Author Topic: Lighting recycling - Homemade transformers  (Read 511 times)
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Formerly "TiCoune66". Also known here as Vince.

Lighting recycling - Homemade transformers « on: January 31, 2009, 06:31:53 PM » Author: Foxtronix
I have the possibility to find pretty easily many tranformers. Can I disassemble them to rewind them into mercury of LPS ballast for example?

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Re: Lighting recycling - Homemade transformers « Reply #1 on: February 01, 2009, 01:25:00 AM » Author: SeanB~1
In my appyship I did make transformers almost from scratch, only using a prepunched laminate assembly and enamelled wire. The cores were made by us from card, and wound to suit. You can use transformers to make ballasts, but you will most likely have to buy new wire to wind the coils, as most are varnished after assembly, and you cannot unwind the wire without damage. The hard part is getting the old laminates apart, as they are also varnished. You have to gently tap the ends of the laminates with a small smooth faced hammer until you can break the varnish free, then remove the laminates from the core. It is then easy to unwind the windings, making a note of the number of turns of each winding. Then you can calculate the required number of turns ( Google for how to wind transformers) to make the desired function. There will be some experimentation to begin with, and probably a few blown tries as you learn, so test only in an outlet with GFCI and use a inline fuse to protect yourself. Test equipment is needed to check, mostly a multimeter to measure AC volts, AC amps and resistance of the windings.
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Re: Lighting recycling - Homemade transformers « Reply #2 on: May 18, 2017, 11:10:20 PM » Author: Lodge
I have the possibility to find pretty easily many tranformers. Can I disassemble them to rewind them into mercury of LPS ballast for example?

Did you have any luck doing this yet ?
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Re: Lighting recycling - Homemade transformers « Reply #3 on: May 19, 2017, 03:48:46 AM » Author: Ash
May be possible, but with a challenge because the cores of transformers and ballasts are designed to have different properties

The magnetic effects in the core behave in a similar way to electrical Voltage, Current and Resistance

In electricity :

Ohms law : I = V / R

Current density : J = I / Area

In magnetics :

Magnetomotive Force [IN] - The magnetic force introduced by the coil. This force equals to the current in the coil I times the number of turns N. For example, a coil of 1000 turns of 10mA and of 10 turns of 1A would make the same force. The MMF in magnetics is like voltage in electricity

Magnetic Reluctance [R] - The resistance of the path in which the magnetic field goes to the magnetic field. For example, in "EI" (common for transformers) or "Ei" (common core for lighting ballasts), the path goes through the center leg and one side leg in a closed loop. Steel is good magnetic conductror and have low reluctance, air is poor magnetic conductor and have high reluctance. The Reluctance in magnetics is like resistance in electricity

Magnetic flux [ϕ] - Think of it as how many magnetic field lines are going through the core. The Flux in magnetics is like current in electricity

Magnetic field [B] - Think of it as how many magnetic field lines are going through a unit cross section (like 1 mm^2). The Field in magnetics is like current density in electricity

Ohms law : ϕ = IN / R

Field : B = ϕ / Area

The MMF provides a link from the electrical world to the magnetic world : The current in the coil and the number of turns determine the MMF

The link back is the inductance [L] : L = N^2 / R

And there is a design limitation :

In electricity wires have limited ampacity. That is, J is limited to some maximum value, and if we cross it the wire overheats

In magnetics the Steel in the core have limited capacity for magnetic field. It simply won't contain more than specific magnetic field. If we try to push more, the Steel gets saturated - which means that it loses its magnetic properties

We are limited in size (unless we want a small lamp ballast the size of a welding transformer), so the core cross section area is limited

Which means the 1st design constraint :
B = limited
Area = limited
B * Area = ϕ = limited
ϕ = IN / R = limited

The Steel used in the core is electrically conductive. Every layer of Steel (in a cross section) acts as a turn of coil made of Steel, which is shorted. As the ballast or transformer works, this turn will act as an unintentional secondary coil, on which voltage will appear and current will flow. Ths current - Eddy currents - is up to no good and it creates losses, heating the core. The core is broken down to isolated thin plates to break the large current paths, but a small path in each plate remains

The 2nd step to minimize the Eddy currents is to lower the voltage in every such "1 turn secondary coil" :

In transformers, V [pri] / V [sec] = N turns [pri] / N turns [sec]

V [pri] is the voltage of the actual coil, determined by the application (ballast drop voltage according to the lamp requirements, or full 120V or 230V in case of transformer)

V [sec] we want as low as possible

N turns [sec] is 1

so : We want N turns [pri] to be as high as possible, to lower the voltage applied to Eddy current loops

But finally, there are only so much turns that will fit in a ballast or transformer of the size we want (and the more turns and thinner the wire is, the higher is its resistance so electrical losses. So we have to find the best compromise between Eddy current and coil resistance losses)

Now imagine a ballast (choke) and a transformer connected to the input voltage without anything on the output (i.e. a choke too, as the secondary coil is not connected)

With a ballast : When the choke is connected in series with a lamp, we want the lamp's working current to go through. It is significant current, so to allow it, the inductance of the ballast must not be too high. Inductance of lighting ballasts is in the range of like 0.1H for some HID chokes (high current) up to 2H for small PL chokes (low current)

With a transformer : Ideally when it is only connected to input power, but nothing is on the output, we dont want it to draw any current. It does, but it is designed to draw as little current as possible, so the inductance is designed to be very high

Choke :

N = want it moderate
L = N^2 / R = want it low
so : R = want it high enough (not close to 0)

Transformer :

N = want it moderate
L = N^2 / R = want it high
so : R = want it low (close to 0)

And here we get it - The core for ballasts have high R, for transformers have low R. It may well be possible to make a working non optimal ballast with low R or transformer with high R, but you have to know the parameters of the core you work with and see if it is do-able

What is the actual structural difference ?

In most ballasts, the E plates and I plates are made so, when the ballast is assembled there is an air gap between the E's center leg and the I's. This is done either by using short I's and not pushing them all the way in (most modern European ballasts), Shorter center leg on the E (in some "transformer shaped" ballasts), or indentation in the I (some Fluorescent ballasts). The air gap introduces high reluctance in the magnetic path

In most transformers, the E plates and I plates are all in the same direction. They are made so, when the transformer is assembled thy fit exactly, minimizing air gaps. In most transformers each plate set is inserted from alternating directions, so there is no "crack" between the block of E's and I's, to distribute that small remaining gap so to reduce its effects as a gap

You may try a different approach, atleast when the ballast is close enough to what the lamp needs :

Get a ballast which is suitable for the current rating, but not for its induction value

Make an autotransformer (with transformer low R core) to change the supply voltage, so the ballast on hand becomes the correct ballast for the lamp at your custom supply voltage
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Re: Lighting recycling - Homemade transformers « Reply #4 on: May 19, 2017, 11:14:55 PM » Author: tolivac
Read some older "ham" radio books,older Popular Mechanics,Popular Electronics have excellent information on how to wind your own transformers.Look in ones from the 1930s.40s,50s for the best info on this.They also have info on how to rewind old auto generators-not alternators to get different voltages-IE 120VDC instead of 6VDC-then you can power the rewound generator with a small gas motor to make a homemade genset.
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