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 Post subject: Isolation Transformer
PostPosted: Nov Mon 21, 2016 4:46 pm 
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I am planning to install a Triad Magnetics N-48X Isolation Transformer in a box with a panel mounted (back) amp fast acting fuse and a single spst toggle switch (on/off). A power on light too . I am going to use a panel output connector on the box.

The purpose of the project is to supply power to radios on my bench. I already have a commercial isolation transformer in a metal box with numerous outlets but wish to make my own.

Any suggestions would be appreciated.


Last edited by Ozo on Nov Thu 24, 2016 3:44 pm, edited 3 times in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Mon 21, 2016 6:03 pm 
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Here's mine. Read Leigh's comment.

viewtopic.php?f=12&t=295857&start=20&hilit=isolation+transformer


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Mon 21, 2016 7:06 pm 
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Macrohenry wrote:


I like the outlet solutions you came up with and may use them but am still looking. I especially like the computer connector which I had thought of too but do not have a pc power supply I want to scavenge parts from. The female connector is $4 (after shipping) from China. Pack of two from Amazon is $6.60 (after shipping)

I think your enclosure (below) is awesome.
Attachment:
transformer.jpg
transformer.jpg [ 48.24 KiB | Viewed 988 times ]


I have a used (from Ebay) Vector-Viz TC261E commercial isolation transformer which has multiple outlets marked AC low, med, high, and DC low, med, high. There is a notice there "400VA Total" indicating that they can all be used simultaneously. There are three DC outlets also low, med, high "500 VA Total". In addition there is a seven position switch marked "SET TO LINE VOLTS" 105,110,115,120,125,130,OFF.
All of the DC outlets came blocked with silicone and the High AC outlet had a removable plug.

I paid a total of $48 bucks for that but this homemade one will be far less.


Last edited by Ozo on Nov Tue 22, 2016 2:24 am, edited 1 time in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Tue 22, 2016 1:52 am 
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Macrohenry wrote:

Thats a great box and it got me thinking. Here is a cute little box (GE T2280A) which is a cube apx. 5"x6" the same size as the commercial unit I mentioned above. I paid $14.95 (after shipping) cheap because it does not work. The back is plastic and the sides have slots but the top is solid. The base is metal. The AC output can go in the back. It already has 120v ac in. I do not know how much space is free inside (not here yet) but I will strip the speaker, PCB etc. and leave the dial, knobs ect.

EDIT: I will power the dial light in the radio as the pilot light. If I have a problem with the light I will install some 120v blue neon lamps like my Marantz dial color.

:idea: Hmm, I could use the radios power switch to operate the transformer. Looks like this will no longer be a radio but will be a dedicated isolation transformer.


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Last edited by Ozo on Nov Wed 23, 2016 1:35 am, edited 1 time in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Wed 23, 2016 12:20 am 
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Here is the panel outlet that I bought and will mount it on the back of the enclosure. I plan to have the Variac ahead of the Isolation Transformer so this is where any new project will be plugged in.

Attachment:
120v Outlet.jpg
120v Outlet.jpg [ 86.84 KiB | Viewed 950 times ]


Last edited by Ozo on Nov Sun 27, 2016 8:05 pm, edited 1 time in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:20 am 
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Location: Santa Rosa, CA
Nice package.

The Triad N-48X is rated at 15 VA. Secondary current is 130 mA. This would not be sufficient to power even a small AA5 radio.

The high secondary voltage in your warning is probably open circuit and will drop to 120V with a load connected.
http://www.mouser.com/ds/2/410/N-48X-781759.pdf

Rich


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:33 am 
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Sorry Ozo, I thought the photo was yours and got confused.

Still, a 2 Amp fuse will not protect a 15 VA transformer.

Rich


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:13 pm 
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Rich, W3HWJ wrote:
Nice package.

The Triad N-48X is rated at 15 VA. Secondary current is 130 mA. This would not be sufficient to power even a small AA5 radio.

The high secondary voltage in your warning is probably open circuit and will drop to 120V with a load connected.
http://www.mouser.com/ds/2/410/N-48X-781759.pdf

Rich

Fortunately I did not buy that yet. I need a bigger (more expensive) transformer. Thanks for the input.

The N-68X is a 50 VA (.435 amps) version available at Digi-Key for $16. The N-73A is 150 VA (.65 amps) is $43.

What is required for most radios? I have a 400 VA Isolation Transformer for everything else I might work on.


Last edited by Ozo on Nov Thu 24, 2016 5:07 pm, edited 5 times in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:15 pm 
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Rich, W3HWJ wrote:
Sorry Ozo, I thought the photo was yours and got confused.

Still, a 2 Amp fuse will not protect a 15 VA transformer.

