On Sat, Jun 16, 2007 at 09:53:39PM -0400, DJ Delorie wrote: > > > 24VAC RMS means 34V peak, > > HA! 24VAC means 38V peak (i.e. after the bulk caps) on my board. Had > to change modules because I designed for 34V.
Eeep, that concerns me. What's the Vf drop on your rectifier? I calculated a peak-to-peak voltage of 37.3V allowing for 10% head room, and then when you subtract diode drops 36V ought to do it. I'm planning to put a 40V MOV or similar on there to handle transients, of course, which will no doubt exceed the normal sine wave peaks. I wonder if your HVAC system might be wired wrong -- most of them have two ways to hook up their 24V transformer, one for 208V and one for 240V, I think. You might be running 240V into the 208V terminal. Or else your mains is >110% of nominal even after line losses, or else your rectifier has impossibly low Vf drops. Or I guess the transformer could have bad tolerances on its winding count. > > so I would ideally aim to have the largest input ripple possible, > > which coincidentally allows me to choose a smaller, cheaper input > > capacitor. > > What I did was put in four smaller caps in a row, which reduces the > ripple current through each. That helps keep cost down too. > > http://www.delorie.com/house/furnace/pcb2/board-full.html Wow.. 4x820uF = 3.3mF total input capacitance. That's motor-start capacitor territory there. How much current are you intending to draw? _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
