Transformer Question

[boomer#...@none.com]

I was looking at the commercial isolation transformers and they are very
costly, so I decided to build my own. After all, all they are is a
transformer with a power cord on the primary and an outlet (and fuse) on
the secondary. And I already have an enclosure to put it in.

I'm looking at a bare transformer to use as an 120v isolation
Transformer. (120v in, 120v out). The transformer primary is 480 / 240.
The secondary is 240 / 120.

This is for single phase 60 cycle AC. (U.S. power).

Will it work if I connect the 240 lugs on the primary to 120 volts, and
use the 240 lugs on the secondary to obtain 120 volts.
Electrically, this makes sense, but I am not 100% sure, so I thought I'd
ask.

Also, this Transformer is rated at 750 va.

Using the calculator chart on
http://www.rapidtables.com/calc/electric/va-to-amps-calculator.htm
750 va should give me 6.25 A output. (Which should be enough amperage
for anything I need to test on my bench).

However, since this transformer was intended to be used at 240 / 480 on
the primary, will it still give me 750 va (6.25 A) on the secondary if I
run it on 120v?

Thanks

[dansabr...@yahoo.com]

My read on this is that the transformer converts input to 1/2 voltage on output. This means that connecting 240 on the input side will result in 120 on the output side (similarly 480 ==> 240).

You need a 1:1 transformer not a 2:1 as described here.

Dan

Note: If the transformer you have has multiple windings or taps, it may be usable as a 1:1 transformer. How many connections are there?

[boomer#...@none.com]

On Thu, 2 Feb 2017 12:52:28 -0800 (PST), dansabr...@yahoo.com
wrote:

In case I was not clear.

Primary is labeled 240 or 480 v
Secondary is labeled 240 or 120

What I want to do is connect 120 volts to the primary winding intended
for 240.

Then use the secondary winding intended to be for 240. This would be
1:1, except I'm running 120 volts into windings made for 240volts.

[Ralph Mowery]

In article <78879ct2du83u9c4r...@4ax.com>, boomer#6877250
@none.com says...

>
>
> In case I was not clear.
>
> Primary is labeled 240 or 480 v
> Secondary is labeled 240 or 120
>
> What I want to do is connect 120 volts to the primary winding intended
> for 240.
>
> Then use the secondary winding intended to be for 240. This would be
> 1:1, except I'm running 120 volts into windings made for 240volts.

You will probably have to reduce the current drawn as the size of the
wire will be smaller than if it was for 120 volts.

[Look165]

It would be OK but you'd better put the 2 240 lugs in parallel on each side.

This is needed for having the maximum available power.

boomer#687...@none.com a écrit :

[boomer#...@none.com]

On Fri, 3 Feb 2017 09:01:08 +0100, Look165 <loo...@numericable.fr>
wrote:

>It would be OK but you'd better put the 2 240 lugs in parallel on each side.
>
>This is needed for having the maximum available power.
>

Huh? You lost me.
Yes, I know what the word parallel means, but what do mean?

On the primary side, I use the 240 lugs, and connect them to a power
cord.

On the secondary side I connect the 240 lugs to an outlet.

That's really all there is to it, (not including any fuses or switches I
might include).

--

As far as this project, I have abandoned it, due to learning from the
replies, that the output current would be halved, from 750va to 375va.
I need a supply which outputs at least 500va.

I have an isolation transformer with a 100va output. It works ok for the
"American Five" (five tube) hot chassis radios, but I want something
with more current for larger amperage needs.

I saw this transformer on ebay and thought it would work. I did not know
that the current would be halved, which is why I asked abotu this,
before buying it. I'll have to just keep watching ebay for something
more suitable that is affordable. My other thought is to wire a 240v
outlet to my bench and use some of the 240 to 120 v transformers on ebay
that sell for small dollars compared to the 120 to 120 transformers. But
the problem with that, is that I often work on stuff away from my bench,
and then I would not be able to use it.

I dont need it tomorrow, so I'll just keep watching for something more
affordable that will give me the power I need. Either way, I'm sure I'll
end up buying a transformer and making my own isolation device. The
commercial ones are very costly, especially the ones that output above
250va. I already have plenty of power cords, outlets and enclosures to
make one. And wiring it up is about as simple as any project can be.

Thanks to all who helped!

[Look165]

Just unlink the two winding by cutting at the middle point which is the
common one (it makes 4 separate windins).

