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using a 110 v wall wart on 220 v

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  • using a 110 v wall wart on 220 v

    I needed some low voltage DC to control some relays on my spot welder. Since the welder is 240 volt, I thought the following would work. i took a 9V DC adapter and figured if i ran it on 240 I'd get 18v rms. I cut the case off and replaced the capacitor with a 35 volt one.

    installed it in the spot welder and turned the main power on to the welder. a few seconds after turning on the switch, I've smoked something in the transformer. I find a 250V 1a fuse under the tape in by the windings. fuse shows infinite resistance so obviously it is toast. I check the + & - hookups, where i had the DC from the power supply hooked into the rest of the circuit, and it shows infinite resistance as it should - unless the foot switch is hit, the circuit is open

    so why, other than charging the 1000 uf cap, would the transformer draw any current let along enough to burn out a 1amp fuse? If the secondary is an open circuit, the primary doesn't draw any current does it?
    .

  • #2
    Sho'nuff it do..........

    it is called "magnetizing current". In your case, however, the high voltage raised the "magnetizing current" up to and well past the point at which the iron core was 'carrying all the magnetism it could" (it was 'saturated") and basically the coil reverted to being an "air core" coil, which has virtually no opposition to low frequency AC, since it's "inductance" is very low.

    Your wall wart might have tolerated as much as 140VAC, it HAS to tolerate 132 VAC to pass UL. But no way 240V, unless designed for it

    A 240V transformer will work OK, but often not as efficiently, on 120V.

    it's all about the "volt-seconds".
    1601

    Keep eye on ball.
    Hashim Khan

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    • #3
      thanks JT, this electronics will be be the death of me (hopefully not literally). seems I'm perpetually one bit of knowledge away from making my electronics do as i ask of them. I didn't realize there was much more to it that than the ratio of the turns on the coils and how much current the windings could take......guess I've got to learn about Weber's.
      .

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      • #4
        Some manufacturers should be strangled with burnt magnet wire for putting those 'almost ready to blow' transformers in the hands of the public. Of note were the cable converters which pretty much all got so hot in normal use (what other use could you put them to?) that they seemed ready to do a meltdown into your tv set. But I digress.

        Two 110vac wall warts can be wired in series for use on 220 IF they are exactly identical. The outputs can be paralleled for more current at the same voltage, or wired in series for double the voltage at the same current. They must be identical and they must be loaded equally, a situation which is automatic if the outputs are wired together as stated above. The real concern is how to physically wire the primaries in series. If they have a power cord, that's easy, though you'd have to change the plug to a 220v plug. If they have only the two prongs, then you could possibly mount a dual socket in a suitable electrical box, wire on an ac cord, then twist off the connector jumper between the two brass screw terminals (not the white or chrome screw side, those screws don't get used in this application) . Wire the leads from the ac cord to the two brass screws. Of course, the two warts would have to be able to both be plugged into the socket at the same time.

        Though this works, I can't vouch for the legality of wiring an electrical box and socket this way. You're on your own if you do it. If you do, then avoid using any wall wart which has switch selectable outputs. And of course you need to wire the outputs together with the proper polarities. For parallel connection, it's positive to positive, and negative to negative. For series connection, it's positive of one to negative of the other, no other connection to this point, then the two remaining leads, one from each wart, become the positive and negative output leads.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Wouldn't it be easier to.....

          Hi guys;

          While I find all this discussion about using plug-in power supplies, electrical engineering & makeshift wiring to be a learning experience, wouldn't it just be simpler & cheaper to go to your local HVAC controls supplier & get a little 20 or 40 VA multi-tap control transformer. (Adapts to all common supply voltages...eg. 120,208,240 VAC etc....) Cheap too.....

          That's often my solution for conversions, small charger repairs, control circuits & the like. Then again, I always have some in my service truck, so I'm spoiled.

          I thought Webers were carburators or BBQ's.....

          Hope that helps;

          Rick

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          • #6
            Why not just get someone in the UK (or Oz) to send you a 240v wall wart?
            Just got my head together
            now my body's falling apart

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            • #7
              Here is one potential solution:

              http://www.mpja.com/prodinfo.asp?number=7841+TR

              Pretty cheap as well.

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              • #8
                You could also use only one hot from the 220 and get 110. I have a compressor thats 220, plugs into the wall via 220 plug but the fans on it are 110 v using one hot + ground. But I accept no responsibility for any electrical issues caused by this.......

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                • #9
                  Ahidley's solution is the one I was going to recommend, but you MUST have a neutral for your machine. Do *NOT* use the safety ground for this purpose, you will put current on the frame of your machine. This means a total of 4 wires.

                  Do consider that you may spend on a chunk of 4 wire cord, outlet, plug etc, what it would cost you to buy a surplus 220v transformer designed for powering control circuits.

                  Or, if you are dead set on converting a wall wart....convert this one for $.50....it will cost you more in postage than the $.50 price

                  http://www.surpluscenter.com/item.as...1-3029&catname=
                  Paul Carpenter
                  Mapleton, IL

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                  • #10
                    Any travel store has converters that will safely reduce the 220 to 110. I bought a step-down transformer for my trip to Italy. I used it for charging my cell phone, iPod, and camera. There are other types that are used for hair dryers, etc., but they will not work for electronics.

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                    • #11
                      thanks for the ideas, don't worry i wouldn't use the ground else the entire machine would be live as i didn't' run four wire. I know there's lots of ways to do it, I'll pick up an appropriate transformer....it wasn't that the $3 for a transformer, it was more the convenience of doing with what is already sitting in a drawer. Since that didn't work I wanted to understand what went wrong, and as per usual with the group, i wasn't disappointed.
                      .

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                      • #12
                        Might check Allied Electronics

                        Allied lists transformers for what you need. Allied # 967-2429 115/22 in, 20V out. $6.77

                        Other voltages for the same price. Almost cheaper than screwing around with a wall-wart...

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