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Transformers Answered

I'm building a power supply for a cnc router powersupply. The output has to be 36 volts at 12 amps. I'm going to use 6 of the 25.2 volts, 2 amps transformers at radioshack (I have a coupon). When I rectify it it should be about 36 volts. Couple questions about transformers 1) don't transformers essentially short out an AC socket? I don't wwant to start a fire. 2) how can I have a LED indicator that indicates that each transformer is working? I don't want to use a huge resistor, because that seams inefficient. 3) how big of a filter capacitor do I need? I have a 33000uF capacitor, think it's a bit overboard? I know I need at least 4800 uF for just stuff like motors, but the only capacitors I have that works above 50volts is that capacitor. 4) can you connect AC in parralel? Can someone draw be a diagram?


well I am no exspert on the matter but if you can't , or it isn't safe I have been living dead or darn lucky! Cause I have been running a power supply I built about a year ago almost daily, it putts out 60 voltsD.C. total and with the flip of a switch it backs out to 14 for chargeing batteries, the charge side is "I can't remember for sure" 3 or 4 various Wallwarts ans they are combined with about 6 or 7 others at the switch to get the higher voltage after going through my home built Rheostate. built from old electric heater wirer filiment. Maybe it shouldn't or wouldn't but it DOES work

> 1) don't transformers essentially short out an AC socket? I don't wwant to start a fire.
. It sure looks like it would, but the reactance of the coil presents a higher "resistance" to the source than one would suspect.
> 2) & 3)
. Don't know for sure. If I were going to do this, I'd get one large xformer to do the job.
> 4) can you connect AC in parralel?
. Certainly. Connect one side of all your loads to one side of the source. Connect all the other wires to the other side of the source. Just make sure the total load doesn't exceed the capacity of the source (10-15A, for US wall sockets).

the only reason of the multiple xformers is because I can't find one cheap big xformer, it's cheaper to do with smaller ones. One question I forgot: If the output of an xformer is 25.2 volts at 2 amps (50.4 watts), would the input be 117 volts at ~0.45 amps (~50.4 watts)?

. When dealing with reactance, it's not just the simple P=IxE (please don't ask me to explain why, I don't fully understand it - see link above), but, for your purposes, it's pretty close. There will also be some inefficiencies, so the figure will jump a little more. For safety's sake, I'd use 75-100W for load calcs.
. BTW, I'm not convinced that you can hook up xformers in parallel like you want to do. Better check with someone more knowledgeable than I before plugging anything into the mains. My experience with xformers was in installing/replacing them, not engineering the things. I picked up some info along the way, but I'm no expert.
. You may be able to salvage a xformer from an old stereo or TV. The rated voltage of the xformer can be higher than 120VAC (or whatever your source is), as long as the turns ratio is correct. And a xformer works just as well "backwards" - ie, turn a step-down xformer around and it makes a good step-up xformer - just make sure you stay within the voltage limits.

thanx, and if anything goes wrong I can just flip a breaker switch for the room I'm working in. My understanding of inductance is electricity pulsing back and forth, hitting it's self and lagging. As for hooking stuff in parrallel I don't think I have to. Primaries can be esily be hooked in parrallel, and it's cheaper to buy a couple of bridge rectifiers than 1 big one, so I could just hook up all of the pluses and minus together.

> I can just flip a breaker switch . If it's not too hard/$$, I'd suggest installing a new, small (say 5A (~600W) or maybe even 1A (~120W), depends on the generator) breaker in the box and wire the generator to that. Most home breakers are 15-20A (with a few 10s thrown in). . > My understanding of inductance ... . LOL We're on about the same level. ;) . > As for hooking stuff in parrallel ... . I don't know enough to confirm or deny with any certainty.