Rich


Thanks, looks like I am going with a larger Xmfr anyway.


Last edited by Ozo on Nov Thu 24, 2016 7:18 pm, edited 2 times in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:26 pm 
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Using an isolation transformer with more than one device powered could result in a shock hazard between devices :shock:

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 3:40 pm 
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Chas wrote:
Using an isolation transformer with more than one device powered could result in a shock hazard between devices :shock:

Right, that is why there is only one outlet in my unit (see the OP). You must be looking at the other posters device.. The double outlet is discussed in the thread which he supplies a link to.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 5:56 pm 
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You might want to look at this one: https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&pa=181315&productId=181315

Looks like a reasonable price when compared to what they bring on YouTube.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 6:03 pm 
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If you intend to work on AA5 radios, you would need something like 50VA.

The tube heater string takes 0.15 A x 120 V = 18 watts. Probably another 5 watts max for B+ voltages. You might get away with 25VA, but why push it?

Rich


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 6:25 pm 
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I use a 50 va, very seldom. It is just the transformer with a single, old school outlet. A gift from my late Father-in-Law when he stopped his repair shop. Same for the Powerstat, has a single U ground outlet, fused and a boost switch. I prefer separate devices, occasional one will get assigned to some project for a week or so. I have other Powerstats of greater v.a., these were salvage from panel mount so they got packaged into gallon paint cans. I don't have a "Dim-Bulb" lash up, I make one up on the fly, then seldom use it, I prefer to liven a chassis with a remote B supply and see if there are any hidden issues before I consider filters. Every tech has his own protocols dealing with testing, safety, etc. I use multiple Plugmold on the bench, after an episode with a long length of wire solder drooping across a the prongs of a plug, I turned the Plugmold end for end so the neutral side was up :)

GL

Chas

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 6:35 pm 
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Rich, W3HWJ wrote:
If you intend to work on AA5 radios, you would need something like 50VA.

The tube heater string takes 0.15 A x 120 V = 18 watts. Probably another 5 watts max for B+ voltages. You might get away with 25VA, but why push it?

Rich
The 50 VA N-68X Isolation Xmfr is $16 at Digi-Key or Mouser. That is what I will get. The 300 VA unit suggested by Hondo is $50. I like the light weight of the N-68X (1.7 lbs.) as well as the small size. No need for overkill. Like I said, I have a 400 VA isolation transformer (used $35 + $13.45 shipping) for big stuff and I am not working on big stuff.

http://catalog.triadmagnetics.com/Asset/N-68X.pdf
Attachment:
N-68X_sml.jpg
N-68X_sml.jpg [ 44.82 KiB | Viewed 878 times ]


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Thu 24, 2016 7:20 pm 
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Ozo wrote:
Rich, W3HWJ wrote:
Sorry Ozo, I thought the photo was yours and got confused.
Still, a 2 Amp fuse will not protect a 15 VA transformer.Rich

Thanks, looks like I am going with a larger Xmfr anyway.


Looks like 258 mA max current on the radio I am currently working on so I am thinking a 300 mA fuse would be appropriate. I will have to change fuses if I am working on a radio with a higher current requirement. Am I approaching this correctly?


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 2:31 pm 
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I have been told that the Tamura 3FD-410 power transformer provides isolation for half the price and it does but true isolation transformers are used for safety reasons.

This is what Triad Magnetics says about the N-68X:

Description:
The N-68X is power transformer for isolating equipment from direct connection to the
power line. It is constructed with non concentrically wound coils. The primary and
secondary are wound on separate arbors, then assembled on a laminate core
side-by-side separated by insulation. This prevents electrical connection under
normal or overload conditions between the primary and secondary windings.
Safety:
These units are designed with 1500V isolation between winding to winding and
between winding and core. Materials and construction are rated for Class B
insulation system.

Here is an information sheet on the of the 3FD-410 Note the schematic:

https://www.digikey.com/product-detail/ ... -ND/285634


Here is a schematic of the NX-68X.

http://catalog.triadmagnetics.com/Asset/N-68X.pdf

I am no expert but would love to hear any expert opinions on this subject. I should probably started another thread for this but I am selecting a transformer for my project so thought it appropriate.


Last edited by Ozo on Nov Fri 25, 2016 3:13 pm, edited 2 times in total.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 2:58 pm 
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The spec for the Tamura is only 6VA --not enough for powering radios.

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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 3:02 pm 
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pixellany wrote:
The spec for the Tamura is only 6VA --not enough for powering radios.


OOops. I meant 3FD-410 not 3FD-41. Editing above post now.


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 Post subject: Re: Isolation Transformer
PostPosted: Nov Fri 25, 2016 3:10 pm 
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My comment applied to the 410....which is linked above

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