# passenger car wiring



## Bwells (Mar 30, 2014)

I have been working on lighting some passenger cars for awhile now but took the good months off and just returned to the train room. I had left off at the fourth car and everything works as planned. I just finished car #5 and when I connect it to car 4 the whole thing goes dark. I do have a lot of capacitance in the circuit but my reasoning was that I wanted to hold up the LEDs for awhile after power down, slow dim. It doesn't work but they are still in the circuit. When I connect the fifth car to the fourth the whole thing stopped. I pulled the shell off of what I call the power car and checked some spots and found that the 7809 voltage regulator was only passing 5.32 VDC which apparently is not enough to light the LED strips I am using. The 7809 is rated at 1.5 amps so I doubt I am over working it. I'm leaning toward the excessive capacitance and thinking this maybe too much. No problem as I can remove them but my question is, when a voltage regulator goes bad does it drop the output? Below is a rough diagram of my circuit. I have replaced the voltage regulator but have not tried hooking it back up, gun shy I guess.


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## Lemonhawk (Sep 24, 2013)

I assume the LED's have the proper resistors. You may need to put a resistor in series with the caps and diode across the resistor. The resistor will limit the current going into the caps and the diode will full voltage/current go back into the circuit. On turn on, the caps act like a short until they build up the charge, hence the current limiting resistor. But you don't want to limit anything going out out hence the diode. The 7809 will use a lot of current all the time as they are not very efficient but that start-up short probably wiped it out.


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## gunrunnerjohn (Nov 10, 2010)

I think you have a misconception about power ratings. While the regulator is rated at over an amp, that's with a pretty large heatsink! With no heatsink, 50-75ma will be more like the maximum.

The capacitance has nothing to do with the failure. However, a more efficient way to use the capacitors is have all the capacitance before the regulator, you'll get much better performance.

How many LED's in each car?


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## Bwells (Mar 30, 2014)

Good point John. If the caps are in front of the 7809, they would charge to 12.5 volts but the way I did it only charges them to 9. I think I'll lose the big ones as they aren't doing what I want. There is no heatsink on the 7809 and I would say when I add the 5th car total length of LED strips is 4 1/2 feet. I still have one more car to do which will add another 11". Ugh, a heatsink maybe a complete redesign! I do have weights on the car floor.


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## Bwells (Mar 30, 2014)

Lemonhawk, I am using the standard LED strip lights so I don't think any resistors are needed. The excessive capacitance is not doing what I planned so I am going to remove them. A cap in front of and behind the voltage regular should take care of any ripple. It sounds like I need a heatsink for the 7809 or one that passes 5 amps! Not sure but this is a bummer as my homemade circuit board is really cute. By the way, model railroading is fun.


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## gunrunnerjohn (Nov 10, 2010)

Well, you have identified your problem, you're trying to drive way too much lighting from one little regulator. It would do it with a big heatsink.

FWIW, they have thermal shutdown, so it should have survived the overload.

For jobs like this, I developed this little module. I bought the switching power supply board on the left off eBay for less than a dollar, and I build the top board to add the bridge rectifier, bulk filtering, and the choke for DCS compatibility. This board can comfortably push out 1/4A without getting hot, it's a step up from linear regulators.


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## PoppetFlatsRR (Jul 29, 2018)

You guys are amazing. My level of ability it to buy another light and hope it works. Someday I hope to understand all of this. Doubtful that will happen. Thanks for sharing, even though I can't understand it at all. Dumb as a rock.


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## Bwells (Mar 30, 2014)

Okay, what is a switching power supply board? The way I look at it is I need a bridge to change to DC and a voltage regulator to step down the voltage, nothing more. Can I add just a heatsink to the voltage regulator? Do they make larger voltage regulators that can handle the load? This is HO so width of components is maybe 7/8". I do have some large heatsinks from some RC car speed controllers that I could cut down to fit.

Edit: It did survive one episode and while I took it apart to inspect it and test, it worked. So I did the same thing again and now nothing. I know you don't do the same thing twice and expect a different outcome but now I am positive that is true.


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## gunrunnerjohn (Nov 10, 2010)

FWIW, for HO, I'd use the tiny regulator module I have with a bridge and capacitor in front of it. The board I showed above is about 7/8" long and 3/4" wide. I have another lower capacity board that's less than half an inch wide and about 1" long that I've used as well. Both are DC-DC boards and require filtered unregulated DC on the inputs.

A brief description of the differences between a linear regulator and a switching regulator.

_Linear regulators are a great choice for powering very low powered devices or applications where the difference between the input voltage and output voltage is small. They are a simple and cheap solution, but linear regulators are normally inefficient because the difference between the input voltage and regulated output voltage is continually dissipated as heat.

