Constant lights with dc

Model Railroader Electronics and DCC
21

You need to put a bridge rectifier in front of that circuit instead of the diode if the track polarity is going to change.

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22

Did that used to be called a wheatstone bridge?

23

No, the wheatstone bridge was a primitive circuit to measure an unknown resistance, we just use a multimeter nowadays. :smiley:

The Bridge rectifier is a component that has four diodes that converts AC to DC or will adjust the polarity of a DC input to always be the same on the output.

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24

Ahem - the Wheatstone Bridge is still widely used for a variety of applications, with strain gauges almost always used in a Wheatstone Bridge configuration.

There are a couple of advantages of a bridge rectifier over using a single diode. One is getting ā€œfull waveā€ rectification and the other is no DC on the secondary winding.

25

That is exactly what I had used from a post somewhere on the web that made the diodes start smokin at full throttle. I donā€™t remember where I saw it (there have been so many) but it said to use 4 in4001 diodes and 1.5 bulbs.

26

Alright, after reading so much my eyeballs are smokin,this sounds like what Iā€™ll try.On somebodies link the author sezzz take a supertex cl2n3-g regulator and wire it in series with the anode side of an led to the ground side of the power source. This would be thru the frame. Of course the cathode goā€™s to the hot side of the motor. Anybody disagree?

27

I forgot to thank everybody for the help. This has been quite the journey.

28

Note that the CL2 does not like reverse polarity, and the DC voltage you send it should be filtered. If the motor reverses polarity, you need a diode, and for filtering a 47uf cap or larger.

29

Thats good because I canā€™t find anybody that has one. But! While hunting for that I came across a 20ma led driver with a diagram to hook it up. That and some 3 mm ledā€™s are in the mail. I rebuilt an automatic transmission from an 88 dodge pickup with way less confusion than this.Seems like everything I come across is out of date or obsolete. If this doesnā€™t work Iā€™ll drill holes in the damned thing and put wooden matchsticks in it and make a lap.

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