I have to agree with Ulix. If neither one of the poles is marked, then it
would almost have to be an ammeter type gauge. One way to check for sure
whether it will fry your sender is to use a meter before hooking it up to
your sender to check the current flowing out with the wires first attached
one way, then reversed. If no change in current, then you can reverse them
and your gauge will register properly without frying the sender.
Bob
-----Original Message-----
From: Ulix Goettsch <ulix@u.washington.edu>
To: Larry Miller <millerls@ado13.com>
Cc: spridgets list <spridgets@autox.team.net>
Date: Tuesday, June 29, 1999 12:20 PM
Subject: Re: Fuel gauge polarity?....Old Dog, New Tricks
>Larry,
>wouldn't that suggest that your new gauge is an "ammeter type" as Bob
>mentions?
>Ulix
>
>On Tue, 29 Jun 1999, Larry Miller wrote:
>
>> This is all well and good, but, based on all of this, can someone explain
>> why my gas gauge works backwards? I just assumed it was hooked up
backwards
>> and have not bothered to swap the wires. Now I'm afraid to swap them.
>>
>> The gauge is a new Smith's gauge and the connections are not marked "T"
and
>> "B". They have no markings at all.
>>
>> Larry Miller
>> http://www.ado13.com
>> "If you want a Sprite, start out by asking your wife for a Porsche."
>>
>>
>>
>>
>>
>>
>> ----- Original Message -----
>> From: Wiedemeyer <boxweed@thebest.net>
>> To: Pete <pete@the-mix.com>
>> Cc: spridgets list <spridgets@autox.team.net>
>> Sent: Tuesday, June 29, 1999 7:31 AM
>> Subject: Re: Fuel gauge polarity?....Old Dog, New Tricks
>>
>>
>> > Frank and Pete,
>> >
>> > After reading about your experience with frying the sender unit after
>> > reversing the wires on the fuel gauge, I just had to find out why this
>> > happens. I had mistakenly believed that the fuel gauge was a simple
>> ammeter
>> > parallel type arrangement where the needle draws a very tiny amount of
>> > current for deflection while the bulk of the current is shunted through
>> from
>> > one pole (B) to the other pole (T). If this were the case, reversing
the
>> > wires would cause the needle to deflect in the opposite direction, but
>> would
>> > not result in more current going through to the tank. After looking up
>> how
>> > a fuel gauge actually works, (in Automotive Encyclopedia by Toboldt,
>> > Johnson, and Gauthier -- $48.50 and worth every penny) I now see why
>> > reversing the wires will burn out the sender unit: The fuel gauge is a
>> > "thermostatic gauge", which has a very large resistance in series
between
>> > the B and T poles. This reduces the current that ultimately gets to
the
>> > sending unit. If the wires are reversed, the large resistance is
bypassed
>> > and much more current goes directly from the battery to the sending
unit,
>> > which fries it. The idea behind the thermostatic gauge seems
ingenious
>> to
>> > me because it uses the heat accummulated in the resistor to warm up the
>> > bi-metal fuel gauge needle, which causes it to move when the ignition
is
>> > turned on. There's never any current "felt" by the needle, which would
>> > explain why the fuel gauge itself almost never fails. I guess it's
never
>> > too late to learn something new.
>> >
>> > Thanks,
>> > Bob
>> > -----Original Message-----
>> > From: Pete <pete@the-mix.com>
>> > To: Frank Clarici <spritenut@Exit109.com>; Wiedemeyer
>> <boxweed@thebest.net>
>> > Cc: Doug Ingram <dougi@home.com>; spridgets list
>> <spridgets@autox.team.net>
>> > Date: Tuesday, June 29, 1999 9:56 AM
>> > Subject: Re: Fuel gauge polarity?
>> >
>> >
>> > >
>> > >>> Yeah. Just reverse the wires when attaching them to the gauge.
>> > >>>
>> > >>
>> > >>Doug
>> > >>
>> > >>Yes it will work but DO NOT REVERSE THE WIRES!!!!
>> > >
>> > >>If you flip the wires on the gauge you send 12 volts to the sender
which
>> > >>is grounded + connected to - = smoke!
>> > >
>> > >I can vouch for that.
>> > >Reversing the wires would be like putting the battery in backwards
(yes,
>> > >I did that)
>> > >and frying your negative earth tach instantly (yes I did that)
>> > >
>> > >I am learning a ton though.
>> > >
>> > >Pete
>> >
>> >
>>
>
> Ulix __/__,__ ___/__|__
>..............................................(_o____o_)....<_O_____O_/...
>http://students.washington.edu/~ulix/ '67 Sprite '74 X1/9
|