CD player power adapter from car cigarete lighter socket

The electric system in a car can reach as high as 14.2Volts when the alternator is charging. I am not saying that someone was wrong just by thinking (12V).

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I didn't mean it like that, its just that the only reason that the zener was there was because Tansis suggested that it would protect the regulator from high voltages!! That was why I was a little bit supprised. Sorry if I offended anyone.

poly non-polarized

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forgive my inferiorness, but you mean ployester caps, yeah?

Tim,

I don’t think you have offended anyone all is cool.
It is easy to think 12 Volt systems and then a 13V Zener is of curse OK.
Good Luck!

Ante :roll:

lol, thanks Ante.

errm, ok - I built it. And somthing odd is happening...

Bassically, i built it as per Tansis's 2nd diag, but missing out the Zener, and adding a fuse (3A for testing) in line with the 12v supply.

I switch it on and measure the output voltage. 8.3v. Thats odd. So I put a resistor accross the output to give it a load, and measure the voltage then. Still 8.3v. I check my wiring. All good. i check the reg, and it says 7806 on it, and I assume it is what it says it is. Oh yeah, I should mention that as I was using a 7806, I missed out the resistor divider.

anyway, the last thing I checked was the voltage going into the whole circuit (not that it should make a difference, as the reg can handle a wide range of input voltages), and despite the fact (I was using a mains adapter, rather than a car cigy socket) it said "12Vdc 500mA" my multimeter measured around 24v. which didn't make much sense. So I though my multimeter may be on the way out, and this may be the reason that my measuremt of the output was strange. I tried replacing the battery, to no avail.

Oh yeah, also, when I put my resistor accross the output, I worked out the current that should be going through it (using I=V/R), and measured the current using my multimeter, and got a readin of 0, or more accuratetly, 0.00 - which is also odd.

What do you reackon, is my multimeter over the hill?

One last possibilty, I looked at the data sheet for the 7806, and the pinout diag was from 'top view'. I assumed this meant the side with the writing, rather than the side with the heatsink. Was this right? If it wasn't it may explain my strange readings.

I just don't really get it.

Sorry for going on so long, but I didn't want to waste your time by letting you suggest things I'd already tried.

Thanks,

Tim

Tim,

Try measuring a known voltage to eliminate any faults in the multimeter. Use a PP3 or something alike where the voltage is known. About the mains adaptor, if it is not a stabilised one it can carry higher voltage when the load is lower than the marked (500mA) but 24V is too much anyway I think. Dumb question : which range are you using on the meter AC or DC?

Ante :roll:

I measured a brand new AAA (normally about 1.5v) and got 1.62v - I can't find any other new batteries, and I don't want to test old ones, because I don't know what state they will be in.

DC range, AC range would be silly... :lol:

The mains adapter used to be a battery charger for a scanner, but I don't think it has any charging circuitry built in.

If I put a PP3 and a couple of AAs in series, that would give me 12v and a way of testing the whole darn thing...yeah?

Cheers

Tim

grrr_arrghh said:

The mains adapter used to be a battery charger for a scanner, but I don't think it has any charging circuitry built in.

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It will be a simple un-regulated power supply, so 24V with no load is quite possible - under full load it will probably come down closer to 12V.

i tested it with my circuit on it as a load, and it still came to 24v. I have just remembered I have a variable voltage PSU from my model railway from when I was a kid (man, that makes me feel old...)

ok, I have done some other tests, on batteries, other power supplies (loaded), and have decided that my multimeter is completly, well it just doesn't work. I'm not sure what word you would use there.

But anyway, until such a time as I have the money to get another one, is there any easy way of measuring voltage/current? I have connect some various fans and things to my regulator, and I reackon it is about 6v (they spin at about the speed I would expect them to...)

Could someone answer this quickly (just to eliminate it):

I said:

One last possibilty, I looked at the data sheet for the 7806, and the pinout diag was from 'top view'. I assumed this meant the side with the writing, rather than the side with the heatsink. Was this right? If it wasn't it may explain my strange readings.

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I tested it using another multimeter, and it all works perfectly. So it was my multimeter.

Cheers guys, thanks for all the help on this (what i though would be quick) project.

Thanks again

Tim