That might be the best way, if I use that older step down trans. I would have to run a 220 line over to my work area. Might be the better . Then would only need variac.


will check that in a bit, have not checked.

Actually, there are also isolated versions available. They have an inner winding layer that is only an isolated primary, and the variable tap winding is wound over it. I have seen photos and catalog listings. They do cost more but they eliminate the need for a separate isolation transformer.

 

Have checked for continuity from the input to output of the transformer to see if it's actually isolated?

they are not.. the 2 input on the 240 side have continuity with both outputs on the 120v side. So this is not usable right?

 

so much for trying to save a buck.. I have a large transformer if I still have it and if its good. It was a 200-300 amp dc battery charger booster. I am sure that's 120 to 12v

 

they are not.. the 2 input on the 240 side have continuity with both outputs on the 120v side. So this is not usable right?

It may be possible to open the transformer and separate the two windings. On some the connections are accessible.

 

they are not.. the 2 input on the 240 side have continuity with both outputs on the 120v side. So this is not usable right?

That's strange as none of the ones I dealt with ever did. They look like this:



You will have a resistance between 1&2 and 3&4 but that's it. There should not be continuity for example the primary 1&2 and secondary 3&4. Then too just because I never came across one while over there doesn't mean anything. I just find it peculiar.

Ron

 

It may be possible to open the transformer and separate the two windings.

Not likely.
It's probably an autotransformer (since they are relatively cheap and small), with the winding shared between the input and output.
The single winding is just tapped at the half-way point for 120V.

That's strange as none of the ones I dealt with ever did. They look like this:

That's for a true isolation transformer.
This is a travel transformer for using appliances on a different voltage, where isolation is not required.

 

Not likely.
It's probably an autotransformer (since they are relatively cheap and small), with the winding shared between the input and output.
The single winding is just tapped at the half-way point for 120V.
That's for a true isolation transformer.
This is a travel transformer for using appliances on a different voltage, where isolation is not required.

I don't think this is a travel transformer. Here is my take on what it is. When US Military or Civilian Components of the Department of Defense receive accompanied tour orders abroad, Europe for example, the US Government ships their what is called "Household Goods". The OP mentions in his first post:

Looking around in old parts I have laying around. I have one of those euro 240v step down to 120v 1000w transformers,

I want to say mine was 3.0 KW but what I am seeing here is not an everyday travel transformer but a large 1 KW step down single phase transformer. They are widely sold in Europe, especially around US military installations. I bought mine at a local hardware store in Italy during my DoD time as a Naval Engineering Support Unit engineer. The Americans would then run extension cords all over for things like kitchen appliances and about anything else 120 VAC that ran fine on 50 Hz. I bought a US 19 cubic foot refrigerator freezer from a guy getting a divorce and his wife returning to the US so he was going into bachelor quarters. Anyway my take is this is the sort of transformer the original poster has and this was before any of the newer design inverters were around. Beats me. This was circa mid 80s for me.

Ron

 

now what is the difference between a travel trans and a non-travel trans? Both are portable. I'll take a few picts later of it.

I do not know the age of it, it was given to me by a friend, guess 15-25 yrs old

 

I would suspect a travel version has the secondary referenced to earth ground (set up a neutral)..
Max.

 

how big of a variac do you need. seems like 1-2 amps would be more then enough for most things. Would be nice to have variable current too. I am sure that $$$

 

Depends on what you need it for. Jameco has some Value Pro inhouse isolation transformers in a nice benchtop package that are CHEAP! A 5A isolator and a 2KW variac (or less) should be ~$200.

 

what is the difference between a travel trans and a non-travel trans?

Most travel transformers are autotransformers, since they are much smaller and cheaper than a standard transformer.
Most other power transformers are standard types with isolated primary and secondary for safety.

I would suspect a travel version has the secondary referenced to earth ground (set up a neutral)..

I would think the neutrals are tied together and the safety (earth) ground is just passed through.

Would be nice to have variable current

You mean a current limit?
No variable transformers have that other than a fuse that blows when the limit is exceeded..
They just vary the voltage and the current is whatever the load impedance takes.

 

Depends on what you need it for. Jameco has some Value Pro inhouse isolation transformers in a nice benchtop package that are CHEAP! A 5A isolator and a 2KW variac (or less) should be ~$200.

not seeing a valuepro item at jameco? they have a isolation transformer benchtop 99.95usd Similar to valuepro?
https://www.jameco.com/z/GRP-1200-Benchtop-Transformer-Isolation-120VAC-7A-60Hz-450VA_2214336.html

some variac prices off amazon 500w 49.00usd, 1000w 72.99usd..

 

Most travel transformers are autotransformers, since they are much smaller and cheaper than a standard transformer.
Most other power transformers are standard types with isolated primary and secondary for safety.
I would think the neutrals are tied together and the safety (earth) ground is just passed through.
You mean a current limit?
No variable transformers have that other than a fuse that blows when the limit is exceeded..
They just vary the voltage and the current is whatever the load impedance takes.

I believe Mr. Carlson lab has a variable voltage and variable current unit?

I have a carbon pile resistor that can handle 600amps DC, makes a lot of heat and burns off the dust at 600. Not sure you could use anything like for a AC load.

 

It's actually 4A https://www.amazon.com/gp/product/B...c45-cd78f07a84d8&pf_rd_r=K2HW1D43QC378KJ2B5DJ

 

It's actually 4A https://www.amazon.com/gp/product/B...c45-cd78f07a84d8&pf_rd_r=K2HW1D43QC378KJ2B5DJ

that's identical to the one Jameco list now @ 7amps for same price, it must be newer one.

 

Most travel transformers are autotransformers, since they are much smaller and cheaper than a standard transformer.
Most other power transformers are standard types with isolated primary and secondary for safety.
I would think the neutrals are tied together and the safety (earth) ground is just passed through.
You mean a current limit?
No variable transformers have that other than a fuse that blows when the limit is exceeded..
They just vary the voltage and the current is whatever the load impedance takes.

Passing through the ground line in an isolation transformer totally defeats the isolation intent. That reality has been beaten to pieces in other fairly recent posts.
A "travel transformer" is an easily portable device, usually intended for short use rather than constant use. Also, they generally come with adapters for different mains outlets. And they are seldom, if ever, designed to be hardwired in.

 

I would think the neutrals are tied together and the safety (earth) ground is just passed through.

Why would you tie the neutrals together?
.Although essentially that happens when the earth ground is connected to a secondary conductor, making it a neutral.
It has to be done at the right point per NFPA.
Max.
[/QUOTE]

 

I have one of those euro 240v step down to 120v 1000w transformers,

If this is either a travel transformer or a UK work-site version, then I would fully expect to the secondary having a earthed neutral.
At least that is what I would consider safe if I had reason to use one.
Max.

 

I see the UK 240v to 120v work-site transformer has a CT grounded neutral on the 120v side, similar method to the N.A. C.T. neutral. (60v-0-60v)
Max.