# PWM AND HEAT



## John J (Dec 29, 2007)

Does Pulse Width Modulation cause heat in some componants?

Can it cause eletrical componants in your engine to over heat?

Wasn't there some manufacturer who had trouble with PWM and his Motors.


I was just in another post and thought of something else.

Could PWM, depending at what frequency you are operatating at ( probably at slow speed) cause gear failure like we see in the NW-2's 

I am having trouble with my SD-45s when I use my 27 MGHZ trackside mounted in a box car. 

It apears I do not have this problem with my old style Air Wire recievers.

JJ


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## rmcintir (Apr 24, 2009)

What component is heating up? My SD-45s have run well at 10-20KHz PWM with no heat issues at all. If you had said Bachmann, some of them have motor noise suppressors that definitely do not like PWM and MUST be removed. Any open frame motor may overheat as well. Some of these could be found in LGB locos. The can motors used in the SD-45 are fine, although with 4 motors it can draw quite a bit of power and a small receiver probably won't power it well under load.


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## Del Tapparo (Jan 4, 2008)

Proper PWM frequency is debatable amongst the experts. But in general, you don't want it too low or too high. Either one can increase heating of the motor. And of course it depends on the characteristics of your motor. In general terms, I think frequencies of 1KHZ to 20KHZ work the best. However the lower frequencies are audible. I use 20KHZ in my controls. Don't know of any problems yet, and I get excellent speed control over the entire range. For the average large scaler: not something you need to worry about.(Edit: except whining motors or motor hum can be pretty annoying).


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## Greg Elmassian (Jan 3, 2008)

Yes it not only can cause heat, it DOES cause heat, more heat than if you were running "pure dc" like a Bridgeworks power supply. 

BUT! Aristo locos have run on PWM power for years with no problems. 

Some motors had very little margin for additional heat, LGB made a big deal out of this, but many people run LGB locos on PWM and any LGB loco with a DCC decoder is already running PWM. 

So, I would think this concern with today's locos and modern decoders and power supplies is unfounded. 

Get an older decoder, or a PWM supply with a goofy frequency, well, then, it could (and has) cause problems. 

Bottom line, for the stuff you have JJ, in the words of the song: "don't worry, be happy!" 

Regards, Greg


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## TonyWalsham (Jan 2, 2008)

When you burn energy you generate heat. 
In layman's terms; 
1. With regular linear DC the most heat is generated at the controlling device. ie the power transistor, and requires heat sinking and often fan cooling. There is only a relatively small amount developed at the motor(s). Although this motor heat can escalate if the motors are pulling a very heavy load. 

2. With PWM output ESC's most of the heat is developed at the motors. This is not a problem if the motors are well ventilated to disperse the heat efficiently. The motor blocks in AristoCraft locos are well ventilated. The motors in many older LGB locos are not well ventilated and can overheat quite badly. That is not to say that the motor drivers do not develop heat. They do. Just not to the extent DC motor drivers do. It does depend on a number of factors including how efficient the PWM output transistor is.


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## Greg Elmassian (Jan 3, 2008)

I think the question was about PWM doing something different. 

The rapid rise times of the pulses do indeed cause more motor heating than "analog dc".... you are shoving a pulse of power into an inductor, and it's natural inclination is to resist, which makes more heat. 

I think most people are more concerned with motor damage/aging, but I have had instances where it's hard to get heat of the decoder out, especially since some motors are now fan cooled. 

Regards, Greg


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## Jerry McColgan (Feb 8, 2008)

Posted By John J on 11 Jun 2010 03:52 PM 
I am having trouble with my SD-45s when I use my 27 MGHZ trackside mounted in a box car. 

It apears I do not have this problem with my old style Air Wire recievers.

JJ 


Hi JJ,

This topic is beyond me other than I would think that your SD-45 is most likely Aristo-Craft (unless someone else makes a SD-45) so I would think it is pretty unlikely that PWC would cause a problem with it since all Aristo motors are most likely optimized for PWC.

If for some reason the PWC is causing a problem and you are using a 27 MHZ TE why not just switch the TE to linear and see what happens? If your problem continues it is probably nothing to do with PWC (I don't know the difference between PWC and PWM but if all is Aristo it should not matter).

What kind of problem are you having? Do you have a fan on your Train Engineer?

Jerry


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## Greg Elmassian (Jan 3, 2008)

With JJ in the desert, I would guess he has heat buildup in the box car. 

Many people use stock cars for the ventilation. 

Regards, Greg


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## John J (Dec 29, 2007)

Just to add a little diversity to this post. 

Change the word Heat to Current. 

No does that change the discustion any?


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## Greg Elmassian (Jan 3, 2008)

yes, it makes some of the sentences not make any sense at all! 

What is it that you REALLY want to know JJ? 

If you are trying to understand the things that use up batteries, you need to think of amp hours on a battery and watts used by the system... 

Regards, Greg


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## Gary Woolard (Jan 2, 2008)

I believe I've heard that some of the small 'coreless' motors, such as the one in LGB's little "Chloe", have greater problems in dispersing heat, and therefore LGB recommended not running the Chloe on PWM. Dunno if it's true, but I play it safe and only run my Chloe on linear power.


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## Greg Elmassian (Jan 3, 2008)

It's true, coreless motors seem to be a lot more sensitive and often are completely sealed, so no cooling air moves through them, to boot. 

We have this issue with very small motors in smaller scales. 

Regards Greg


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## TonyWalsham (Jan 2, 2008)

As long as the pwm frequency is high enough, at least 5 Khz, Faulhaber have said it is safe to use pwm with their motors. 
Most of the ESC's today are running at around 20 Khz.


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