TVS surge suppression for relay outputs driving 24VDC coils

I am using a relay output card with 24VDC coils (motor contactors, Solenoid valves), and I'd like to use TVS diodes to protect the relay contacts from surges. I was wondering if anyone has any info on how to pick the appropriate device? For example, this page has lots of TVS diodes to choose from:
http://www.newark.com/jsp/content/printCatalog.jsp?display=single&cat=catalog128&page=363

Does the current draw affect which diode I should use, or is there one of these that would be best for all 24VDC coils?

Can I use bidirectional diodes to prevent the possibility of them getting installed backwards in the field, or will bidirectional not work correctly with DC coils?

Or is there a different device that you would recommend?

I welcome all recommendations. Thanks!

Look here for the theory:
http://en.wikipedia.org/wiki/Flyback_diode
and here for practical applications:
http://groups.google.com/group/sci....read/thread/f67136cd905c4fce/6ab2ddf92059d817

Automation direct has a 2 level terminal block with a diode.
their number is 1-800-633-0405.
item # DN-D10DR-A TERMINAL BLOCK, DIODE

regards,
james

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We wire hundreds of solenoids a year. We switched from diodes to MOV's, they can't be wired backwards like diodes and work fine in most applications. Incorrectly wired diodes can cause alot of damage. Check out Canfield they sell excellent surge suppression devices.

Remember that MOVs have a breakdown voltage where they will conduct and have no polarity.

So make sure you get an MOV with a voltage rating higher then your operating voltage or it will conduct under normal voltage, overheat, and catch fire!

Been there, done that...

Surge Suppression Info

You are absolutely right; I have attached a file that does an excellent job in explaining advantages and disadvantages of the different types of surge suppression devices.

Good reference! That one went in the "save" folder. Thanks.

No Problem, had this thing for years helped shed some light on it for me.