Then put them in parallel at primary and secondary (and in phase !).

Philips used to do this all the time.

boomer#687...@none.com a écrit :

[Phil Allison]

Look165 wrote:

>
> Just unlink the two winding by cutting at the middle point which is the
> common one (it makes 4 separate windins).
>

** OK - so 240 & 240 plus 120 & 120.

>
> Then put them in parallel at primary and secondary (and in phase !).
>
>

** Nah, that makes a 240 to 120 step down.

But only if the parallel pairs of windings have the *exact* same number of turns.

If not, you get major overheating.



.... Phil

[Look165]

Exact !! But for me it was obvious

Well...not completely exact :

What counts is the magnetic flux seen by the 2 windings ; Since they may
not be at the very same place is might not imply the same number of turns.

Generally, these winding are executed (manually or automatically) by the
"2-wire in hand" method.


Phil Allison a écrit :

[Phil Allison]

Look165 is a top posting nut case & troll e:

>
>
> Exact !! But for me it was obvious
>
> Well...not completely exact :
>
> What counts is the magnetic flux seen by the 2 windings ; Since they may
> not be at the very same place is might not imply the same number of turns.
>

** More complete bollocks for a complete bullocker.

> Generally, these winding are executed (manually or automatically) by the
> "2-wire in hand" method.

** Not in the case of the 240V-240V windings, only a lunatic would wind them as a bifilar pair and rely on the enamel alone.

BTW:

You have no fucking clue about the insulation needed for a 1:1 isolation tranny - do you ??

Fucking tenth wit top poster troll.




.... Phil

[Look165]

Next time, try to think before replying.

Only a stupid idiot would connect primary and secondary in parallel.

What I was meaning is to disjoint the two half-windings and put them in
parallel ON EACH SIDE.


The insulation in that casen is 240/2=120V
(170V peak to peak).


I have designed hundreds of transformers in my life (certified UL EN
etc..) and also planar transformers !

I realized several transformers for EDF (the French Electricity
Corporation), all of them compliant.



Phil Allison a écrit :

[Phil Allison]

Look165 is a absolute fucking IDIOT wrote:
>
>
> Only a stupid idiot would connect primary and secondary in parallel.
>

** So must be one of your type.

> What I was meaning is to disjoint the two half-windings and put them in
> parallel ON EACH SIDE.
>
>

** Precisely what I was thinking you meant.


> The insulation in that case is 240/2=120V
> (170V peak to peak).
>

** But when wire is *SERIES* places 480V between adjacent enamelled wires.

>
> I have designed hundreds of transformers in my life (certified UL EN
> etc..) and also planar transformers !
>

** Then you need to be taken out an FUCKING SHOT DEAD !!

You fucking tenth wit wog top poster.

Go fuck yourself - you damn LIAR




.... Phil

[legg]

On Thu, 02 Feb 2017 14:26:41 -0600, boomer#687...@none.com wrote:

>I was looking at the commercial isolation transformers and they are very
>costly, so I decided to build my own. After all, all they are is a
>transformer with a power cord on the primary and an outlet (and fuse) on
>the secondary. And I already have an enclosure to put it in.
>
>I'm looking at a bare transformer to use as an 120v isolation
>Transformer. (120v in, 120v out). The transformer primary is 480 / 240.
>The secondary is 240 / 120.
>
>This is for single phase 60 cycle AC. (U.S. power).
>
>Will it work if I connect the 240 lugs on the primary to 120 volts, and
>use the 240 lugs on the secondary to obtain 120 volts.
>Electrically, this makes sense, but I am not 100% sure, so I thought I'd
>ask.
>
>Also, this Transformer is rated at 750 va.
>

The 750VA rating applies to the part at it's label voltages. If there
is a dual primary - two windings which, connected in series, will
support 480V and which, connected in parallel will support 240V, then
a primary current of 1.5A is expected in each winding under rated
operation.

Reducing the voltage does not change the current capability of these
windings. If you halve the applied voltage, you halve the throughput
power rating, in this case, to 375VA.

A less efficient winding method, with a single tapped winding, will
use different gauge wire for the 240V section of the winding.

The same considerations apply to the secondaries.

Wired as 240in to 240out will produce a 1:1 isolation transformer.

RL

[legg]

Windings with the same label voltage will have the same turns. This is
checked automatically/electronically during fab. Unbalanced turn coils
are discarded/scrapped.

RL