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Old 31st May 2020, 1:31 pm   #1
Mullard_Nut_74
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Default How to identify an unknown transformer.

Hi all,
I have a Western Electric transformer but I know nothing about it.
A search of the model number on Google turned up nothing.
I remember when Google used to be useful.

Is there any way to measure and tell the input voltage of the primary winding?
As it came out of a piece of US air force equipment I am worried it may be a 120V transformer so dont want to hook it up to Australian mains till I am sure.
Unfortunately there was no input voltage marked on the equipment either. But since it was a valve unit I figure at least one of the secondaries will be 6.3 volts.
Pictures attached
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Old 31st May 2020, 2:04 pm   #2
trobbins
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Default Re: How to identify an unknown transformer.

You would need to assess winding DCRs for the maximim currents levels, based on power dissipation. Assess turns ratios of the windings. Use a variac to plot magnetising current of the likely primary windings. See if winding layout is visible, as primaries are typically wound nearest core for a PT. A capacitance meter can sometimes provide supporting evidence of winding layout.

If you have no clue about original application, or frequency, you may be able to deduce a 120 versus 240 primary, but all information should be collated.
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Old 31st May 2020, 2:12 pm   #3
stevehertz
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Default Re: How to identify an unknown transformer.

If you know which winding is the primary, then bring it up on a variac and see if you can make sense of what's coming out of the secondaries, for example, as you say, they might be 6.3V. So, if you get 6.3V out of a secondary when the input is say 120V or so, there you have it, it's a 120V mains trannie.
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Old 31st May 2020, 2:12 pm   #4
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Default Re: How to identify an unknown transformer.

The dimensions of the lamination stack should give you a rough idea of the VA rating. The windings' DC resistances should separate the lower voltage ones from the higher voltage (although in a large transformer the mains primary might have quite a low resistance). Then it's a matter of applying a very few AC volts to the lowest resistance winding and, with care, measuring the open circuit voltages on all the others. If you can pick out the 6.3V winding then you might be able to work out which is the primary from there.

Cheers,

GJ
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Old 31st May 2020, 2:36 pm   #5
Mullard_Nut_74
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Default Re: How to identify an unknown transformer.

I should have taken photos before completely gutting the unit.
One lot of yellow wires was connected to all the valves hence the guess at it being a 6.3V supply.
From memory both the purple and blue wires were connected to 2A glass fuses so I have no idea which is Active or Neutral.
Also there is 2 sets of the purple and blue wires so its possible one combination could be 120 and anotther 240 volts.
Then there is another set of black wires out the bottom that connects back to the transformer which could be a center tap as I know these are sometimes grounded.
I just had a btainwave and sent photos and an email to Western Electric and hope they can give me a data sheet on the transformer.

I will do the testing with a Variac once my variac is installed in its enclosure and running properly.
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Old 31st May 2020, 4:46 pm   #6
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Default Re: How to identify an unknown transformer.

Just one thing that comes to mind with me, this is just biased on some of the surplus power units with transformers I see from military aircraft use 'cold war' etc is that they could be 400 to 1000Hz use as opposed to the standard 50 to 60 Hz domestic. In which case the primaries would provide a low reactance to mains at standard frequencies.

Just a little something else to throw in the mix, if it was from actual aircraft use?

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Old 31st May 2020, 10:11 pm   #7
Mullard_Nut_74
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Default Re: How to identify an unknown transformer.

It was not from a plane.
It was out of a calibrator range, whatever that is.
It read 50 - 1200 Cycles and then again over the fuses it said
50 -1200 ~ 2A Fuses.
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Old 31st May 2020, 10:46 pm   #8
Leon Crampin
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Default Re: How to identify an unknown transformer.

If you know which winding was connected to the valve heaters, apply 6.3V to it from a suitable transformer, and measure the voltages of the other windings. There will be a small error using the transformer in reverse, but it should give you a good idea of the voltages available. If you have two windings each giving a plausible primary voltage (say 120V), the one with the lower DC resistance is the primary. The core looks good for 50/60 Hz, but a soak test off load will show excessive heating if this is not the case.

Leon.
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Old 1st Jun 2020, 4:14 am   #9
Mullard_Nut_74
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Default Re: How to identify an unknown transformer.

So I could potentially lift the working 6.3V from a working radio and drive the transformer in reverse.
Sounds dangerous but just my kind of experiment.
I think I will give it much contemplation before trting this though.

Thanks for all the tips..
Western Electric have no data on this transformer either.
Seems a lot of the companies that are still around have no historic data on their own equipment.
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Old 1st Jun 2020, 7:29 am   #10
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Default Re: How to identify an unknown transformer.

Quote:
Originally Posted by Mullard_Nut_74 View Post
Seems a lot of the companies that are still around have no historic data on their own equipment.
Yup, and expect it to get worse.

Competition is a lot fiercer now than it ever was. Having space, whether physical or server space for archives costs money. Having an employee as a librarian or archivist even as a part time activity costs money. Breaking someone off their normal activities to search for an answer for one individual with a transformer produced long ago isn't going to sell any more transformers to him. There is no visible profit from helping.

Of course, there are some nice companies who treasure their past and want to maintain their reputation as good guys, but the ones who don't, get business advantages. In a dog-eat-dog world, they are going to beat the good guys in the race to the bottom.

* * * * * * * * * * * * * * * * * * * * * * *

What valves was the 6.3v winding powering? This should confirm the voltage and also give an estimate of the current rating - very useful if you intend using the transformer.

You can also measure its inductance, and from this determine a magnetising current (treating it as if it were a primary) from this compared to the current rating, you can get an idea whether it really is any use on 50Hz.

