Beginner's Gainclone, Safety and, The Power Supply Board (please contribute)

[AndrewT]

Originally posted by MJL21193
Computer power supplies are complete, stand alone units with the safety earth connected to the metal case internally.
Where is the confusion?

I see a three pin IEC socket.

[Juergen Knoop]

ionomolo was referring to laptop PSU's
regards

[Mooly]

Hello Andrew,
Providing it is certified, and even then you hear tales of "substandard" shall we say products.

[MJL21193]

Originally posted by Juergen Knoop
ionomolo was referring to laptop PSU's
regards

All of the units I've seem here (Canada) are grounded also - three pin input. Something like 20VDC output, 2 pins.

[Mooly]

As I say my laptop (U.K.) has a 3 pin inlet which "Must be grounded"

[ionomolo]

Originally posted by AndrewT
I hope Ion clarifies what he means and what he considers safe.

If some computer PSUs need a Safety Earth and this is provided by the bolted/riveted connection into a Safety Earthed computer case, then omitting the required Safety Earth from the PSU is potentially Fatal.
If he means find a PSU that is built to double insulated standard and use that in it's intended way, then OK.
But, I ask the questions
and I'll ask a further question,
are there any double insulated computer PSUs on the market, even in Spain?

I was refering to psu's like the one in the picture of post 105 by Juerguen Knoop. I bought them at the supermarket for $20 and, as you can see from the picture, they have a 2-pin input so there is no safety ground. I havn't encouraged anyone to "hand-disconnect" safety earth!

Whether they are safe or not, well, since laptops have metal screws and jacks i belive doing a gainclone with these supplies to be as safe as plugging them into your laptop. I don't expect things bought at the supermarket to be extraordinary dangerous, but you should not touch the wires anyways.

The couple i bought have the "double-insulated" symbol.

[Nuuk]

I bought a couple and they have the "double-isulated" symbol.

How are you using them Ionomolo? As a pair to get around +/-15-16 volts?

[ionomolo]

Originally posted by Nuuk


How are you using them Ionomolo? As a pair to get around +/-15-16 volts?

Yes, i placed a pair of standard dc female jacks like the ones that laptops have on the gainclone so as i don't have to cut the wire from the psu to keep the warranty! the positive from one jack goes to the negative of the other and to 0V. I did try various models and there is a zappa one which in spite of not being safety-earthed does not have the double-insualtion logo. This was the cheapest, the smallest and also the most noisy (obviously big chokes and caps don't fit there), so i suggest to go for a better one. I set them at 20V 3.2A but they can go up to 24V 2.8A. Not the most powerful thing i've seen but they do the job very well for a beginner project. I use them in 16V 4A for my class-A experiment as i've found that finding a transformer that has that current capability with so low voltage is impossible here and shipping a weighty transformer very expensive.

For "high-end" power i use "aqueduct" filtering (putting several pi-filters in series. The on-board cap should have very low impedance from 100Hz and i let the logic at the supply to take care for the bass. I've found no problem at all and the chokes i use are free as i take them from broken computer smps.

I'm very happy with the results and i belive it's a nice supply for newbies both for price and safety reasons (absolutely no construction/modification of mains-wired equipment).

I have no idea how these are designed but if it's done properly the current-limiting function should not present any more dissipation than normal operation so it would also be very safe for the circuit.

[Nuuk]

Yes, if the correct SMPS are used like you are using them, I agree, it would remove a lot of the angst (and potential pitfalls) for first-time builders!