What Voltage to Use With PWM Controller?

[BG John]

I'm trying a cheap Chinese PWM controller on one of my DC layouts. Power is coming from a 13 volt DC wall wart power supply. Is it OK to power the layout from 13 volts with PWM, or should I reduce it? The layout is only half a branch terminus plus fiddle yard, so locos won't be going very fast. What's a good voltage to aim for that won't risk trashing any motors?

 

I'll also be using this to provide 5 volts to an Arduino though a voltage regulator, so it's no problem adding another voltage regulator, but I think it will reduce the voltage my a minimum of a couple of volts (I haven't tried them yet).

 

 

[BG John]

The Arduino has a V_in pin that gives you the input voltage from the jack bus. For PWM, 13V is fine. If still in doubt, use 9V instead.

Thanks. I think I'll fit a regulator anyway. I'd like to be able to see how 12v locos run on 7.4v, as part of my experiments with radio control, so this is an opportunity to try it.

 

I want 5v for the Arduino to provide separate power relays and servos, so I don't risk overloading the Arduino outputs, so will run the Uno off 5v too.

[Theakerr]

I purchased about 10 of these cheap Chinese PWM controllers.  According to the data sheet they can take up to 24 VDC.  I am using 18 VDC with no problems except when I get the polarity wrong and they literally go up in smoke.

[34theletterbetweenB&D]

...I'd like to be able to see how 12v locos run on 7.4v....

 Be sure to test every design you are thinking of using. Characteristics vary widely between designs, and that's before taking any account of manufacturing variation within production of a design. Some motors used in current OO will run very slowly on PWM maximum output from 7.4V input, and if they happen to be coupled to a high ratio gear train you may see a scale 1 or 2mph: creeping along rather than slow in other words.

[BG John]

I purchased about 10 of these cheap Chinese PWM controllers.  According to the data sheet they can take up to 24 VDC.  I am using 18 VDC with no problems except when I get the polarity wrong and they literally go up in smoke.

Have you got video of that? I bet it's not as dramatic as a Lipo battery being overcharged though!

[BG John]

 Be sure to test every design you are thinking of using. Characteristics vary widely between designs, and that's before taking any account of manufacturing variation within production of a design. Some motors used in current OO will run very slowly on PWM maximum output from 7.4V input, and if they happen to be coupled to a high ratio gear train you may see a scale 1 or 2mph: creeping along rather than slow in other words.

I've got a variety of motors, ranging from very old to a few new RTR, plus a number of different types of cheap Chinese motors. There won't be many locos running on each of the layouts I'm building though. I'll probably replace some of the older motors anyway. I'm trying to find decent 3 and 6 volt motors for use in 4mm scale RC locos, as I can then run them on a single 3.7v Lipo battery. The trouble is that there aren't many options. My original plan was just to use RC in O gauge, where I'm not re-motoring my Dapol Terriers, so I need to find out whether I need to step up the voltage or if they are OK on 7.4v. It's all very complicated and confusing!

 

Anyway, I can gradually start experimenting, and see what works, and what doesn't.

[DCB]

I would worry about not having overload protection on a wall wart, equally batteries pack a lot of amps if shorted.

 

The lower voltage you can get away with PWM the better your locos will like it, maybe get one of those variable voltage power packs from Maplin etc with various tappings from 1.5 to 14 volts.   It is ideal if the PWM control has to be flat out for your locos top speed as the motors run much smoother with wider pulses than higher voltages and short ones.

[BG John]

I would worry about not having overload protection on a wall wart, equally batteries pack a lot of amps if shorted.

 

The lower voltage you can get away with PWM the better your locos will like it, maybe get one of those variable voltage power packs from Maplin etc with various tappings from 1.5 to 14 volts.   It is ideal if the PWM control has to be flat out for your locos top speed as the motors run much smoother with wider pulses than higher voltages and short ones.

Overload protection is something else I need to look into. The power supply for this layout is only 13v at 1.4A, but I'll be using laptop power supplies for some of my other layouts. It's on my to-do list. It's taking time to get all this stuff together, as I'm also learning about using Arduinos to control everything on the layout. This layout has a stand alone PWM controller running off the same power supply as the Arduino, but I'm planning wireless remote control for other layouts, with a PWM motor driver controlled by an Arduino.

 

That's an interesting point about the voltage for PWM. I'm using one of these voltage regulators, so can set it to any voltage I choose. As each layout will only have a couple of locos for regular use, it shouldn't be too difficult to get the best setting.

[d00m]

Out of interest do those voltage regulators give the same output regardless of input? Also what is the max mamp/amp output?

[BG John]

Out of interest do those voltage regulators give the same output regardless of input? Also what is the max mamp/amp output?

They do give the same output, within a fraction of a volt. Very useful when I have a selection of power supplies ranging from 13 to 19 volts. If you buy any, you may need to do quite a lot of anti-clockwise turns before the voltage starts changing. Mine were all set for a high output voltage, and I originally thought they were faulty!

 

These are advertised as 3A maximum. They are available from lots of suppliers, who sometimes quote different figures. I think you may need to add a heatsink for high currents. I think for modern loco motors they should be more than adequate.

 

They're much cheaper if you buy from China, and you can find them on AliExpress quite a bit cheaper than eBay. Search for LM2596, and you're spoilt for choice! There are also versions with an input/output voltage display, and you can also get some that limit current as well as voltage. I spotted some heatsinks on AliExpress when I was looking for a couple with voltage display, if you think you need them. Without a voltage display, I had no problem setting the voltage with a multimeter on the output, but I want a couple that are quick to adjust for testing.

[d00m]

Thanks for that. They are very cheap compared to the individual components needed to build one and they are small!

I will be buying some as they will be perfect in conjunction with a home brew circuit I have for constant carriage lighting using 5 v led strips available on a roll from Ama**n sold as 'USB warm white'.

I am still dc pwm using an old system - 'ECM Compspeed' which are very few and far between on a certain auction site...