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0.83V 130A

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noel shelley17/01/2021 12:42:48
387 forum posts
9 photos

Gentlemen, For some time a large transormer has been waiting to be used for something ! The primary winding is marked 0-240-400-? this is unreadable and the secondary is 0.83V at 130A. There are numbers on the top,20-60,and 4600-16.The identification markings are in a white ink hand written It is very heavy and seems very well made, the sec connections are a pair of 1/2" studs ! A) Who made it ? B any ideas as to what it's original purpose was ? C) what purpose can I best put it to ? Noel

One thought is that the 4600- 16 is the turn ratio.

Edited By noel shelley on 17/01/2021 13:12:34

Ady117/01/2021 12:45:42
4235 forum posts
593 photos

A few pictures will probably get you some decent responses

John Haine17/01/2021 12:58:35
3663 forum posts
206 photos

A, no idea. B resistance or spot welder. C doorstop. Or one of those!

br17/01/2021 13:12:50
461 forum posts
3 photos

0.83 V is interesting ?


Edited By br on 17/01/2021 13:13:21

Jeff Dayman17/01/2021 13:28:33
2073 forum posts
45 photos

With the high amps and low volts at the secondary I'd guess it was for welding purposes, but apart from that no idea. Have not come across one with numbers just like that. Pics might help get responses.

Robert Atkinson 217/01/2021 13:29:53
904 forum posts
17 photos

The output ratings give a power of about 100VA / 100W which is not that big for a transformer.
As John H says the output voltage indicates a resistance / spot welder is the most likely application. A phot with something for scale (CD is good) would be helpful.

Robert G8RPI.

noel shelley17/01/2021 16:56:33
387 forum posts
9 photos

my pictures11 131.jpgHeres are a couple of picsmy pictures11 130.jpg

Howard Lewis17/01/2021 19:16:13
4448 forum posts
8 photos

If the low voltage output is AC you could use a voltage doubler rectifier circuit to produce half cycle DC, although 1.86 volts still isn't a lot

Unless you want to recharge a LOT of NiCads!


not done it yet17/01/2021 19:27:36
5628 forum posts
20 photos

My guess is that it would have been used for inducing a strong magnetic field around a conductor - for something or other...

John Olsen17/01/2021 20:33:40
1147 forum posts
92 photos
1 articles

It doesn't seem like enough for a spot welder, where a single turn made from layers of copper sheet would be more usual, and a current more like 1000 Amps. A filament transformer for some sort of large vacuum tube might be a possibility.


Gordon A17/01/2021 21:30:26
157 forum posts
4 photos

Resistance soldering unit for etched brass loco kits etc or a demagnetiser perhaps?


Oven Man17/01/2021 21:36:10
106 forum posts
8 photos

Could have been part of a strip hardening furnace where the nichrome or other heat resisting steel liner is used as the actual heating element. This was a technique used 50 or 60 years ago but I haven't seen anything recently. Transformer looks like it is at least 50 years old.


Robert Atkinson 217/01/2021 21:59:07
904 forum posts
17 photos

Still think a small resistance welder. The sort of thing used for thermocouples or electrical connection e.g nichrome heting element to copper terminal. The size implies a conservative rating for the core so a high duty cycle application. The 240 / 400V primary imples industral use. I did wonder about a filament transformer but most valves are fussy about current and 0.83V at 130A is 0.063 ohms total circuit resistance so very little tolerance for connection resistance etc. I'd expect to see a few primary voltage fine adjustment taps if it was a filament transformer.

noel shelley17/01/2021 22:26:07
387 forum posts
9 photos

Spot or resistance welding was my first thought. The 240v & 400v tappings are clear to read but there are 2 other tappings, that could be 110v or 200v and the other 415v. It is 4 times the size of a microwave transformer running at 900w, the primary posts are 2Ba, if it's rating is only 100VA it is all very over kill. Something this big drawing .5A at 240V and 2Ba posts ? Kicking off a big mercury rectifier ? 240v /.83v =289.1 4600/16 =287.5 it may be a coincidence but 4600-16 may well be the turn ratio and would tally with the 240v to .83v

Keep the ideas coming - please. Noel

martin haysom17/01/2021 23:48:52
14 forum posts

how about magnetic partial N D T

Alan Johnson 718/01/2021 02:46:30
102 forum posts
16 photos

With your multimeter measure the winding resistances and draw a diagram with the connection points and the resistance between them, and the iron core, then publish it here.

If you have one, an insulation tester set at 400 volts between the 240/400 side and the iron core.

I would suspect the 240 / 400 etc. side terminals are connected to each other, and not the 1/2" stud side and DEFINITELY NOT THE iron core!

Alan Johnson 718/01/2021 08:25:12
102 forum posts
16 photos

If you test the transformer windings as per this test it would help.

transformer test sheet.jpg

Robert Atkinson 218/01/2021 12:27:21
904 forum posts
17 photos

I might also have been a induction heater for bearing races

Robert G8RPI.

noel shelley18/01/2021 16:11:48
387 forum posts
9 photos

Right ! Leakage to ground better than 100meg. Resistance, 0 to tapping 1 - 0.17, 0 to2(240) 0.24, 0 to 3(400) 0.78 and 0 to4 1.18 all values in Ohms. The resistance on the secondary is so low as to be difficult to measure, less than 0.1

any help ? Noel.

Alan Johnson 719/01/2021 02:46:56
102 forum posts
16 photos

1st. Observation: the insulation resistance appears good, all be it at a very low test voltage from the multimeter.

2nd. Observation: as the ratio of resistance between windings is not the same, I suspect smaller diameter wire was used as the voltages get higher. This is a common practice in transformer manufacturing when costs count. As an example, the 240V winding has a resistance of 0.24R (a nice convenient number), so I would expect (if the wire was the same size) for the 400V winding to have a resistance of about 0.4R, but it does not.

Now to apply some voltage to it! You will need an incandescent lamp. Old fashioned 100W lamps are good, but a modern halogen lamp will work. This is connected in series with the supply to the transformer. The purpose of the lamp is to limit the current flow in the transformer. If it had shorted turns current flow would be large, so the lamp limits this.

Connect initially to terminals 0 and 4, and connect the supply earth wire to the frame of the transformer.

You are now dealing with MAINS VOLTAGE THAT CAN KILL YOU. Don’t proceed if you are not confident with what you are doing! Wear safety glasses and gloves.

Energise and wait for smoke, or a burning smell. No smoke or smell the transformer is probably OK. If there is an earth leakage, your household supply earth leakage circuit breaker will trip. If it doesn’t trip you can proceed. If it does, you are the owner of a piece of scrap metal!

Measure some voltages – same as you did with the resistance tests, and report back. Remember to use the AC voltage setting on the multimeter, and remember these are MAINS VOLTAGES, SO DON’T TOUCH!

Series Test Circuit.jpg

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