[Diy_efi] Re: Looking for circuit to turn transfer pump off at certain voltages

[Bevan Weiss]

----- Original Message -----
From: "Toyota Supra" <turbosupramk3 at hotmail.com>
To: <diy_efi at diy-efi.org>
Sent: Sunday, November 10, 2002 4:02 PM
Subject: Re: [Diy_efi] Re: Looking for circuit to turn transfer pump off at
certain voltages


> hey bevan, thanks for the reply, maybe this will help clarify ...
>
>
> here are the specifics, my gas tank is a saddle tank, meaning that it has
> two sides to it like saddle bags on a horse. now the pumps are on the left
> side, and the mechanical venturi valve that used to transfer the fuel from
> the right side, had to be removed.
>
> so my dilema is, how do i get fuel from the right side of the tank, to the
> left side where the fuel pumps sit, so that i am not driving around on
only
> a 1/2 tank of usable gas, even though the entire tank is full?
>
> well, my design thought was to have a transfer pump intank, that drew from
> the right side, to the left side, at all times that the car was on, except
> for when the right side of the tank got low on fuel. this is because the
> fuel acts as a lubricant to the transfer pump, and if it ran dry for any
> period, it would probably burn up.
>
> so the way i decided to control the transfer pump was to use the existing
> sending unit that is in the right side of the tank (which reads 0 to 3.5v,
> full being 0v - bone dry being 3.5V) and use that sending units output as
a
> reference signal for the circuit, and having that circuit turn a relay off
> (or on) to control the power to the transfer pump.
>
> i appologize if this reads confusing and that it is so long, but i wanted
to
> be as detailed as possible. if you think your circuit design would work,
i'd
> be very grateful if i could have a copy of it. thank you for the reply

Hmm, so you can't just have a tube connecting the two saddle-tanks together
at their lowest point (to distribute the fuel evenly over both tanks), this
would certainly be the easiest way to let the pump see two tanks.  I realise
that having the tanks connected in a more vertical manner would be a better
solution but it may not be worth the trouble.

I can't think of an optimum way of doing this (easily), as even a comparator
type circuit isn't what you really want, it would mean that the pump is on
when the tank is near full and off when the tank is getting empty, which
isn't an optimum idea, you wouldn't be able to use all the fuel this way....

I think perhaps that looking outside the usage of a pump is required... (or
perhaps a non standard type of usage).

I have no real ideas about this kind of stuff, only the electronics and
that's not the ideal solution to this one.

FWIW, the comparator circuit that I was refering to was a simple opamp (ie
741), with a VREF on the non-inverting input that is the switching point of
your fuel tank, and have the inverting input connected to the actual fuel
sensor itself (after sufficient low pass filtering).  Then you can add in
some hysteresis if required/desired simply by applying some feedback to the
circuit ( a resistor/voltage divider from the output back to the
non-inverting input).

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