How to vary voltage with a constant current ( DC motor supply)?

[BGAmodz]

I have acquired a speed variator that i was planning to use for my project application , but i have noticed that the voltage is constant and current is variable .

And since the DC motor i got is turning a torque needy mechanism , i need to vary the voltage only , in other words only RPM should be controllable but still maintaining sufficient current requirement .

Is there an electronic way to do so ?

 

[crutschow]

You can't vary current and voltage independently. One or the other can be held constant but not both. A motor will take the current it needs if you apply a voltage. If you lower the voltage then it will take less current. The voltage supply just needs to have sufficient current capacity for the maximum motor current (which can be 10 times or more the nominal current when starting).

What is this "speed variator"?

 

[cowboybob]

Have you considered PWM (Pulse Width Modulation)?
https://www.google.com/#q=pwm+techniques+for+dc+motor+control

 

[dr pepper]

Sounds like what you have is a current source, the device will adjust the voltage up to a maximum in attempt to maintain a preset current.
As Cruts says you cannot limit one without affecting the other.
We need more info on your 'variator'

 

[Pommie]

If you feed a motor with a constant current then it will produce a constant torque from stall right up to when the voltage limit is reached. Is this what your variator is used for?

Edit, Google has no references to electronic variator. However, mechanical variators appear to be a continuously variable gearbox to give constant acceleration. A constant current source on an electric vehicle would also give constant acceleration (for the pedants, in a vacuum).

Mike.

 

[dr pepper]

Variator is a trade name by the firm P.I.V., they made/make gearboxes that have continuously variable gear ratios, usually from a chain with sliding laminations running across 2 pulleys that can slide open and closed varying the diameter, one of them being driven open/closed by a motor or handle, the other follows under spring tension but is at the opposite end of diameter adjustment.

 

[kinarfi]

I have acquired a speed variator that i was planning to use for my project application , but i have noticed that the voltage is constant and current is variable .

And since the DC motor i got is turning a torque needy mechanism , i need to vary the voltage only , in other words only RPM should be controllable but still maintaining sufficient current requirement .

Is there an electronic way to do so ?

On a dc motor, torque can be monitored by monitoring the current, speed can by monitored by monitoring the voltage. If your project needs torque, you may want a current source, but as stated earlier, they depend on each other.
During my days on an diesel electric oil rig, we would test the breakers by pinning the rotary table and applying full power, the voltage/speed meter would stay close to zero and the torque/current meter would go to ~ 1300 amp and trip the 1000 amp breaker and not even load the generator because the phase shift was close to 90 degrees.

 

[4pyros]

This is a variator; with pictures;
https://en.wikipedia.org/wiki/Continuously_variable_transmission

 

[BGAmodz]

Sounds like what you have is a current source, the device will adjust the voltage up to a maximum in attempt to maintain a preset current.
As Cruts says you cannot limit one without affecting the other.
We need more info on your 'variator'

On a dc motor, torque can be monitored by monitoring the current, speed can by monitored by monitoring the voltage. If your project needs torque, you may want a current source, but as stated earlier, they depend on each other.
During my days on an diesel electric oil rig, we would test the breakers by pinning the rotary table and applying full power, the voltage/speed meter would stay close to zero and the torque/current meter would go to ~ 1300 amp and trip the 1000 amp breaker and not even load the generator because the phase shift was close to 90 degrees.

Thanks for the interest in this topic .

So basically i want to reduce the motor speed (220 VDC/2.4A) for the project needs , but in the same time having a sufficient torque power to move the mechanism even at 24 V.

The speed controller that i have now don't do that , it is btw a thyristor based one and it varies the speed by varying the current , but the mechanism i have needs to be slowed down without losing current for the torque power .

I hope i explained well .

NB: By VARIATOR i just meant speed controller

 

[4pyros]

You need a PWM controller. What is you input voltage or supply voltage?

 

[BGAmodz]

You need a PWM controller. What is you input voltage or supply voltage?

Its 230 VAC

 

[dr pepper]

You have what sounds like a fancy light dimmer.
To get what you want you'll need to close the loop and have speed feddback to circuit that controls the variator to maintain a constant speed.