DC Motor Speed Control

[DEVELONET]

Hello, I am interested in finding out how a mechanical type speed control or speed selector works. I know very little about electronics but enough to get myself in trouble. What I have is a trolling motor that has a rotating speed and direction adjuster (fwd 3 speeds, Rev 2 speeds) and I want to make a control panel with two toggle switches... fwd/rev for one switch, hi\low speed for the other switch. A photo of the guts of this speed control is located here..

http://www.develonet.com/speedcont.jpg

What I would like to know is how these little copper plates determine the speed or if they do. Are they simply acting as resistors? I did not see any other components or chips in this unit. Any help is much appreciated.
Thanks,
Kirk

 

[Skogsgurra]

That looks like a switch that switches windings in the motor in and out and probably also reverses them.

What you can do is 1) verify that the windings are connected directly to this switch 2) make a detailed table (or diagram) showing what windings are connected and where they are connected when the switch is in different positions 3) hook up your switches so they perform the same.

You could also (probably, no guarantee) use a simple PWM controller and some preset setpoints that you select with a set of switches.

Gunnar Englund

http://www.gke.org

 

[OperaHouse]

That's interesting, I have the same project that has been on the back burner since last year. I'm building an electric boat with one of these motors hidden. Looks like the same unit. Mine also had two smaller sense wires that I couldn't determine the purpose for. Seemed to change the speed slightly if removed in forward direction and not in reverse. I thought temp or speed feedback. I assume this has PWM electronics for speed potted in the plastic. It doesn't have to be big. I only looked at it for a couple minutes to get some mechanical infor a year ago.

 

[Cardoso]

Is it an AC motor? 3 phase?
If so, my guess is that the little device switches windiwngs in the motor, adding or taking poles and hence changing the rotation and direction speed.

If this is the case, the copper plates only select the speed and direction of the motor. Still haven't figured out why the motor doesn't have 3 reverse speeds though.
But it is the cheapest way to have different speeds in a motor, I can guarantee you that!

If it is a DC motor, and depending on the speed you want it to turn, you should find some cheap ways to varie the speed. Look for DC motor PWM control and you'll find loads of schematics.

 

[ScottyUK]

But it is the cheapest way to have different speeds in a motor, I can guarantee you that!

Really? Motors wound for pole-changing service are expensive, long lead time, and are larger and heavier than their fixed-speed equivalents. The economic argument between using a standard motor + VSD or a multi-speed machine with two-speed controlgear is very close. We've just replaced six 125kW two-speed motors with standard 4-pole machines with a top-of-the-line VSD, and the economics came out in favour of the motor + VSD, without considering the many other benefits.

Anyway, the title of the original post was DC Motor Speed Control, so let's not take this thread off into the weeds by starting a discussion of AC machines. Feel free to start a new thread though!

----------------------------------

I don't suffer from insanity. I enjoy it...

 

[Cardoso]

My mistake for the DC motor... :$ LOL sorry, gotta get some more sleep