Sorry Fuel Baffle Story

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Lake Sailor

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My fuel gauge has been acting up for some time, so while the motor's out of the boat, I thought I'll just fix it.

Floats are a common problem, right? So I check mine, magnets are all on it, floats in gasoline. Not it :(

Multimeter shows open circuit at the plug. Aha, I says its the old F1 fuse, which I now know about all about from this forum. So I cut into the baffle at what I judge to be the right place:



Surpise! No fuse there. So, I cut another window at the solder lugs:



Now here, the board checks good but still OC at the plug. Turns out, it is OC between that nail thru the pink wire and the solder lug. Can I get to that? Maybe I can dig out what looks to be the potting:



Well, turns out that the thing is made in some kinda multi-step molding process, and this "potting" is about as hard as a rock, or anyway the rest of the baffle :banghead:



At this point, I judge it to be non-repairable. But I continue the forensics, just for the entertainement value. So I saw the whole top off the thing and extract the board intact.



Notice the F1 fuse is located about exactly where the sealing lip or whatever you call it is. Seems to me this would make for a difficult repair by the cut-a-window and plastic weld method. I suggest another repair method for the truly ambitious:

First, saw the whole top off as shown. Second, fix the board as needed. Third, counter drill the two fuel passages in each sawed half,



and insert some stainless tubing or something, with some gas-proof sealer. Fourth re-assemble the baffle, maybe plastic welding the joint. Said completed joint is underneath the rubber boot which attaches the baffle to the tank and is completely invisible without removing the boot. Cool huh? Lemme know how it turns out :)

So, hows this thing work in the first place? Well the board is a circuit with a bunch of resistors (the short things) along it in what I would say is a series circuit:



And what appear to be a number of magnetic switches (the long things).



As the float travels from the bottom (empty) to the top (full) it apparently closes the switches, shortens the circuit, and decreases the circuit total resistance. You can pass any kind of magnet along the board and watch the resistance change. So there. BTW, many books are written about what I don't know about electronics. So there, again.

Interesting excercise, yes, but by now this baffle is REALLY not repairable. Given the way it went bad, I didn't feel good about a used one. Lucky to find a NOS at a decent price. All's well that ends well :)
 
Yea, when it comes to sitting on top of 15 gallons of fuel, I don't take the time or hassle. Just buy the baffle new and it will work another 10 years.
 
WOW! That is an autopsy of a fuel sending unit! I just found one NOS on the bay for $130 and replaced mine as well... I had the bad fueld float last year and replaced the float. Had the short this year and decided not to try to fix it and just replace the entire unit. I almost cut my old one open as you did but decided to toss it. Glad you did this to yours so now I can see what the guts look like up close! THANKS for the pics!
 
Its really not rocket science and a repaired one is much more dependable than a used one.

There is no voltage on the circuit, it just changes the ohms, or resistance.

I do sell repaired ones ready to rip for guys not interested in doing it themselves.
 
I agree, very nice autopsy job, I think you've presented an excellent understanding of how the thing works and is constructed. Imagine the consequences if one of those magnetic reed switches was to stick or not close, the reading would be off. So yeah, it's not just the fuse blowing (so bizarre to place a fuse on a fuel sending unit, what's this world coming to?) or the magnets falling through the screen and into the tank as an empty ski bounces down the road on it's trailer, the terminal connections can loosen as well! :O

I was fortunate, mine had a blown fuse and it was soldered on the trace side of the PCB near the top there. I bridged the fuse with some solder, using my 40 watt weller iron and didn't bother closing the window back up b/c I don't think a boat needs that particular feature provided by this design b/c there is much less fuel slosh. :)
 
Yeah, just trying to add a bit to the body of knowledge :)

[MENTION=2932]sportster[/MENTION], yeah fuses are traditionally placed somewhere ACCESSIBLE. Not this one :cuss:

Minnetonka, repaired how?
 
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Its on the right side...its a micro fuse. Just heat it up and knock it off, put a glob of solder in its place.

The reason the fuse is there is in case you hooked it up to power wires somehow; if you are worried about that add a 1/4a glass fuse and a waterproof fuseholder to the wire on the outside...the way it should have been built.
 
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