Xformproj

Homemade Transformer Projects
Auto winder
9500 Volt Home Brew Transformer
2500 watt homemade transformers
X Pig Transformer
Formulas for making your own transformers
Materials used in making a transformer

To wind the secondary's of my homebrew transformer I first had to build an auto winder. It is controlled by a PIC microcontroller. It counts the number of turns per layer , the total turns and displays counts on an LCD . Also generates the step pulses for the stepper motor, and controls the solid state relay for the gear motor.
I hit a momentary switch to start a layer. After a predetermined number of turns it pauses the gear motor to allow me to add the inter layer insulation. Once I add the insulation, I hit the momentary switch again to start the next layer.
To control the wire spacing an old dot matrix printer print head guide is used. I soldered some brass tube to some brass flat stock and screwed it to the platform where the print head used to be. It takes 3 half steps to get the proper spacing for 30 AWG wire, on this setup. To provide some wire tension I clamped 2 pieces of dry sponge, with an aligator clip, behind the wire guides.
On each full revolution of the gear motor, a lever switch is tripped, the micro bumps the stepper motor to the left or right depending on the layer.
If there is some problem I can hit the momentary switch to pause the winding.

click to enlarge

The wire guide is from an old dot matrix printer. I removed the print head and installed the brass guides.
The 6 RPM gear motor is on the right of the front spool.
The micro switch is wedged between the gear motor and it's mount.
The bobbin being wound is a secondary for the 2500 watt transformer shown below.

click to enlarge	Controller
Click to enlarge	The software for this project was written with the PIC Basic Compiler from MicroEngineering Labs. It is similar to the Basic Stamp version of BASIC. My program dosen't use any resourses not available to the Basic Stamp and should be fully compatible with no changes. Click below to download text file. CLICK HERE TO DOWNLOAD SOFTWARE

Home Brew Transformer

Transformer - new home brew transformer.
Stretch core - I took a 15/30 nst core and added 1.25" to it. I cut up another core and used that material. The reason for this effort is so I will have enough space to wind the secondaries, and include current limiting shunts. The secondarys are wider than the originals.
I used adding machine paper(3 mil thick, 2.25" wide), soaked in polyurathane as the interlayer insulation. As each layer was being wound I brushed on polyurathane.
I removed 30 turns from the original NST primary.
Completed twins on right.

Specs:
primary:        250 turns (original primary)            #14 aluminum magnet wire
secondarys:   10500 turns each (21000 total)       #34 copper magnet wire
output:         9500 volts       120 ma

2500 watt home made transformers
Secondary wire is 28 AWG. Each secondary has 6000 turns, which is all I could fit in the space. The interlayer insulation is made of cut up, brown artist craft paper. It is 7 mils. thickness. This should be adequate when they are immersed in oil. I made the bobbins out of very heavy cardstock paper. The inner part next to the core is two layers. They were then coated with polyurathane.

click to enlarge

This is the core for my first HB Transformer. The Neon transformer is a 15KV/60 milliamp for scale.
The core was originally from a welder. I used a side grinder to seperate the core halves. I then split each half in half, creating enough core material for 2 transformers.

Home brew transformers, using welder core. I have tested them on a TC, works great! I am running them with the primarys connected in series, at 220 volts. The secondarys are connected in parallel.

Click to enlarge

Measurements for each transformer.
Measured input:
primary 120 volts 20 amps
Measured output:
secondary 12500 volts 220 milliamps

Windings:
Primary 130 turns 12 AWG enameled wire Secondarys: 6000 turns each, 12000 turns total 28 AWG enameled wire

The green cutting board strips screwed to the top of the transformers keep them from tipping over in the case.	The insulators are salvaged from my old neon transformers.
The final resting place for my home brew transformers. The construction of these boxes was an experiment that has worked well. I welded up a steel frame out of light steel tube. Then I cut 1/4" masonite to fit inside the frame. Using Elmer's Probond polyurathane glue I glued to bottom and sides to the metal frame. The Probond glue actually foams up and fill and small gaps. This glue is very strong, bonds to practically anything, very highly recommended. There are no nails or fastening devices at all. I then coated the inside with polyurathane clear finish. Same stuff used on secondary coils. Total wieght with oil, around 75 LBS. No leaks.

