On Mon, Apr 05, 2010 at 05:26:12PM +0000, Andy Pugh wrote: > On 5 April 2010 13:38, Erik Christiansen <dva...@internode.on.net> wrote: > > > A) Is it safe to interrupt Motor Power to my 7i40s, with hairy great > > inductive motors on their outputs? (OK, mostly resistive under load, > > but then back EMF might also be deadly if V+ is open-circuited?) > > I don't know how relevant this is to your situation and the 7i40s but > I found that an effective way to prevent relays exploding on my > Robotwars robot (3 x 24V 750W motors, peak current 300A) was to wire > conventional (and inexpensive) bridge-rectifier modules into the > circuit with the AC terminals across the motor, and the +ve and -ve to > the batteries. That way any voltage > Vcc + 0.6V is shunted back into > the supply lines.
Ouch! Here we only have the big filter caps in the motor supply. They'll shunt a transient, but the field energy of a rotating machine is what the automotive bods call a "load dump". On just a 12v system, that goes up to 80v for tens of milliseconds, unless absorbed. Nearly 30 years ago, I built a "super-transorb" for an automotive manufacturer, to do that. It wasn't much more than a (e.g. 20v) zener, base to emitter resistor, and a fat bipolar power transistor across the supply. One does the whole system. I could supplement the 7i40 overvoltage protection with one of them. Erik -- The surest way to corrupt a youth is to instruct him to hold in higher regard those who think alike than those who think differently. -- Nietzsche ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users