> -----Original Message-----
> From: Steve Laifman [SMTP:laifman@flash.net]
> Sent: Friday, February 19, 1999 9:19 AM
> To: Theo Smit
> Cc: 'tigers@autox.team.net'
> Subject: Re: Fuel Pump over Muffler
>
>
>
> Theo Smit wrote:
>
> > A good rule of thumb on tantalum caps is 5x the working voltage. So, at
> least 60
> > V rating, and preferably more, since you're dumping all of the solenoid's
> > current into it.
>
> Thanks for the 'ratings multiplier'. Do you have any Idea how BIG a 60V
> Tantalum
> is. As I recall, they are pretty small fro their capacity and rating (and
> expensive, relatively).
>
[] I just did a little check in the lab; a 2.2 uF, 50V tantalum is less
than 1/4 in. on a side in the surface mount package. Since the size is
proportional to the capacitance and the voltage, a 0.5 uF, 100V shouldn't be
larger than that, if you can find them. A mica cap should work as well, and you
can get those in higher voltage ratings, and they won't be too much larger.
> > I haven't looked into the pump electrics at all, but doesn't it have some
> kind
> > of pressure shutoff in it? When I turn on the ignition, it clicks for a few
> > seconds and then stops. When the car is running, I assume the pump is
> pumping
> > but I can't hear how often it clicks over the engine noise.
>
> Slowly at idle, after filling the bowl rapidly in the morning, and very fast
> at
> speed.
>
> Yes, that is exactly how it works, but nothing very complex. When the pump
> feels a
> back pressure from the carburetor needle valve inlet, it stops. When the carb
> float sinks, opening the valve, the pressure drops and the pump fills up the
> bowl
> again. I believe this is just a simple spring loaded contact. Remember, this
> is
> OLD technology that has stood the test of years of service and British
> complacency
> with things electric, and veneration of traditional values. Similar SU pumps
> were
> used in pre-war British cars, and I'm not saying which war. {9->
>
[] I'll have to dig into mine one of these days and see if there's
something simple that can be done. One thing that is relatively easy is to use
the points to drive a transistor, which then actuates the solenoid. That way
there's no arcing, since the solenoid load dump is absorbed by the transistor
(which needs to be up to the task, but that's not hard to arrange).
Theo Smit
tsmit@novatel.ca
B382002705
> --
> Steve Laifman < One first kiss, >
> B9472289 < one first love, and >
> < one first win, is all >
> < you get in this life. >
>
>
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