I got one of these 2 amp 12 volt AC transformers http://www.altex.com/%2FTransformer-12V-Center-Tap-1-Amp-TR121-P143673.aspx to power the atlas snap switches with signal indicators, since the transfomer didn't come with any instruction so I connected the 2 black leads to the snap switches and 2 of the 3 leads (2 reds and 1 green which I assumed is the ground) to the 2 prong plugs. When I plugged the assembly to the 120 AC house socket, the whole thing would vibrate and hum and immediately follow with smoke coming from the wires underneath my layout, I immediately unplugged the whole thing thinking to myself that I would either be eletricuted or started an house fire. Do any one of you have experience with the wiring of this thing, should I wire it so the 2 black leads from the winding to the household 120v and the 3 leads go to the snap switches instead, did it wire them incorrectly somewhere.
Before you asked, yes I did install the required resistors to all the LEDs.
I strongly recommend that you only do any 120V wiring under supervision so you don't hurt yourself or burn your house down. If you don't know which wire is which DON'T PLUG IT IN.
The transformer should have two wires coming out one side and three out the other. The side with three wires is the low voltage side. If you wire it backward you will INCREASE the voltage.
The output of the transformer is AC. LEDs require DC. The snap switches will work with AC, but only with momentary contact. You need either a push button or a momentary contact switch between the transformer and the switch. If you wired it direct you have probably destroyed the switch motor and the LEDs. If you wired the transformer backward you might want to think about replacing the wire as well.
Dave
Lackawanna Route of the Phoebe Snow
I guess a picture would help.
Did you wire this through the control button?
It sounds like you wired a short circuit. If the smoke came from the wires, then you probably only toasted the wires, not the switch machines or the indicator LEDs.
It takes an iron man to play with a toy iron horse.
You really have to learn something about transformers before using them. Ask first before you cook yourself.
The two leads are for the 120vac. The three leads are for 12 volts between to leads and 6 volts from the center lead to each outer lead.
The article assumes you know what you are doing. 12 volts center tapped means there is a center tap on the secondary which by definition means three leads. The frame of the transformer is ground. The center lead "might" go to ground or common depending on the application.
You might have fried the secondary of the transformer by putting 120vac on it. The secondary is low resistance compared to the primary. I would toss the transformer as the insulation on the winding may be cooked and not be any good.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Another thing that can happen is the voltage can actually multiply if you hook the AC to the wrong side if it didn't fry the winding. What you could potentially get is 1200 volts.
Springfield PA
Hamltnblue Another thing that can happen is the voltage can actually multiply if you hook the AC to the wrong side if it didn't fry the winding. What you could potentially get is 1200 volts.
No way. The resistance/impedance of the secondary winding is too low compared to the primary winding. All you do is smoke the secondary winding.
Well at least in the reality I live in.
Lesson Learned: Don't play with electricity if you don't know what you're doing.
Wow, that sounds so scary, yes I did indeed wired the whole thing backward, just glad that I get to live to tell the whole thing and not cooked and fried myself by1.2K volts in the process. How do I check if the transformer is still ok, or should I get a new one. My old 1 amp powerpack of 20 years just doesn't have enough juice to power all 20 LED indicators and throw the switch at the same time, that's the reason I got the 2 amp AC transformer instead. The switch would stuck to the middle sometimes and would reluctantly complete the transition some othertimes.
Although in normal use the voltage would be only 12 volts at the secondary, I would still toss the transformer.
Normally the primary and secondary on transformer are isolated but wound on the same core so possibly no other damage but if the secondary windings have shorts between the different secondary wires, it will possibly put an extra load on the primary. The transformer wires have a thin coating on them and cam be damaged by excess current. Better toss it and be safe.
LED's need DC voltage by the way.
Rich,
What do I do with the center tap wire from the secondary, can I cut and conceal it with a electric tape. does polarity make any difference in AC, all the primary and secondary side of wires are the same color for some reasons, either 2 black or 2 red.
AfricangreyI got one of these 2 amp 12 volt AC transformers http://www.altex.com/%2FTransformer-12V-Center-Tap-1-Amp-TR121-P143673.aspx to power the atlas snap switches with signal indicators, since the transfomer didn't come with any instruction so I connected the 2 black leads to the snap switches and 2 of the 3 leads (2 reds and 1 green which I assumed is the ground) to the 2 prong plugs. When I plugged the assembly to the 120 AC house socket, the whole thing would vibrate and hum and immediately follow with smoke coming from the wires underneath my layout, I immediately unplugged the whole thing thinking to myself that I would either be eletricuted or started an house fire. Do any one of you have experience with the wiring of this thing, should I wire it so the 2 black leads from the winding to the household 120v and the 3 leads go to the snap switches instead, did it wire them incorrectly somewhere. Before you asked, yes I did install the required resistors to all the LEDs.
Essentially what you did was wire it for step up, not step down. So you ended up with 1200V on what you thought was the secondary.
Looking at the picture, the top of the device, the side marked "120" is the primary. Since it says 6.3-0-6.3, the means 12.6V center tapped, which is the winding with the three leads.
I do this every day, so I know you can step 120V up to unbelievable levels very easily with the right transformer.
AfricangreyRich, What do I do with the center tap wire from the secondary, can I cut and conceal it with a electric tape. does polarity make any difference in AC, all the primary and secondary side of wires are the same color for some reasons, either 2 black or 2 red.
Just tape up the center tap lead. I have done that many times when I did not need that connection.
Polarity make no difference with AC in this xfmr.
