much on its individual characteristic and its general type. Is the proposed change in load going to be a new fixed level or is the load going to vary?
The make and model of the motor will be stamped on it somewhere and the manufacturers could probably help you with its load / speed characteristics. 10hp is quite a beefy machine and it could be difficult to regulate its speed. I assume it is an AC motor.

 

[rickcjmac]

Do you understand how to model a motor in terms of the back-emf, and what determines the current.

No, that's totally foreign to me. I know what current is and that's about it.

How do you know it is only using 3 HP? What do you want? To Increase the speed of the wheel? (You want to increase the Load? .. from the motor side this does not make sense - how are you adding load? )
What type of motor is this?

I am about 90% sure that the power is being calculated with measured current and voltage. Essentially the wheel has a light brake on it. I want to increase the brake force but maintain rpm. It'll be difficult to make the change, so I need to be sure it'll work, so I'm trying to find out if my motor will keep up the speed and somehow compensate for the added load by drawing more current, thus using more power. As you can tell my electrical knowledge is pretty limited. It is an AC motor, I will try to get better specs on it.

I think that would have been very relevant information for the OP. (??)
The way your motor responds to different loads is going to depend very much on its individual characteristic and its general type. Is the proposed change in load going to be a new fixed level or is the load going to vary?
The make and model of the motor will be stamped on it somewhere and the manufacturers could probably help you with its load / speed characteristics. 10hp is quite a beefy machine and it could be difficult to regulate its speed. I assume it is an AC motor.

Sorry, I didn't know that made a difference. The current load is fixed and the new load will be fixed. Again, I'll try to get the motor specs and post them so we know exactly what we're looking at.

Thank you again for all of your help!

 

[sophiecentaur]

Essentially the wheel has a light brake on it

Yet again, this doesn't make sense to me. Your 3kW output,/input? that would imply the brake is doing about 4hp of work on something (hot?). The brake would be getting pretty hot ( or something else in your system). A real 3kW input means a real 3kW has to go somewhere. Hence my suggestion that the original power measurement was just VA and not W.
But I am totally confused as to what this is all about. You claim to know no EE but you seem to be running a pretty powerful EE experiment. Can you enlighten us?

 

[rickcjmac]

The wheel does get pretty hot but it's all steel so that's not a big problem. I came across this motor curve.:

It's not for my motor (I still don't have the exact specs of the motor) but if I understand correctly it shows that as motor load increases the watt input increases. That's what I was asking in the OP. Right now the motor is using 3 kW input and doing 3 kW of work, minus system losses. If I require say 5 kW of work from the motor the input will change to 5 kW to compensate. Do I have that right?