3 wire motor controller

Community Projects
1

Hi All,

I need to try and replicate the functionality of a motor controller for an aquarium pump. The pump / motor is a 24v 75w motor which has 3 wires going to it (I am guessing +ve, -ve and control? ) and at the moment it has a little external controller which allows you to change the speed of the motor and stop / start it.

The reason I want to replicate the functionality is that I have a project which I have been working on that allows me to control most aspects of the aquarium from a web app using a rapsberry pi and a couple of Arduino’s etc. There are multiple motors I need to control and I am sick of having to get under the aquarium each time, choose between 4 different controllers to control the pump(s) I want so I would like to move all the functionality of the motor control back to my custom controller. If it was 2 wires for the motor, I am sure I could figure it out pretty easy with PWM and some Mosfets but this 3rd wire has thrown me.

Below is a picture of 2 of the controllers I need to replicate - functionality wise they are the same it is just that the smaller one controls a smaller motor - looking at them they are using a voltage regulator which seems to be connected to the 3rd wire in some fashion but they have removed the centre leg of the regulator - even getting that far I am still not overly sure what is going on.

http://pics.dontyell.net/album/AquaMan/ … 154336.jpg

http://pics.dontyell.net/album/AquaMan/ … 154405.jpg

http://pics.dontyell.net/album/AquaMan/ … 154017.jpg

http://pics.dontyell.net/album/AquaMan/ … 153654.jpg

Can anyone provide any tips on the best way to go about replacing these controllers so I can control the motors from Arduino?

Cheers,

Ben

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The pump / motor is a 24v 75w motor which has 3 wires going to it (I am guessing +ve, -ve and control? )

Guessing will not work. It is essential to determine the exact function(s) of the motor leads, and the nature of any control signals present (voltage levels, current, timing of any pulses, for all possible motor states). You will need an oscilloscope to get started.

The images of the bottom board suggest that the pump is a brushless motor, whereas the images of the top board does not. The two pumps/controllers may be completely different designs.

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jremington:
Guessing will not work. It is essential to determine the exact function(s) of the motor leads, and the nature of any control signals present (voltage levels, current, timing of any pulses, for all possible motor states). You will need an oscilloscope to get started.

The images of the bottom board suggest that the pump is a brushless motor, whereas the images of the top board does not. The two pumps/controllers may be completely different designs.

If I thought guessing would work, I would not have posted here looking for suggestions :slight_smile:

I just realised that the first image is cut off for some reason, here it is again -

http://pics.dontyell.net/album/AquaMan/ … 154336.jpg

Both controllers seem fundamentally the same - the smaller one has a 78M05 Voltage Regulator on it - http://www.futurlec.com/Linear/78M05.shtml and looking at the DS, it outputs 5, 6, 8, 12, 15, 18 and 24V.

The larger one has 6 of the 78M05’s on it - once again with my limited electronics knowledge, hazarding a guess that would be to increase the current handling capability of the controller? (each 78M05 will handle 0.5A) The larger motor seems to be rated at 75w @ 24v so that would be 3.125a? 6 x 78M05’s would be 3a and you could push it a bit with the heatsink?

I agree that an oscilloscope would be the best way forward here but unfortunately I do not have access to one - I do however have access to a number of these motor s which I am happy to sacrifice in the name of learning :slight_smile:

This is where my understanding starts to fall over though - if it is simply a voltage regulator controller the speed of the motor, how do I control one from a micro-controller like Arduino? And if that is also correct, what is the relationship between the VR and the 3rd wire?

If this is a brushless motor, am I better of trying an ESC? Looking at some examples online, I can interface with an ESC via PWM.

Lets say I can get my hands on an oscilloscope - what should I be looking for?

A lot of questions and assumptions I know

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I see only one 78M05 regulator (on the top board), and that would probably be for the microprocessor. I suspect in this case that the power controlling circuitry is in the motor itself.

It would be interesting to know what chip(s) are under the heat sink on the bottom board, but whatever is there undoubtedly handles the motor power. I can’t imagine a situation in which voltage regulator ICs would be used for that purpose.

I suggest to find a friend with some knowledge of electronics to help you with the analysis.

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I managed to find out from one of the reefing forums that the 3rd wire is simply a 0-5 volt signal (not PWM)- you simply apply a voltage between 0 and 5 volts to control the speed.