The gas tubes will protect by carrying the brunt of the current of big 'hit' instead of having the zeners carry all of it. The zeners begin to conduct at first, but if the voltage continues to rise the gas tubes will fire.
A TVS is very similar to a zener in usage here. I did not use them because I have backed up the zeners with gas tubes, which although slower than zeners or TVS's are much more robust than either. The 60v rating of the tubes does mean that if the voltage rises fast enough at the zeners and they can't cope, then the tubes will fire and pass nearly all the current to ground after that. Of course that would also mean that there is a large instantaneous current through the zeners, but it would be very short duration. You could use larger zeners if you wanted, can't hurt. The impedance of the wires to the wind genny will knock down most of the rest of resulting spike. Yes, it would have been better to use a small value (ohms) resistor in series to the wind genny to knock down what would be left but then you mess with the voltage sensing function of the wind gennys internal regulator, and since most wind gennys have a considerable length of wire running to the unit which will generate plenty of inductance at these pulse speeds, there will be plenty of impedance. Another reason I prefer zeners over TVS's here is because I have found that zeners are more reliable when used as a 'crowbar' for overvoltage circuits. TVS's can take a bigger hit, but will overheat faster and burn out sooner when continuously operated at a large 'clamp' current. I wanted to have some short duration over voltage protection here as well as rapid transient protection. I have a link here to a page showing several similar suppressor designs. They only keep it to 200V or so, for telephones. http://www.epanorama.net/documents/surge/telesurge.html I do note the size of the zeners in the last design is larger than mine. In the large load protector which I sent the schematic for, the relay only acts *AFTER* the transient has been clamped by the zeners. It is there to provide *surge and over voltage protection* (not transient protection) and to keep the zeners from doing all the work and getting too hot. It doesn't matter that the relay and fuse work slowly because the zeners are very fast and they will catch the transients. Before they will get 'cooked' the relay will open. A few years ago my boat took an almost direct lightning hit (neighbors saw it and said it was either direct or just a few feet away, I think most likely it was a few yards away at most) and several of the devices that had the small load protectors had signs of melted insulation to the protector. Out of eight electrical devices which were connected to these small load protectors and turned on, one failed and was economically irreparable, one was damaged but I repaired it, and the other six were fine, although as I said there was evidence of an over 2000 volt 'hit' or strike (the value of a rectifier diode that failed which was 'in front' of the surge protector was 2000 volts reverse meaning that the protector saw at least 2000 volts for an instant). So they do work to some extent at least. The wind genny had no protection and it bit the dust. I should have a better chance next time. -Ken _______________________________________________ Liveaboard mailing list [email protected] To adjust your membership settings over the web http://www.liveaboardnow.org/mailman/listinfo/liveaboard To subscribe send an email to [email protected] To unsubscribe send an email to [email protected] The archives are at http://www.liveaboardnow.org/pipermail/liveaboard/ To search the archives http://www.mail-archive.com/[email protected] The Mailman Users Guide can be found here http://www.gnu.org/software/mailman/mailman-member/index.html
