How to Identify Unknown Shell Type EE Transformer Windings for 6V to 120V Inverter?

I have a transformer, with no labeling whatsoever, that I am attempting to ascertain the design of. It is being used to invert voltage from 6V to 120V to power a 4 Watt F4T5 Fluorescent lamp. Since I am still using the transformer, I am not keen on tearing it apart to see how it is built and was wondering if there was any other way to ascertain its layout.

Here are the specifics of the transformer.

Type: Shell
Lamination: EE
Bobbin: Single

Please refer to the attached diagram for information on the lead assignments.

First I tested for continuity, then for resistance.

2 - 3 Continuity only with each other (Primary?)
1,4 - 7 All show continuity with each other (Secondaries?)

1 - 4 (0.7 Ohms)
1 - 5 (0.7 Ohms)
1 - 6 (3.5 Ohms)
1 - 7 (3.8 Ohms)

2 - 3 (0.8 Ohms)

4 - 5 (0.6 Ohms - These two are connected together via a trace on the PCB)
4 - 6 (3.4 Ohms)
4 - 7 (3.8 Ohms)

5 - 6 (3.6 Ohms)
5 - 7 (3.7 Ohms)

6 - 7 (0.8 Ohms)

Additional Information

The bulb uses bipin T5 connectors. Orienting the bulb in a top and bottom position...

Lead 6 - Connects to one of the two pins on the top of the bulb
Lead 7 - Connects to the other of the two pins on the top of the bulb
Lead 5 - Connects to both pins on the bottom of the bulb

After drawing this out, it appears to me that the secondary coils are wound in three layers, attached in parallel with their center taps joined. I can see the outermost (primary?) coil just under the yellow outer tape of the transformer, it seems to make about 4 turns. Please see the attached diagram on my first impressions of this transformer's layout.

This seems to be a custom transformer, and while I have done a great deal of searching to see if I could find a manufacturer who makes a product similar to this, I am at a loss.

Thank you in advance for any information you might be able to provide me.

Respectfully

Aaron

Voltech makes transformer testers which can determine this for you. You might be able to send a transformer to them for analysis or send it to another transformer company who can measure you and tell you what it is and see what you have and if it can be built.

Please would you upload photos of the transfomer and the interior of the lamp unit ?
Does the circuit you show illustrate the entire circuit of the lamp unit ?
Did you isolate (disconnect) the transformer from all other components to test the resistances ?
Did you subtract the resistance of your test meter leads ?
As Colin mentions, the transformer must be driven by an AC source (obviously not 6V DC).
If the transformer is the original part in a standard commercial fluorescent lamp unit, it is unlikely to be a special custom made device.
Are able to safely test the AC output voltages without touching any live parts ?
Pin 1 is not marked on your circuit diagram.

As drawn in your diagram, the terminals at the top of the tube (from pins 6 & 7) are receiving approximately equal and opposite voltages with respect to the bottom of the tube (from pin 5), so the tube would not fire. The tube is receiving a higher voltage to its heater element than to its length.

(Would someone please correct me gently if I've missed something obvious ?

The success of transformers like this are often highly dependent on the exact placement of windings relative to each other. A series of transfer function and leakage inductance tests can give you an estimate of where the windings are, but it is quite likely that there will be subtleties of placement that are missed.

There really is no substitute for taking it apart!

It's always a the first thing I do for a power supply design review, even if I have the manufacturer document. You will be surprised at the things you discover during this process.

For more information on transformers and testing, please go to our Design Center at www.ridleyengineering.com. It's free and full of a lot of practical design and measurement tips.