Switching regulators are efficient because the series element is either fully conducting or switched off so it dissipates almost no power. Switching regulators are able to generate output voltages that are higher than the input voltage or of opposite polarity, unlike linear regulators. The versatility of these converters allow configuration for buck, boost, buck-boost, flyback, inverting in isolated and non-isolated applications._


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## Bwells (Mar 30, 2014)

Good post John. Thanks for the tutorial on the two types of regulators. I'll follow your advice of a bridge, cap and the switching regulator. I found this on Amazon and will give it a try.
https://www.amazon.com/eBoot-MP1584...544114194&sr=8-8&keywords=switching+regulator


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## gunrunnerjohn (Nov 10, 2010)

Looks like the one I use on my little sandwich board. Same parts in all the same places. You can figure this one is good for 300-400 milliamps with no additional heatsinking. It should solve your problem.


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## Bwells (Mar 30, 2014)

It should be here Saturday so I'll give it a try. I'm going to Radio Shack tomorrow to grab a couple bridges. I'll let you know about the outcome. I have a feeling it is going to be an ugly configuration but we'll see! Thanks again.


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## gunrunnerjohn (Nov 10, 2010)

Remember the bulk capacitance after the bridge and before the regulator board.


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## Bwells (Mar 30, 2014)

Yes sir, got that. I'm just hoping the wire connection holes will accept the solder in screw connectors. I have some 5 mm, 3 mm and I think 2mm. It would make life easier but I'll find out.
https://www.alliedelec.com/phoenix-...MI9c-dqcWM3wIVA9VkCh2Huw5rEAQYAiABEgICOPD_BwE


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## gunrunnerjohn (Nov 10, 2010)

It's not going to work with any of those, the connections that are next to each other on the corners are the same connection, the + and - are on opposite corners. You'll have to break out the soldering iron.

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BTW, you're paying way too much for those terminal blocks! 

How about ten of them for a dollar?

https://www.ebay.com/itm/10pcs-2-Po...76517d7:g:brYAAOSwI4ZbZDRK:rk:7:pf:0&LH_BIN=1


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## Bwells (Mar 30, 2014)

I assume the two holes next to each other are connected which is good as that will give me a screw for the bridge and one for the capacitor on each input. I have a bunch of them That is the quickest pic I could find since I don't know what they are called. I'm hoping the holes are 5mm apart on each corner, four gizmos soldered in and perfect!

edit: that is a good price, I don't remember what I paid for them.


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## Bwells (Mar 30, 2014)

How do they do that? 99 cents with free shipping from China. Simply amazing. It would probably cost me 50 cents to mail you a postcard! Something doesn't add up.


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## gunrunnerjohn (Nov 10, 2010)

Bwells said:


> I assume the two holes next to each other are connected which is good as that will give me a screw for the bridge and one for the capacitor on each input. I have a bunch of them That is the quickest pic I could find since I don't know what they are called. I'm hoping the holes are 5mm apart on each corner, four gizmos soldered in and perfect!
> 
> edit: that is a good price, I don't remember what I paid for them.


Well, unless you're using the "_new metric system_", they're only 2.5mm apart. 



Bwells said:


> How do they do that? 99 cents with free shipping from China. Simply amazing. It would probably cost me 50 cents to mail you a postcard! Something doesn't add up.


The reason stuff from China is so cheap is called E-Packet.

The Postal Service is losing millions a year to help you buy cheap stuff from China


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## Lemonhawk (Sep 24, 2013)

With all the trouble messing around with the power supply and such I wonder if just getting a cheap decoder would work just as good. You could also turn the lights on and off via the throttle!


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## gunrunnerjohn (Nov 10, 2010)

A decoder isn't likely to supply enough power to light five coaches, is it?


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## Bwells (Mar 30, 2014)

Good idea but I wonder if the amp draw would be too much for a decoder. I'm trying to light 5 feet of LED strip lights so I will try what John suggested and see what happens.

Edit: didn't see your post John but I'm actually lighting six!


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## Bwells (Mar 30, 2014)

I have received the switching voltage regulator and I'm now trying to figure out how to add a cap bank before it and after the bridge rectifier. I have 3 1F super caps rated at 5 volts so I need to put them in series and I will be feeding them with 12.5 volts. From what I understand, John mentioned to use a Zener diode to balance them and I have 3 4.7 volt zeners but I am not quite sure on the direction of them. Below is a drawing of the total circuit and a blowup of the cap bank in question. Are the zeners configured correctly? If you see anything amiss here let me know. The cap bank should have a total capacitance of 1/3 F which should hold up the LED strips for awhile.


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## gunrunnerjohn (Nov 10, 2010)

What in the world is all of that???

Just add bulk capacitance after the bridge rectifier and before the input leads to the switcher! Perhaps start with 2200F at 35 volts and see how that works.

It looks like you're trying to use supercaps, those are not necessary unless you're trying to hold up the lights for seconds or minutes.


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## Bwells (Mar 30, 2014)

Shoot John, I thought I did a good job. Yes, the bulk capacitance is after the bridge and before the regulator. Flicker is of no concern due to my wheel pickup arrangement and yes, I want to hold up the LEDs as long as 1/3 F will last. How about my zeners, are they oriented the correct way?


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