3-wire 'step down' transformer (230 to 115) where do..

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  #1  
Old 03-02-12, 07:00 PM
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3-wire 'step down' transformer (230 to 115) where do..

hi folks- new here..I bought a 3 wire step-down transformer so I can get 115 off of my 220 power source. This is in a 220 welder. I have two live wires running to the terminals on switch in the welder from the wall. Both 110 ea. My transformer only has 3 wires..as such: wire (A) 115 (B) 230 (C) '0' ..so how do I wire this up so I got the two wires to run a 110 fan in there? Why would the transformer only have one wire marked 230 when their are two to get 230? thank you- Gene
 
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Old 03-02-12, 11:29 PM
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Why would you write their when by the context you should use the word there? Also, unless you live way out in the sticks your voltages are 240 and 120, not 220 and 110. Further, you do not have two wires that are 110 each but instead have a standard 240/120 residential service.

Obviously you bought an autotransformer which has only one winding. From the 0 connection to the 230 connection is one continuous winding with the 115 connection half-way in between. This can be used to either boost 120 (115) volts to 240 (230) or to decrease 240 (230) volts to 120 (115) volts. To drop the 240 to 120 you connect the 0 and the 230 connections to the 240 volt line and then connect the 120 volt fan to the 0 and 115 connections.

Didn't you get any instructions with the transformer? It would probably have been less expensive if you had simply bought a 240 volt fan.
 
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Old 03-03-12, 04:37 PM
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I am confused as well as concerned. Your post says you are using a "220" welder as a power source. Are you using the welder, or the receptacle that supplies the welder with 240 volts? If you are using the welder, why?
I also guess you are just "playing" with this transformer, as I see no practical application since you have both 240 volts and 120 volts available. You could take two steps to the right or left and plug your fan into a 120 volt receptacle.
 
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Old 03-03-12, 04:43 PM
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Thanks Furd..

Thanks on the hook up info- appreciate that. as far as rest..I never was good at grammer or electical so always just refered to it as 220/110..but obviously that is more your entrprise in that field than I- thats why I'm posting here. figured most would know what I meant or for that matter not make a differance in solving the question. But shoot..I can do couple things maybe as good or better. Can Bench Press 500lbs at 58..can tear down/repair a small engine half sleeping. But grammer and electricity isn't one of my better abilitys. I will be more percise in the future. Thanks again- Gene
 
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Old 03-03-12, 04:56 PM
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explain scenero..

Accually Chandler- I'm getting the power 'inside' the welder from the welder switch terminal The cooling fan is 'inside' the welder also. I have access to several cooling fans except they are 110/115 but not the 220-or whatever is coming into the welder. Fans cost me '0' dollars and step-down transformer is brand new but LOS. No instructions. I got the transformer for $12.95 + $5-$6 shippg. the fans sole purpose is to help cool the welder and $18 transformer is far cheaper than 220 original fan for $170. These are equal in rpm..just take lower voltage. and..not that I should ever need another- But I got more if ever should be the case. hope this sounds logical..but fact is it is a done deal- just need to hook the wires up (right I hope)- thanks..Gene
 
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Old 03-03-12, 06:03 PM
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Actually Furd told you how to wire it. The main thing is you need to determine the center tap. Is there anything that would indicate one of the three wires are different from each other? Does one come out the center of the winding and the others on each end. Can you post pictures? http://www.doityourself.com/forum/li...-pictures.html Do you have a multimeter?
 
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Old 03-03-12, 06:42 PM
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I'm a stickler for using correct spelling, grammar and punctuation because it is necessary for proper communication. Proper communication is vital to understanding. Otherwise I have to guess and I don't want to guess incorrectly.


Chandler, Ray, he did state that the connections on the autotransformer were marked and I did give him the information necessary on how to connect the autotransformer for his application. Here is a graphical representation of an autotransformer so it can be readily seen how to connect.


(Image courtesy of allaboutcircuits.com)

The bottom connection is the 0 volts connection, the center is the 115 volts connection and the top is the 230 volt connection. The source (left is the 240 volts from his welder receptacle and the "load" represents his 120 volt fan.

Now, rather than using the autotransformer IF the wiring to the welder receptacle has a neutral (normally not used with a welder) he could replace the three-wire cable to the welder with a four-wire cable, change the receptacle and plug to a four-wire model and then wire the fan between the neutral and one of the 240 volt wires downstream of the switch.
 
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Old 03-04-12, 04:30 AM
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Now, that the entire story is being told, I like Furd's suggestion of rewiring the welder to a 4 wire receptacle and using the neutral and one leg. Too simple and you don't have to rely on the autotransformer.
 
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Old 03-09-12, 03:00 PM
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Why not a seperate cord-connection to supply a voltage that is equal to the voltage-rating of the cooling fan ?
 
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Old 03-09-12, 03:12 PM
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Would Art 450.4 be applicable to this auto-transformer connection ?

Mod Note: 450.4 Autotransformers 600 Volts, Nominal, or Less.
(A) Overcurrent Protection. Each autotransformer 600
volts, nominal, or less shall be protected by an individual
overcurrent device installed in series with each ungrounded
input conductor. Such overcurrent device shall be rated or
set at not more than 125 percent of the rated full-load input
current of the autotransformer. Where this calculation does
not correspond to a standard rating of a fuse or nonadjust-
able circuit breaker and the rated input current is 9 amperes
or more, the next higher standard rating described in 240.6
shall be permitted. An overcurrent device shall not be in-
stalled in series with the shunt winding (the winding com-
mon to both the input and the output circuits) of the au-
totransformer between Points A and B as shown in Figure
450.4.
 

Last edited by ray2047; 03-09-12 at 03:49 PM.
  #11  
Old 03-09-12, 03:39 PM
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Yes. asujopjregosdifyhw-fkod[
 
  #12  
Old 03-10-12, 12:22 PM
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Is overcurrent protection required for the conductors supplying the cooling fan motor if these conductors are "tapped" off the conductors that supply the welder?.
 
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Old 03-10-12, 12:41 PM
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No. The downstream conductors would be sized according to the maximum capability of the autotransformer and therefore be protected by the primary overcurrent protection.

Unless you are asking about the alternate I suggested in using a neutral lead and one hot conductor and in that case the answer is yes.
 
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