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Author Topic: Amertran plate transformer  (Read 2768 times)
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AG5CK
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« on: April 23, 2017, 10:48:23 PM »

Is anyone familiar with the secondary taps on one of these old dinosaurs? The primary side seems simple enough but I'm not sure about the strand of wire someone used to bridge 8 & 9. I replaced it with something easier to see after wiping the dust off. The amplifier it came out of was not safe to power up and I removed the transformer to find the data tag.

As it is 15.5 vac into 1&4 gets 210vac out of 12 & 5. I don't know that this is correct but is how it was connected in the amplifier. The previous owner bought it as a project and suffered a stroke before working on it so he couldn't give me much information.


* plate iron tag.jpg (4621.43 KB, 4032x3024 - viewed 270 times.)

* plate iron.jpg (4171.51 KB, 4032x3024 - viewed 229 times.)

* plate iron sec.jpg (3590.17 KB, 4032x3024 - viewed 239 times.)
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KA2DZT
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« Reply #1 on: April 24, 2017, 02:00:38 AM »

Use an ohmmeter to try to figure out how the secondary terminals are connected.  Label shows only two voltage outputs 3000/1250.  Lot of terminals for only two.  See if all the secondary terminals are connected to only one set of windings (measure from each terminal to ever other terminal).  Remove the jumper to do this.  Xfmr may be wound with two separate secondary windings.  Terminals 5 and 12 may be the outer ends of each winding and jumping pairs of the other six terminals create the CT.

If this is the case, then it would seem that there are three different voltage level outputs not just two.

Take the ohmmeter readings with NO power on the xfmr.  

Fred

Thinking further,  having to jump terminals on the secondary of a plate xfmr would almost certainly indicate that there are two separate windings.
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W3RSW
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Rick & "Roosevelt"


« Reply #2 on: April 24, 2017, 10:31:16 AM »

After ohming the windings out, I'd place 6.3 AC from a small fil.  xformer across the primary in two variations and start measuring and plotting / sketching what I see on various combinations of the secondary. -- Fun.

Also see if any of the windings are internally connected to the case. May be critical if contemplating a potential HV bridge circuit.  

Oh and bake it in mummy's oven at about 140F with the racks out and a piece of plywood under it to protect oven floor for several hours before applying full voltage. Wait till mums goes to see a sister, etc. for a whole day or so.  Grin. Turn on kitchen fan too.
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RICK  *W3RSW*
AG5CK
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« Reply #3 on: April 24, 2017, 03:16:51 PM »

Thanks for the input. I will do some more testing when I get a chance and see what I can find. After looking at an old Amertran brochure I found here I believe it has split windings on the secondary. With the jumper removed the sec voltage is lower than the primary. I suppose that could also be a sign of a burned winding.

Im going to have to pull some strings on the oven. Mine is electric.
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KA2DZT
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« Reply #4 on: April 24, 2017, 03:31:29 PM »

Thanks for the input. I will do some more testing when I get a chance and see what I can find. After looking at an old Amertran brochure I found here I believe it has split windings on the secondary. With the jumper removed the sec voltage is lower than the primary. I suppose that could also be a sign of a burned winding.

Im going to have to pull some strings on the oven. Mine is electric.

If you remove the jumper and still connect to 5 and 12 you only have the volt meter on two open windings.  Put the volt meter to 5 or 12 and then read voltage off the taps  5 with a tap and then 12 and the other set of taps. 

First thing to do is remove all power and do some ohmmeter testing.  Let us know what you find.
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AG5CK
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« Reply #5 on: April 30, 2017, 01:48:43 PM »

Thanks to all for the tips. I found no shorts from any of the taps to the case and no shorts from any primary to secondary taps.

On the primary side I have .4 ohms from 1 to 2 and 3 to 4. No continuity between 1&3 or 2&4

On the secondary side
-tap 5 to 6 = 19 ohms, 5 to 7 = 20.9 ohms, 5 to 8 = 23 ohms. 
-tap 12 to 9 = 23.2 ohms, 12 to 10 = 20.6 ohms, 12 to 11 = 19

I figured pictures would be better than me trying to describe the rest.


* taps.jpg (3857.82 KB, 4032x3024 - viewed 192 times.)

* tap 2.jpg (2711.18 KB, 4032x3024 - viewed 229 times.)

* volts.jpg (2967.63 KB, 4032x3024 - viewed 214 times.)
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KA2DZT
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« Reply #6 on: April 30, 2017, 03:25:06 PM »

Your findings are exactly what I thought you would measure.  The xfmr is wound with identical side-by-side windings both on the primary and secondary groups.  You can tell by the nearly identical ohmmeter readings between corresponding terminals.

The tap pairs create the CT for the full wave secondary.  Max voltage is with 8-9 connected together.  10% drop with 7-10 and another 8% drop (from 7-10) using 6-11.

You would only connect together ONE pair of taps, each pair giving a minor adjustment in the output voltage.

Only thing that doesn't make any sense is the label that indicates only two levels of output voltage (3000/1250).  How they come up with the 1250 is a bit of a mystery.  Only thing would be running the full 230v primary on 115v

Fred

Taking a closer look at your voltage readings and ratios.  The xfmr is designed to run with a FW bridge rectifier yielding about 3KV with 8-9 jumped.  Using a FW rectifier with 6-11 jumped (CT) the output is about 1250v
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