Low Voltage Transformer Operation

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gigster

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Ok I think it might be better if I understand whats going on in making a auto battery charger.
So a 5 wire 12v 5 amp transformer: 120v in the 2 black primary wires and out at the 2 red outer wires is 12v if I move one of the volt meter leads to the center yellow wire it reads 6v.
Now if the output voltage A\C and I want to charge D\C is that what the diodes are allowing?
And is the cap. giving me the negative for the battery?
Since I have a 10amp. rectifier can the 2 outer red leads be put to the ~ term.
and use the + & - to go to the battery?
 
A 12VAC transformer has a peak voltage of 17V. The rectifier drops it to about 15VDC and the capacitor keeps the output at 15VDC which is too high to charge a lead-acid battery without a resistor to limit the current and something to turn it off when the battery is fully charged.

Maybe the value of the capacitor is low enough to allow a lot of ripple that will reduce the average voltage and reduce the average current.
 
if I move one of the volt meter leads to the center yellow wire it reads 6v.
Click to expand...
That's the centre tap, the two leads either side of it will read 6V with respect to it but 12V across them; this is because they're opposite phases.
 
So if the center 6v wire was connected to one of the outer wires would you gain more output voltage? or whats the purpose of the center wire?
 
No, you get 12V across the outer wires and 6V from the centre wire to either of the outer wires.

The centre wire is useful when you want a bipolar power supply.
 
Im a mechanic so I do alot o 12v d\c but I also get into residential electrical.
Now to get a volt reading on a car I need to have the neg. lead go to ground.And when checking 120v a\c I would use the neutral or ground. So how does it work when I put one lead on 1 120v leg (phase?) and the other lead to the other 120v coming in and you get the 240v reading without going to grd. or neutral? I it because of the alternating current wave?
 
In North America we have one phase of 120VAC, the opposite phase of 120VAC and a neutral that is grounded between them. So 240VAC is available for high power like air conditioning , stoves and clothes dryers. Everything else is connected to one of the 120VAC and neutral.
 
It depends on the supply in your area, 120V supplies are like audioguru said, 220V - 240V supplys just have a 0V neutral and a 220V - 240V phase. If you're connecting an inverter to your car the neutral lead should be connected to the car chassis.
 
what I mean is how does a volt meter read voltage (in this case 220v) if the neg lead and the pos lead are both on power wires
 
There is no such thing as positive and negitive on an AC supply. AC is alternating current so how can there be a positive or negitive? With AC we talk about neutral, phase/hot/live. To measure voltage of an AC system, you either measure between two phases or a particular phase to neutral.
 
Yes I realize that but alot of dvom's have a red lead marked volts\ohms\ma
and a black lead marked common & a picture of a rake looking affair (earth\ground) thats why I said it like that. Anywho I was just curious as to how the meter (dvom) gets a voltage reading\ display when both leads are put to power\hot\voltage wires. I have always assumed it was because its alternating current.
 
It doesn't, you need one wire on the phase and the other on the neutral.

Unless you're talking about the type that beeps when near a wire; well that type works by sensing the electirc field but it won't give you a voltage reading just whether the voltage is present or not.
 
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