do you know this inductance with three wires

[iso14000]

Hi folks

I have , from a former teardown, this inductance in a drawer.
I decided to measure it .
with L/C ringing after a voltage ramp up I found a quite large inductance : 4 Henry, for ESR of 4 ohms between two wires
the third wire seems almost shorted one the two that exhibit an inductance behavior

This (large) inductance comes from a UPS that gived up, and I was surprised to find it , thinking of chopper filter

the question is : do you have an idea about the third wire?

[TimNJ]

Depending on the topology it was used in: Some sort of tapped inductor? Do you measure any inductance between the third wire and some other wire?

4H seems pretty large though! Feel like I'm off.

For example:

[Andy Watson]

Probably a custom part made to order. Looks like rasmi are still in business:
https://rasmi.com/
Does the type number align with any of their current products?

Magnetic amplifier ? Auto-transformer ?

[iso14000]

Hi

thanks both of you.
at the beginning I didn't believed my RLC meter (a creepy one) , so I used the good old method to make ringing the L by a known C, and I found the L=4H.....
yes  like you.

after reading your comments, I did some extra investigation, and Yes it looks like a tapped inductor.
I found a transformer effect by a 1:5 ratio

I'm puzzled about the utility for such a thing...

If i remember well, that UPS used 2x12V lead acid , so I guess by this ratio , a chopper could give 24*5=120V
.... but here in europe we are set with 230Vrms....

[floobydust]

It might be wired as an autotransformer, to provide a fixed voltage boost to cover line voltage sags. I have seen that in UPS as well.
I would inject say 6-12VAC into a winding and see what comes out.

[iso14000]

it is exactly what I did, 1Vrms on the "primary", I measured almost 5.5Vrms on the "secondary"

unless, I didn't catch it... and the DC section was supplied by 3x12V lead acid. so 36V where available.
and with a boost tapped , with a n~5.5 , let's make a 0.5 D.C. the output voltage should be 7.5*Vin so =>270V

the latter isn't so far from 230*1.414=>325.... probably DC is a little higher...

I beleived tapped structures suffer of leakage inductance issue...

thanks guys!