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On Monday, April 7, 2014 8:00:29 AM UTC-5, Thierry Schembri wrote:
John uses the meanwell T60C (http://s100computers.com/My%20System%20Pages/The%20Box/The%20Box.htm#The_Power_Supply), I'm wondering how he stepped the -15/+16 up to -16/+16, or maybe  using -15/+15 is fine on the S100 bus? (the voltage regulators on the cards would work fine with -15/+15??)

My "development" S100 motherboard has mean well supplies and all the ones I've seen have a little trimmer next to the output connectors and you just dial them up to the correct voltage.  They are 15V nominal but from memory you can wiggle the trimmer and vary by quite a few volts.

I'm guessing the peculiar selection of voltages available for mean well supplies is because you can generate any voltage at all from 0 to whatever using them by picking the closest one and wiggling the trimmer a bit.  So I have a "7.5 volt" supply but it now outputs perfect 8.0 volts.

I have basically zero current draw on my 16V lines so I'm using 1 amp "pack of cards" sized supplies.  The modern boards don't use +/- 16 but I have some long term plans involving analog/audio/RF stuff, in my infinite spare time, etc.  So I'd be using a couple mA to run some opamps.  I did the same thing as suggested earlier in the thread with hooking up the + output to ground on the -16 volt supply.

RS-232 is supposed to be liberal in what it accepts so +/- 10 "should" work just as well anyway.  From memory, +/- 5 is pushing the limits of whats technically tolerable WRT the RS-232 spec on the read side although stuff will usually work even if a bit out of spec.  Some old boards might do something with the +/- 16 that isn't drive RS-232 of course, and as such may require a perfect 16 volts.  Or maybe not.