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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Toss the transformer. It’s probably shorted inside or at least some of its insulation is damaged. I would toss the cord and plug you used to plug it into the wall with too. Did you route the wires to the switch machines through any switches to control them? You should check these switches to see that they’re not shorted. Toss the LEDs and their resistors. They will all be burned out. I would very carefully examine all the wiring under your layout that received that horrendous overload, looking for burned insulation and bare wire. Replace any damaged wire that you find. Finally, check that your switch machines are still working properly.
To test the switches, if you had any in the circuit, the best tool is a multimeter. If you don’t have one, you can make a simple continuity checker with just two parts. Get a 9 volt battery with a connector which has wires sticking out of it and a 12 volt bulb which has wires sticking out of it. Join one of the bulb’s wires to one of the battery’s wires (doesn’t matter which). The remaining bulb wire and the remaining battery wire are your probes to check for conductivity. If you touch the two of them to something which conducts electricity (like a rail) the bulb will light up. Now connect your little tester between the center terminal of a switch and one of the outer terminals. Flip the switch back and forth. The bulb should light in one position and not in the other. Connect the tester between the center terminal and the other outer terminal. Flip the switch back and forth. The bulb should light in one position and not the other. If the bulb lights in both positions or doesn’t light in either position, toss the switch.
To test your switch machines, just wait until you get a proper power source and connect them to that and see if they work properly. Your power pack may have two pairs of screws on the back. One will be labelled “track” or “variable DC.” That connects to the rails. The other output is usually 16 volts A.C. That’s what y
Atlas switch machines require a relay to turn the LED lights on and off. Atlas markets a “Snap Relay” made for this purpose.
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.
I would look at the Atlas switch machine and snap relay wiring diagrams for wiring instructions.
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.