[T2] Gas gage weirdness

[Robert Mann]

   A couple y ago we had a vague inconclusive discussion of another part
shown in your Bentley schematic connected to the fuel guage,* viz*. the
'vibrator'.  I gained no understanding of this device, except that its
function has to do with damping unwanted oscillations on the guage.  For
all I know, if this enigmatic component goes wrong, the results may be
those which you've been observing.

Robt Mann
'73 1600dp Devon camper



On Fri, Feb 22, 2019 at 1:44 PM c.dreike <c.dreike at verizon.net> wrote:

> Started testing my gas gage and sender. The sender worked when I
> installed it. Currently the tank is very low and the sender reads about
> 80 ohms. According to The Samba this is about correct. The senders run
> from about 3-5 ohms at full to about 70-80 ohms at empty.
>
> When connected, both of the gauges I have read full and a little past.
> The battery voltage is about 11.98. The voltage across the gauges are
> 6.57 on the original gauge and 7.98 on the reproduction gauge.
>
> On the test bench connected to a bench supply, the original gauge reads
> full at about 6.5V and the reproduction gauge reads full at about 7.2V.
> As I reduce the voltage to the gauge, the reading goes down. At 0 volts
> the gauges read empty.
>
> Per the test specs in Bentley, the gauges should read full at about 12V,
> battery voltage. Both my gauges peg when attached to full battery voltage.
>
> I have double checked the wiring against the schematics and all looks
> correct. The circuit looks simple enough. +12V on one side of the gauge.
> The other side of the gauge connects to the sender (5-80 ohms) and the
> other side of the sender connects to ground.
>
> I'm an electrical engineer with lots of experience with simple stuff
> like this and this stuff makes no sense to me. I must be missing
> something. (Kinda like mistaking the wire stripe colors on the turn signal)
> Anyone have ideas on what I should be looking for or doing differently?
> I'm stumped. I'm about to build an inverting operational amplifier
> circuit that would drive the gauge so that it would see 0 volts at empty
> and about 7V at full.
>
> TIA
> Chris
> 71 Sunroof
> 64DD Kamper Kit
> _______________________________________________
> type2 mailing list
> type2 at type2.com
> https://www.type2.com/lists/type2/listinfo