I have the same issue actually - I'm needing to run a 10A12v motor off a 30v supply. Currently I have 2 supplies but I've been toying with the idea of carefully PWMing the 30V straight to the motor. Is this a good idea or a bad idea? Thanks, DougM On Mon, Jul 25, 2011 at 9:01 AM, Denny Esterline wro= te: > Ok, so I have product that has a small 12V motor running off a 48V bus. > It's exceptionally low duty cycle, about 5 seconds a day. And low power, > about 500mA. Given that, I had been using a couple resistors and a zener > diode to power it off the 48V bus. It's a little less than elegant, but i= t's > been working fine and fit within my space constraints. > Recently I was asked to build a variation of it that needed a larger moto= r. > I'll spare you the gritty details, but eventually I found a suitable moto= r > and shoehorned it into position. It was also rated 12V so I gave no thoug= ht > to powering it. > > Now the face-palm moment - it needs more current (duh). > > The kicker is it needs at least 2A to start and drops back down to about = 1A > when running. Attempting to alter the resistor values to accommodate the = 1A > run current leaves it with a very anemic startup (won't start under load) > and adjusting the resistors to allow 2A for startup results in excessive > speed or very unhappy zeners. > > The simple fix would be bigger zeners, but I can't seem to find anything > bigger than 5 watt rated parts. > > The elegant fix would be to lay out a small buck regulator, time is not m= y > friend. This needs to ship before I could have boards made. > > The quick fix would be an off-the-shelf DC-DC converter. I haven't been a= ble > to find any smaller than about 2"x2"x1" thick and they all seem to need t= o > be PCB mounted, see above. > > So, I'm turning to the list for out-of-the-box suggestions?? > > > > Thanks > -Denny > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .