$4 to $15 PWM 12v DC Throttle

[Sumner]

Depending on what you have laying around you might be able to build this 12v PWM DC Throttle for as little as $4.00. I had seen this motor controller used for a DC throttle a couple places including on here so though for under $10 I'd give it a try.

I'm happy enough with it that I'll probably use it instead of the TECH II I've been using when testing used DC locos I've bought prior to installing a decoder in them. I have a lot and all of them will probably never get a decoder. I have a large yard planed for the layout and I'm considering wiring it so I could run a DC or DCC engine in that area and this throttle might be a better option vs. the TECH II as I'll have it on a tether so it would be more convenient for yard work vs. the larger stationary throttle.



The TECH II does have a little better control under 3mph (N scale mph). I can get the engines to creep down to 1 mph or less with it.



This throttle is very good down to 2-3 mph which I feel would work fine working the yard.



I bought the motor controller on Amazon ( HERE ) but you can find them a number of places.



Before designing a case and wasting potential time ….



..... I spent about 20 minutes soldering up some wires and picked out a power supply and gave it a test run. Satisfied that it was working well went ahead and designed a case for it. I have a number of the plug-in-the-wall power supplies like the one shown above. When things quit working I throw them away and keep the power supplies.

The controller is good for up to 2 amps according to the specs and I had a 2 amp power supply but decided to use a 1 amp that I have. It is suppose to have a circuit breaker but I didn't try shorting the track during my limited testing.



….. and ….



….. moved the controller and toggle switch into the case.



I had to modify the case a bit and have print files up with the modifications. I haven't and probably won't print it again so would like feedback if there are any problems with the print files that are up.



Might also look at other options for the shape of the case but there again probably won't spend the time on that as for my purposes at the moment it works/holds/feels fine.



You can find a demo of the throttle on YouTube ( HERE ).

The print files for the case on my thingiverse.com account ( HERE ).

A couple other links:

HandCab (modeled off a GP7/9 control stalk ( HERE )

Straight and Curved SpeedTraps ( HERE ).

Sumner

[mmagliaro]

That looks like a reasonable choice for a small PWM controller.  Another Amazon reviewer said they scoped it and the frequency is about 13 kHz, so there shouldn't be any motor noise.  Do you have any issue with locos creeping?  That same reviewer said that at minimum throttle, the average output voltage to the track is about 1.5v, which is a little high.

[Sumner]

That looks like a reasonable choice for a small PWM controller.  Another Amazon reviewer said they scoped it and the frequency is about 13 kHz, so there shouldn't be any motor noise.  Do you have any issue with locos creeping?  That same reviewer said that at minimum throttle, the average output voltage to the track is about 1.5v, which is a little high.

I just ran a little test and I have no electrical background so keep that in mind.

The knob on the controller does turn to 'off' and in 'off' no track voltage.  With no loco on the track I'm reading 1.8 volt in the lowest position, just before it clicks 'off'.

Just tested two locos, Kato E8/9 and Kato SD40.  Bought these off eBay a few years back and they have just been sitting and I haven't run them and they look brand new so think the previous owners didn't run them much if at all.

As soon as I put either on track the track voltage dropped from 1.8 volt to .1 volt with the knob at the lowest setting (not in 'off').  There is no movement.  Both start when the track voltage gets to 1.7v to 1.8v.  They both keep running down to about 1.4v which using my SpeedTrap speedometer is around 3 mph.  About 1.3-1.4 volts they both stop.

With my TECH they will run down to .5 mph to 1 mph.  I measured that speed the other day with the SpeedTrap but didn't have a meter on to read the track voltage so don't know what it was and the throttle was in 'pulse' mode.  I couldn't get them to run under 2 mph with this throttle and that was hard.  Good control down to 3 mph though.

When they stop I don't hear any humming or other noise from the loco.  Going forward for my needs I'll use this throttle over the TECH II.  If I set the layout's yard up to be able to run DC there at times (layout is DCC) this throttle on a 10-12' tether it will be easier to use vs. the larger TECH II.

Sumner

[mmagliaro]

Getting only 0.1v average voltage with a load on the rails is excellent.  That means your PWM circuit is getting down about as close to zero percent duty cycle as you can hope for.  And using a pot with an on/off switch, of course, gives you a good mechanical way to shut it fully off.

At 13 kHz, with such a low voltage, I'd be very surprised if you hear anything.   Looks like a good choice for a PWM controller.

[Tom L]

Thanks for the info in this post!  I’ve been meaning to build something like this for a switching layout I’m building but wasn’t sure what controller to use. I just got to it and hooked it up for a test.  Wow…no motor buzz and very smooth!   I had to buy multiple components from Amazon, it was like $35 for enough stuff to build 3 with leftover cases and dpdt switches (minus power supplies as I have several). Here is a photo next to a varipulse.  The case I got holds everything pretty easily, it could actually be a little bigger to fit better in my hand. I find the varipulse to be “buzzy” at the slow speeds I operated at, so this is going to replace it. 

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Thanks again for the post!

