# POWERING 5 VOLT SMOKE UNITS WITH MORE THAN 5 VOLTS



## Madman (Jan 5, 2008)

This topic has been covered many times in the distant past. However, I need a refresher course in simple electronics. I want to install 5 volt smoke units in some of my locos that do not have the circuitry to step the power down to the required five volts. Would someone please post a diagram or description of the parts I need to accomplish the task?


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## Greg Elmassian (Jan 3, 2008)

5 volt regulator, buy one from Radio shack, the circuit is on the package... just a couple of caps for noise reduction/filtering, 3 terminal device, input, output and ground. 

Regards, Greg


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## K27_463 (Jan 2, 2008)

The correct answer depends on a few more things. What voltage are you starting with? Is it pure DC like a battery, or is it rectified from some sort of power supply? If straight DC , then you do not even need the caps Greg mentioned. However, a 5 v three leg regulator cannot dissipate enough power to regulate down to 5v from more than 12 volts or so if mounted in free air . If you have 15- 24 v starting out, then you will need a very good sized heat sink on the 5v regulator, and you may need to go 2 stage, for example take 20v down to 12 with a 12v heat sinked regulator ( 12v three leg device such as 7812/7912, ) and then in turn step that 12v output down to 5v with a 7805 device. TO 220 case style heat sinks are very cheap and readily available for three leg devices such as these. Be aware that in such a scenario , whether 2 stage or not, you will make a lot of heat and are burning off a lot of voltage. One more point: you can run 5v smokers at 9volts pretty well, does not shorten life much and really improves output, just keep it wet when on. 9v three leg regulators exist also. 

Jonathan/EMW


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## Dan Pierce (Jan 2, 2008)

LGB runs their lights and smoke units on 6 to 6.8 volts. 

You can get a 6 volt regulator (7806). 

Also, you can place a diode in the ground leg of the 7805 and get 5.7 volts. 

http://1stclass.mylargescale.com/danpierce/LM7805.jpg


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## Madman (Jan 5, 2008)

I'm not sure that I understand your diagram. The two wires that are indicated by AA +/- to battery, are these the wires that would be connected to the smoke unit? Otherwise, I am assuming that the bridge rectifier would be labeled as such on, lets say, the All Electronics site, as would the voltage regulator. Does the LM on the regulator indicate anything?


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## Greg Elmassian (Jan 3, 2008)

What Jon sais about heat sinking is very appropriate, I should have mentioned the heat sink, and that, depending on the current, you might not be able to use the lm7805... 

There are also 3 amp, 3 terminal regulators, but they are expensive: 

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM150K STEEL-ND 

Regards, Greg


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## Dan Pierce (Jan 2, 2008)

The diagram I posted was for the bubble car (pustfix) and the AA was for the AA battery connections. 

So Dan the madman, this AA connection would be lights or smoke units. 

Remove the diode and place a wire in its place and change to a 7806 for 6 volts. 

Greg is correct, a heat sink is required and I mount mine on the weights inside engines. Also the 220 case is 1 amp for most mamufacturers. 

These devices used to be labeled LM7805, but now are just the generic 4 digit number, the last 2 being the voltage output. 
I have found.. 7805, 7806, 7808, 7809, 7812, 7815 for 5, 6, 8, 9, 12, and 15 volts. There is also a 7.5 volt unit available.


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## Madman (Jan 5, 2008)

OK Dan, I have it right up to the capacitors. Are they the symbols indicated with a plus and minus sign separated by two horizontal lines? It looks like you have two shown on your diagram. One on each side of the 7805.


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## Dan Pierce (Jan 2, 2008)

You are correct on the capacitors for the + and - signs. 

Glass ceramic is best for the one on the left if you can find then and can be .1 uf to 1 uf, and I prefer 35WVDC as some power supplies go over 25 volts. 

The capacitor on the right is set to be 220 uf for 200ma load, and should be bigger if the load is bigger. Working voltage just needs to be higher than the regulator output.


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## Madman (Jan 5, 2008)

Dan, thank you for your help. Before I make the purchase of the required items, I would like to ask that you take a look at what I am looking at on All Electronics site;
http://www.allelectronics.com/mas_a...0_width.500_modified.1237373195.366.7806T.jpg 



 6 Volt Positive Regulator 1 AMP















1 1/2 Amp 400 PIV Full Wave bridge rectifier 


















0.1UF 50V Radial Ceramic Capacitor


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## Greg Elmassian (Jan 3, 2008)

Heat sink? 

looking good... 

I have not consulted the way you rate the regulator, it's got to absorb the higher voltage too... 

Regards, Greg


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## Dan Pierce (Jan 2, 2008)

The voltage input for a lot of 7806's is 25. 

Again the heat sink can be the metal weight in an engine, and remember the heat sink will also be the center lead of the 7806. 

Since LGB smoke units are under 150 ma, the heat sink is plenty big enough even if it is 20 volts at 200ma giving 4 watts.


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## Greg Elmassian (Jan 3, 2008)

To dissipate 4 watts takes a sizable heat sink... the metal weight has a couple of drawbacks, often the mating surface is not real flat, so you could get poor conduction. That can be corrected of course. 

The bigger problem is that a chunk of lead does not dissipate heat very well, not like a heat sink with more surface area, and anodized black to increase it radiation characteristics, so be sure it's a big chunk of metal, and there is some ventilation, even if it's just convention currents causing the air flow... 

I had some stuff that worked fine until the entire lead weight got hot, then I was stuck. Of course, this was running for several hours. 

Regards, Greg


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## Madman (Jan 5, 2008)

As for the voltage input, I run my trains around 10-12 volts more or less. More toward the less side









Thats a good pont on the lead weight getting hot. My trains usually run for an hour or more. Making a heat sink out of a piece of scrap aluminim won't be difficult.

So the message I get, is that what I have pictured from All Electronics should fit the criteria that Dan Pierce laid out in his diagram. Is this correct?


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## Greg Elmassian (Jan 3, 2008)

The "looking good" was meant to say "the parts were fine". 

You can probably pick up a small heat sink for the regulator there too... but if you run 10-12 volts, by all means try it on the lead weight first.... 

Regards, Greg


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