Hi,
I have an unmarked torroidal transformer with about 8 or 9 wires attached.
How can I calculate the output voltages on these secondary rails.
I have an unmarked torroidal transformer with about 8 or 9 wires attached.
How can I calculate the output voltages on these secondary rails.
Measure DC resistance between each wire and the rest and make a table. This information will allow us to draw some hypothetic winding configuration.
The next step would be to inject a small known AC voltage, lets say 10V AC, into one of the hypothetic windings, and then measure the voltage induced in the rest of the hypotethic windings. The current drawn from the 10V source should be very small, otherwise a smaller voltage should be employed.
Be careful when measuring because those 10V AC put into one of the secondaries may as well produce 100V AC into the primary.
Once one or more primaries have been identified, testing them for 120V or 230V operation is as easy as connecting them to 230V with a conventional light-bulb in series. If the bulb lights, it means that the transformer is saturating and the voltage rating of the winding has been exceeded.
The next step would be to inject a small known AC voltage, lets say 10V AC, into one of the hypothetic windings, and then measure the voltage induced in the rest of the hypotethic windings. The current drawn from the 10V source should be very small, otherwise a smaller voltage should be employed.
Be careful when measuring because those 10V AC put into one of the secondaries may as well produce 100V AC into the primary.
Once one or more primaries have been identified, testing them for 120V or 230V operation is as easy as connecting them to 230V with a conventional light-bulb in series. If the bulb lights, it means that the transformer is saturating and the voltage rating of the winding has been exceeded.
Hi,
play safe rather than adventurous, because what follows is mostly guesswork.
1. wire up a mains light bulb in series with the mains power line as follows.
Plug top live pin to light bulb fitting pin1.
light bulb fitting pin2 to trailing mains socket live pin.
Connect neutral straight through from mains plug top to trailing socket neutral.
Connect plug top earth to trailing socket earth.
Insulate any exposed mains connected parts. Keep this for all future testing. Change the light bulb wattage to suit different equipment loadings.
2. plug the new light bulb into the mains: bulb should be off.
3. plug an appliance into the trailing socket:light bulb should glow or be bright indicating current flow.
4. disconnect appliance.
5. insert all the transformer wire ends into separate terminals of a terminal strip. This is to prevent inadvertant shorting and allow relatively safe voltage measurement.
6. using a short length of double insulated 2core mains cable,
connect purple wire to plug top neutral
connect red wire to plug top live.
7. plug your transformer plug top into the light bulb trailing socket and switch on. The light bulb should flash and go dim or go out. If it stays bright switch off and post us.
8. Carefully measure the voltage from purple to green, purple to brown, purple to blue, purple to red. You should get an increasing series of AC mains voltages. If any of them are above the incoming mains voltage then I figured wrongly.
9. measure the voltage orange1 to black, orange2 to black and orange1 to orange2. These will hopefully be low voltage with black as centre tap, but could be 110Vac so be careful.
10. Don't call us if it blows up.
play safe rather than adventurous, because what follows is mostly guesswork.
1. wire up a mains light bulb in series with the mains power line as follows.
Plug top live pin to light bulb fitting pin1.
light bulb fitting pin2 to trailing mains socket live pin.
Connect neutral straight through from mains plug top to trailing socket neutral.
Connect plug top earth to trailing socket earth.
Insulate any exposed mains connected parts. Keep this for all future testing. Change the light bulb wattage to suit different equipment loadings.
2. plug the new light bulb into the mains: bulb should be off.
3. plug an appliance into the trailing socket:light bulb should glow or be bright indicating current flow.
4. disconnect appliance.
5. insert all the transformer wire ends into separate terminals of a terminal strip. This is to prevent inadvertant shorting and allow relatively safe voltage measurement.
6. using a short length of double insulated 2core mains cable,
connect purple wire to plug top neutral
connect red wire to plug top live.
7. plug your transformer plug top into the light bulb trailing socket and switch on. The light bulb should flash and go dim or go out. If it stays bright switch off and post us.
8. Carefully measure the voltage from purple to green, purple to brown, purple to blue, purple to red. You should get an increasing series of AC mains voltages. If any of them are above the incoming mains voltage then I figured wrongly.
9. measure the voltage orange1 to black, orange2 to black and orange1 to orange2. These will hopefully be low voltage with black as centre tap, but could be 110Vac so be careful.
10. Don't call us if it blows up.
This is the winding configuration that I have derived from the values of your table:
Winding 1: orange - black - orange
Winding 2: red - blue - brown - green - purple
Your table also tells me that your multimeter measures 0.2 or 0.3 ohms even when both tips are shorted, am I right? Next time that you do any low value resistance measurement, you should find out this error value and substract it from the values obtained.
In order to find out voltage ratios, you should inject a small AC voltage between one of the oranges and the black wire, as I previously mentioned. Then you should measure the voltage obtained between each pair of wires in each winding and make another table.
Winding 1: orange - black - orange
Winding 2: red - blue - brown - green - purple
Your table also tells me that your multimeter measures 0.2 or 0.3 ohms even when both tips are shorted, am I right? Next time that you do any low value resistance measurement, you should find out this error value and substract it from the values obtained.
In order to find out voltage ratios, you should inject a small AC voltage between one of the oranges and the black wire, as I previously mentioned. Then you should measure the voltage obtained between each pair of wires in each winding and make another table.
Eva said:
Hi,
Yes it measures 0.3 ohms when the pins are shorted.
Would it be possible to pulse dc through the tx instead?
ash_dac said:
Yes, It is possible as I use that technique for checking and measuring SMPS high frequency transformers, but you will have to build a pulse generator if you don't have it, and an oscilloscope would be also required to see pulse voltage and polarity through each winding.
However, for 50/60Hz transformer measurement it's much easier to use low voltage AC power provided by another transformer, or even from some wall-wart AC adaptor borrowed from any appliance.
Eva said:
Hi,
Yes i'm looking around the house for a low voltage ac wall-wart but all I can find is dc !
I'm sure I've got one but I might go and buy one later (I suppose I could find a use in a cdplayer afterwards)
you can use your soundcard and a program like trueaudio -- this gives you an a.c. dvm and signal generator -- if you use a small 10kHz signal you won't load the sound card too badly as the impedance of the transformer will be relatively high at this frequency.
trueaudio is available as freeware, or you can purchase a full-blown edition for $99 -- here's a link --
http://www.trueaudio.com/
i use a signal generator to check transformers --
trueaudio is available as freeware, or you can purchase a full-blown edition for $99 -- here's a link --
http://www.trueaudio.com/
i use a signal generator to check transformers --
At 10Khz winding capacitance is probably going to excessively load the soundcard or signal generator. Test frequencies in the 400Hz to 1Khz range are more convenient for 50/60Hz transformers.
The primary input capacitance figure for a typical 500VA toroid is in the range of 100nF. Of course, this figure is valid only for frequencies below the point where this capacitance starts to resonate with leakage inductance, which may easily happen around 10Khz for standard mains transformers (another reason to avoid mesuring at high frequencies).
Eva -- first, we should split this conversation from this thread as it is getting a bit theoretical
i am measuring a much lower parasitic capacitance, deriving the value from f=1/(2PI sqrt(LC))
i am measuring a much lower parasitic capacitance, deriving the value from f=1/(2PI sqrt(LC))
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