X Pig Transformer
Well I burnt the other transformer. So I had to build my own X-PIG, a pig size transformer with an X Ray core. The finished transformer is a monster.

Click to enlarge

60KV XRAY TRANSFORMER - original configuration
Photo at left
Two 125 KV, 400 ma. rectifier arrays in front of secondaries
Photo on right.
Secondaries are wrapped with copper flashing. The 3, "feedback" transformers are wound on 1.5" thick ceramic bobbins. The wire is cotton covered magnet wire.

Finished product. new primarys and secondarys
Size: core 12" X 14" overall: 18" x 20"
Primary turns: 80 /100/120 taps each
Primary wire - bifilar winding of 12 AWG heavy nylese
Secondary turns: 8000 each secondary - 16000 total
Secondary wire - 28 AWG formvar
Weight: Approx 75 Lbs.

This puppy is dangerous.

Measured output: At 100 turns primary
20000 volts .400ma see misc page for jacobs ladder test

I have built a box for this transformer using the same methods as the HB transformer box described above. With the transformer, filled with oil, it weights over 100 LBS. I lifted the filled box with a chain hoist and there were no cracks or leaks. That ProBond glue is amazing stuff.

Formulas for designing your own transformer
This is a basic starting guide. See my links page for sites with the heavy details.
The examples are for transformers with 2 secondarys connected in series.
1. Measure the transformer core. There are two main considerations for core size.
Winding window. For E I or EE cores there will be a certain ammount of space for the windings. Since home made windings usually take more space than factory windings, space may become critical on small cores. One way around this is my stretch core shown above. This problem will show up in the discussion about materials below.
The other main consideration is the core cross section area measured in square inches. This is only the leg of the core that actually goes through the primary windings. A small neon transformer may have a center leg only 1.22" X 1.75" = 2.18 square inches.

2. Calculate primary turns.
Small NST example: core area 1.25" X 1.75" = 2.18 sq. in.
N = (E X 10^8) / (4.44 X F X A X B) Where F = frequency   A = area in sq. inches.   B = magnetic flux assume 60,000 E = voltage
N = (K X E) / A         Where K = 6.50 when f = 60 hz or K = 7.507 when f = 50 hz
6.50 X 120Volt = 780     780 / 2.18 Sq. inch = 357 turns
approx. turns on original - 300 - 325

X Ray transformer example: core area 3.2" X 3.2" = 10.24 sq. in.
6.50 X 120 = 780 780/10.24 = 76.17 turns
approx turns on original primary - 76

Microwave oven core example: core area 1.55" x 2.55" = 3.952"
780 / 3.952 = 197.36 turns
approx turns on original primary - 130

No wonder small transformers always have so many primary turns. Bigger cores require fewer primary turns.
Manufacturers may not always use the full # of turns. On some NST's and MOT's there have been fewer turns than calculated. On the Xray transformer they used the full required turns. For full output one should try to get as close as possible.

3. Calculate secondary turns.
Small NST example: 350 primary turns
Turns Per Volt = primary voltage / primary turns
Nst 120 / 350 = .342 TPV
XRay 120 / 76 = 1.57 TPV

Say the desired output voltage is 15Kv or 7500 volts per secondary.
Therefore, turns secondary = output volts / tpv
NST 7500 volts / .34 TPV = 22058 turns
XRay 7500 volts / 1.57 TPV = 4777 turns

Here are some more formulas to help calculate voltage and current.

E = Voltage I = Current(amps) S = secondary P = primary T = turns

Voltage and Current

Voltage and Turns

Current and Turns

EP = ES X IS / IP
IP = ES X IS / EP
IS = EP X IP / IS
ES = EP X IP / IS

EP = ES X TP / TS
TP = EP X TS / ES
ES = EP X TS / TP
TS = ES X TP / EP

IP = IS X TS / TP
TP = IS X TS / IP
IS = IP TP / TS
TS = IP X TP / IS

Materials:
Core Size:
Bigger is better:
1. Increased core cross-sectional-area allows less turns to be used for
   the same voltages at both windings. (More volts/turn.) This reduces
   resistive losses. Makes it much easier to wind.
2. Increased winding window allows thicker wire to be used.   Also
   reducing resistive losses.

