Yes, it behaved all around Ohakune, but on the journey home to Palmerston North it was a different story . . . much coaxing was needed. BUT, I MADE IT.
Come to think about it the electric pump is about the only thing that has caused me strife on a long trip . . well that’s if one excludes a ring coming through the top of a piston on a South Island tour many years ago, back when I was using Jowett pistons!
I had a spare pump at home (of course!), but on examination of them both an interesting thing was noticed. One had a resistor fitted and the other had a capacitor . . . and I have been told of others which have just points alone.
A search of the internet revealed that over the years SU have tried to reduce the arcing by using resistors, capacitors, diodes and Zener diodes . . . these were attempts to reduce the VERY high back voltage generated by the solenoid coil at the time of the points opening (much like a ignition system is designed to). Without these devices (some of which were inclined to be marginal in effect!) there was sufficient energy available to relatively quickly pit and burn the points contacts . . . to a point where they wouldn’t conduct at all (my problem!).
The latest, and more modern, method to suppress the high voltage is to use a device called a TVS diode (Transient Voltage Suppressor) of suitable specifications.
Basically the bi-directional ones work like this:
a/ Being bi-directional the diode is not affected by the polarity of the car (hook it up any way is okay).
b/ It is two special diodes back to back within the case.
c/ What is special is that the diodes will allow electricity to pass one way (as is usual with diodes), but unlike “normal” diodes which block the electricity when the polarity is reversed, the special-ness of the TVS means that it still does that but, when the voltage reaches a certain value it DOES conduct and dumps the very high voltage to earth,
d/ You can see then, that if a TVS is chosen that has a “dump” voltage of say 30 volts on a vehicle that has a 12 volt system everything works fine . . . except those pesky ultra high and damaging volts don’t have to pass through the pump points . . . they get dumped by the device when the circuit reaches about 30 volts!
Now for some more good news!
The TSVs are SO CHEAP. Here in NZ I bought 2 for $9.00 (including GST). The tails on the device are just the right length to be curled around to make a terminal under the appropriate screws and the pump’s Bakelite cap still fits on without any trouble.
What you ask for at JayCars Electronics is Catalogue # ZR1177.
Another number is Fairchild 1.5KE24CA if you want to try different source.
For those overseas a big outfit like Radio Spares have them too. Here’s the NZ link to the specifications.
http://newzealand.rs-online.com/web/sea ... &R=5438450
PLEASE NOTE: I HAVE JUST FITTED THIS MODIFICATION to my Jupiter, It may not last! If it does then fine, but I am going to carry a spare pump anyway . . . . . Why, someone else may need a working pump!
Cheers.
Leo.
