[TriEmbed] Inexpensive 120V (15A) to 240V (7.5A) transformer?

Shane Trent shanedtrent at gmail.com
Tue Apr 12 08:28:10 CDT 2016


Robert,

I am leaning toward an autotransformer. I am trying to bump a 120V AC
generator output up to 240V for an inverter/charger that has a split-phase
240V input. I have never worked with auto transformers so I was not sure
how to view the current handling.

Shane

On Tue, Apr 12, 2016 at 8:55 AM Robert Gasiorowski via TriEmbed <
triembed at triembed.org> wrote:

> Get any 240V, 1kW transformer with dual primary (2 x 120V.)
> Make one side common, connect center to 120V, the second side will give
> you 240V (non-isolated.)
> You will end up with what's called autotransformer. ATs are much smaller
> than isolating transformers.
> I used this type of transformers to power US made appliances like
> microwave ovens in EU (220V->110V.)
>
> On Tue, Apr 12, 2016 at 6:45 AM, Josh Wyatt via TriEmbed <
> triembed at triembed.org> wrote:
>
>> What are your power requirements?
>>
>> A few ideas...
>>
>> 1. If all you need is high voltage DC for charging a battery bank, you
>> could use a voltage doubler. Check out the full wave circuit here:
>> http://www.daenotes.com/electronics/devices-circuits/voltage-multipler
>>
>> 2. You could buy two identical 120vac-to-12vac transformers and use one
>> for boost. Connect transformer 1 in the conventional way, to provide 12vac.
>> Connect the 12vac output of transformer 1 to the 12vac winding of
>> transformer 2; the "output" of transformer 2 will now have 120vac which you
>> can place in series with your line voltage for 240vac. (make sure it's in
>> phase or you'll get 0 volts out).
>>
>> 3. Alternatively, search ebay for 'control transformer,' as this is a
>> pretty common need and application in the electrical world. Be sure to
>> choose it properly for the voltages and power you expect. For example,
>> http://www.ebay.com/itm/Square-D-9070T150D1-Industrial-Control-Transformer-SCHNEIDER-ELECTRIC-/272208984055
>>
>> Lastly - It goes without saying, but be careful; you're dealing with
>> lethal voltages here.
>>
>> Thanks,
>> Josh
>>
>> On Mon, Apr 11, 2016 at 11:14 PM, Kevin Schilf via TriEmbed <
>> triembed at triembed.org> wrote:
>>
>>> Hi Phil,
>>>
>>> I don't know what Shane has in mind, but that is an interesting idea
>>> about using two receptacles; although, Mr. Murphy will probably ensure that
>>> opposite phase receptacles will be several feet apart as you note.  :-)
>>>
>>> Why not just add a two pole, 240V circuit breaker assuming you have
>>> space in the panel and can reasonably run wire from your load to the panel?
>>>
>>> BTW, I think there may be a typo in your email, should be:
>>>
>>> AWG 10 -> 30 A
>>> AWG 12 -> 20 A
>>> AWG 14 -> 15 A
>>>
>>> To anyone reading this post, same impedance at twice the voltage = 4
>>> times the power delivered.  Please be careful and consult a licensed
>>> electrician if in doubt.
>>>
>>> Sincerely,
>>> Kevin Schilf
>>>
>>> ------------------------------
>>> *From:* Phil Smith via TriEmbed <triembed at triembed.org>
>>> *To:* Shane Trent <shanedtrent at gmail.com>; TriEmbed Discussion <
>>> triembed at triembed.org>
>>> *Sent:* Monday, April 11, 2016 6:59 PM
>>> *Subject:* Re: [TriEmbed] Inexpensive 120V (15A) to 240V (7.5A)
>>> transformer?
>>>
>>> If you can find outlets close to each other whose hots (x and y) are
>>> from adjacent circuit breakers, then you could combine x,y, and g (ground)
>>> using two plugs to get 240V, although the outlets are likely only rated at
>>> 120V, 15A (14 AWG wire).  Another way of looking at it is x=+120V, y=-120V
>>> (relative to Neutral n here n ~= g except at high current draw.  Often
>>> wiring within a single residential room is from a single circuit breaker.
>>> Interestingly, the National Electric Code (NEC) rates 10, 12, and 14 AWG
>>> wire at 15,20, and 30 amps no matter how long the wire is, analogous to the
>>> state of SC once legisilating the value of pi to be exactly three.  AWG<10
>>> wire is not subject to this arbitrary amperage and equations for resistance
>>> and reactance are used instead.
>>>
>>> Phil
>>>
>>>
>>> On Monday, April 11, 2016 5:16 PM, Shane Trent via TriEmbed <
>>> triembed at triembed.org> wrote:
>>>
>>>
>>> Hey all!
>>>
>>> I am looking for a transformer to setup 120V up to 240V. I recall seeing
>>> a transformer company at the Hamfest last year but do not remember the
>>> name. Can anyone recommend a vendor? Does not have to be a high-end design.
>>> Is powering a charging system that corrects for variations in line voltage.
>>>
>>> Thanks for any suggestions!
>>>
>>> Shane
>>>
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>>
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