I'm looking for a device that will work in the same manner as a L298N motor controller. The L298N uses a PWM signal to control the on-off state of the motor. It supplies full input voltage at full current demand of the motor.
What I need is a device that will maintain the input voltage level while using a PWM input to vary the amount of current allowed to flow to the motor. It needs to handle 24v at 2a. Is this a thing I can buy off the shelf?
The concern is that the motor will be held in a stalled position most of the time. My thinking is if I limit the current supplied to the motor it won't suffer from the effects of stalling it.
Thanks.
John

 

Are you saying that you will detect the stall and use the PWM to adjust the motor current?

 

No. I won't be detecting the stall. The PWM control signal will be provided by an Arduino Mega2560.

 

Sorry, just one more clarification. When you say "device" do you mean an IC to put on your board?

 

That's OK. I don't think I'm explaining it very well.
Device= (hopefully) a pre-assembled plug&play unit that has a PWM control circuit, the power supply input, and the controlled output to the motor. Similar in design to a l298n motor driver. https://www.amazon.com/Organizer-Co...n&qid=1645647565&sprefix=l298n,aps,136&sr=8-3

 

That's OK. I don't think I'm explaining it very well.
Device= (hopefully) a pre-assembled plug&play unit that has a PWM control circuit, the power supply input, and the controlled output to the motor. Similar in design to a l298n motor driver. https://www.amazon.com/Organizer-Controller-H-Bridge-Stepper-Mega2560/dp/B07V3DRMGW/ref=mp_s_a_1_3?crid=30O5N937XRGN3&keywords=l298n&qid=1645647565&sprefix=l298n,aps,136&sr=8-3

Well, here is a possibility. Though it would have to be adapted, I don't think it would be too hard. It's based on the TB67H450FNG from Toshiba which is an integrated H-bridge with PWM input control. The chip is probably one of the best bets for the functionality I think you want. If not this board perhaps you can find another based on it.

 

That does not seem like what I am looking for.
Our conversation is forcing me to better articulate what I am looking for. That's a good thing.
Picture if you will a motor with an amp meter hooked up in series (as ammeters are) and a voltmeter hooked up in parallel with the motor. As the PWM input signal to the (as of yet unidentified) control device increases; the voltmeter will read 24 volts from the moment the motor starts turning and will stay at 24 volts. The amp meter will indicate a controlled increasing current flow until the motor reaches its maximum speed. So even if the motor is stalled there will not be an increase of current because the control device is not allowing additional current.
So, I guess I'm looking for a PWM controlled, constant voltage, variable current flow, Bi-directional motor controller.
How that for a description?
John

 

So, the motor is a load that has a particular voltage/current curve, that is, if you apply a particular voltage at a particular load the result will be a particular current. But you want to limit the current. OK, current limiting is a thing. However, given the relationship between voltage and current how would you keep the voltage constant but vary the current?

Power supplies that hold voltage constant varying the current to do it. Supplies that hod current constant vary voltage. Because the two are inextricably coupled you can trade one for the other but you can’t hold both constant unless you vary a third thing: resistance.

So it seems what you want is something that varies the resistance of the load using your PWM signal. Of course, you would most obviously do that by controlling speed, which doesn’t help you. You could put an electronic load in the circuit and control that so that you have a constant wattage supply that holds voltage fixed and varies current by adjusting resistance.

Of course that would be very silly. It would waste a lot of power as heat.

The only thing I can think of is to put a clutch on the motor so if it encounters enough torque so stall the clutch lets it spin until whatever it is trying to turn is easy enough for it to do that.

This is how I understand your situation. It is possible someone else might see something I don’t.

 

So, the motor is a load that has a particular voltage/current curve, that is, if you apply a particular voltage at a particular load the result will be a particular current. But you want to limit the current. OK, current limiting is a thing. However, given the relationship between voltage and current how would you keep the voltage constant but vary the current?

I guess if the current is limited it wouldn't matter what the voltage is. My concern is I don't want to burn out the motor from excessive current when it's in the stalled state.

 

I just found this video. DC 775 need how many amps? - DC 775 Full load Amps - Kaç amper çekiyor? - YouTube
As you can see the stalled amps draw is pretty extreme. I would like to "cap" the amp draw. I could probably continue to use the L298N for direction and speed control. Just limiting the maximum current allowed to flow is what I'm really after.

 

I just found this video. DC 775 need how many amps? - DC 775 Full load Amps - Kaç amper çekiyor? - YouTube
As you can see the stalled amps draw is pretty extreme. I would like to "cap" the amp draw. I could probably continue to use the L298N for direction and speed control. Just limiting the maximum current allowed to flow is what I'm really after.

Yes, and current limiting is generally done by dropping the voltage. The stall current of a motor is the highest it will use, and there will be a specification for how long the motor can tolerate it. But, if limiting the current to say, 2A at all times works, a current limiting power supply will work. On the other hand, when the motor is standing still before voltage is applied, it will have a very low resistance and develop that stall current until it starts moving.

If you can tolerate limiting the current to some value that makes ordinary operation possible than, except is the motor cools itself with a fan on it's own shaft, it shouldn't be harmed by the ordinary current level.

I also wonder how you will know when to stop limiting the current if you have to do it dynamically. That's what I think a clutch would be a good way to go. If you want dynamic operation, something like this, maybe: https://www.ato.com/electromagnetic-clutch-100nm

 

Thank you for all your help. I'm familiar with those type clutches. I scavenged several wheelchair motors from the landfill that have clutches on them. They are much larger motors that I plan to use for a Stewart Platform (my next project). I think I'm armed with enough knowledge now to cobble something together for testing.
Thanks again.
John

 

Thank you for all your help. I'm familiar with those type clutches. I scavenged several wheelchair motors from the landfill that have clutches on them. They are much larger motors that I plan to use for a Stewart Platform (my next project). I think I'm armed with enough knowledge now to cobble something together for testing.
Thanks again.
John

I do hope it was helpful. If you need more help, please don’t hesitate to stop back.

 

If you plan to reduce the current to limit the possibility of damaging the motor, you are really going to reduce the power delivered to the motor.

PWM works by reducing effective power (even though voltage is delivered at full, the average power in the PWM signal is controlled), and would be the simplest for you to implement.

 

After some searching, I put together a chain of components that work very well.
I am currently using an Arduino Mega board and a BTS7960 bi-directional motor driver to drive a 775 motor. This "combo" drives my DIY flight simulator rudder pedal.
There is one issue though. The native PWM frequency of the Arduino is 980 Hz. This makes the motor crazy loud. The frequency can be changed. The highest available frequency is 32 kHz, which is too high to use with the DC motor. The next highest available is 4 kHz. While I can't hear 4 kHz, my wife can. So it seems I still need to transform the PWM into a smooth variable voltage/current that won't make the motor sing it's 1 note song. I'm half tempted to attach a little RC servo to a rotary pot...
Thanks.
John