Fuel gauge safety

[BogMonster]

I had an intermittent problem with the fuel gauge in my RIB and what I discovered this morning worried me a bit, just after any thoughts.

I thought it was connections on the top but it turned out to be a bad connection (slightly loose) where the sender unit was bolted through the metal plate that it is mounted in - the effect being that the metal chassis that provides the earth path to the actual sender bit, wasn't making a good contact so when you wiggled the connection on top, sometimes the gauge would work and sometimes not. Tightened it up and all ok.

Is this dangerous i.e. could it have created a spark, or is the resistance of the fuel gauge so high that there is no chance of this happening? The whole sender unit is a bit mickey mouse with one thin wire going down to the potentiometer thing at the bottom. I suppose they are designed to be inherently safe if they are for immersion in petrol, what does anybody else think?

[jyasaki]

Well, the gauge is powered by 12V, which has the capacity to spark, but I would doubt that, as long as the power lead itself doesn't short to ground, that you would get anything close to what's needed to spark.

Looks like the standard is 240 to 30 ohms (or thereabouts), so the full scale current range is 50mA to 400mA.

Now that I think about it, I'm not sure how the gauge is normally wired. 12V to gauge to sender to ground would make sense (and give you a bit more resistance in the event that the power feed to the gauge did short), but I don't know.

jky