Pulse Width Modulator PMW: Electric motor variable speed controller

[DanielG]

This might be informative to anyone with an electric Kayak or anyone who uses electric motors to power your boat. It's been talked about here in other threads, usually in relation to Kayaks.

 

Last fall I installed a Pulse Width modulator on my two motor, minn kota 35 lb/thrust, electric catamaran. Homemade of course. (see lower thumbnail) I originally had one motor connected directly to 12 volts. The second used the 5 speed controller that came on the motor that I relocated to a console. The controllers have limited lifespan located outside of the motor for some reason. I had gone through two of them.

 

The Pule Width Modulator is an electronic device that is basically a motor variable speed control. As I understand it, it sends rapid pulses to control the speed that is very efficient. For the first time I've put about 6 hours on it this spring and I must say, that if it holds up I'm impressed. And the thing is available on amazon or ebay for about 17 bucks. Many of them have a reversing switch wired in. Wiring and incidentals add another $5. And it's simple. Two wires connect from the battery and two connect to the motor. Screw down connectors marked motor + and -, and battery + and -. 

The variable resistor is smooth and very linear. i.e. it goes from 0 to max with a smoothly variable speed increase.

 

Comparing it with my other motor which is turned on full with a switch or off, no in between. I'd say the PWM produces about 90% of the thrust of the direct connection. I expected that. The nature of the unit and the way it works should give about 10% longer battery life though from what I've read.

 

This is the one I got. They come in many varieties. Look up 'pulse width modulator' on amazon. I chose this one even though I had to add my own DPDT reverse switch because it was 60 amps. Many of the others are 30-50.

 

[schplurg]

These have been mentioned before, I think I mentioned them once, but it doesn't hurt to do again. Rarely see or hear of anyone using these, probably because most people don't know they exist.

 

I haven't bought the trolling motor yet but I will be using one of these when I do.

 

Just connect it between the motor and the battery. Very cool, especially for a yak I think.

[Stankyninja]

Great job DanielG.  I am going to do the same with mine asap.  Just curious, how big was your battery your using?  I have a 30lb Minn Kota and I am going get a 30ah lithium battery for it.  I was hoping that after the PMC, i can run at least 4-6 hrs on this setup.  

[MN Fisher]

33 minutes ago, Stankyninja said:

Great job DanielG.  I am going to do the same with mine asap.  Just curious, how big was your battery your using?  I have a 30lb Minn Kota and I am going get a 30ah lithium battery for it.  I was hoping that after the PMC, i can run at least 4-6 hrs on this setup.  

4-6 hours on a 30ah battery? Possible, if you don't run 'all out' often. I have a 30lb MinnKota as well and after looking at the specs, got a 75ah battery. Here's the specs - thrust is how many pounds it delivers, AMPS is the draw - so at speed 5, your 30ah battery will last 1 hour.

SPEED AMPS THRUST

 

1           8           4

 

2           10         6

 

3           14         10

 

4           20         15

 

5           30         30

[Way2slow]

Not new, I still have one of these I bought when they first came out.  Been so long don't remember with, sometime back in the 70's I think.  Funny too, they want twice as much for that used one as I paid new.

https://www.ebay.com/itm/274635413867

 

PWM is like a very fast switch turning the motor on and off. As you decrease the speed, the longer the off pulse and shorter the on pulse.   By limiting the on time, the motor can still develop the power needed but requires much less power (basically wasted power) to do that.

Similar to the new variable frequency AC motors in a lot of high efficiency refrigeration compressor in used now.   That's also why you have to be very careful what kind of generator you use for backup power.

[Bankc]

Thanks for the review!  I may add on one day, if I ever decide to permanently mount my motor to the stern.  But right now, I have it mounted to the side, and the handle is just too convenient.  

 

If you want to, you could rig up another DPDT switch to bypass the PWM controller, and give you a direct connection option.  Kind of like an overdrive switch to maximize efficiency at full power.  Just wire it before the input of the PWM and have the two outputs wired so one runs to the PWM's input, and the other to the PWM's output (where the motor is connected).  It might be wise to hook a pair of diodes in series at the output so that the bypassed power can't feed in through the output of the PWM.  It probably wouldn't be an issue, but a little extra safety wouldn't be a bad thing.  

[Jimbojackson]

Add a cooling fan, lots of heat.