On Sat, 1 May 1999 12:37:03 +0200 Tjaart van der Walt writes: >Remember the usually-forgotten diode between the negative side of >the=20 >relay coil (on the collector) and GND. This way you guarantee that >no=20 >excessive - voltages get on the GND line. How will installing a diode that way keep negative voltages from the ground line? It is connected to the ground line in such a way to route any negative voltage right to it. Such voltages won't occur in normal operation anyway. If they did, the transistor would start to conduct in "inverted transistor" mode and shunt the voltage to the ground line (and to the drive resistor, which may be more of a problem). The original problem was a capacitor on the *output* side of the relay failing. This would indicate some problem with the interaction of the relays and the loads. Diodes, transorbs, RC snubbers, etc. should be applied to keep transient voltages from inductive loads being switched off under control. Unless the properties of tantalum capacitors are really necessary, use aluminum ones instead. They are much more resistant to damage from overvoltage. But it's not only a problem of capacitors failing, as spikes of at least 20-30 V on the 12V supply are bound to mess up something else. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]