# Giving RPM input to a DC Motor Speed Controller



## MattsAwesomeStuff (Aug 10, 2017)

I don't think any Series DC controller has knowledge of RPM.

You would need a sensor on the motor itself to know its speed, and then you can take that and use it to alter the throttle given to the Curtis.

I dunno, maybe you could resolve it by knowing the voltage and current, but, I wouldn't mickeymouse about if this is important to you, just get a cheap speed sensor for the motor shaft.


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## tallatghazi (Sep 29, 2018)

Hi,
I wish we could use Engine's Crank Shaft Sensor (to get RPM/Speed of the Engine's fly wheel) but then how we will use that produced AC voltage (generating from magnetic crack shaft sensor)? How we will translate that AC voltage variation for the input of Controller's throttle.

Target:
Target is take Engine's LIVE RPM (using any IR/RF device having RS232 interface) and to give it to a DC Motor Speed Controller (Curtis 1244) and then run the motor on SAME as engine's Live RPM.

Curtis 1244 offers 5 different types for Throttle input, as below:
Type 1: two-wire 5kΩ–0 throttles
Type 2: 0–5V throttles, current source throttles, three-wire potentiometer
throttles, and electronic throttles—wired for single-ended operation
Type 3: two-wire 0–5kΩ throttles
Type 4: 0–5V and three-wire potentiometer throttles—wired for wigwagstyle
operation
Type 5: CAN-Nodes throttles

QUESTION:
is it possible to use any of above mentioned Throttle input TYPE?


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## brian_ (Feb 7, 2017)

Why would you want to do this? The application determines the speed accuracy required and other requirements of the control system.

Inherently a brushed DC motor controller has no direct control of motor speed.


MattsAwesomeStuff said:


> I don't think any Series DC controller has knowledge of RPM.


... and so this is true - the controller doesn't really need to know the speed.



MattsAwesomeStuff said:


> You would need a sensor on the motor itself to know its speed, and then you can take that and use it to alter the throttle given to the Curtis.


I agree; the obvious solution is to use a separate controller which adjusts the motor controller input to achieve the desired motor speed (which is the engine speed). Any microprocessor-controlled motor controller could do this itself... if it were programmed with the speed control logic and had a speed sensor input. I don't know if there are any controllers which do this.

I did look at a couple of Curtis models, and while the pump controllers refer to "speed", they don't control to a specific motor speed. There might be a model with real speed control, but I don't know which one it would be.



MattsAwesomeStuff said:


> I dunno, maybe you could resolve it by knowing the voltage and current, but, I wouldn't mickeymouse about if this is important to you, just get a cheap speed sensor for the motor shaft.


Guessing from voltage and current wouldn't be reliable or accurate, so I agree that that a speed sensor is required.


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## brian_ (Feb 7, 2017)

tallatghazi said:


> Target:
> Target is take Engine's LIVE RPM (using any IR/RF device having RS232 interface) and to give it to a DC Motor Speed Controller (Curtis 1244) and then run the motor on SAME as engine's Live RPM.
> 
> Curtis 1244 offers 5 different types for Throttle input, as below:
> ...


If the separate speed controller is a microprocessor-based device, the CAN input might the easiest to use. Using CAN would avoid converting the digital result of the speed controller's calculation to analog, just to feed it to the motor controller where it is converted back to digital.

The Curtis 1244 is a "SepEx" (separately excited stator winding) motor controller... is that really the motor type which you are using? It's not a problem at all... just a bit unusual for DIY EVs.


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## tallatghazi (Sep 29, 2018)

Thanks for your kind inputs, lets put a real time case, may be like this I could able to more easily highlight my required target.

I want to convert my diesel car to a hybrid (Diesel + Electric). Along its engine, I would like to install an extra DC Motor (which will share Engine’s LOAD by synchronizing 100% with same RPM) using a controller.

Please check this video for your reference: https://www.youtube.com/watch?v=4-Vck6oCi3A

Now my question is that will your previously mentioned solution of using Speed Sensor work 100% correctly? or will there be any changes to the plan?

