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DIY DC Controller - any ideas


Dan6470
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Hi, just to come in on this.

I'd recommend a simple emitter follower circuit, 16vac transformer a 2 amp bridge rectifier and a 33uF smoothing capacitor.

This will give you really good control of motors ranging from Triang to modern and will be acceptable for use with coreless motors and micro motors without undue buzz.

The all important ripple will be 100hZ here in the UK.

 

Hope this helps

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14 hours ago, mikesndbs said:

Hi, just to come in on this.

I'd recommend a simple emitter follower circuit, 16vac transformer a 2 amp bridge rectifier and a 33uF smoothing capacitor.

This will give you really good control of motors ranging from Triang to modern and will be acceptable for use with coreless motors and micro motors without undue buzz.

The all important ripple will be 100hZ here in the UK.

 

Hope this helps

Some sort of current limit required else in fault conditions you either fry the motor or fry the controller or both.

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17 hours ago, mikesndbs said:

Hi, just to come in on this.

I'd recommend a simple emitter follower circuit, 16vac transformer a 2 amp bridge rectifier and a 33uF smoothing capacitor.

This will give you really good control of motors ranging from Triang to modern and will be acceptable for use with coreless motors and micro motors without undue buzz.

The all important ripple will be 100hZ here in the UK.

 

Hope this helps

 

That doesn't use the available DC supply so he would need to purchase the transformer which may not be as cheap as the DC supply he already has.

I used emitter follower types for years but having seen how well my locos run on DCC I believe an H bridge circuit will do very well. In fact I think I will build one for the odd DC loco I still have.

 

Don

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The PSU he mentions in a computer one these are generally not the simple transformer bridge rectifier smoothing capacitor type. It is probably a switched mode power supply of some sort. I am using a 15v 35W samsung one to power a small DCC system and have a similar one from MERG to power their DCC system. Some of the these days work at a higher voltage than I would want to use. The one powering my laptop is 19v at 2.23A rather more than you need for a 12v motor probably running on 8 to 10v a lot of the time and drawing no more than 0.5A.  As Keith says you need a power limiter in case there is a short.

 

Don

 

 

 

 

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Thanks for all the replies. The controller I want to build is this one..

It looks like the one from Roger Amos's book. I have also seen a similar one on here under "home brew controller". Both are feedback units.

Both seem to suffer from lack of overload protection, though in the youtube version he drops in a 1amp thermal cut out at the end. This appears to have been put into the negative line..is this right and is this the right solution?

I have the ex-PC power supply delivering 12v, though I am happy to use my 16v ac gaugemaster transformer as I now understand that the "ripple" effect seems to be important.

Any other comments gratefully received!

 

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1 hour ago, ikcdab said:

Thanks for all the replies. The controller I want to build is this one..

It looks like the one from Roger Amos's book. I have also seen a similar one on here under "home brew controller". Both are feedback units.

Both seem to suffer from lack of overload protection, though in the youtube version he drops in a 1amp thermal cut out at the end. This appears to have been put into the negative line..is this right and is this the right solution?

I have the ex-PC power supply delivering 12v, though I am happy to use my 16v ac gaugemaster transformer as I now understand that the "ripple" effect seems to be important.

Any other comments gratefully received!

 

 

The 1 amp trip/set can be fitted in the input line to the circuit so that it will protect everything after.

Note the 33uF capacitor that needs to be fitted to the DC input line as well.

This prevents buzz on some coreless types but dose not negate the control ability.

 

The use of a low power PSU initially is highly recommended to guard against faults early on, if not a 5 watt 1 or 2 ohm resistor in the supply line for testing can help.

Good luck and let us know how you get on.

 

 

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57 minutes ago, mikesndbs said:

 

The 1 amp trip/set can be fitted in the input line to the circuit so that it will protect everything after.

Note the 33uF capacitor that needs to be fitted to the DC input line as well.

This prevents buzz on some coreless types but dose not negate the control ability.

 

The use of a low power PSU initially is highly recommended to guard against faults early on, if not a 5 watt 1 or 2 ohm resistor in the supply line for testing can help.

Good luck and let us know how you get on.

 

 

Thank you! This is the circuit from rmweb that I was intending to follow.

Screenshot_20200603-212305.png.0a2ab719eab2a66b54afb0dc498b7088.png

 

Slightly different from Roger Amos and the youtube series but very similar.

Do you mean for the 1amp tripset to go on the positive rail just after the rectifying diodes? And the capacitor in series in the similar location?

 

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47 minutes ago, ikcdab said:

Thank you! This is the circuit from rmweb that I was intending to follow.

Screenshot_20200603-212305.png.0a2ab719eab2a66b54afb0dc498b7088.png

 

Slightly different from Roger Amos and the youtube series but very similar.

Do you mean for the 1amp tripset to go on the positive rail just after the rectifying diodes? And the capacitor in series in the similar location?

 

 

 

Hi, place the 33uF 35 volt capacitor across the positive and negative rails of the power supply input, watch polarity. Place the trip/set in series with the positive rail of the PSU and circuit.

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1 hour ago, ikcdab said:

Thank you! This is the circuit from rmweb that I was intending to follow.

Screenshot_20200603-212305.png.0a2ab719eab2a66b54afb0dc498b7088.png

 

Slightly different from Roger Amos and the youtube series but very similar.

