battery charger output voltage

[96terrano]

need help, here, does a normal 12v car battery charger put out the same volts and amps as a car alternator? eg, could i run a car radio off a battery charger or would it make magic smoke

[(RIP) PLANK]

not usually a very stable supply, of course it all depends on the make and model of the charger, have you got an old car battery you could put in line?

[supergnome]

If you look at the output of a charger on a scope it is very rough and not a flat line ( constant voltage) as is a battery. Dont run anything from the charger, It won't like it. You can as Plank says put it in a parallel circuit with a battery and that will remove most of the saw tooth edge of the wave from the charger. They are not the same as power supplies for CB's or ham radios which use silicon diodes with the output smoothed by large capacitors to give a much flatter line similar to a battery. David.

[96terrano]

cheers, i've got a few batterys about

[96terrano]

what about somthing like this with a 12v motorbike battery in parallel

http://www.ebay.co.uk/itm/12V-TRICKL...item2a1e40ee70

[(RIP) PLANK]

no, as it's only half an amp, if you had a good battery and left it charging when you weren't listening then yes. But this would not provide the power your stereo would use

[96terrano]

ok, hang on, i just found a video on you tube, let me go and get it

[96terrano]

here's one way http://www.youtube.com/watch?v=SM5PdaDa66k

and there's also this way with a computer psu, http://www.youtube.com/watch?v=V5ipPBnT_NI

[(RIP) PLANK]

Originally Posted by 96terrano

here's one way http://www.youtube.com/watch?v=SM5PdaDa66k

and there's also this way with a computer psu, http://www.youtube.com/watch?v=V5ipPBnT_NI

haven't seen the videos but the computer PSU one seems the best method, as that should be a better output, in these situations Ohms law is your friend

[96terrano]

Originally Posted by PLANK

haven't seen the videos but the computer PSU one seems the best method, as that should be a better output, in these situations Ohms law is your friend

psu it is, well, see you forever, as i'll nick the psu out this computer

[glanrichbex]

If you're going to use a computer PSU, don't do what the idiot in one of the clips has done by shorting two of the output cables.

It's a switchmode supply and all switchmodes have current sensing. If you stop drawing current it will collapse the loop and it will shut down.

To keep it running, it will need to see a load on the 5volt rail ( yellow ).

Connect a 12volt 21W standard car bulb between a yellow and black ( this will glow slightly but is needed to draw a few hunderd milliamps )

You can now safely use red 12volt and Yellow 5volt Blue -12volt.

[96terrano]

Originally Posted by glanrichbex

If you're going to use a computer PSU, don't do what the idiot in one of the clips has done by shorting two of the output cables.

It's a switchmode supply and all switchmodes have current sensing. If you stop drawing current it will collapse the loop and it will shut down.

To keep it running, it will need to see a load on the 5volt rail ( yellow ).

Connect a 12volt 21W standard car bulb between a yellow and black ( this will glow slightly but is needed to draw a few hunderd milliamps )

You can now safely use red 12volt and Yellow 5volt Blue -12volt.

Ok thanks for the info, I'll see if I can get a psu off my uncle. He plays about with computers and communication equipment. He's got some cool stuff

[rustic]

Just for the record...

If you used a standard battery charger as a 12 volt supply, you would have to add capacitors to the output, at a rate of 1000 microfarad per amp, so if you put 4700uF on the output, the supply would be good for just over 4amps.

HOWEVER:
This will raise the peak voltage on the supply and capacitor to well over 18 volts, so then you have to set about creating a regulated supply.

13.6 volts will be good for car rate items, car radios included.
I use the LM317 regulator which is only good for 1.5 amps, it will need a heat sink, and of course all the protection items, fuse, case, ventilation, switch etc

For higher currents you will need a higher current regulator, assuming the battery charger is able to produce this current.

So using a computer power supply will be the best thing, it is ventilated with a fan, but also you might need to link 2 pins which is the equivalent of an on off switch on the computer to get it working as well, that's what I did when I wanted a 5volt supply as well as a 12 volt supply.

Hope it helps,
Best regards, Rustic

[96terrano]

Originally Posted by rustic

Just for the record...

If you used a standard battery charger as a 12 volt supply, you would have to add capacitors to the output, at a rate of 1000 microfarad per amp, so if you put 4700uF on the output, the supply would be good for just over 4amps.

HOWEVER:
This will raise the peak voltage on the supply and capacitor to well over 18 volts, so then you have to set about creating a regulated supply.

13.6 volts will be good for car rate items, car radios included.
I use the LM317 regulator which is only good for 1.5 amps, it will need a heat sink, and of course all the protection items, fuse, case, ventilation, switch etc

For higher currents you will need a higher current regulator, assuming the battery charger is able to produce this current.

So using a computer power supply will be the best thing, it is ventilated with a fan, but also you might need to link 2 pins which is the equivalent of an on off switch on the computer to get it working as well, that's what I did when I wanted a 5volt supply as well as a 12 volt supply.

Hope it helps,
Best regards, Rustic

Thanks, yeah I think a psu is the best. I did hear about bypassing the internal switch with a paper clip

[96terrano]

spoke to my uncle and he hasn't got any psu's just now but i found this that might work

http://www.ebay.co.uk/itm/NEW-500W-S...item3cc78ecef9