At 08:50 PM 4/26/97 +0800, you wrote:
>valve which would pass current in one direction, but not the reverse. He
did not
>have a clue how this would keep the contact points from burning. Can someone
>explain to me, IN VERY SIMPLE TERMS, how this works? What size (rating, or
>whatever) diode do I need to buy, and exactly where do I solder it on my fuel
>pump's contacts?
>
Very simple terms, hmmmmm.
The fuel pumps guts are an electromagnet; a coil of wire and an lump of
iron. By the nature of the beast a current passing through a coil will
attempt to maintain flow due to the collapsing field when the voltage is
turned off (the points open). This is what cause points to burn. As they
open the current attempts to jump the gap and arcing and burning is the
result. The current jumping the points is in the opposite direction of the
magnetizing current. A diode works by providing a path for this reverse
current through the diode and coil instead of across the points. The diode
is placed directly across the coil. When the coil is energized the diode
blocks current so all the available current goes through the coil. When the
points open the INDUCED current( backwards) can chase it's tail round and
round through the coil and the diode till it's dissipated.
The diode size should be based on a minimum of the rated current of the
coil. I don't have a clue right now what that should be but it's not hard to
figure out, I'm guessing somewhere around 3 - 5 amps. Connecting the diode
should be easy too but it depends on the cars polarity. If you get it wrong
you'll pop the fuel pumps fuse as soon as you turn on the ignition. Cheesey
ASCII art follows, It's just to give you an idea. It's NOT to be followed
for installation!
coil points
(+)--+----mmmmm---+-------|/|-----------(-)
| |
+-------- |< --------+
(-) diode (+)
As for your NRS not knowing how this works, I'm not surprised. In my
experience anything more technical than "Where're your batteries?" will
stump most of them.
Cheers,
___ \______ Ross MacPherson
/ __ \ __ / /------|) arm@unix.infoserve.net
/ (___)---------/ (___) Vancouver, BC, Canada
1947 MG-TC 3528 1966 MGB-GT
|