Unlabelled and disconnected mains primary wires

Assuming the beast also has a secundary, --possably even marked with a voltage-- I would apply that voltage (from another transformer) and measure the voltages on the primary terminals.

Look for single wires, indicating winding ends, rather than taps ?

Arfa

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I hadn't actually thought of that but problem is which crosslink/s? for 110 or 130 V operation. From the deformation set into the leads it was probably D-E used in the UK so D-A probably 250V. The others can stay disconnected if need be , as unlikely to ever be used outside the UK

The first step is to rearrange the chart so it makes sense. The highest resistance is A-D. so A and D are the ends. A-E is the lowest resistance, so the top line of the chart should now read

--- A E C B D A ---1.5 8.5 9.2 12.5

But a better way to look at is is the increments A-E = winding a = 1.5 E-C = winding b = 7.0 C-B = winding c = 0.7 B-D = winding d = 3.3

NOW let's relabel, and assume that the maximum input voltage is 250 volts (because it's a convenient multiple of 12.5). So the voltage across each segment (and the taps for each segment) becomes:

A a = 30 E b = 140 C c = 14 B d = 66 D Which doesn't make sense for a dual voltage supply UNLESS you assume multiple gauge wires were used. Which is not unreasonable, factoring in a desire to save $.02 per device.

Suggestion: A variac (turned down to a very low voltage) would work, but just about any transformer with an output voltage of 10 -15 volts should do it. Feed the low voltage AC into the end wirings and measure the voltage at each tap. Calculate from there.

PlainBill

Crosslinks ? From your original message I read that all primary connections connect to one continuous winding.

Transformers designed for minimal copper use contain 2 identical sets of windings. Those get connected in parallel for use on 115 volt and in series for 230 Volt.

As long as there is DC continuity I wouldn't attempt any cross wiring ;-)

Then by ratio of resistance, the 0.7 ohm tapping C-B is 20 volts making C-D

Similarly, E-C is another 100 volt tapping ( using thinner wire) making E-D

Again, A-E is another 20 volt tapping making the whole winding 240 volts.

.... Phil

This is what was confusing me , I don't often come across USA transformers , they must have plenty of copper to waste and unnecessarily larger transformers. Only ever seem to see 2 separate primaries in the UK , in the main, maybe some 10 or 20 V taps in addition. For this continuous one and generally for this sort of mains transformer. The"240V" ends cannot be returned to form one 110V connection and a mid point the other 110V connection for that option, as counter winding sense for the two "halves" and so no secondary volts. So part of the winding wasted and the 110V section of primary perhaps a larger gauge. I suppose measuring inductance may have helped

If it is truely a USA only transformer, it will not have a winding higher than 120 volts! USA makers were not export oriented, and the few export units were typically fitted with different transformers, but the run-of-the-mill domestic production was made with a 120 volt primary (only). Export models were typically setup for 100/120/240 volts. (Japan, USA & and other countries with an approximate 120 volt standard, and other countries with an approximate 240 volt standard.)

Makers were (and still are) incredibly cheap, and will resort to all kninds of tricks to save a penny. I don't see many (if any) who will waste money on copper that will (in their opinion) never be used.

About the best thing would be to measure the primary volts while powering the secondary with its rated voltage. However, I suspect you don't know the secondary specifications either, so that is difficult.

I'd probably look at the secondary and give it a known, low voltage (say 6 v AC) and measure the ratio of the primary voltages. That would be better than static DC resistance measurements which can easily be affected by inductance and wire gauge.

Which makes sense!

I cannot see what the economic argument is in wasting copper , weight and space. Both methods require a break in winding the primary. The 2 separate coil system requiring a break and a pair of tails coming off. The continuous system probably requires a break in gauge of wire and only one tail but 3 dissimilar wires joint at that point - surely not a cheaper option.

"PeterD"

The standard domestic voltage is 100 volts and may be as low as 90 volts in some places.

The AC frequency varies too, 50Hz and 60 Hz being used in differing parts of the country - means that most Japanese made products for domestic use are designed to accept either frequency.

.... Phil

"Nutcase Kook is So Full of S*it "

Most audio amps made in the UK between the mid 1960s and late 1990s had multi-voltage, single winding AC transformers.

Check any old schem from Marshall, Vox or Sugden etc, et alia.

.... Phil

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Do you know the approximate secondary voltage? If yes. apply that voltage to the secondary using a variac or some other transformer. Then measure the various primary voltages. I have done that many times when all else fails and I didn't want to take a chance on frying the transformer. Should work just as well east of the big pond as on the west side.

you never mentioned what you're even talking about, or what it's from.

Assuming it's something like an "international" linear power supply, there would be windings for 100, 120 220 and 240 volts based off a combination of terminals. US made transformers for domestic only use would generally max out at 3 or 4 terminals for

here's a diagram of how these international transformers work:

Geeze Phil, read... Japan is 100, USA and other countries with approximately 120 volts, and still other countries with 240 volts. Completely clear to everyone else...

OK, for you:

"PeterDope"

It is a very common myth that Japan has 120 volt AC, 60Hz power ( like the USA) when it does NOT !!

Your post repeated that myth.

Cos of eBay, second hand Japanese local market electronics is now being sold to folk in all parts of the world to use - most of whom mistakenly think that it can be used on 120 volts AC or with a 240 to 120 volts step down tranny.

.... Phil

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would be

terminals. US made

terminals for

That transformer type is the 2 separate primaries, not the subject of this thread. Does anyone have the generic name for these wasteful construction made in or for USA , for export kit ? the ones with a (electrically) continuous single primary winding

Autotransformer.

What results from driving the secondary with a low voltage?

Grant.

there

this

or

single

My understanding of the term autotransformer is primary and secondary electrically continuous, ie no electrical isolation