Early Unusual Transformer Design

[ChristianFletcher]

I have a Regentone WIB battery eliminator that I’m going to try and restore as a project. But I have found it contains what is a most unusual transformer or at least I have never seen one similar. If you look at the outer windings these are iron and think this is used as the magnetic core. Can anyone enlighten me to the name for this style of transformer or provide any information about it. I was wondering if the transformer had an inner core ? Please see pictures attached. I am also making a video about the restoration

https://youtu.be/rPG3I4s7lf0

Thanks Chris

[duncanlowe]

Reminds me of a more modern toroidal transformer. Can I just make out a former in there? Is it magnetic material?

An inverted toroid, wire is in a cylinder which is easy to wind. The outer and inner core is all the iron bits which don't have to connect, easy to wind... until we had winding machines for toroids.

[kalee20]

As MM says!

Sometimes it's called a Hedgehog transformer.

[ChristianFletcher]

Ok a Hedgehog sounds like a good name to me. The problem I have is that the insulation has broken off the wiring right up to the point it enters the bobbin. Luckily I have managed to peel back some of the hedgehog spines to reveal the wire. Hoping to try and sleeve it with something. Better insulation test it first etc.

Thanks Chris

[Jon_G4MDC]

There's a different spelling around and a photograph which tends to back it up.

https://www.antiqueradios.com/forums...c.php?t=123487

[ChristianFletcher]

Originally Posted by Jon_G4MDC

There's a different spelling around and a photograph which tends to back it up.

https://www.antiqueradios.com/forums...c.php?t=123487

Thanks Jon that’s great information

Chris

[Jon_G4MDC]

Yes I had never encountered these before.

It would seem that the Hedgehog name came first and the version which dropped the d was commercially made in America. Fascinating.

Hopefully it's repairable. The outer looks bound with string and then taped. It should be possible to open it completely and get at the windings with luck.

[ChristianFletcher]

Managed to sleeve the old wiring and epoxied it down. It was a struggle getting the iron winding back down but done it now. The winding continuity and insulation resistance measures good for all windings. So I just have to see how it works on a live test. It would be interesting to measure the efficiency and look at the iron and copper losses compared to a modern transformer. I’m guessing efficiency wasn’t a consideration and it probably only supplied 20mA

Thanks regards Chris

[Herald1360]

Someone once told me (not the most traceable source if information, I know) that the difference in efficiency between a power transformer with an open ended iron wire core and one with a laminated core closed magnetic path was only a matter of a few percent.

So for low power this odd TX should be fine.

[kalee20]

Ah, but this configuration isn't open-ended, it's still a closed iron path with the ends of the wires going through the winding's centre pole bent around the outside so they overlap.

(True mains transformers with a magnetic path completed by air do exist, but they are very few and far between. Coupling between primary and secondary is crummy, and the huge number of turns needed to get sufficient inductance to stop the no-load current being Sky-high means that winding resistances are large).

[Radio Wrangler]

Originally Posted by Herald1360

Someone once told me (not the most traceable source if information, I know) that the difference in efficiency between a power transformer with an open ended iron wire core and one with a laminated core closed magnetic path was only a matter of a few percent.

That's why ferrite rods don't work.

David

[daviddeakin]

So all those things that look like windings are actually forming the iron 'core'?

Ferrite rods are leaky, that's how the radio waves get in.

[kalee20]

Originally Posted by daviddeakin

So all those things that look like windings are actually forming the iron 'core'?

Yep!

It is just like a Ferroxcube core.

[ChristianFletcher]

I am not a transformer expert but Is there any interresting test I can do on the transformer. I was thinking of finding the turns ratio and maybe having a look at the iron and copper losses. The specification also says 50 to 100Hz so maybe a frequency sweep. I guessing back in the 1930 there was still big variations in the electrical supplies.

[kalee20]

If you connect the transformer to a variable supply (with a voltmeter across the supply to be sure you're hitting it with full voltage) via a wattmeter, leaving the secondary completely open-circuit, the power drawn is virtuall all core (iron) losses. (The primary current is relatively low, and secondary currents are zero, so winding losses are negligible).

Then if you dump the voltmeter in parallel, but put an ammeter in series, and this time short-circuit the secondary, wind up the input till you see the normal loaded primary current drawn. This time the voltage is low, so the magnetism in the core is low and iron losses will be negligible. The figure on your wattmeter thus will be copper losses.

Add the two figures together to get total losses at full voltage and full load.

[ChristianFletcher]

Originally Posted by kalee20

If you connect the transformer to a variable supply (with a voltmeter across the supply to be sure you're hitting it with full voltage) via a wattmeter, leaving the secondary completely open-circuit, the power drawn is virtuall all core (iron) losses. (The primary current is relatively low, and secondary currents are zero, so winding losses are negligible).

Then if you dump the voltmeter in parallel, but put an ammeter in series, and this time short-circuit the secondary, wind up the input till you see the normal loaded primary current drawn. This time the voltage is low, so the magnetism in the core is low and iron losses will be negligible. The figure on your wattmeter thus will be copper losses.

Add the two figures together to get total losses at full voltage and full load.

Brings back memory of the power lab experiments at university. Im guessing the load would have been around 20mA. I think I may run the risk of accidental damage and also not sure what my watt meter will read down too. I assume I need to be measuring true power rather than VA

[turretslug]

Something rings a bell about Mr. Faraday's first transformer (or at least a demonstration item) having a bundle of iron wires as its core. "Sorry Mike, no lams here, no-one's invented a use for them yet...."