[Geezer (OP)]

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Anybody care to hazard a guess as to what this is for, and what it came out of? I'd never seen anything like it until now.

[RD]

The things on side-A look like reed switches, (whose connections are opened or closed when a strong-ish magnet is brought close), the components on side-B look like resistors.

I've never seen anthing like that, but an array of reed switches could be used to sense the position of something, if it had a magnet attached. It would have the advantage over a potentiometer-type position sensor that there would be essentially no wear* on the sensor (no friction). The disadvantage would be the position information would be quantized rather than continuously variable: the reed switches are either on or off. 

[* Worn potentiometers are electrically noisy and could be a source of (position) measurement error, and maybe even sparks: (reed switches are hermetcally sealed, a spark at the contacts of a reed switch could not ignite any flammable gas/vapour present ]

[RD]

Eureka ! ...

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http://www.meder.co.uk

[Geezer (OP)]

Yeah! Dead right RD. It's actually the fuel gauge sender for a motor boat.

This particular one is set up as a resistor with ten possible values that feeds a gauge on the dashboard. It goes inside a sealed tube that is inserted into the top of the tank. A float containing a magnet surrounds the tube.

It's been acting up since it got some water in it, so I'm going to replace all the reed switches.

[CliffordK]

Oh,

I thought you were asking about the Lincoln Head Penny....  And I had absolutely no idea what it would be used for!!!

[RD]

It's been acting up since it got some water in it, so I'm going to replace all the reed switches.

IMO I would look for a poor connection first before replacing anything, e.g. look for corroded wire or a “dry” solder joint.

I would not replace the reed switches unless I found a faulty one, not just because I’m a cheapskate but because they are matched to the strength of the magnet, replacements may have a different threshold.

[SeanB]

Would be better to get a new one, and make sure it is waterproof. The traces on the board and the resistors themselves are corroded as well, and if you replace the reed switches ( easy enough, though they are going to be expensive in small numbers) you will run into problems later when the board finishes corroding through tracks and the resistors go intermittent.

[Geezer (OP)]

I've no idea who manufactured it, and the place where I bought the boat closed last year. As "hawkeye" has observed, somebody (me) replaced one of the reeds on a previous occasion with one that he salvaged from an old keyboard switch - hence the unusual "extension" on one of the switches.

The reeds are on order already, so we'll see how it goes. They seem to be pretty average (cheapo) variety reeds. I'm sure they will cost a lot less than a replacement unit - even if I could find one.

[SeanB]

You should be able to find the probe from an online supplier, or Ebay, if you have a part number for either the transmitter or the indicator. Funny thing about reed switches is that they pretty much are close in required operate and release ampere turns if you look at units that are the same size, the only variations occur if you use bigger or smaller units, or ones that are designed for high voltage or high current use.

just note that a lot of these are mercury wetted units, easy to see from the contact surfaces being silver coloured, mercury free units use gold flashed contacts.

[Geezer (OP)]

There are similar senders on the market, but I suspect this one is some ersatz equivalent. I've never seen one quite like it, and I suspect the outfit that made it went TU some time ago (based on the quality of this one, I'd be amazed if they are still in business.)

I could upgrade to something a bit more substantial, but that would probably entail some serious changes to the port on the fuel tank, and that could turn into a major PITA. The fuel gauge on a small boat like mine is a bit of a joke anyway. It provides a vague indication of the presence or absence of fuel when the boat is stationary in a flat calm with no crew on board. The rest of the time it bounces around all over the place and is seriously affected by the attitude of the hull.

The good news is that if it's bouncing, there is fuel in the tank. When it stops bouncing there is no fuel in the tank, but that condition is usually detected by other means. It's always best to take along a can with a few gallons of "reserve".

Edit: I think this one might actually be compatible. If my repair job does not work, I might have to get one of these.

http://www.wemausa.com/tank_sensors/details_SSS_SSL_tank_sensors.htm

[SeanB]

Should work, and probably will give a more stable reading.

[Geezer (OP)]

I put in the new reed switches and sealed the whole thing up with RTV (silicone rubber). Seems to work fine. Hopefully lasts a long time!