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Transformer question.
Transformer question.
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Old 12th October 2019, 06:17 AM   #1
Tony D. is offline Tony D.
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Join Date: Feb 2001
Location: Vancouver, B.C., Canada
Default Transformer question.

I salvaged this transformer and power supply from a Denon DVD player. Tonight I attached an electrical cord and plugged the transformer in and did not get any reading with my meter on the AC setting. As far as I can tell the grey and black wires in the photo are the primary and the 6 back and grey twisted wires are the secondary.

The transformer ID number is written on the top: D00 233 645 5701 1 with another number: GT 552 TK (Y) written below it. I spent 20 minutes scouring the NET for information on this transformer but no luck. Anyone know of a resource I missed for transformer I.D.?

Also am I correct in my assumptions about the input/output?

Thanks for any info.


Tony
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File Type: jpg TRANSFORMER.jpg (522.3 KB, 299 views)

Last edited by Tony D.; 12th October 2019 at 06:32 AM.
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Old 12th October 2019, 07:26 AM   #2
ubergeeknz is offline ubergeeknz  New Zealand
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Do you have the model number of the DVD player it was salvaged from? From that you may be able to find a service manual / schematic. OEM part numbers are often (deliberately) unhelpful.
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Old 12th October 2019, 08:14 AM   #3
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
Hi Tony,

I have salvaged a lot of transformers and even found some where I do not know the origin. I have a simple method I use to analyze a transformer:

I use my Ohm-meter for a start and try all combinations of wires to find out which wires are connected to which. The wire(s) with the highest DC impedance is normally the primary. "Normally" because if you recover the transformer from a particular use like the power transformer in a micro-wave, it has a higher secondary voltage than primary voltage. There may be more primary wires if it is meant for different input voltages. The primary windings are normally grouped together.

Then, I draw a small sketch of how the wires are connected to one another through the windings. If there is no DC impedance, you will have no useful output voltage (only a noise voltage without power).

Then the voltage test. I connect a 1A fuse in series with the primary and connect the primary side to the net (WATCH OUT FOR THE HIGH VOLTAGE ON THE PRIMARY SIDE! DANGER!).

I know from my sketch from which secondary wires I can expect an AC voltage. No DC connection - no AC voltage. DC connection and a good primary connection and you will have an AC voltage of some kind on the secondary, unless the wires are connected by a regular short-circuit. The voltages I measure I can add to my sketch.

The power capacity I estimate from the size and eventually information on the apparatus I got it from about maximum power consumption of the apparatus.

Your photo does not well show the wires coming out of the transformer.

Last edited by FauxFrench; 12th October 2019 at 08:21 AM.
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Old 12th October 2019, 09:45 AM   #4
korpberget is offline korpberget  Norway
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And if connected backwards - even higher voltages!
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Old 14th October 2019, 08:44 PM   #5
Tony D. is offline Tony D.
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Join Date: Feb 2001
Location: Vancouver, B.C., Canada
Thanks for the replies. I have downloaded the service manual / schematic and it is not much help as the transformer/power supply have no identifying/spec. information. But I now know that the transformer outputs 15 volts-AC on one set of the secondaries. My confusion about the output measurement in my original post was because I made the measurements with my meter set on volts-DC...it was late and I am prone to dumb-assery when I am tired.

I now know that the power supply outputs 18 volts-DC but I need 15 volts-DC for my project and there are no trim pots to adjust the output voltage...any ideas on how I can reduce the output to 15 volts?


Tony

Last edited by Tony D.; 14th October 2019 at 08:55 PM.
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Old 14th October 2019, 09:04 PM   #6
edbarx is offline edbarx  Malta
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Join Date: May 2018
It all depends on how much current you are going to use. If it is below 1A you can use a regular chip, say a 12V regulator and add a resistor between the output and IC common terminal, and another resistor from the IC common terminal to circuit ground. To increase the voltage linearly, use a linear pot connected in series with the second resistor that connects to circuit ground. You will have to allow several milliamperes to pass to allow for the regulator's internal current flactuations.

Let us say, you are going to allow 10mA to flow through the resistance chain.

With 12V, the resistance between the regulator's output and regulator's common will be:
V = IR => Ra = 12/10e-3 = 1.2kOhm

Since you need 15V, allow 2V across the other resistor:
Hence, Rb = 2/10e-3 = 200 Ohms.

And allow another 2V across the preset:
A 220 Ohm linear preset should allow you to adjust the voltage from 14V to 16V.

Post Scriptum:
The current rating of a 1A voltage regulator, can be increased by using a power transistor whose maximum base current rating is higher or equal to the chip's maximum output current. In this arrangement, the power transistor's base is connected to the chip's output, the collector to the positive terminal of the power supply, and the emitter becomes the new enhanced output. To allow for Vbe, use a diode in series with the resistor chain with one end connected to circuit ground.

N.B: Power transistors require a heatsink even for testing purposes.

Assumptions: The chip is assumed to have a negative common and positive output. With this arrangement, the power transistor has to be NPN.
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Thanks for helping me design my first amplifier.

Last edited by edbarx; 14th October 2019 at 09:22 PM.
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Old 14th October 2019, 11:41 PM   #7
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by Tony D. View Post
Thanks for the replies. I have downloaded the service manual / schematic and it is not much help as the transformer/power supply have no identifying/spec. information. But I now know that the transformer outputs 15 volts-AC on one set of the secondaries. My confusion about the output measurement in my original post was because I made the measurements with my meter set on volts-DC...it was late and I am prone to dumb-assery when I am tired.

I now know that the power supply outputs 18 volts-DC but I need 15 volts-DC for my project and there are no trim pots to adjust the output voltage...any ideas on how I can reduce the output to 15 volts?

Tony

There are some heatsinks with transistors or voltage regulators. If you tell us the types, perhaps we can adapt the circuit. It seems rather simple.
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Old 18th October 2019, 04:23 AM   #8
Tony D. is offline Tony D.
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Join Date: Feb 2001
Location: Vancouver, B.C., Canada
Quote:
Originally Posted by FauxFrench View Post
There are some heatsinks with transistors or voltage regulators. If you tell us the types, perhaps we can adapt the circuit. It seems rather simple.
Thanks for all the replies guys. I have identified the regulators on the board an indicated them in the image attached. I am a rank amateur when it comes to this sort of thing so any and all help is appreciated.
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Old 18th October 2019, 04:29 AM   #9
ubergeeknz is offline ubergeeknz  New Zealand
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78xx - positive reg
79xx - negative reg
Last 2 digits indicate output voltage
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Old 18th October 2019, 05:45 AM   #10
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Quote:
Originally Posted by Tony D. View Post
Thanks for all the replies guys. I have identified the regulators on the board an indicated them in the image attached. I am a rank amateur when it comes to this sort of thing so any and all help is appreciated.

Hi Tony,
Thanks for checking. Could you please list the type numbers from left to right in plain text? I have major problems reading the small red numbers on the photo.
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