On 4/21/06, Wouter van Ooijen wrote: > > Wouter, we have talk about this several times on this list > > and on others. > > 1N5819 has only 40V breakdown voltage. It's less than 2x24V requested > > by any engineering design requirements. > > you might have a point here > > > Also the motor load is 5A, > > no, the power supply is 5A, the *stall* current of this motor (there is > a heavier motor too, this is the smaller one) is only 300 mA. Well, then my point is wrong (for the current), except maybe if you change the sense of the rotor without stoping it for a while ? Or if the rotor have a high load on his shaft which is creating large inertia. The self induction can kill the suppresing diodes, but usually the killing comes from current flow (as max peak power dissipation on diode) and not because of voltage. However schottky diodes aren't too good at any huge spikes, just because the junction has low parasitic capacitance and short spikes are jumping happy through it. > > > while your maximum supressed current is 1A (25A/8mS maximum maximum > > peak current). > > Change diode with at least 100V one and check if your maximum peak > > current through diodes tooks more than 2-3mS. If yes, choose a 2A > > diode. > > which diode would you suggest for 2A/100V? With these new informations 1A should be enough, but choose a bigger voltage for diodes. > > I think your points are probably valid, but not the root cause of this > problem. The circuit contains two H-bridges, and this problem occured in > one leg of the H bridge for the smaller motor! The poorless diode crash the first one, but it could be any of the four. Check if your clockwise and anticlockwise movement of the motor are eating both the same current. I bet there is a difference and could be a bigger one. > > Oh, and you are quick responder: I don't even see my original question > on the list :) Don't worry, you're compensating the hardware guy side by your software guy side, which is huge evolved, you deserve fast answers, even not entirely usefull. greetings, Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist