Rectifier diode assistance

Thread Starter

megawatts

Joined Dec 24, 2008
35
Bertus and SgtWookie,
Thank you both for clarifying things for me. It has not been my intention to create an electronic monster here for this project of mine.

Let me get a bit more specific with my plans. I have an actual (taken out of service) railroad signal which has three color lenses. These three lenses are luminated by a separate bulb for each lens which will be activated by a 12vDC timer card. The bulbs are 10v/18w which either ac or dc will energize, just need to be at a very low voltage range.

My power source for this card is the 110-115vAC transformer that I mentioned earlier in this thread. Both the transformer and the signal are of the same manufacturer, therefore wanting to keep all equipment compatible to each other. I was hoping some sort of small device could be used to step-down the voltage and then convert it from AC to DC to operate this card and eliminate the "let the smoke out" effect as stated by SgtWookie.

Since I live within 60 miles of at least 3 Radio Shack stores, I thought this would be an easy and convenient choice. True, Radio Shack stores did quite an overhaul of their businesses some years ago and practically got out of the electronic component sales and went with RC toys/phones/speakers and the like.
Going with a more reputable supplier like Mouser or DigiKey would be a much smarter choice especially if I want to do what I have set out to accomplish.
I'll do a little more seaching through the online catalogs and see what I can come up with.

Thanks again,
Roland

BTW Bertus,
I'm from Kansas, USA
 

SgtWookie

Joined Jul 17, 2007
22,230
Let me get a bit more specific with my plans. I have an actual (taken out of service) railroad signal which has three color lenses. These three lenses are luminated by a separate bulb for each lens which will be activated by a 12vDC timer card. The bulbs are 10v/18w which either ac or dc will energize, just need to be at a very low voltage range.
OK, that's a new curve.
18W at 10V = 1.8 Amperes. The LM317 regulator will not be able to source that much current.

However, if you have a 10vac tap from your transformer, you can use your relay controller board to control that current; providing that the relay contacts are rated for at least 5A @ 10VAC. The over-capacity is necessary due to the "surge current" when the lamp's filaments are cold.

The higher the current rating of your relay's contacts, the better - it will mean they will have a much longer lifespan.
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
SgtWookie,

I thought that since you provided a choice between a LM317 and a 7812 voltage regulator, I would opt for the 7812 since it would eliminate the two resistors, thereby making things less complicated.

I have reviewed the timer card schematic drawing again and here is what I have noted on it: Input 10-16vDC; Output 36w/3a@12v
acutal: 50w or 4a continous.
These current readings were provided by the manufacturer.
The bulbs are GE which are indentified as 10v/18W
At night these are a very bright light which seem to shine for miles thus quite efficient for railroad useage. The signal also incorporates special lenses and mirrors to help deflect the light path. I was told that the lower the voltage, the longer the bulb will last. For the past several years now, railroads have gone to dark signals up to a certain point of distance for train movement to help conserve energy and bulb life. I currently have one signal on a timer which allows an on time of about 7 hrs. a day.
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
SgtWookie,

Acutal should be actual.

I can get several different readings on the AC side of the secondary taps. DC is what I need to power the timer card. If I had another rectifier like the one I am using for the other operating signal, I would be in business, but I purchased this transformer hoping to use it with the three light signal.

I don't plan on electrifying this signal until Spring so I have plenty of time to get things ready during these cold winter days in Kansas.

Roland
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
SgtWookie,

I did an online catalog (Mouser & DigiKey) search of the components you indicated on the schematic drawing you did for me. What do you recommend using for installing the components and is the drawing still going to benefit me with my plans for powering the 12vDC timer card to operate my three light signal?

Any other advice would be greatly appreciated.

Roland
 

SgtWookie

Joined Jul 17, 2007
22,230
I can get several different readings on the AC side of the secondary taps. DC is what I need to power the timer card. If I had another rectifier like the one I am using for the other operating signal, I would be in business, but I purchased this transformer hoping to use it with the three light signal.

I don't plan on electrifying this signal until Spring so I have plenty of time to get things ready during these cold winter days in Kansas.
It's not a big deal - you can use the supply circuit I put together to control your timer board. You can power your lights with AC from various transformer taps; whatever compromise you choose to make between light output and the life of the lamps themselves.
 

SgtWookie

Joined Jul 17, 2007
22,230
I did an online catalog (Mouser & DigiKey) search of the components you indicated on the schematic drawing you did for me. What do you recommend using for installing the components
Well, a circuit board would be good. You can get small "generic" pre-drilled circuit boards at your local Radio Shack. I don't have a part number for you offhand; it's late and I'm tired.

and is the drawing still going to benefit me with my plans for powering the 12vDC timer card to operate my three light signal?
Certainly!

You know, if you don't mind paying a bit more for the convenience, there are various websites that offer voltage regulator kits that come with all the parts and a circuit board. If you're not very experienced with electronics, this is often a good way to go, as you'll have a circuit board already laid out, and step-by-step instructions on how to put the thing together.

