favorite diode for relay coil spikes and motor shutoff spikes?

Depends.

used to be 1n4004 or something like that, as they were such common general rectifier, not sure what the common SM type is these days.

Colin =^.^=

1N4005, of course.

But you may want to add a series resistor to shorten the dropout time.

-- Many thanks,

Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss:

email: snipped-for-privacy@tinaja.com

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I remember some time a few years ago I last bought a bunch of 1N4000 series diodes, and 1N4007 cost hardly at all more, and I had a little need of some higher voltage ones.

As for value of the resistor to shorten dropout time: Figure how much voltage you can comfortably handle, resistor and diode combined. In most applications, you also have to add the power supply voltage, such as when the application is a transistor switching a relay. Subtract the diode voltage (.6 or .8 volt or whatever), and the power supply voltage in the likely event this adds to what the switching transistor or whatever has to bear. The remaining voltage is voltage drop of the resistor, peak. Divide that by the maximum coil current (usually the worst case steady state coil current) and that is a resistor value - use the next available lower available value.

- Don Klipstein ( snipped-for-privacy@misty.com)

time.

1N4000

need

much

most

when

power

drop

Tyco app note

recommends a zener + diode but they do qualify the situation with regard to NC contacts.

Another less common technique (although widely used in relay based telco exchanges) is to use a CR unit (capacitance - resistance series unit). This technique has the advantage of being non-polarity concious and does not greatly affect relay release time while quenching the tendency to erode in-line relay contacts due to arcing.

Evox Rifa app note

American Zettler provide some broad guidelines in this document