hon30critterI'm learning so much about electricity I think I'm back in grade 9 shop class! No, correction - I'm learning way more than I learned in grade 9 shop class!
It looks really cool though because I did put it in a solid oak base! - had wood shop also.
Sheesh guys!
I'm learning so much about electricity I think I'm back in grade 9 shop class! No, correction - I'm learning way more than I learned in grade 9 shop class!
Thanks Randy
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
It's not just no load, that filter capcitor essentiually pumps the rectified DC output to the peak AC voltage - the 12.6 rating is RMS. Multiply by square root of 2 (about 1.4) to get peak - about 17.8 volts. Between no load and variations in the line voltage, 18 volts or so is what I'd expect from that power supply. Under load it will fall somewhat, as the transformer's output sags - but since it's a 5 amp transformer, loading to a peak of 3 amps shouldn;t drop it much.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Texas Zepher:
I got the uncouplers for a really great price. The killer was that the shipping cost to Canada ended up being more than the uncouplers! Still worked out to $10 or so per uncoupler with the power supply as a bonus so I'm happy.
Thanks for taking the time to look at the power supply.
hon30critterI just purchased seven Kadee #309 electronic uncouplers on eBay and they came with a home built power supply. Needless to say, I am concerned about the reliability and safety of the power supply. It puts out 18.5v DC.
That power supply looks fine to me. Much better than some of the 2nd (3rd) hand ones that were scrounged up on the club layout.
betamax, randy and others:
I didn't like the look of the power cord either and I did notice that the circuit wasn't grounded. I have the skills to change it to three wires with ground no problem. I just have to go buy the parts. While I am at it I will invest in a fuse and perhaps a power on indicator, although I plan on wiring the layout room so all power goes off with one master switch. That I will get an electrician for.
betamax:
Thanks for the explanation about the output voltage being higher without a load. I wondered why I was getting 18 volts when the transformer was rated at 12.6.
Thanks again everyone
That looks like a old Radio Shack designed supply. I build one using a plastic project box years ago and the plans and components list were in a Radio Shack project book. They had step downs in various amps listed.
I added banana jacks, binding posts, a cigarette lighter type jack and a Auto diagnostic under dash connector, I use it to power everything from circuits to tools. I also fused it to the rated amperage rating.
Mine is rated 12.5@2amps.
Jim
Randy,
I did say if he had no output to check the fuse resistor,,,it is actually there so an overload or reverse polarity don't blow the cap.....I have seen it happen before,on much larger cans.
Cheers,
Frank
That sandbar resistor is on the output side, not sure why that would even be needed, though it will serve to limit current. By how much depends on the actual resistence of those Kadee coils.
Looking closer, I notice that line cord looks like a salvage piece from at least 30 years ago, if not older. I would inspect it for cracks in the insualtion,. especially around the plug and where the strain reliefe is going into the case. If it's in good shape and not cracked or worse, then all is ok, but if it has started to crack from exposure, replace it before using.
Dave,
I was only going by the pic,for the size of the transformer,,,if it's a 5 amp.that is even better,and 18 gauge stranded wire is perfect..And If you want it grounded,,just do as I suggested,that will work perfect. No need to rewire the cord,if it is not needed,,KISS...Have Fun!! And should you ever have no output,,the first thing to check,is that ceramic fuse,with it unplugged,check for continuity, if you have it it's fine,if you don't it's open and needs to be replaced,,simple..
Use a momentary switch or push button to control the uncouplers. It only takes about 60 sec to burn the coil out. Use one rated at least 3 amps.
hon30critter Hi everyone: I just purchased seven Kadee #309 electronic uncouplers on eBay and they came with a home built power supply. Needless to say, I am concerned about the reliability and safety of the power supply. It puts out 18.5v DC. I opened up the steel box in which it is installed and all the logical parts are there: transformer; rectifier; capacitor; on/off switch; and what I believe is a resistor wired in series to one of the output terminals. The transformer has two pairs of wires coming out of it: one pair is rather small gauge (perhaps 24ga.) and the other pair is somewhere around 14 - 18ga. However, when I look at the connections I noted that the 120v input wires are wired to the small gauge wires and the larger gauge wires are wired to the rectifier. That seems backwards to me. Putting 120v into 24ga seems risky. Am I right? Second question is: if the transformer is wired backwards can I simply reverse the wires? If that is a dumb question please forgive me. If you think the thing is a good paper weight please say so!
