5V 3A PSU

Graham Slee wrote: Next step to wire it all up and test it. Then "wrap metal" round it. By the way, it's upside down right now. The heatsink will be at the top.

That's looks like a lot of heatsink - COOL!

It is difficult to judge physical size but is there any reason why metal opposed to the PSUs plastic casing?

Richardl60 wrote: It is difficult to judge physical size but is there any reason why metal opposed to the PSUs plastic casing?

British made ABS is rated at 60 degrees celsius whereas Chinese made ABS is rated at a much higher temperature. The exact temperature being whatever is convenient for it to gain underwriters or Canadian approval. Physics doesn't seem to enter the equation.

ABS like uPVC starts to soften at 60 C and any transformer in contact with it - which it would be if mounted in it - must not exceed 60 C.

In a fault condition the fault must be minimised by a protective device (fuse) such that the case does not exceed 60 C. This is why the PSU1 is rated at 200mA output current because the primary fuse had to be rated at 63mA (125mA US) such that in the worst fault possible it would open preventing the unit exceeding 60 C. If the temperature could go higher under worst case fault conditions, the PSU1 could have been rated at nearly 1 amp, like many ABS Chinese PSUs are . . .

The above being required under its IEC60950 approval. That's a proper approval by engineers . . .

With the 5V 3A PSU (now with 3.3V too) we want 3 amps. In a worst case fault condition I can already see the possibility of it getting hotter prior to the fuse opening, so forget ABS (ABS being used for injection moulding).

It is far easier to use a metal case, which also affords heat dissipation. And another thing which makes life easier is to mains earth the metal case such that it complies with IEC60950 without jumping through the many hoops a double insulated PSU requires.

This power supply will not have a IEC60950 approval, but will fully meet with the standard. Why not? If I did get it approved it would cost me £10,000 or thereabouts, and with only around 10 customers it would increase its cost by £1,000, and with margins it would probably end up being priced at £2500.

So this one will not be offered in the main site but on here only.

Since posting the photo I realised that the Proprius style case would not only be a suitable size (there you go Richard - that tells you how big it is), but will probably also heatsink the power supply sufficiently (and look better into the bargain).