Powering it up on 6.3v 50Hz from a very beefy transformer will allow you to measure the voltages of the other windings and identify tappings.

As said, the primary is likely to be the lowest DC resistance one(s) where you find others of a similar voltage.

BUT if it has dual primary windings, to do the series/parallel trick for 120/230v input, then you also need to find the relative phases of these windings. Connect them in series. Is the voltage across the ends of the pair now the sum of the individuals? or a lot less?

So by now you should know the primary windings and their tappings and the correct phase for combining them with a voltage selector. You should know the current rating of the 6.3V heater winding.

What was used as a rectifier? This will give an upper bound on HT winding current rating.

David
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Old 5th Jun 2020, 11:02 am   #11
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Default Re: How to identify an unknown transformer.

Hi David,
All the Tubes were military spec JAN (Joint Army Navy) and quite interesting to research about that whole thing.
5 x metal can 6AC7
2 X metal can 6AG7
1 X 5Y3GT
1 X 6SN7-GT
1 X 6SN7W
And 1 x really interesting little tube unmarked.
Its either a a relay or some kind of crystal.
It does say Crystal on one side and D-168342 on the other.
Photos of that attached. Tricky little ****** to photograph.
Also 2 x HUGE oblong capacitor cans that are bigger than my wallet.
And unfortunately heavier as well.
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Old 5th Jun 2020, 12:20 pm   #12
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Default Re: How to identify an unknown transformer.

D-168342 is a WECO number (Western Electric Co) so far as I know.

It was used in the SCR-545-A which so far as I can make out was used as part of a mobile radar setup:

https://archive.org/details/Handbook...2up?q=d-168342

If that's any use.

Lawrence.

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Old 5th Jun 2020, 1:31 pm   #13
Mullard_Nut_74
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Default Re: How to identify an unknown transformer.

I did find a model number but still having issues locating the voltage in the data I found.
RAAF SIGNAL CALIBRATOR MODEL Ts/102A SERIAL # 9 A

The pictures I found look the same and all 10 tube numbers are a match. Must be an error in their data because it says NO crystals were used in this model.
Unfortunately their picture is not clear enough to see any voltage markings on the case.
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Old 5th Jun 2020, 1:35 pm   #14
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Default Re: How to identify an unknown transformer.

I think I have to assume that being a US device built by Western Electric that it would be 120 Volts. Although many other WE built military products I found photos of or data about were 115 Volts which seems a really odd voltage.
Would this have been a standard voltage on US Navy ships perhaps?
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Old 5th Jun 2020, 2:13 pm   #15
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Default Re: How to identify an unknown transformer.

115v was the standard US voltage before they changed it to 120V around 1984.

With the voltage variation tolerance (5%), it can vary between 114 and 126V.
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Old 5th Jun 2020, 11:04 pm   #16
Mullard_Nut_74
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Default Re: How to identify an unknown transformer.

Do the US also have 240V as well?
I was always confused by a quote from the movie "Mr Mom" when he said he was going to rewire the house and was asked if he was going to make it 220. His reply was 220-240 Whatever it takes.
Also a Youtube channel I regularly watch also talks about his 240V outlets.
Do they have different plugs for 120V & 240V cause that would be confusing and dangerous if mixed up.
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Old 6th Jun 2020, 12:32 am   #17
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Default Re: How to identify an unknown transformer.

USA pole transformers as far as I know are 110-0-110 volts with all three wires going to the meter.
110V sockets have different blade thickness or spacing.
https://www.plugsocketmuseum.nl/NorthAm1.html
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Old 6th Jun 2020, 12:58 am   #18
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Default Re: How to identify an unknown transformer.

Quote:
Do the US also have 240V as well?
Yes, as Refugee says, many domestic supplies are 120-0-120V with lights and normal 120V outlets connected between one hot and neutral, while high-load appliances such as tumble dryers and large air-conditioners run at 240V between the outers. Electronic goods are almost always 120V (historically 110 or 115V) as 240V outlets are normally only provided where the load justifies them.
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Old 6th Jun 2020, 1:08 am   #19
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Default Re: How to identify an unknown transformer.

You could describe the American system as six-phase. Their mains is distrubuted as three basic phases, as ours is, but as Lucien says, the final transformers give 120-0-120v 180 degree two phase feeds to a property. The other pairs of phases are distributed to other properties, trying to keep the whole thing balanced.

Industrial users can have the three main phases, pretty much as ours have.

In may ways it's quite a sensible system, but sometimes they try to run too much power to things before they go to 240v feeds. Seeing kilowatt amateur radio power amplifiers with a '110' input for example.

I still think a lot of their fittings look more appropriate to doll's houses, though.

David
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Old 6th Jun 2020, 1:31 am   #20
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Default Re: How to identify an unknown transformer.

AFAIK the standard configuration is a 120-0-120 supply with the centre-tap grounded, serving all single-phase consumers. If a small 3-phase supply is required, a 208V high-leg (the B-phase) can be brought in to make 3-phase 240V. Being an edge-grounded delta system, 120V supplies can't be derived from centre-taps in the other two pairs of phases as these would not be grounded and therefore not suitable as single-phase neutrals. The system is therefore intended to run with unbalanced loading on the LV side, and indeed sometimes supplied in open-delta with a main single-phase transformer serving A & C and another single-phase transformer for the less loaded B-phase.

A separate 3-phase supply in one of a number of different voltages and configurations is specified for commercial users where the high-leg system would be insufficient or impractical. The variety of different voltages and non-interchangeable plug types is baffling to the European onlooker accustomed to 400/230V supplies. See:

Tables of NEMA plug and socket types for various US electrical supply configurations

In any event, most US single-phase electronics that are not universal voltage, are 120V.
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