Random wiring turns out to be a fuel sender

Duncan_Hill · 2024-06-09 22:03:54

Blue Opal's documentation indicates that she has a pneumatic/air pressure based setup (Tank Tender) for measuring tank levels - water, waste, and diesel. The waste one rusted, and has been pulled out; some day I'll replace it. The water one works just fine, though it only monitors one tank and Blue Opal had two (had being the operative word; I pulled out the bag-style one, and it was ... ugh, yeah, no not going back in.

However, when I was looking at the top of the fuel tank the other day, it finally twigged that there were three wires coming off of the top of the Vetus plate, and I had no idea what they were or where they went. This weekend, while everyone else in Dun Laoghaire was off participating in a local regatta, K and I investigated that wire. It required that K went down the hole (the port locker), and I contorted myself into the top of the starboard locker to tug on the wiring until K could see what moved. The wiring ran down the side of the tank (behind the plywood), under the tank, through the cutout below the tanks into behind the engine, up the starboard bulkhead by the exhaust, and vanished into the cubby above the engine. This cubby has the wiring for the Yanmar panel, the Tank Tender's hoses, my bodged-in hour meter for the engine, the 12V cigarette socket, the Webasto heating controls, and the cold plate controls for the galley cold box. Oh, and two fuses that I don't remember installing, so I need to check my notes (they're the right style that I would have installed them). So not too many wires...

After a bit of tracing, cutting of zip ties, and so forth, we proved (with a long lead and a multimeter) that there was indeed a pair of terminals on the end of a flat black cable that went all the way back to the top of the tank.. but connected to nothing. Well, the ground/black was connected, but the red was just hanging out in mid-air. There's no fuel gauge in that space at all, just the Tank Tender.

Decided to pull the sender out, and investigate it (photo to follow later). It's a simple mechanical one, and it's broken. Plopped the multimeter into resistance mode, and no matter where the arm was the resistance was consistent (so I can't even tell if it was a Euro standard 0 - 190 ohm, or American 230 - 33 ohm). Have concluded thusly that the sender is borked, and it'll have to be replaced if I want to have any kind of electronic monitoring (or hooking up to the boat bus some day). Wema seem to be a reasonable brand, though if anyone has evidence otherwise I'd be happy to hear it.

Anyway, that's one more set of wiring documented. Random wires are.. interesting.

Duncan_Hill · 2024-06-10 07:19:07

Osculati sender
This is what I found in Blue Opal's diesel tank. Looking around, it looks very much like an Osculati 27.160.00

Could be some other brand, but it certainly looks right.

A bit of corrosion. However, not what I'd expect to cause the resistance change to not work.

I could try cleaning it up, but I'm of a mind to get something like a reed-switch sender instead.

Charles_Grossie · 2024-06-10 08:59:02

That's very interesting Duncan. Another one of the jobs I have yet to tackle, as my fuel gauge/sender arrangement doesn't work either, but the connections appear to be there (but untested as yet).
It would be good to know what brand/model of a replacement sender is suitable too.

Duncan_Hill · 2024-07-06 07:25:02

I ended up purchasing and installing a Wema S5 fuel/water sender, with associated gauge calibrated to the European resistance specification. No problems installing it at all, the pair of red/black wires from the existing installation could be reused (the ground isn't needed, but could be left attached to the tank anyway). In my case, I went for a unit that's slightly shorter than the tank is deep, so it'll read empty before the tank is actually empty. I estimate I'll have 6 litres of fuel left when it reads empty, but at that point it's ~2 cm of fuel in the bottom of the tanks, and the pickup has a good chance of picking up air if it's rough. Been there, done that, have the "I had to be towed by the RNLI" t-shirt.

The only pain is someone replaced two of the M5 machine screws with M6, and I'll need to ream out the new fitting's holes to suit - it won't clamp against the seal fully if I don't do this (because of course they're both on the same side of the fitting). M5s just rattle in the fixture point and don't grip the threads.

Last edited by Duncan_Hill (2024-07-06 07:25:57)

Duncan_Hill · 2024-07-06 17:57:30

https://www.cricalix.net/2024/07/06/fuel-senders/ has more photos, including the lit gauge - it can light with red or orange, or not at all. Wired it in using wago connectors, as I have one in the cubby to make a small positive bus.

#1 2024-06-09 22:03:54

Random wiring turns out to be a fuel sender

#2 2024-06-10 07:19:07

Re: Random wiring turns out to be a fuel sender

#3 2024-06-10 08:59:02

Re: Random wiring turns out to be a fuel sender

#4 2024-07-06 07:25:02

Re: Random wiring turns out to be a fuel sender

#5 2024-07-06 17:57:30

Re: Random wiring turns out to be a fuel sender

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