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Slow speed running in DC
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 Posted: Thu May 30th, 2013 09:25 pm
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kiwimark
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Hi all
   I have heard that a resistor across the terminals of a DC controller will help with slow speed running. As my layout is a 4x1 micro I do not need speed just fine control. I cannot seem to find any info on the subject as to resistor selection. I am using an older MRC Tech 2 controller.
Thanks in advance

Mark



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 Posted: Thu May 30th, 2013 11:28 pm
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Helmut
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@Mark
a liitle bit late, I just stumbled across your posting. That was true in the long-gone days when they used rheostats for speed control, and you had to adjust the resistor's value to the one used in your throttle. The tech2 is one of the more advanced electronic controllers whose characterisitics cannot be bettered by such measures.

Last edited on Thu May 30th, 2013 11:28 pm by Helmut



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 Posted: Fri May 31st, 2013 01:56 am
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kiwimark
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Thanks for that, I can assemble a car engine blindfolded but I am electronically challenged, I cannot seem to get any sort of grasp onto anything electron related.

Mark :cool:



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 Posted: Fri May 31st, 2013 02:41 am
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Herb Kephart
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Lack of ability to "creep" is usually an indication of friction in the mechanism with modern locos and power supplies.

Herb



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 Posted: Fri May 31st, 2013 03:29 am
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oztrainz
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Hi Mark,
FWIW, as a cheap test try a 5K ohm or 10K ohm potentiometer on the circuit downstream of your controller. Adjust you potentiometer so that you get the maximum top speed you want at 12V from your contoller. This will not defeat any friction in the mechanism however it should give you a finer control on your throttle because you are using the full range of the throttle to control a smaller voltage range to the locomotive motor.

You should be able to pick up these potentiomters at a Tandy/Radio Shack store or similar for a few dollars cost. Look for one that can handle a 1 amp load and it shouldn't get get hot or drag too much juice through you throttle.

if you are still getting jack rabbit starts take Herb's advice and check your mechanism. If everything is running smoothly mechanically, with even the standard throttle you should be able to get you loco to creep a sleeper a second or slower. With the body removed on an older style motor where you can see the armature, you should be able to see the motor cog through each comutator segment. if the problem is downstream of your motor at the wheels, if you rock the reverse switch you might see a bind at the same spot as the wheels go round. I would also be watching for the armature moving longways and tightening up on the worm gear as the volts are applied.

What brand of chassis are you using? If it is Bachmann they have been having issues with cracked gears on some models. Listen for a distinct "clicking" sound in the mechanism. It is the usual give away for a cracked gear

Good Luck

Last edited on Fri May 31st, 2013 03:35 am by oztrainz



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 Posted: Fri May 31st, 2013 09:08 am
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Toeffelholm
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Hi,

my friend KEG has a runaround track on his desk for testing purposes and for to run the locos that are still DC. As a simple solution to get rid of bad slow speed behaviour, he hooked up a DelTang Rx60 to the track, feeds it with a big capacity battery and uses his Tx21 transmitter to control his locos.

This way he runs his DC locos that need track power without any changes to the locos, but has the benefit of the excellent PWM motor control of the DT receivers.

A transformer could be used for power supply of the Rx60 as well, if it is less than 16V. But then you may need some additional electronic components and in case of interest you should ask DavidT who is active here as well.

Juergen

Last edited on Fri May 31st, 2013 09:11 am by Toeffelholm



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 Posted: Fri May 31st, 2013 08:32 pm
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kiwimark
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I have no problems with the locomotives its just that as I am building this for my grandson I do not wish to see a loco charging through the back of a building at 100mph as he can be a bit heavy handed with the throttle while he is learning. I just need to dial back the top speed a bit. A throttle stop may have to be the answer at the moment.
. I may even re-gear the locos to slow them down a bit. Thanks for all the ideas.

Mark



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 Posted: Sat Jun 1st, 2013 12:39 am
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oztrainz
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Hi Mark,
In that case, wire in the potentiometer on one of the wires between your controller and track, set your throttle to full volts and adjust the potentiometer to get the maximum speed you want to allow your grandson. Leaving the knob on the potentiometer in the same position, take the potentiometer out of the circuit and measure the resistance in the potentiometer with your multimeter using the resistance setting.

Buy a fixed resistor "close" to the same value (say less than + or - 10%, if in doubt go higher as it will give a slower top speed) and current carrying capacity and wire it in to where the potentiometer was. This fixed resistor will probably cost less than $1. You now have a fixed "limiting resistor" that will prevent your grandson driving your loco like 'Mallard" on its world record speed run. :)



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 Posted: Sat Jun 1st, 2013 12:51 am
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kiwimark
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Thanks John, I actually understand what you are describing and for me that is saying something. I will give that a try in the next couple of days.
Thanks again
   Mark



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