Source for 12v to 120v transformer
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  1. #1
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    I see alot of surplus gear motors, actuators, and other goodies cheap but they are 12 volt, where is a cheap source for step up transformers. I dont mean those tiny things used for lights, I want something that will handle 10-15 amps. Any one know of a source?

    Chris

  2. #2
    art_deco_machine Guest

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    You just take a 120 to 12 vac transformer and turn it around backwards.

    But I don't understand you. If you want to run 12 vac stuff from 120 volts, you want a step down something.

    You want an industrial electronic supply house. DigiKey or Allied might have it.

  3. #3
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    eBay is always a good place to start. Here's one that may work http://tinyurl.com/lypk7

    There are surplus transformer sellers listed in magazines like Industrial Equipment Digest. Finding the correct transformer (at the price you want) can be a challenge.

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    For 12V to 120V, I believe you would be actualy
    looking for an Inverter.
    Jamie

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    24V output transformers are real common. A 240-24 hooked to 120 will give you the 12V out. From what I've seen though, a majority of 12V stuff is DC.

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    060507-1349 EST USA

    muleworks:

    Your question should have been phrased "120 to 12".

    Two of many transformer manufacturers are Stancor ( www.Stancor.com ), and Signal Transformer ( www.belfuse.com/SignalTransformer ).

    There is a Stancor P8644 with full load output of 12.6 V @ 10 A with 117 V input. Output is higher with less load. The 12.6 derives from tube days when heaters were 6.3 or 12.6 V for many tubes.

    Stancor you probably get from Allied or Newark. Signal may have some distributors, or direct from Signal. Both web sites are hard for you to figure out. In Signal pick General Purose, Chassis mount.

    You speak of 12 V devices. Are these AC, DC, or AC-DC? Only AC, or AC-DC will work directly from the transformer output.

    .

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    How about the flea market or garage sales? You should be able to get 10+ amp battery chargers cheap. If you need AC take out the rectifyier. I guess that would be closer to 14V but does it really matter?

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    12/24 VAC transformers are also used for low voltage landscape lighting. Finding one without a timer, photocell, etc. might require a bit of looking.

  9. #9
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    A good (cheap!) source for 12VDC power supplies is an old computer power supply. Most of them will have a 12V rail good for 10A or more. The larger PSUs from servers will supply the > 15A you want, although those are harder to find "free."

    I use several PSUs in the shop for powering pumps (my TIG water cooler), fans, and so forth. The pump on my TIG cooler uses roughly 5A to 7A, depending on pressure, and a 250 watt AT PSU runs it fine. That one doesn't even need a load on the 5v rail to work.

    A brief search on the web will give you the pinouts for the different styles. Here is an excellent reference: PSU pinouts The two most common PSUs are the AT style, and the ATX style. Of the two, ATX is slightly preferable, but for powering motors it really doesn't matter which type you get.

    The one thing you need to know is that the typical computer PSU won't regulate 12VDC unless there is a residual load on the 5VDC rail. There are a couple ways to do that. I normally connect a 50 ohm, 3W power resistor across the 5V rail & ground. YOu could also use a 6v flashlight bulb. I found one PSU that wouldn't work with a 50ohm load; I put a 20 ohm, 10W resistor on it and then it worked fine. The largest value you can get away with is the one to use.

    I have a whole box full of power supplies that were donated when I asked my friends for old computer supplies. All free. All of them work, too. Just ask, and you shall receive...and receive...and receive... until you tell your friends to stop giving you that junk!

    Regards,
    Glenn M.

    [ 05-07-2006, 10:23 PM: Message edited by: GlennM ]

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    Don't know how they are now but in the 60's I took an old TV transformer and found 3 taps, 6 V 12 V and 18 V . I added 2 switchs and a diode bridge (for DC). I used it for a slot car track. Anybody remember slot cars?

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    I see alot of surplus gear motors, actuators, and other goodies cheap but they are 12 volt, where is a cheap source for step up transformers.
    Aren't you going bckwards

    You have 120 volts at the wall, and a motor that needs 12 volts. So you want a 120-volt to 12-volt transformer, not the other way around. These are readily available standard products. Try Mouser http://www.mouser.com or Grainger http://www.grainger.com or other industrial distributor.

    Surplus Sales of Nebraska http://www.surplussales.com has a large selection of surplus and NOS transformers, as does C&H Distributors http://www.chdist.com .

    Or if you can't find anything that meets your requirements and you want a custom-made transformer ($$$), try Heyboer Transformer http://www.heyboertransformers.com or Peter W. Dahl Co. http://www.pwdahl.com

    [ 05-08-2006, 04:23 AM: Message edited by: The real Leigh ]

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    Slot cars? 'Way before my time. Waste of time anyway. Wanna buy a box of slot car junk?

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    Other sources might include All Electronics, HSC, or Surplus Center:

    http://www.allelectronics.com/
    http://www.halted.com/
    http://www.surpluscenter.com/

    If the device is DC, you might look for a switching power supply... otherwise, a transformer will work. Also, remember that if you are building your own DC power supply from a transformer, bridge rectifier, and capacitor, that the DC output voltage will be about 1.414 times the transformer's AC output voltage.

    Oh, and the timer/photocell/whatnot in a lighting transformer can often be bypassed (or otherwise locked on) if need be...

    [img]smile.gif[/img]

  14. #14
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    Oh, and the timer/photocell/whatnot in a lighting transformer can often be bypassed (or otherwise locked on) if need be...
    Of course they can, but why pay for stuff that you don't need? The lighting transformers do have the advantage of convenient power cord and screw terminals for the low voltage, as well as a circuit breaker/thermal overload.

    Another possibility that hasn't been mentioned yet is a "buck-boost" transformer. Connected as an isolation step-down transformer, you can get low voltage AC out of one of these pretty easily.

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    For 12V DC - try for a car battery charger. Fairly cheap way to go. Check the Amp rating, some are as low as 3Amps. 15Amps should be easy to find. I have seen some for charging truck batteries upto more than 80Amps. Oh and if you or a friend know eletrons you can butcher err um modify for 12volt AC.

  16. #16
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    look around the c.b. shops, they sold a lot of
    power supplys for running c.b.s at home on the
    bench, they are fairly husky, about 6-8 amps and
    can be found in flea-mkts for 5 bucks,or so,

  17. #17
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    >> but why pay for stuff that you don't need?

    That assumes that you had a choice in the matter... consider, for a moment, somebody diving thru the "$3 As Is" bin at their local surplus-mart, and running across a suitable power supply -- all except for the fact that it's got a photocell on top.


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