Wire size:
Primary
Primary wire should be magnet wire. Other types can be used, hovever there are considerations. The insulation should be as thin as possible. The insulation should be able to handle the temperature. Wire wound on the core will get hotter than normal. Insulation should be able to handle some substantial voltage stress.
Magnet wire fits the bill on all. The drawback is that larger sizes are not as easy to find and costly.
Choosing the size is of course dictated by the current. There are plenty of charts around. Usually 12 AWG magnet wire can handle up to 20 amps for short runs. If using PVC coated wire, bear in mind that the wire will run hotter. So don't rely on temp rise charts.
Secondary
For me, #34 AWG is about the smallest wire I can work with. This is fine for smaller transformers. A typical 15Kv 30 ma. NST would have 38 to 40 AWG wire. So using 34 - 32 AWG should make a very robust secondary.
Larger transformers up to 5000 watt transformers can use up to 28 AWG.

Wire chart for common secondary wire.

Wire Size(AWG)	40	38	36	34	32	30	28
Ampacity(amps)	44 ma	74 ma	117 ma	187 ma	304 ma	477 ma	761 ma

Interlayer insulation:
Artist Craft paper works great for transformers in oil. Don't use cheap craft paper for mailing packages. Artist paper is low in acid and made out of finer, better quality pulp.
If the transformer is to be used dry then better precautions are needed.
Polyetheleyne is an good, cheap material. A draw back is a low melting point. I have tried this but I didn't really like it. The main reason is that I want the inerlayer insilu to have some stiffness to support the new windings. Paper is thin but gives good support. In the stretch core I used adding machine tape, soaked in polyurathane. Then as the windings are being put on I brushed on poly. It sounds like a big mess but it was not to bad.
Mylar , teflon They works fine. May degrade in oil.

Example - Max voltage for each secondary is 7.5Kv for a 15000 volt transformer.
Heavy build magnet wire insulation is rated from 4 - 7KV. On my Neon transformers the insulation is only ~.002" thick.
If you need to conserve winding space use thinner insulation in the inner layers( ~003") and thicker insulation(~.007) on the outer layers where the voltage is higher. Any voltage spikes fron a Tesla coil will zap the outer layers first. Extra cautions here will help. On the XRay transformer about 10 outer layers were space wound, getting gradually wider spacing on each layer. On my X-Pig transformer there was plenty of room for the windings so I used 2 layers(.014") of craft paper on the outer 10 layers.
Real Important: Leave enough empty space on the ends of each layer to prevent flashover. Don't under estimate this problem. Leave "At least" , .25" up to .75" on heavy duty transformers.

Coil Forms:
Making coil forms

More Formulas

Reactance
Reactance in a circuit is the opposition to an alternating current caused by inductance and capacitance, equal to the difference between capacitive and inductive reactance. Expressed in Ohms.
Inductive Reactance X(L)
Inductive reactance is that element of reactance in a circuit caused by self-inductance.

X(L) = 2 X 3.1416 X Frequency X Inductance(Henrys)
X(L) = 6.28 X 60 X .1(100 millihenry)
X(L) = 3768 X .0001 = 37.68 ohms

Capacitative ReactanceX(C)
Capacitative reactance is that element of reactance in a circuit caused by capacitance.

X(C) = 1 / (2 X 3.1416 X Frequency X Capacitance)
X(C) = 1 / (3768 X .00001) 10 uf
X(C) = 26.53 ohms

Voltage drop calculations - Inductance negligible
V = Drop in circuit voltage
R = Resitance per foot of conductor(Ohms/ft.)
I = Current in coindutor(amperes)
L = length of conductor(feet)
D = Cross sectional area(Circulir mils)
K = Restivity of conductor
     K = 12 for circuits loaded with more that 50% capacity
     K = 11 for circuits loaded with less than 50% capacity
     K = 18 for aluminum conductors

V = (2K X L I) / D