## Step 4: Wind the new transformer secondaries

tip: draw tally marks on your table to keep track of the number of windings.

How does a transformer work?

The primary winding is an electromagnet connected to alternating current.

The humming magnetic field of the primary induces a current to flow in the secondary winding. If both windings have the same number of turns, the output voltage is the same as the input.

(minus a smidgin due to eddy currents, resistance, etc.)

If the secondary has more turns than the input, its output voltage is higher. That's the type of transformer you started out with.

OUTPUT VOLTAGE = INPUT VOLTAGE * (NUMBER OF SECONDARY TURNS) / (NUMBER OF PRIMARY TURNS)

Our primary has 100 turns and gets connected to 100 volts AC. We're winding 20 turns on the secondary, so we'll get about 20 volts out.

The available POWER STAYS THE SAME regardless of what the output VOLTAGE is.

POWER (WATTS) = AMPS * VOLTS

If the primary is made take 1000 watts (100 volts * 10 amps) out of the wall, we'll be able to take 1000 watts out of the secondary. With 1/5 of the windings, we can draw 50 amps out of the secondary.

That's the cartoon version with play numbers anyway.

Over here in our shed full of reality we've got two of these beasts in series and plan to short the outputs through a welding rod like Jennifer Beals.

Let's just say we're going to pull a whole lot of amps, which is why we need to wind our secondary with such thick wire.

The copper conductor in ten-guage wire happens to be 1/10" (0.1") in diameter.

Here's a table of conductor diameter, guage, and current rating.

http://www.chrisfrydesign.com/transformercalc/

230v * 20 turns on 2nd = 4600

4600 / 112 turns on primary = 42.67v

13amps * 230v = 2990w (could round it up to 3000w)

is that correct? if so then surely i would only need a single transformer to do the welding? as you guys are using 2 to achieve output voltage of a simlar value

which would mean i would be getting over 100amps right?

http://www.ehow.co.uk/how_6505440_calculate-transformer-volt-amp-rating.html

looking at number 4 it says that if your reducing 120v to 12v your doing it by a factor of 10 and thus the input amps would be times that factor to give you the ouput.

to work out my amps i would assume i would need to work out the factor for my voltage so

input 230v / out put 41.67 = 5.51

input 13amps * 5.51 = 71.63amps out

am i doing this right? I think this should be the approximate amount of amps i would be putting out from 1 transformer

what this means the the US is that with your 50amps (as above) you will need more so doubling up your transformers gives you 100amps and your in the golden zone.

with my higher power and slightly higher amps with one tansformer I would only be able to get 71.63amps so its clear i also need to double up too.

so heres what i got, I have 2 transformers with the following

A) 112 turns on the primary

B) 132 turns on the primary

assuming I will be doing 20 turns on the secondary and the input voltage is 230v with 13amps, i work out its output and my factor for each transformer and then work out its amps

----------------------------

working out A)

230v * 20 turns on 2nd = 4600

4600 / 112 turns on primary = 41.67v output

input 230v / output 41.67v = 5.51 (the factor)

input 13amps * 5.51 (the factor) = 71.63 amps output

-----------------------

working out B)

230v * 20 turns on 2nd = 4600

4600 / 132 turns on primary = 34.8v output

input 230v / output 34.8v = 6.60 (the factor)

input 13amps * 6.60 (the factor) = 85.8 amps output

-------------------------

so once i combine the 2 transformers output

85.8 amps + 71.63 amps = 157.43 amps total output

41.67 volts + 34.8 volts = 76.47 volts total output

now the problem is what wire do i use, i found this site which has a handy table for the amps different wires can handle

http://www.powerstream.com/Wire_Size.htm?nowritefs&nowritefs

so i need wire that can handle up to 85.8 amps for B) and 71.63 amps for A)

looking at the chart i found I would need to use 7 gauge wire in the UK which can handle up to 89amps as you guys in the US are generating around 50amps 10 gauge is fine.

problem with this is that 7 gauge is much thicker so will i get the turns in, well thats where someone on instructables has the answer, you have to work out the area you have to use check this out

http://www.instructables.com/id/Easiest-Microwave-MOT-SalvageRe-use-Tutorial/

this is a series of videos that explain how to prep the transforms and in one of them it shows how to work out the area and how to wind your cable to use the best space and if the wire your planning to use will fit.

good job i salvaged the fans from those microwaves, of course if you used wire that is enamel coated then i suspect you could fit the 7 guage in, but i'm thinking it will be tricky if its covered in a standard insulation.

i'm rambling i should go to bed, its 2.20am

from Kaychi.

thanks alot for the idea

http://www.geocities.com/aaawelder/index.html