Controller Troubles

[SeeYou190]

Harrison...

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Everything Randy said, plus one more thing.

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When testing a power pack output, it is always a good idea to have a lightbulb across the rails to provide a little bit of a load and current flow. This makes your meter checks "dynamic" instead of "static".

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Have you tried it with a locomotive?

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-Kevin

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[rrinker]

 What's wrong is that you are working with an old rheostat power pack. The voltage on the rails changes only because there is a load being drawn by the loco's motor. When using a meter, which if it's halfway decent has an input impedence of something like 10 megaohms, there's effectively no load at all. There's probably nothing wrong with your circuit at all.

 Now here's the problem - if that old power pack you took apart was made for HO scale - it will run old BB locos and older stuff just fine, but modern locos will do the same thing the meter did - take off at full speed as soon as you move the throttle off the stop position, and not be controllable. Most modern locos have motors that draw a fraction of the power of old locos, so the load is too small for the rheostat to actually drop any real amount of voltage.

 An N scale one MIGHT work. But then it would be unable to control any older locos or any with higher current motors.

 This problem was solved with transistor throttles, the voltage on the rails does not depend on the load of the motor, and you can easily watch the voltage change even with a multimeter.

                                              --Randy

 

[richg1998]

I was wondering when he said slide thing? What is he using? Does he has strong electronics understanding?

I remember some very old throttles that used brass strips off multiple secondary contacts of the transformer.

Right now we are all guessing is why I asked for a schematic along with a photo of parts.

Rich

[GMTRacing]

Well Big Daddy since it's half time (UConn/Tulane) I marched downstairs and fired up my trusty MRC and you are exactly right. Voltage varies with the throttle. Is the problem because our intrepid Harrison has cut out everything from the old transformer save the rheostat?  Like I said, electrics are not my strong suit.   J.R. 

[BigDaddy]

GMTRacing

As soon as you crack the throttle, you should see the voltage of the unit but the actual current supplied will increase as you move the throttle (less resistance).

My MRC doesn't work that way.  The more I turn the throttle, the more the volts increase.  The engine speeds up because it sees more volts not more amps.

[GMTRacing]

Harrison,

  Electrics are not my strong suit and I'm sure someone with actual knowledge will answer this better. I think you are confusing voltage and amperage. The slide piece of your controller is a variable resistor. As soon as you crack the throttle, you should see the voltage of the unit but the actual current supplied will increase as you move the throttle (less resistance). J.R.

[BigDaddy]

Harrison

I attached the wires from the power to the terminals on my Railpower 1370

I get the wrong end of the stick on posts like this.  To me that means power goes from terminals to the Railpower 1370 as the handheld.  But a 1370 looks exactly like what you describe as the power pack that you stripped down.  What is the handheld?

edit  As I read this over, if it goes from 0 to 100 when you move the base throttle any, it must be a fault in the base throttle.

[richg1998]

Draw a schematic of what you have will make a lot more sense than a photo of the parts.

A schematic is how we normaly construct an electronic project.

Rich

[Harrison]

Today I took apart an old power pack, planning to turn it into a handheld throttle. I cut and removed all of it exept the slide thing that controls the speed and the direction switch. I attached the wires from the power to the terminals on my Railpower 1370 and turned it on. I then tested the wires to the track with my voltage meter. With the stationary throttle on full and the "handheld" on full, the meter reads full, but at half, it still reads full. When the handheld is at stop, the meter reads nothing, but as soon as I advance the throttle, the meter goes right up to full. What gives? I can post photos if the is helpfull.