If the only solution is to use a speed sensor to get Engine's RPM then how speed sensor and controller will communicate with each other to run DC Motor on 100% same RPM (as of Engine)?

I have not yet purchased any DC Motor or Controller, So I am open for any suggestion.


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## brian_ (Feb 7, 2017)

tallatghazi said:


> I want to convert my diesel car to a hybrid (Diesel + Electric). Along its engine, I would like to install an extra DC Motor (which will share Engine’s LOAD by synchronizing 100% with same RPM) using a controller.


I wondered if that might be the plan. It is a simple parallel hybrid.



tallatghazi said:


> Now my question is that will your previously mentioned solution of using Speed Sensor work 100% correctly? or will there be any changes to the plan?


Since the the electric motor is mechanically connected to the engine (by a belt in the video), there is no need for the speed control that is being planned. The motor can only turn in synch with the engine, no matter what you do with the motor controller.

More importantly, you cannot successfully use speed control for the motor. Imagine if your control system was just one percent off of the correct speed (too high), and the engine was turning at 2,000 rpm, so the controller was trying to drive the motor at 2020 rpm: the controller would apply full power to the motor instead of sharing the load. Just one percent low and the controller would be trying to reach 1,980 rpm, so it would be applying no power at all. You need to be asking the motor controller for a chosen level of torque or power, not a specific speed.

All you need to do to share load is provide the controller with a "throttle" signal to be used for torque control. That can be the same as the engine's load input (which is not actually "throttle", because it is a diesel). Of course a functional hybrid needs more sophistication than that, with multiple modes of operation (including regenerative braking unrelated to the engine's "throttle" setting), as implemented in every production hybrid.


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## tallatghazi (Sep 29, 2018)

Yes target is exact that "I want to convert my diesel car to a hybrid (Diesel + Electric). Along its engine, I would like to install an extra DC Motor (which will share Engine’s LOAD by synchronizing 100% with same RPM) using a controller" 
But it can (sorry for the correction) be a Diesel or a Gasoline Engine.

The point regarding load & torque that you have raised is very important.

So you are saying that I should buy for a DC Motor Torque Controller instead of a DC Motor Speed Controller?

If yes, then are there any videos, textual or any kind of guidance available on internet regarding "Syncing DC Motor's Torque with Engine's Load" or "Syncing Torque Controller with a throttle signals (which usually gives 0.5v to 3.0v to car's ECU)"

On this forum or any other forum (according to your knowledge), has any worked on this model before?


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## brian_ (Feb 7, 2017)

tallatghazi said:


> The point regarding load & torque that you have raised is very important.
> 
> So you are saying that I should buy for a DC Motor Torque Controller instead of a DC Motor Speed Controller?


I think we discussed that there are few if any DC motor speed controllers, so all of the available controllers (such as anything from Curtis) are designed to control motor torque, and would be appropriate.



tallatghazi said:


> If yes, then are there any videos, textual or any kind of guidance available on internet regarding "Syncing DC Motor's Torque with Engine's Load" or "Syncing Torque Controller with a throttle signals (which usually gives 0.5v to 3.0v to car's ECU)"
> 
> On this forum or any other forum (according to your knowledge), has any worked on this model before?


Although many people consider DIY hybrid projects, very few people (if any) actually build them.

The examples to copy would be every parallel hybrid that has been put in production, such as the Honda Insight and Civic and any other hybrid with a conventional transmission, and all of the mild hybrids (or belt-alternator-starter systems) from companies such as GM. Of course it's difficult to determine the details of their control designs by examining the vehicles, so technical publications by the manufacturers would be the best source.


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## tallatghazi (Sep 29, 2018)

Thanks for your all input, its really great information and giving me my directions. Basically what I am targeting is an IMA (Integrated Motor Assist) technology.

Please do let me know if you find ANY forum or Information related to "DIY IMA" and also if you know any ready-made controller available in the market for IMA scenario (I am also search but you are a good expert).

Thanks!


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