# Voltage finding help!

Discussion in 'General Electronics Chat' started by tonymaull, May 10, 2010.

1. ### tonymaull Thread Starter New Member

May 10, 2010
5
0
Hello

Im trying to find what voltage a old mixer uses. The machine had no power cable, and my knowledge of electronics is very small.

The power input is a 4 pin DIN cable arranged in 180 degree arc (never seen this before to supply power. Pin's 1 and 2 are connected together inside to the blue cable, 3 and 4 to the brown.

The brown then enters the PCB via a switch. It then branches out. One branch then runs through two lamps (both currently blown) in series, then through a 330 ohn resistor (large reddy brown resistor with a orange, orange, black then gold band), then back to the blue pins.

The PCB was damaged with some of the track lifting and some wires loose, which ive repaired. I would guess this is from the wrong voltage going in. I dont want to do this again.

Has anyone got any suggestions on how I can find the right voltage for the mixer?

There is no manual, no internet infomation or writing anywhere to give me a clue.

Thank you all!!

2. ### Norfindel AAC Fanatic!

Mar 6, 2008
235
9
Does the power input go into a diode bridge and capacitor? If it's so, the input is ac, and you can guess the ac voltage is going to be *lower* than the (capacitor rating / 1.414) - 1.4, and higher than the next smaller (capacitor rating / 1.414) - 1.4

You can probably use a variable voltage supply, start low, and go up until the mixer starts to work right.

3. ### tonymaull Thread Starter New Member

May 10, 2010
5
0
Hi, yes the power goes into a 1400 diode (small black with grey band), then into a 2200uf 35v capacitor (large blue).

There are two sets of 'diode into capacitor'. Both directly from the live power input. They both go then straight into the blue netrual cable back to the power input.

The suggested voltage to try is therefore 35v ac?

Thank you tons for your help so far.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
Whoa. Capacitors charge to peak voltage. 35 VAC is measured as RMS. The peak voltage is right at 49 VAC. That blows up the capacitor (probably already bad from age).

And it's never a good idea to run a cap at the voltage rating. I would look for an AC input of 14 - 18 volts. That would give you on the order of 24 volts to operate with. 12 VDC may be enough.

That's probably a 1N4000 diode - good for 1 amp and 50 volts peak (never run them at peak, either).

5. ### retched AAC Fanatic!

Dec 5, 2009
5,201
316
Listen to the man. He speaks the truth.

Without using the RMS voltage, you can end up popping things all over the place.
Also, using components with twice the rating you need, is also good practice. It will save your knees and elbows. Diving out of the way when caps "blast-off" towards you isnt as fun when you get older.

6. ### tonymaull Thread Starter New Member

May 10, 2010
5
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Great thank you all.
As a newbie i'm slowly understanding all this (with the help of wiki).

Beenthere... am I right in saying a 12 VAC input will become 12 ADC after going through the diodes and capacitors?

7. ### Norfindel AAC Fanatic!

Mar 6, 2008
235
9
Nope, a 12 Vac input will turn into approximately $12 \times \sqrt{2}$ Vdc (diodes drop aprox. 0.7v each, also).
You mean current with Adc? Current is dependant on the impedance of the circuit.
Take a read at http://www.allaboutcircuits.com/vol_2/chpt_1/3.html . You can learn a lot by reading all the site.

8. ### beenthere Retired Moderator

Apr 20, 2004
15,815
293
If you're too lazy to do the square root, just multiply by 1.4. That is pretty close.

9. ### tonymaull Thread Starter New Member

May 10, 2010
5
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Hi, update

tried a 12 v power input, but not having any effect (apart from the bulbs ive replaced). There is a chip on the pcb which apparently is a voltage regulator, which outputs at 15v. The input can be anything upto 20v.

Have done some reading tonight and bit more clued up on what AC/DC is about.

Im going to have to buy a larger varaible power supply to test beyond the 12v one I have.

Any more thoughts or advice is appreciated.

10. ### Norfindel AAC Fanatic!

Mar 6, 2008
235
9
Why do you say "apparently"? Isn't the chip code visible?

11. ### tonymaull Thread Starter New Member

May 10, 2010
5
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Yes it is. Needs 24v. Also managed to pop a capacitor!
When its all working ill dance a jig!

Thanks again.