Hi everyone:
I just purchased seven Kadee #309 electronic uncouplers on eBay and they came with a home built power supply. Needless to say, I am concerned about the reliability and safety of the power supply. It puts out 18.5v DC.
I opened up the steel box in which it is installed and all the logical parts are there: transformer; rectifier; capacitor; on/off switch; and what I believe is a resistor wired in series to one of the output terminals.
The transformer has two pairs of wires coming out of it: one pair is rather small gauge (perhaps 24ga.) and the other pair is somewhere around 14 - 18ga. However, when I look at the connections I noted that the 120v input wires are wired to the small gauge wires and the larger gauge wires are wired to the rectifier. That seems backwards to me. Putting 120v into 24ga seems risky. Am I right?
Second question is: if the transformer is wired backwards can I simply reverse the wires? If that is a dumb question please forgive me. If you think the thing is a good paper weight please say so!
No, the light gauge wires are perfectly acceptable for the primary circuit. You're pulling about half an amp.
You should change the line cord to a three wire grounded cord with the appropriate plug. Having 120V inside a metal box without a ground is very dangerous. Should something go wrong and the line voltage gets connected to the chassis, it could kill or seriously injure anyone who touches it and happens to be grounded. People can be injured badly when they are thrown, or their muscles contract and their hand/arm hits something.
Now, if the secondary says 12.6, that is what it is, under load. Don't let the meter fool you, the open circuit voltage will be higher.
If you don't know how to change the line cord, ask someone qualified to do it.
OK! The experts have spoken!
My fears were not justified but I wanted to make sure.
By the way, the transformer output is rated at 12.6v and 5 amps according to the printing on the secondary side. Does that make any difference to what you have said? I failed to mention the amp rating in my first post.
If I can pick your brains a bit more, the Kadee uncoupler instruction sheet calls for 16v DC @ 3 amps. Will this setup provide enough power, and are the yellow and green wires leading from the output terminals heavy enough to handle 3 amps even though the power will only be on for short periods?
Also, for those of you who have used the #309 uncouplers, is it feasible to use a momentary on/off switch to operate them?
Thanks for your information. I appreciate your help very much!!
I would not worry about getting a shock,in the least,,with that set up...If you are paranoid about it,,,drill a hole in the case near the AC cord,get a length of 18 gauge stranded wire with a eyelet at one end,screw that into the case,tape that line to your line cord,all the way to the plug end,leaving a little bit of wire longer then the plug end and with another eyelet,screw that to your outlet cover mounting screw,,,,now your are grounded...
But it is still not necessary......IF it was,I would be dead already,from any plug without three prongs on it,,including three MRC 20's..
It's wired correctly, but I'd put a pilot light and fuse on the input side so you'd know it was on.
As stated, when you reduce voltage you increase current, so the current draw on the 120VAC side is very little, thus the small wires are perfectly adequate. Transformers aren;t 100% efficient, so it's not exactly proportional, but it's still orders of magnitude, as in, at 50% efficient, a 2 amp output as 12V would require 0.4 amps input at 120V.
The transformer steps the voltage down approx.. 10 to 1, 125 v in and 12.6v out. For a 2 amp output the input current is 2/10 amp. Reverse the leads and you will get 1250v output and smoke---for a short period on time.
Given that the box is steel, the only comment I have is it could use a grounded cord/plug combo. That would kick up the safety some. Any internal short could cause a nasty shock at the metal on/off switch. There are a number of good places to connect the ground inside the box, like the transformer mounts. Also, some of the solder joints look sort of bare. Thing doesn't look too bad though, I've seen worse!
Lou
Without getting into a whole bunch of tech,,,,that is wired correctly, for a Full wave Bridge Rectifier,circuit with a Capacitor Choke Filter,for giving regulated filter DC current to the output,the value of the rectifier and the Cap..will increase the output voltage,from the 12.6 transformer, The resister like part is a overload fuse for the output....From what I see from the pics,it looks like a,2 or 4 amp,power supply...Hope That Helps..
Perhaps these pictures will help:
Here is the box:
here is the transformer label:
Here is an inside view. The brown wires are the 120v input:
This is the back of the transformer. Note that the secondary says 12.6v:
Thanks