Erik Christiansen wrote: > On Fri, Apr 09, 2010 at 02:17:28PM +0200, Roland Jollivet wrote: >> A DPST will perform the function fine, unless you want DPDT for some other >> reason. > > Hmmm, maybe you meant to type SPDT? Even leaving one side of the motor > connected to the H-bridge output, we have to switch the other side of > the motor away from the H-bridge to a shunt resistor. I've collected > components, and am starting to build that up. (The relays to hand are > only SPDT, after all.) > > Now, should I connect a pair of back-to-back hefty zeners or transorbs > across the motor, to clip the hundreds of volts of back-EMF which could > be generated by interrupting 10A flowing in the motor winding? The shunt > resistor is not in circuit until the relay armature completes its > travel. That could be enough to let the magic smoke out of the 7i40's > H-bridge FETs, unless there's very robust protection there. > > Alternatively, using Andy's bridge rectifier idea reduces the number of > great fat zeners required. I then just have to add one common > overvoltage shunt across the supply rail, close to the four > motor-stopping relays. > > Thanks for the suggestions. (I'd hate to blow up a 7i40 by guessing > wrongly while trying to increase protection against mishaps.) > > Erik > Return on search for "snubber circuit design" returns volumes of links to circuits you can use to solve your problem. The following is a good example of theory and practice http://www.cde.com/tech/design.pdf
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