I'll have to take a look later; time for me to sign off.
 

SgtWookie

Joined Jul 17, 2007
22,230
Here you go:
http://www.electronics123.com/s.nl/it.A/id.440/.f
This $10.83 kit takes an unregulated AC or DC input, and gives you a regulated DC output between 1.5v and 30v.

If you wish to look at the instructions before you buy it, they are here:
http://www.kitsrus.com/pdf/k68.pdf

The voltage rating for it's C1 and C4 is a bit low for it's stated ranges, but that was likely a compromise to keep the actual board size small. It should work just fine for your purposes.

One caveat: when you are setting the output voltage on this regulator, you will need to have a load on it's output. The LM317 regulator needs to have at least 10mA load on it's output to achieve guaranteed regulation. As designed, this kit only has a 5mA load due to R1 being specified as 250 Ohms. This means that you will need at least an additional 5mA load to correctly set the output voltage.

So, what value resistor would one need to cause 5mA current to flow when 12V is placed across it? We can answer that question using Ohm's Law:
R = E/I, or Resistance = Voltage / Current
Our voltage = 12, and our current = 0.005 Amperes, so 12/0.005 = 2,400 Ohms.
To allow for a comfortable margin for error, you could use any resistor between 1k and 2.2k Ohms as a load.

But now one needs to check the power dissipation in the resistor; so we'll employ another permutation of Ohm's Law:
P = EI, or Power in Watts = Voltage * Current
Since we haven't determined the current at 12v through the 1k resistor, we can use another permutation:
P = E2/R (Power = VoltageSquared / Resistance)
So, P = 12*12/1000 = 144/1000 = 0.144 Watts

For long life of the resistor, you double the power requirement: 0.144 * 2 = 0.288 Watts

We're over 1/4 Watts, so you would have to go up to a 1/2 Watt resistor if you were going to keep a 1k Ohm resistor in the circuit on a permanent basis, or use a larger resistance.

We didn't calculate the current through the 1k Ohm resistor yet, so let's do that.
I = E/R = 12/1000 = 0.012 Amperes = 12mA. Combined with the 5mA current through R1, we'd have 17mA total circuit current.

Another option:
Replace R1 with a fixed 120 Ohm resistor
Replace R2 (pot) with a fixed 1k Ohm resistor
This will result in a fixed nominally 12v output without the minimum 5mA load requirement.
 
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Thread Starter

megawatts

Joined Dec 24, 2008
35
Thanks for the updated information. It looks like I need to act rather quickly if I choose to go the route you suggested as they only have two (2) of the voltage regulators in stock. It appears to be a simple product to use and incorporate in between my transformer and timer card.

I truly appreciate your time, patience, and knowlege in helping me with this project. I will keep you advised on how things turn out.

Many thanks again,
Roland
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
Bernard,

Each light is on for approximately 40 sec. depending on how you adjust the speed control. The principal of the device is the same as a traffic light.
Just guessing, these transformers weigh approximately 10-15 lbs. each. They are railroad transformers, therefore quite heavy; like most railroad equipment.

I spent 28 years in the natural gas transmission industry, so I am used to working with heavy parts, pieces, and associated equipment. The lightest thing used on a natural gas compressor engine were the spark plugs!
 

Bernard

Joined Aug 7, 2008
5,784
Your transformer should eastly handle the board and light[one at a time].Are the lamp drivers part of timer board?,I dad that impression.A LM350T regulator will output 3A., and should fit in Sgt Wookie's schematic. As I remember Hugoton was near the gas fields, but my guess you are in Ness Co.
 

SgtWookie

Joined Jul 17, 2007
22,230
I'll stick with my recommendation to use the 12vdc supply to power the relay board, and to use the AC from the transformer to power the lights.

There's no pressing reason to use DC for the lights. The more power that has to go through the regulator, the more heat will be dissipated there.
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
Bernard,
The voltage regulator kit that SgtWookie recommended has been shipped and I am awaiting its arrival. I believe things will work out ok. I'll keep you and him posted.

I am several counties east of Ness Co. But you are right, Hugoton and Ulyssess are almost right on top of the gas fields of western Kansas. I did a three stint with the gas company in the Oklahoma Panhandle before returning to east central Kansas. And yes, Toto, western Kansas is very flat; eastern Kansas isn't. :D
 

Bernard

Joined Aug 7, 2008
5,784
Looking forward to your final report, it is much appreciated when a conclusion is reached-good or bad.and reported.
' spent quite some time working out of Hays, and most of SW Kanas on seismic exploration crew.
 

Thread Starter

megawatts

Joined Dec 24, 2008
35
Bernard,
I can email you some photos of the workings of my US&S H-5 "dwarf" signal if you like.
I have seen those seismic exploration crews in action and it is quite a sight to see; all of those trucks and power cables lined up behind one another. A crew did some exploring not far from the last station I operated from and I don't think they found much to proceed with.
 
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