please could someone identify what this is....(picture)

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rancid rock

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hey,

could you please tell me what this is and explain what it does.

the battery isnt connected, as u can see if u enlarge the attached images.

(attached images)

thanks,
 

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This is a simple DC power supply board made by an amateur/hobbyist. The red and black wires require connection to a low voltage AC power source, like a power transformer. The rectifiers and large capacitor change the AC to a noisy DC. Then the DC is connected to a 12 volt linear regulator. The output of the 12 volt regulator is connected to the input of a 5V linear regulator. The output of both regulators is fed to two places each, the terminal block for connection to loads, and the LEDs which illuminate when the voltages are present. It is not clear what is attached to the other end of the red and black wires, but it might be a toggle switch.

The purpose of this circuit is to change an AC voltage into two regulated DC voltages, such as is typically done in a simple DC power supply with the addition of a power transformer.

A battery would not normally be connected to this circuit.
 
RadioRon is correct, this is a simple DC power supply, you probably couldn't pull much curent from it though because the regulators are not heatsinked, if they were you could probably pull an ampere of each line, as long as the AC power source can supply it. Do you have the part numbers of the regulators, i am guessing they are L7812 for the 12V and L7805 for the 5V (i could be wrong)

hope this helps
 
actually, the red and black wires clearly go to a switch. you would need to apply AC power to the two pads marked "VAC" on the underside. The switch is simply in series with one of the AC input tracks, ie - a power switch.

And yes, re-do all those solder joints, half of them aren't even covering 50% of the solder pad Whoever made it seems to have done a pretty nice job laying out and etching the PCB, but a terrible job assembling it...
 
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Ah yes, now I see that the red and black are attached to a power switch which is wired in series with one of the VAC connections. A transformer would then hook up to the pads labelled VAC as evandude teaches.

It is kind of unusual to have a power switch on the output side of a transformer, so one might speculate that some other AC source is used. Or perhaps the primary of the transformer is not accessible or serving other functions, like the 28volts used in hardwired home heating systems, where the transformer is attached to an electrical box? Well, who knows?

It is also a bit odd to have a floating copper pour like this board has, but then I would guess that the maker was trying to spare his etchant chemical the burden of etching those areas.
 
yeh ok sweet thanks heaps, yeh it is a massive toggle switch heh...umm about this heat sync?...is it really a problem cause i was hoping to use this circuit board (i found recently from ages ago) to run a project i have mapped out. How would i go about this heat sync?

Ziggy_dan: they voltage regulators are L7812 and L7805.

RadioRon: It's an old school board made with PnP Blue, thats why only some areas are etched.....and no shortage in chemicals

evandude: what kind of AC power are we looking at here....i vaguely remember rubbing out a number before the "VAC" hmm....i think it was modified from the origonal design maybe.....
 
i thought they can handle 1 ampere but this datasheet says 1.5A

https://pdf1.alldatasheet.com/datasheet-pdf/view/89077/STMICROELECTRONICS/L7812.html

edit: sorry you have to click the link next to download on the page above(if that makes sense??)

i am not to sure about how to work out the size heatsink required for a given input voltage or current drawn, i'll look through some old notes and post if i find it.

just out of interest...

what are you going to use the circuit for?
what input voltage are you going to supply?
how much current will you be pulling?
 
iv'e used a few of them before, they've got fair size heatsinks on them, they do get very hot when abused i.e. full current for a few hours (evil lol)

one of them blew, too much abuse.

they only cost like 50pence each so i wasn't to bothered, that datasheet i provided has some good circuit design ideas, i might look into.

p.s. use thermal compound between them and heatsink.
 
thank heaps hehehe.

if u wanna see the PICAXE-08M i am using

refer to the post about why isnt my PIXCAXE-08M working hehe
 
rancid rock said:
evandude: what kind of AC power are we looking at here....i vaguely remember rubbing out a number before the "VAC" hmm....i think it was modified from the origonal design maybe.....
Click to expand...

when passed through the bridge rectifier (4 diodes) and charging that large capacitor, the AC input will produce a DC voltage (with some ripple)

the magnitude will be 1.414 times the magnitude of the AC input, minus two diode drops (estimate 0.7v each)

You need to make sure this value is below the maximum input voltages of the regulators (somewhere around 20-30v if i remember correctly) but high enough that they can regulate properly.

So, if for example you used a 12VAC transformer, you would have about 15.5 volts feeding the regulators, which is probably a good level, but slightly higher might be safe because of the several volt dropout voltage of the 12v regulator. Just don't go too high, because higher input = more dropped across the regulators = more heat generated.
 
What voltage are you going to apply? and what current are you expecting to draw from each regulator?

with this information you can calculate the power dissapated and therefore the size heatsink you require.

or just use the largest heatsink you can fit on the board and monitor the temperature.

hope this helps
 
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if the 12v is purely for door relays, motors etc it probably doesn't need to go through a regulator. Just fliter the output of the rectifier with a capacitor.
Only equipment that is voltage sensitve would need a regulator.
 
The heat sink is a radiator to just like on your car, they're bolted on through the hole you'll see at the top of each regulator,if memory serves the centre pin is the output and is connected to the metal plate so use mica insulators and heat sink compound.
 
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