Tom L
Wellington CO

[Sumner]

....Wow…no motor buzz and very smooth!   I had to buy multiple components from Amazon, it was like $35 for enough stuff to build 3 with leftover cases and dpdt switches (minus power supplies as I have several). Here is a photo next to a varipulse.  The case I got holds everything pretty easily, it could actually be a little bigger to fit better in my hand. ..............

Glad it worked out.  If you don't mind I'll add your pictures to the throttle info on my site....

https://1fatgmc.com/RailRoad/DCC/page-36.html


The option to buy a case for those without a printer would be really nice. If you find time and can give me links to the parts you used I'll add those also. 

I like how you exited the case with the power cord.  I bought the cord shown ( HERE ) but haven't used it yet.  What did you use?

Thanks and you can PM me or post the info here.

Sumner

[Tom L]

Sure, you can certainly use the images if you like.  Here are the enclosures I used

https://a.co/d/3pWXKzD

And the wire is pretty much the same but I used lighter gauge. I have about 7 ft of cord so I can access both sides of my little layout.

https://a.co/d/33odJEc

I used shrink tube around the wire at the hole in the enclosure and a small zip tie inside to keep it in place.

Similar to your tests, with the knob all the way to the stop but not clicked off, I get .08v to the rails.  It dimly illuminates the lights on my Kato RSC2 but there is no movement or sound from the motor.  The engine wasn’t unusually warm or anything after switching cars around for 30 minutes or so.

Tom L
Wellington CO

[Sumner]

Thanks I added the images and links ...

https://1fatgmc.com/RailRoad/DCC/page-36.html

Sumner

[peteski]

Similar to your tests, with the knob all the way to the stop but not clicked off, I get .08v to the rails.  It dimly illuminates the lights on my Kato RSC2 but there is no movement or sound from the motor.  The engine wasn’t unusually warm or anything after switching cars around for 30 minutes or so.

Tom L
Wellington CO

There is no way 0.08V will illuminate any LED.  Did you measure in AC or DC range?  Either way, if the PWM frequency is high enough then even the AC range of most multimeters will not accurately measure the voltage.  Since it is a PWM throttle, any usable voltage present on the output will be in a form of full 12V square pulses. Those can easily illuminate the LED (which, depending on its emitted color needs 1.7-3V to glow).  LEDs are very fast devices, so they can emit light on such shot burst of voltage.  With the very low duty cycle (throttle at minimum speed), the human eye will see a faint glow.

[mmagliaro]

This experiment just demonstrates what we already knew... high frequency PWM is a great way to control a DC motor (that's why DCC decoders use it!)  The only things you have to manage are getting the frequency high enough to avoid motor noise, and getting the duty cycle low enough at "off" so that you don't get enough power to the motor to make it creep.  That PWM module you are using has scored on both counts.  I'm not surprised that the Varipulse makes some motor hum at low settings.  According to the instruction sheet for the Varipulse, it uses 60 Hz square pulses that go from 1% to 100 % duty cycle (pure DC, full throttle).   60 Hz square waves are great for making a motor creep, but very noisy.  Older, klunkier motors might need something like that to make they creep (remember, the Varipulse has been around a long time).  But nothing we are using these days needs pulses that slow.

[Tom L]

Did I type an extra decimal place?  Maybe .8 without a loco on the tracks?   Here’s a few pics of the loco light.  In a normally lit room you can’t really see it, I only noticed it when it was stopped on a dark hidden track. Again, it doesn’t produce any noise or movement that I can detect.

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I am using a 6vdc power supply I had lying around and since I’m just switching around on a small layout with one loco, which is a Kato RS or an older Atlas GP, and that seems to work fine.  I tried an Atlas SD7 with the newer slow motor and it needs a little more juice than that.

Anyway, yeah it seems like a nice option for a cheap, easy to build DC throttle. 

Tom L
Wellington CO

[peteski]

The lowest voltage a visible-light LED will start conducting (which means start emitting light)  would be around 1.3V.  White LEDs (which are based on a blue LED with phosphor coating) wwill nto start conducting til around 2.5V  what you are showing on your Fluke could be either some DC voltage leaking into the PWM driver output, or some very low-duty PWM pulses fooling the meter into reading 0.046V DC.  That's not enough to make even a red LED glow, much less a white LED.  The only way to see what is actually on the output of the throttle would be to use an oscilloscope.

But this is all a moot point since the DC motor is not receiving enough power to make it run. I  didn't suspect you of making things up Tom  L. I just wanted to explain why the LED glows while the motor is not running.

[Tom L]

Hey, it’s good to get input from you guys about this stuff....outside of the very basics, electrical stuff like this is magic I don’t understand.  Probably why I stick with DC control!

Tom L
Wellington CO

[peteski]

My brain must have been taking a nap when I posted my last reply.  Tom, I didn't think you were making things up.    I edited my last post.

[Tom L]

Haha….didn't take it that way

Hey, while I’ve got your attention, If I buy a power supply for this, is there anything to keep in mind or is a $6 Amazon wall wart ok?


Tom L
Wellington CO