I have seen the same color wires many times on transformers. With this xfmr, probably trying to save production cost anyway they can.
Which wires smoked? The wires bringing in the 120 vac to the xfmr or the wires going to the LED's and turnouts? Just wondering.
Our club has two twin coil machines and we use 12 volts AC with 12 volt bulbs for indicators for many years. All other machines are DC slow motion.
Probably smoked the secondary, a cheap filament transformer won't make a step-up tranformer when wired backwards - at least not for long. It DOES work with the right kind of transformer - back in the day every car had one that stepped the 12 volts (or going further back, 6 volts) from the battery to 50 THOUSAND volts for the spark plugs. Great for making Tesla coils too.
Back on topic - if you are unsure int he LEAST - DO NOT mess around wiring things that plug in to house current. You need more than a plug with wires - there should be at the bare minimum a fuse and even better a fuse plus pilot light and switch. And all connections need to be carefully insulated. If 120VAC gets into anything on your layout, you can be hurt or killed, start a fire, and/or damage your equipment. Best to stick with a pre-packaged power supply that is UL approved. I DO know what I'm doing and I still prefer to buy something rather than try to make my own.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
The more I read the more scared I got, instead of messing with this further, I think I will just invest on a real power pack rated 2 amp for the accessories. Can any one recommend one to me?
Actually the secondary coil is thicker than the primary. This is because the secondary has higher current with lower voltage. I've seen them survive the 120 and boost up.
rrinker Probably smoked the secondary, a cheap filament transformer won't make a step-up tranformer when wired backwards - at least not for long. --Randy
Probably smoked the secondary, a cheap filament transformer won't make a step-up tranformer when wired backwards - at least not for long.
Randy:
I disagree with your claim that it won't step voltage up, but I do agree with "at least not for long".
Unfortunately a lot of bad things can happen during that "not for long" interval.
Hamltnblue Actually the secondary coil is thicker than the primary. This is because the secondary has higher current with lower voltage. I've seen them survive the 120 and boost up.
While the wire is thicker, the number of turns around the iron core is significantly less than the primary by a factor of 10:1 for a 12VAC transformer). This will cause the impedance to be significantly less, which will draw much more current than the secondary wire can handle, follwed by smoke, burning etc. It may last a short time but you will eventually see these results.
Years back I used to wind my own transformers. I once wound a 12VAC transformer with a 2 - 12ga enameled wire secondary windings. It was on a 400W iron core and I was trying to get 12V @ 30A output. Anyway, I got it wired backwards (didn't label my leads properly when I pulled them through the steel case) and when I plugged it in, it started humming very loudly and dancing on the table. This was an 28 pound transformer and I pulled the plug within a few seconds. It did survive but there was some internal melting of insulation and my nice neat transformer windings didn't look quite as nice afterwards. I've seen much smaller ones catch fire.
Engineer Jeff NS Nut Visit my layout at: http://www.thebinks.com/trains/
It does seem that you are not sure about what you are doing.For 6.99 consider it a lesson learned.If you don`t know how to test it to see if it is still functional find someone who does or throw it away.The safer way is to purchase a used power pack all 120 volt wiring done.with fuses or circuit breaker protected and input /output clearly marked.
..... Bob
Beam me up, Scotty, there's no intelligent life down here. (Captain Kirk)
I reject your reality and substitute my own. (Adam Savage)
Resistance is not futile--it is voltage divided by current.
1. Atlas switch machines require a relay to turn the LED lights on and off. Atlas markets a "Snap Relay" made for this purpose.
2. The LED's are a light emitting diode. Because they are a diode, they only allow current to flow in one direction. Therefore, they do their own rectification and do not require a DC supply in order to operate. You can supply them with AC and they will operate just fine since they only conduct during one half of the 60 Hz cycle.
3. I would look at the Atlas switch machine and snap relay wiring diagrams for wiring instructions.
4. I suggest tossing out anything connected to the secondary of that mis-wired transformer because non of it is rated for 1200 volts and is very likely damaged. It will be very fortunate if the switch machines are not ruined too. 1200 volts even for a moment, is a real killer!
I am a Master Electrician and Inspector and we are all happy you are alive and well. It is surprising how easy and quickly any one of us can get into a life threatening situation. I also prefer to buy manufactured power supplies for those same reasons.
Thanks for all your replies, I really benefited from wealth of info regards to the proper usage and wiring of AC transfomer as such I tossed the one in question and got a brand new 12V 2 amp version. Upon firing, all except one switch and snap relay work just like the 1 amp power pack, thinking about swap it out to a door bell transformer where the output voltage is either 16V or 18V, but one thing I don't understand is the 20VA labelled, does that stands for 20 variable amp, I just want to supply enough juice to momentarily throw the switch and the snap relay. The snap relay in question still acts reluctantly going only half way and stuck in the middle. This one is controlling 2 turn outs and 2 LED signals, any idea?
The 20VA marking means the same thing as saying 20 Watts of power output -- AC Power in Watts is measured as Volts times Amps, so 20VA is 20 Watts.
It stands for "volt amps" which equals watts.
If a 2 amp transformer is not throwing a single snap-switch, either your wire is too thin, or your turnout is gummed up somehow (ballast, glue, or soemthign maybe).
Your best bet for solenoid switch machines it to add a capacitor discharge supply between the transformer and the switch controls. There are commercial ones liek the Circuitron Snapper that work quite well. For one, you won't burn out the switch motor if the button sticks, two it provides a much stronger 'jolt' to make sure they move.