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

Tue Apr 26 16:37:22 CDT 2016

Hey all!,

A follow up question on AC wiring and autotransformers. We are using an
inverter that requires a split-phase 230V source that we want to power from
a 115V single-phase generator (or from a 115V GFI equipped power cord). Our
approach is to use an autotransformer to set up the voltage. Hammond offers
a 1500VA, 115VAC to 230VAC transformer pre-wired with cord, ends and a
breaker that seems to be a good fit. With a 1500VA rating it would be
limited to around 6.5 amps output current.

https://www.hammfg.com/electronics/transformers/line/176

I have only the vaguest recollection of delta-y transforms from my
undergrad so the AC wiring diagram leaves me with a couple of questions.

It would seem to me that with the connection shown, if one side of the
output is used to drive a 115V load it would force current through the
ground connection. I under the impression that sending current through the
AC ground was to be avoided. Wouldn't this wiring arrangement prevent you
from using a GFI equipment line for your incoming 120VAC (because forcing
current on the ground leg would cause a trip)?

My knee-jerk expectation is that the 3rd terminal on the output plug would
be connected to the center tap of the transformer. Is this a bad idea? My
thought is that you would also want to feed the incoming 120VAC ground to
the inverter chassis ground to enable GFI to function properly.

Thank you for your time!

Shane

On Tue, Apr 12, 2016 at 6:25 PM Robert Gasiorowski <rgresume at gmail.com>
wrote:

> There's nothing about current or wire diameter, so I am assuming that 2kW
> one can handle 16A (115V/32A in and 230V/16A out.)
> You may want to confirm with the manufacturer (16A or ~2.5mm windings,)
> but they look good to me.
>
>
> On Tue, Apr 12, 2016 at 6:11 PM, Shane Trent <shanedtrent at gmail.com>
> wrote:
>
>> Robert,
>>
>> I am leaning toward a Hammond 170J. This is a 2000VA model that appears
>> to have 3 leads. I can set the input power limit on the inverter/charger to
>> specify a maximum load on the 230V output side. Any concerns or
>> recommendations for an output current limit?
>>
>>
>> http://www.alliedelec.com/hammond-manufacturing-transformers-170j/70180833/
>>
>> http://www.alliedelec.com/images/products/datasheets/bm/HAMMOND_MFG/70180829.pdf
>>
>> Shane
>>
>>
>> On Tue, Apr 12, 2016 at 5:07 PM Robert Gasiorowski <rgresume at gmail.com>
>> wrote:
>>
>>> Shane,
>>> you will need either transformer with two 120V primaries or one 120V
>>> primary and one 120V secondary.
>>> The windings must be no less than 8A (there will be losses) and have
>>> power capacity of at least 1kW (900W in theory.)
>>>
>>> If you have an old 2kW+ APC UPS, you will find a nice, heft trafo inside
>>> that you might be able to use for this.
>>>
>>> See attached
>>>
>>>
>>>
>>> On Tue, Apr 12, 2016 at 9:28 AM, Shane Trent <shanedtrent at gmail.com>
>>> wrote:
>>>
>>>> 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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>>>>>>>
>>>>>>>
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>>>>>>>
>>>>>>
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>>>>>>
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>
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