Post by Nantonos » Sat Dec 27, 2014 12:27 pm

Alex, thanks for posting these measurements. There have been a couple of other PSU projects announced recently, I asked whether the announced current rating was nominal, peak or steady and got evasive answers. Asked what the ripple was at 80% load and got zero answers.



So you posted my answers without my having to ask!



In summary, the 15V/50VA provides a steady-state 1.5A. It remains in regulation, as you showed, at 0% 40% 73% 80% and 100% of rated load. Voltage stayed constant (worst case was -11.975 on full load compared to -12.000V unloaded) and ripple stayed close to the baseline scope measurement at below 2mV rms. That is a great result!



I share the concern about 85Ãƒâ€šÃ‚Â°C in free air being a bit high; you also gave a result for a 13.5V/30A (so, 1.1A steady if the 13.5/60VA is rated 2.2A steady) with a more reasonable 48.5Ãƒâ€šÃ‚Â°C in free air. (It will be higher inside a case).



You also demonstrated the futility of rules of thumb like "80% load will be fine". The MFOS nominal 1.5A supply dropping out of regulation somewhere between 40% and 73% load and the Doepfer PSU2 nominal 1.2A dropping out somewhere below 91% (difficult to say much from a single measurement).



I'm glad you didn't go the marketingese route (3A nominal, and that is on both rails so hey, buy the L-1 6A power supply!!!!) but instead went for solid measured results. Other companies offering power supplies could usefully do the same measurements on their own stuff (unless they are knowingly selling tech with poor results, of course).



There are aspects of the design I don't like. The 120V/240V jumpers use uninsulated wire. That seems dangerous. I would have prefered to see an insulated rotary switch on the inlet, or insulated links on the PCB.



Ribbon cable seems a poor choice for bus to PSU connection (but I see you also offer a screw terminal option). I would have preferred to see multiple spade/faston connections for the +12V, 0V, and -12V outputs. Otherwise people are tempted to daisy-chain from one busboard to another. The 0V return needs to be low impedance.



And I would have expected larger heatsinks (but like your approach of measuring temperature rise rather than guessing/hoping).



I see you plan to use a 13.5V/60VA transformer to give a constant-load 2.2A supply, with lower heat dissipation due to dropping less voltage in the regulators. That seems a good approach, provided regulation and ripple is as good as your earlier results. I look forward to seeing the measurements when you have the new transformer available.

Last edited by Nantonos on Sat Dec 27, 2014 1:10 pm, edited 1 time in total.