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PWM Controllers


Ian_H

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Hi,

 

I have been looking at DC controllers for some time, presently I use a H&M Duette but its a bit long in the tooth and I would like to experiment with PWM.

 

I have found two controllers, one I think uses the 555 timer and the other a 556.

 

http://www.ebay.co.uk/itm/141053442054?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

http://www.ebay.co.uk/itm/130983448241?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

 

From the descriptions you will see that the first one, using the 555 timer operates at 16 KHz whereas the second one operates at 500Hz.

 

So my question; Which of the two controllers would be better for controlling RTR locos?

 

Thanks

Ian

 

 

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These controllers are not intended for model control, so do not expect good results, but the second one looks like the best one to try. If you can find a way of adjusting the PWM frequency you might be able to make a good controller.

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A PWM controller for LESS than FIVE pounds ? ? ?  You don't expect a quality product, do you?

 

Having bought other similar electronic boards from Hong Kong / China I would expect these products to be very good quality.  Typically expect made up circuits to be a fifth of the price that you'd expect to pay in the UK.

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Hi Suzie

 

 but the second one looks like the best one to try.

 

Can I ask what makes you think the 2nd one, I assume with a 556 timer @ 500Hz, would be the better of the two? I thought the lower Fq would cause buzzing of the motor whereas the 1st one at 16KHz will probably not buzz (my hearing packs in around that fq ... so much for my liking for flash HiFi equipment :scratchhead: ).

 

Best regards

Ian

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A PWM controller for LESS than FIVE pounds ? ? ?  You don't expect a quality product, do you?

 

I think the construction looks pretty good. Also, a high price doesn't necessarily equate to a quality product. But if the controller turns out to be useless what have I lost? You could say almost £5.00 but that would be wrong because most of those components could be reused in another circuit!

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I think I read on another thread that these controllers don't go down to zero volts so you may not get the best control from it.  It could be used for layout lighting even if it not usable for loco control.  The ability to dim your ligting could be handy.

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Hi Andrew,

 

That was me :-) One of these, at least, is advertised as 0 - 100% so should give full control.

 

Andrew

 

I didn't notice that, or lets say I didn't notice that the other one, using a 556 timer?, had a duty cycle of 5 ~ 95% as opposed to 0~100%. Thanks for pointing that out. Also the 555 version is at 16kHz so probably won't rattle but what about heat?

 

Thanks once again

Ian

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Hi

I modified the amplitude modulated PWM controller by Roger Amos to use Mosfets and a second 555 to provide a reference 100Hz.

I set the current limit to trip at just above the current taken by one of the older locos. I also preset the feedback .

It works well. But I would not recommend it for a novice builder. You ideally need a digital storage oscilloscope when playing with one of these,

it makes it very easy to see whats happening. the output voltage does go right down to 0V.

Build cost around £7.50, Mosfets are lower cost than bipolar transistors like the 2n3055, and they run cooler as the on resistance is much lower.

I did find that Maplin are now selling FR4 stripboard, its much nicer to work on and the tracks don't lift as they do on SRBP board

 

Richard

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