Fuel Gauge conversion to negative earth.

D

David Chapman

Guest
OK, I know it's taken a while but I finally sat down tonight and documented
exactly how to rewire the fuel gauge. It's the only tricky part of the
conversion to negative earth.

The negative earth conversion is documented in the archives along with the
reasons to do it, and the fuel gauge conversion, with pictures ! Is now here
http://www.amphicars.com/fuel.htm

David Chapman
 
J

jfriese

Guest
Hello David,
Just last week I decided to tear into a couple of spare fuel gauges,
that I had, to try switch the internal polarity of the gauge. I had
never played with actual meter movements before but I owned an
electronic repair business for 30 years and have repaired camcorders
for the last 10 years so I figured I'd give it a try.
Having no clear idea of the way this particular gauge works, I brought
along a sending unit from one of my cars and went at it. My
particular sending unit measured, on a very accurate meter, 183.6 ohms
with a full tank and 2.3 ohms at empty. I found that the brass posts,
inside the meter, that you have to solder to are set in plastic and
care should be taken to either work very fast with the proper size
iron or use some sort of heat sink clamp to avoid deforming the
plastic. I also found that, after the conversion, the gauge did not
always (I've done 4 of them in the last week) read exactly accurately
either at the full position or empty position and sometimes both. I
noticed that the coils were made to be shifted around the center for
calibration and they were "locked" with a bit of paint. I broke the
paint loose and, from what I could determine, the upper coil
established the "full" end position and the lower coil, the "empty"
end position. By shuffling these coils around, I could make the gauges
work quite accurately. The little brass adjustment piece, that you
mentioned, has a tiny magnet on it and pulls the meter to the bottom
stop when the power is off. Without it, the needle would simply
float. It also acts as a bias for the meter at the low end and acts
as a fine tuning adjustment for the zero position but without shifting
the coils, I couldn't count on it having enough effect to make the
meter work accurately. Moving it also affected the "full" position of
the gauge.
Figuring out these things allowed me to get all 4 gauges to accurately
track with my sending unit. I have to wonder how much variation there
is in sending units and how much it would affect the overall accuracy
of the system. I suspect not much, since I'm sure the sending units
were not paired with the gauges during production.
I hope these findings help our understanding of this modification. I
found doing this modification to be a rather delicate procedure and
wouldn't suggest it to people not familiar with soldering and working
with delicate structures.

John Friese

P.S. Your reasons for converting to negative ground are exactly why I
decided to do it too.


--- In amphicar-lovers@y..., "David Chapman" <davidc@a...> wrote:
> OK, I know it's taken a while but I finally sat down tonight and
documented
> exactly how to rewire the fuel gauge. It's the only tricky part of
the
> conversion to negative earth.
>
> The negative earth conversion is documented in the archives along
with the
> reasons to do it, and the fuel gauge conversion, with pictures ! Is
now here
> http://www.amphicars.com/fuel.htm
>
> David Chapman
 
D

David Chapman

Guest
Re: Re: Fuel Gauge conversion to negative earth.

Thanks John, those are good points. I was impressed with the quality and
accuracy of the gauge, much better than the Lucas stuff I have seen !

As someone has mentioned before these parts were made by Moto Meter for Amphicar
and could well be common to VW and other German cars of the period.

I used a decade resistance box with steps from 0 - 200 ohm in place of the
sender and the pointer position appeared to be correct at all steps after
conversion so I don't think it's necessary to move the position of the coils but
who knows and some of the gauges may be different.

I'll add those comments into the web page, and yes you need a small soldering
iron (no more than 15 watts) good light and a steady hand !

David Chapman

----- Original Message -----
From: "jfriese" <jfriese@mindspring.com>
To: <amphicar-lovers@yahoogroups.com>
Sent: Sunday, January 20, 2002 10:19 AM
Subject: [amphicar-lovers] Re: Fuel Gauge conversion to negative earth.


Hello David,
Just last week I decided to tear into a couple of spare fuel gauges,
that I had, to try switch the internal polarity of the gauge. I had
never played with actual meter movements before but I owned an
electronic repair business for 30 years and have repaired camcorders
for the last 10 years so I figured I'd give it a try.
Having no clear idea of the way this particular gauge works, I brought
along a sending unit from one of my cars and went at it. My
particular sending unit measured, on a very accurate meter, 183.6 ohms
with a full tank and 2.3 ohms at empty. I found that the brass posts,
inside the meter, that you have to solder to are set in plastic and
care should be taken to either work very fast with the proper size
iron or use some sort of heat sink clamp to avoid deforming the
plastic. I also found that, after the conversion, the gauge did not
always (I've done 4 of them in the last week) read exactly accurately
either at the full position or empty position and sometimes both. I
noticed that the coils were made to be shifted around the center for
calibration and they were "locked" with a bit of paint. I broke the
paint loose and, from what I could determine, the upper coil
established the "full" end position and the lower coil, the "empty"
end position. By shuffling these coils around, I could make the gauges
work quite accurately. The little brass adjustment piece, that you
mentioned, has a tiny magnet on it and pulls the meter to the bottom
stop when the power is off. Without it, the needle would simply
float. It also acts as a bias for the meter at the low end and acts
as a fine tuning adjustment for the zero position but without shifting
the coils, I couldn't count on it having enough effect to make the
meter work accurately. Moving it also affected the "full" position of
the gauge.
Figuring out these things allowed me to get all 4 gauges to accurately
track with my sending unit. I have to wonder how much variation there
is in sending units and how much it would affect the overall accuracy
of the system. I suspect not much, since I'm sure the sending units
were not paired with the gauges during production.
I hope these findings help our understanding of this modification. I
found doing this modification to be a rather delicate procedure and
wouldn't suggest it to people not familiar with soldering and working
with delicate structures.

John Friese

P.S. Your reasons for converting to negative ground are exactly why I
decided to do it too.


--- In amphicar-lovers@y..., "David Chapman" <davidc@a...> wrote:
> OK, I know it's taken a while but I finally sat down tonight and
documented
> exactly how to rewire the fuel gauge. It's the only tricky part of
the
> conversion to negative earth.
>
> The negative earth conversion is documented in the archives along
with the
> reasons to do it, and the fuel gauge conversion, with pictures ! Is
now here
> http://www.amphicars.com/fuel.htm
>
> David Chapman


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Jon, If you are changing to neg gnd. you probably will be using the GM alternator. Easy to install, reliable and lasts forever! Tony O. in NH makes a nice bracket for installing it. John is the guy for the gauge conversion. I had him do 3 of them for me. They all worked great. I also recommend Johns clutch retrofit and his cork seal for the fuel petcock if he has any left! The gear reduction starter motor is a nice improvement also. More reliable than the Lucas! Waiting, or dreaming for a front disc brake kit. Jack
 
Last edited:

Jon March

Member
Thanks Jack! Agree! In fact I have a gear reduction starter, alternator, dual circuit braking, Johns clutch, and his fuel gauge mod/calibration..and a few other tasty treats he has helped me greatly with. Screen shot 2018-03-13 at 11.17.07 PM.png
 

mike_israel

Amphicar Forum Admin
Staff member
I'm feeling old. This thread started more than 15 years ago when we were still on Yahoo groups. That said, +1 for John's clutch kits and gauges.
 
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