Calibrating a S2 fuel gauge.

PostPost by: 661 » Sat Jun 22, 2019 4:16 pm

I'm having a racing tank made by ATL.
They can supply a sender which does what the S2 sender does, ie for gauge FG2530/71, sender is 0 ohms empty and 90 ohms full.
I'd like to test the gauge to see that it does move correctly for any given sender resistance.

Firstly, how do I wire a positive earth gauge to a negative earth battery as my new loom will be negative earth?

Secondly, what do I need to test it? I have a battery , and an electronic 10V stabiliser. Do I just purchase some (hopefully accurate) resisters from an electronics shop of various Ohms?

Thank you.
Graeme
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PostPost by: Craven » Sat Jun 22, 2019 7:51 pm

Take a look at this, gauge not polarity sensitive pos neg makes no difference. And is NOT voltage sensitive will work with a 12v battery.
https://mgaguru.com/mgtech/electric/fg_10.htm
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PostPost by: Andy8421 » Sun Jun 23, 2019 7:06 am

Smiths produced two types of gauge, one relied on a bimetallic element to the move the needle and was fitted to later cars, the other used an electromagnet to move the needle and was fitted to early cars.

They are easy to distinguish - when the ignition is switched on, the bimetallic unit needle moves slowly from empty to the correct point, the magnetic unit needle flicks to the correct position immediately.

The magnetic model compensated for varying battery voltage internally using two electromagnets, the bimetallic unit used an external voltage stabiliser.

The S2 wiring diagram I found has the early type of gauge, in which case you don't need the stabiliser. You need to have the right sender, gauge (and maybe a stabiliser if using a later gauge) for the combination to work.

After that, you can check the gauge using resistors as shown in the article linked to above - but be aware that the resistance on some sender / gauge combinations is not linear which is to compensate for the response of the gauge. In other words, half full isn't necessarily half resistance. Others may know if this is the case for the Elan.
68 Elan S3 HSCC Roadsports spec
71 Elan Sprint (being restored)
32 Standard 12
Various modern stuff
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PostPost by: 661 » Sun Jun 23, 2019 8:23 am

Thank you both.
The gauge is the early one, FG2530/71.
I was unaware that this had its own voltage stabiliser. I will attach it straight to 12V and see what happens.
I assume it will , as you suggest, compensate for the varying voltages in a 12V system, ie 12.5- 14.5V (-ish).
I'll immerse myself in the linked article

Thanks again.
Graeme
S4 SE
S2 GTS
Caterham 420R
Sold - Peterson JPS Exige
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