Do you mean for the 1amp tripset to go on the positive rail just after the rectifying diodes? And the capacitor in series in the similar location?

 

How exactly does the  voltage "fall" through the 0v point?

What comes out of a bridge rectifier is all the same polarity, it never crosses the 0v point.

power83.gif

In that case where is the BEMF measured?

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3 hours ago, melmerby said:

19v laptop supplies are not unusual for DCC systems

The Z21 uses one

The DR5000 used one but now has an adjustable voltage one.

 

That is fine for DCC but I personally wouldn't want to use it for a simple emitter follower  say you are running a loco  at 10v drawing 0.5A using a  15v PSU the outputstage has to dissipate 2.5watts. Running the same on 19v it has to dissipate 4.5watts. Also if the lco stalls the higher voltage will mean a higher stall current and fry the motor much quicker. However for a Garden line using heavier 0 gauge motors the 19v could be a better bet.

 

I too am a bit puzzled by Dukedog's explanation. What seems most likely to me is that at low speeds the pulsed nature of the voltage acts a bit like a PWM controller giving the motor a series of kicks from the wave peaks. If you want that effect a proper PWM circuit might be better. 

Don

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I think I understand Dukedog's reference to Back EMF. When a DC permennt magnet motor is running part of the voltage applied is overcoming the resistance of the windings and part is overcoming the resistance to turning effectively the Back EMF. As the supply is a series of half waves. For the start and end of each wave the voltage will be less than the BMF and the motor will start to slow. The middle part of the wave will be higher than the Back EMF and the motor will start to speed up. As there are 100 pulses per second (in the UK) the effect on the motor will not be visible and it will seem to run steady.

 

However the Computer PSU is probably a switched mode supply and is designed to produce a much smoother voltage output although some ripple may be evident. This will reduce the effect Dukedog mentions compared to a plain unsmoothed transformer. The circuit will still work as a simple emitter follower control as the motor will see a much steadier output.  As the peak voltage of a half wave supply is about 1.4 times the mean those high peaks can push through dirt etc when running slow on a low voltage setting, using the unsmoothed supply. 

 

Don

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Thank you for all the advice on here. I have now successfully built the first one...

20200616_134848.jpg.bae1d9ad4f67184c5a25a90a862c2c11.jpg20200616_134831.jpg.4772cdf71f8b0ec127a56d08cd51943a.jpg20200616_134858.jpg.6466d2c6307f25e1f6c097058fafd81d.jpg

 

No real issues aside from a dry joint or two. 

Now to complete the other 4. The faceplates and circuit boards are all done, they just need assembling....

 

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17 minutes ago, ikcdab said:

Thank you for all the advice on here. I have now successfully built the first one...

20200616_134848.jpg.bae1d9ad4f67184c5a25a90a862c2c11.jpg20200616_134831.jpg.4772cdf71f8b0ec127a56d08cd51943a.jpg20200616_134858.jpg.6466d2c6307f25e1f6c097058fafd81d.jpg

 

No real issues aside from a dry joint or two. 

Now to complete the other 4. The faceplates and circuit boards are all done, they just need assembling....

 

 

 

Nice work, have you tested it yet and did you add the 33uF to the input?

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4 minutes ago, mikesndbs said:

 

 

Nice work, have you tested it yet and did you add the 33uF to the input?

All tested ok. I didn't add the capacitor as I read somewhere a good reason why it wasn't needed. I'll try and find the reference.

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6 minutes ago, mikesndbs said:

 

 

Nice work, have you tested it yet and did you add the 33uF to the input?

Just found the ref. In "homebrew controller" he says "Note that there is NO smoothing capacitor, this is because the voltage needs to fall though the 0v point for the back EMF voltage to be measured. If a smoothing capacitor was fitted the controller would still work but, slow starts and smooth slow running would be impossible."

Hope that makes sense!

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17 hours ago, ikcdab said:

Just found the ref. In "homebrew controller" he says "Note that there is NO smoothing capacitor, this is because the voltage needs to fall though the 0v point for the back EMF voltage to be measured. If a smoothing capacitor was fitted the controller would still work but, slow starts and smooth slow running would be impossible."

Hope that makes sense!

 

What power supply are you using?  If it is a switched power supply like the computer ones the  voltage will not fall it is a fairly smooth output. A transformer with a simple rectifier wiill give the rising and falling voltage.

Don

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1 hour ago, Donw said:

 

 

What power supply are you using?  If it is a switched power supply like the computer ones the  voltage will not fall it is a fairly smooth output. A transformer with a simple rectifier wiill give the rising and falling voltage.

Don

Hi Don,  I  using a gaugemaster openframe 16v transformer.

How does that make a difference?

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The transformer output when rectified gives a series of pulses each one half of a sine wave. The voltage will from zeo rise sinusoidally and fall the same back to zero. A computer supply typically uses a switched supply system some of these can take any input from 100v to 240v and through clever circuitry give a fairly smooth DC supply which will always be above zero unless turned off. The smooth supply will not have the ripple effect which aids slow running.

The transformer is a good choice for that circuit.

Don 

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42 minutes ago, dhjgreen said:

Are you aware the heatsink is connected to the collector?

Yes. Is that a problem?

The heatsink is isolated from everything else.

 

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18 minutes ago, ikcdab said:

Yes. Is that a problem?

The heatsink is isolated from everything else.

 

No problem at all, it gives a good thermal link. Just checking you knew.

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