Hi guys have made a transformer have two mild steel bars 60mm x 35mm x 270mm i have 2 x 100 meter rolls of 1.5 conduit wire on primary and 4 x100 meter rolls on secondary the bars are connected with 4 straps 50mm x 6mm x 200mm i have 222 volts at the primary and getting warm quite quick i have tested continuity and all ok secondary i have 82 volts i need 480 the starps are drilled and tapped with m8 set screws any advise please all welcome many thanks

 

Not enough inductance would be my guess.
Do you have a picture?
Max.

 

Hello,

I think that you are having problems with eddy currents.
Usualy transformers are made with a laminated core:
http://sayedsaad.com/fundmental/index_transformer.htm

Bertus

 

Also do you have a complete magnetic circuit - or just a bar with the coils on it?

 

Insufficiently flux linkage ...try this:

 

Do you know the permeability of your steel bars? You also really want soft iron for your core material with laminations preferred. Try giving this a read.
Transformer Construction
The construction of a simple two-winding transformer consists of each winding being wound on a separate limb or core of the soft iron form which provides the necessary magnetic circuit.

Ron

 

Hi guys have made a transformer have two mild steel bars 60mm x 35mm x 270mm i have 2 x 100 meter rolls of 1.5 conduit wire on primary and 4 x100 meter rolls on secondary the bars are connected with 4 straps 50mm x 6mm x 200mm i have 222 volts at the primary and getting warm quite quick i have tested continuity and all ok secondary i have 82 volts i need 480 the starps are drilled and tapped with m8 set screws any advise please all welcome many thanks

Why not just buy a 2:1 ratio transformer? 460/230:230/115 is industry standard design that comes in every VA rating imaginable making them very common and cheap.

Most often they are referred to as instrumentation or control transformers.

 

Why not just buy a 2:1 ratio transformer? 460/230:230/115 is industry standard design that comes in every VA rating imaginable making them very common and cheap.

Most often they are referred to as instrumentation or control transformers.

The transformer needed is £980 + VAT so I have to build this bespoke one i had an old welder transformer that i wound but could only get 375 volts ac from it it is to run my 3 phase inverter

 

Not enough inductance would be my guess.
Do you have a picture?
Max.

 

Aside from the problem of eddy currents and the wrong type of steel, the poor magnetic coupling between the coils is killing it. Those steel straps provide a mechanical linkage but that's about all.

 

As already suggested, you do not have sufficient core mass and also the lack of coupling between pri & sec.
Max.

 

The transformer needed is £980 + VAT so I have to build this bespoke one i had an old welder transformer that i wound but could only get 375 volts ac from it it is to run my 3 phase inverter

Without VA or KVA rating that means nothing to me.

 

If you fill the gap between the two straps of a pair with steel you should get better results, but the outcome may still be disappointing.

 

Some important facts are waiting for you. Read this.

 

Hi guys have made a transformer have two mild steel bars 60mm x 35mm x 270mm i have 2 x 100 meter rolls of 1.5 conduit wire on primary and 4 x100 meter rolls on secondary the bars are connected with 4 straps 50mm x 6mm x 200mm i have 222 volts at the primary and getting warm quite quick i have tested continuity and all ok secondary i have 82 volts i need 480 the starps are drilled and tapped with m8 set screws any advise please all welcome many thanks

Hello,

It was a very good try, i have to say that much

The problem is much like others here have pointed out already, i'll just add a little here. The root issue is that you need too many turns to make it work at 220vac 50 Hz.

The following is based on a continuous core that is made of bar metal that is the same thickness and width around the entire circumference of the core construction. That means the top and bottom of the core in the picture must be fulled with metal also, not just two straps.

First and foremost, the permeability of regular soft steel is much much lower than steel made for transformers and inductors. Steel made for line operated equipment has a max flux density near 20000 Gauss, while regular mild steel might be around 100. That, unfortunately, puts regular steel at a great disadvantage for being used in transformer construction. That's 200 times lower than most steel normally used for this prupose, and because the calculation for saturation flux density would have flux density on the left hand side standing alone and the number of turns 'N' on the right in the denominator, that means when you try to use mild steel vs grain oriented steel made for that purpose you need 200 times the number of turns you would need with the grain oriented steel. That is a HUGE difference which is probably not actually attainable becuase the number of turns is also limited by the window area, and since the wire area that fills the window area is proportional to the number of turns, that means we also need 200 times the window area. So you can start to get an idea how fast this goes south for normal line operating voltages like 120 and 240vac, but let's run a couple numbers...

The main equation is:
B=E*10^8/(4.44*FAN)

I leave out the multiplication symbols for FAN which is really F*A*N so that the spelling is clear and so easier to remember, so it's really 4.44*F*A*N.

In this formula A is the area in square centimeters, so we convert that to square inches:
1 sq cm=6.4516 sq inches

So the formula comes out to:
B=E*10^8/(29*F*A*N)

with area now in square inches. Also, lumping constants brings us to:
B=E*3.5e6/(F*A*N)

which is simpler yet.

Since your dimensions where given in mm though, converting mm to cm we have:
1 sq cm=0.01 sq mm

so for a metal bar that is 60x35 sq mm or 2100 sq mm, which is 21 sq cm.

Using the main formula:
B=E*10^8/(4.44*FAN)

we have:
B=220*1e8/(4.44*50*21*N)

and setting B=100 and F=50Hz we have:
100=220*1e8/(4.44*50*21*N)

and solving for N we get:
N=47190 turns.

That's a lot of turns, and we havent even considered the effects of the four gaps that will result when the construction is clamped together. Any gap, even a small one, will lower the permeability even more which could raise the number of turns fourfold, which if it mattered now, would be even worse. Distance is an important factor in magnetic circuits, and even very small distances can make very big differences, so the gaps have to be almost perfectly fit together. In a real transformer the laminations are often interleaved so that the effects at the gaps is minimized. In solid metal transformers the joining faces of metal are machined so that they fit almost perfectly together.

If we are lucky our steel might be a little better than 100, but even if it is around 200 we still need about 25000 turns, which is just impractical from several viewpoints most notably the effective series resistance which would quickly lower the output voltage when we add a load, or even lower the voltage due to the primary excitation current.

Sorry to say, this idea doesnt seem to work very well.