220 to 110 transformer

[madlabs]

Hi All,

I need a high current 220 to 110 transformer, say 20-30 amps. I plan to use it to run my welder, which is 110V. The thing is when I run it off my genny on 110, I am only using one side of my 220V gen set, and it doesn't get full power. I figger if I go gen 220 > transformer > welder, I will be running the welder from both sides of my gen set. It will also apply when I get a second stackable inverter and have 220 inverter power available.

BUT... It has to be cheap. I was thinking along the lines of microwave oven transformers and rewinding the secondary, or I have an old stick welder I could tear into, something along those lines. Sad thing is when I moved off grid I wound up getting rid of iron that would have worked. Since the duty cycle is low, I have some flexibility in size/core/wire gauge.

Jonathan

[RP]

It would be worth taking the cover off your welder to see if it has a dual primary that could be rewired for 220v.  If the brand is sold outside the US it may very well be 220 capable already.

[joestue]

rewind the welder if it isn't 110/220.

[madlabs]

The welder is a brand new Lincoln 140T and cannot be rewired for 220. I'm reluctant to mess with the xfrmr in it, if I screw up I will be crying. As well, it has lots of electronics inside, so I am afraid of messing that up too.

But thanks for the ideas!

Jonathan

[DanG]

http://www.sunelec.com/outback-power-autotransformer-4kva-120240v-fw-series-fwx240-p-188.html or better.

You could stack Toroid xfmrs - 3500VA  or better to handle the huge current & heating; imagine 10 350VA 1:2 transformers in parallel with forced air cooling.

If you are really gonzo in winding your own I saw a 1:2 step-up toroid core wound out of steel shipping banding, a tightly wound doughnut coil over eighteen inches across and about four inches thick; IIRC they used teflon tape as layer separators for the solid conductor copper windings... The DIY photo log of the project has disappeared from the internet though...

[TomW]

Bad Idea edited out....

[madlabs]

Dan, that xfrmr looks great, but it's too expensive for me. I haven't the slightest desire to wind one, but I just can't afford a purpose built one.

Thanks though!

Jonathan

[joestue]

here you go: http://www.toroid.com/standard_transformers/auto_transformers/step_down_transformers.htm
you can typically double the "rating" of a toroidal transformer with forced air cooling.
Alternatively, buy one of their 1kva isolation transformers and wire it as an auto transformer to get a "2kva" auto transformer.
of course, there's always ebay.
http://www.ebay.com/itm/Stancor-Isolation-Transformer-P-6125-115V-60CY-1-KVA-/180733903702

[jeffbirkle]

Can you rewire the geny to use both sides of the split phase in 110v?

Jeff

[jeffbirkle]

BTW,
I have a 240v welder and it needs a 7000w geny to weld with a 1/8 rod with deep welds. Otherwise a 5/64 rod and shallow welds with a 5000w geny.

Jeff

[madlabs]

Jeff,

I don't know how/if my genny can be rewired to use both sides of the split phase as you suggest. I'll look around and try to figger out what you mean. Do you have any more info/search terms/links for me to investigate?

I may not be able to use the full power of the welder as your second post implies, but I hope to be able to improve the output. The genny in question is a 5kW (so 2.5kW per side). I can weld thin stuff OK but I need a little more power. I do have a 8kW genny, but it isn't installed yet.

Thanks for the help!

Jonathan

[madlabs]

Joe,

Somehow I didn't see your post with the xfrmr links. Those are at least getting close to my price range. The largest there is 1kVa. Considering the low duty cycle of a welder (I don't need to weld non-stop all day long) think I could get away with 1kVa? I'd be pulling (at most, usually less) around 3-3.5kVa.

Thanks!

Jonathan

[joestue]

I would be less concerned about the heat (you will need forced air cooling if you're really pulling 3 kw, even intermittently), but rather the voltage drop under load, and its effect on the welder.

Right now this appears to be the best deal on ebay: http://www.ebay.com/itm/Stancor-GIS-1000-1KVA-Isolation-Transformer-Works-/290611107263
The 1 kva isolation transformer at toroid.com is $160+ shipping, but its probably going to have a lower impedance than that Stancor transformer.
I don't think the 1 kva "auto transformer" which weighs only 7 pounds, is going to do you much good, and its still 110$ plus shipping.

If you do buy a toroidal auto transformer, note that you could connect it in parallel with your generator because you'll be able to add extra turns to cut the circulating current if needed.
However without knowing the resistance of your generator and said toroidal transformer, there's no telling if that's going to do much to load down the other half of the generator.
So what I would do is measure the electrical resistance of your generator (use a 1 amp current source and a volt meter) and call up toroid and ask them what the resistance of that auto transformer is, both the 1 kva isolation transformer and the 1 kva "auto transformer"
They may not know, nor want to tell you, but they might tell you what the wire gauge is which is just as useful.

FYI: IF that stancor transformer is wound with 76 turns of 12 awg wire for a 1.2T excition, it should have a resistance of 170-200 milliohms, which would be a 4-4.5 volt voltage drop for both primary and secondary under a 25 amp load.  However, i have no idea what they wound it with, all i know is the frame size, the fact that it weighs 31 pounds, from there i can work backwards and get a stack thickness of 100-110mm, which means it should have been wound with 10 awg wire but I really doubt they invested that much copper in it.
if you were to pull 25 amps from it connected as an auto transformer you would be looking at a voltage drop of 4-5 volts or 4%; again assuming its wound with 12 awg wire and runs at 1.2T

[wooferhound]

I have a new auto transformer with a 230 volt primary
and the secondary is Auto and rated at 3000va
it weighs 14 pounds
Free transformer, you pay shipping, might fit into a flat rate box, it's 4x5x7 inches.
if you're interested . . .

[madlabs]

Woof,

Wow! What a generous offer! I'll shoot you a PM with my info. Figger out what shipping is and I'll get it to ya ASAP. If you do PayPal I can get it to you quick.

Beats the heck out of my other thought, which is somewhere deep in my storage I have a gigantic variac. Would be a PITA though, as it wouldn't be easy to fit it into my power area.

Thanks woof!

Jonathan

[wooferhound]

I got your private messages
Busy this weekend, will try and get it out early next week.
I'll send a PM to you when I know the shipping cost.

Glad to help ,  This transformer was given to me free, New in the Box

[madlabs]

I can never believe how cool folks are on this board. I have gotten advice, encouragement, good deals and even free stuff. I am a new off-gridder (3 years next June), just scraping by, and the help I have gotten here has been a big factor.

Thanks  to all!

Jonathan

[wooferhound]

I have been struggling to figure out a use for it.
Glad you are getting it . . .