making a powersupply with no grounding pin in the wall

[southtown]

Is this possible, where im from (new zealand) all power outlets are grounded, but over here most outlets are just a 2 prong, im looking at building this, I dont want to touch my power supply and kill myself though if you get what i mean

[brett]

Hi
Making a supply with a 2-prong plug will never give you that protection against a "live" box that a fuse will. 
But lots of places in NZ would have "safety switches", wouldn't they?  Safety switches are FAR better than fuses.  They measure the inflowing and outflowing current, and if there's even a tiny difference (ie a few mA of earth leakage), they switch off.  This is good because the earth leakage might be running through the body of someone.  Portable safety switches are fairly cheap these days.

But I reckon you can never get enough protection, so when I build something for 240V I always get a 3-pin plug and cord (I buy a cheap extension cord from Woolies and cut the end off.  But other times I save $5 and scavenge one off a microwave at the dump  ).  Use a 240V fuse  and you're sweet. (those screw-in holders for M205 fuses are cool)
cheers

[southtown]

sorry i forgot to mention, im in denmark at the moment where most outlets dont have a hole for a grounding pin


also looking at transformers, how many VA do i want? i have a choice between ,35VA and 30 VAc and everything between. im looking at the ultra clean power supply now, it looks nicer

[southtown]

one more question, would this lm317 be fine, it says 0.1A on it, wouldnt it need a higher current handling than this?

http://www.banzaieffects.com/LM317-pr-20312.html

[Minion]

You can get the LM317 in a T0-220 Package which has an output current of over 1.5amps.....

The 100mA ones you are looking at would be good for powering a couple pedals but no more...I would go for the TO-220 ones if you want to power several pedals.....

[Cliff Schecht]

You can get the LM317 in a T0-220 Package which has an output current of over 1.5amps.....

The 100mA ones you are looking at would be good for powering a couple pedals but no more...I would go for the TO-220 ones if you want to power several pedals.....

I was wondering why everybody was saying that the 317 only puts out .1 amps, I kept saying mine puts out 1.5A. I wasn't aware they made a TO-92 size LM317. Mine powers a good 12 to 14 pedals at a time for hours on end at a time and it's never failed.

[slacker]

There's 3 types of 317
317LZ 100mA
317MP 500mA
317T 1.5A

If you want to make a power supply for a number of pedals you want a 317T.

[southtown]

ok now im planning on putting it in a hammond 1590c metal box, what do i do about heat generated by the transformer and the lm317?

[Cliff Schecht]

ok now im planning on putting it in a hammond 1590c metal box, what do i do about heat generated by the transformer and the lm317?

Find an external 12-15V AC external wall wart, they are just big unregulated transformers. I used a 13V 4A transformer that is halfway between the wall plug and the actual power supply, which makes the actual power supply box a lot smaller. I fit 10 output jacks into a 1590B and just mounted the 317T straight to the side of the Hammond box (separated properly with a divider and plastic screw) and it works great as a heatsink.

[gez]

ok now im planning on putting it in a hammond 1590c metal box

Is that wise?   Plastic would be safer (you can even buy plastic wall-wart style boxes).

Personally, I don't build power supplies.  You can buy excellent regulated (suitable for keyboards/pedals etc) PSUs with over 1A current for under £10 in the UK.  If I need more than 12V then I just use an AC PSU and build a rectifier and regulator into the circuit.

[southtown]

ok thanks guys, youre saving me from zapping myself i guess my main reasoning on wanting it to just be a ac plug and a box is ythat ill be moving back to nz soon so ill need to change the type of plug it uses...

[southtown]

sorry for all the newb questions, but if i was to use this http://www.elfa.se/elfa-bin/setpage.pl?http://www.elfa.se/elfa-bin/dyndok.pl?lang=en&dok=2021881.htm then daisy chain a whole bunch of power outputs, then i could use the schematic for the super clean power supply from ggg but just cut out the transformer and bridge rectifier, correct? or preferable this one? http://www.pc-elektronik.dk/shop/productinfo.asp?id=4011

[gez]

It's unclear whether the first supply is DC, but assuming it is then yes you can feed it to your regulator without the need for a rectifier.

The second supply, if it's well regulated (didn't check the spec), you could just use full stop.  If it's not well regulated then you might need to find a low drop 9V regulator as the max voltage is 12V, which might not reach the threshold (can't remember what it is for the LM317 doo dah, I'd need to check the data sheet).  Whatever, you'd need to operate the thing on its 12V setting.

[scaesic]

why don't you just get a switched mode power supply? you can buy one for about 20 quid in the uk, it works on 100-240v (i.e anywhere) and will power about 20 pedals?

http://www.maplin.co.uk/Module.aspx?ModuleNo=48484&criteria=switched%20mode&doy=16m1

http://www.maplin.co.uk/Search.aspx?criteria=daisy%20chain&doy=16m1&source=15

[gez]

If it's not well regulated then you might need to find a low drop 9V regulator as the max voltage is 12V, which might not reach the threshold (can't remember what it is for the LM317 doo dah, I'd need to check the data sheet).  Whatever, you'd need to operate the thing on its 12V setting.

Depends on the manufacturer by the look of things.

National: "Further, all the circuitry is designed to operate over the 2V to
40V input-to-output differential of the regulator"

So, you could just about get away with it.  However, the ST data sheet had test conditions of 3V-40V, so who knows?

If I were you, I'd keep searching for a well regulated cheap supply (it that second one you linked to isn't suitable).  You should be able to find a cheapie in your neck of the woods.  So long as they use a regulator they should be nice and quiet.  In the UK you can by Uniross power bricks for under a tenner and they're as quiet as a (dead?) mouse.*

*They make a range of adaptors and not all are quiet though - do your homework!

[southtown]

that one i linked is unstabilised in english, would a stabilised one be better?

[gez]

that one i linked is unstabilised in english, would a stabilised one be better?

Stabalised = regulated.  That's what you're after if you want to use it stand alone (no additional circuitry), otherwise the first one would do.

[southtown]

ok im sorted then, thanks very much