Log transducer cable replacement

[Fergus]

The cable on mine has a join in it which is now corroded to the point of non-functioning. My sparks guy says it's best to replace the the transducer completely as they come with sealed cable attached and that recabling the existing one is less than ideal - sounds like BS? It's a paddle wheel variant..

 

[Norman_E]

I have exactly the same problem. The darn thing has ordinary copper wire, not tinned, so it was built to fail. If anyone has replaced the wire I would love to know how.

 

[Evadne]

It's only carrying a low voltage signal so if you can strip it back to good metal, as opposed to black and crumbly copper then you can join the wires. If you use a crimp joint on each conductor, then coat each conductor with Scotchkote, let it dry and wrap with self-amalgamating tape covered with PVC tape to protect it, then you will have a watertight join that is at least as good as the original. Crimp joints, properly made, are less prone to fatigue failure than soldered joints, but it's not a big deal for something like this.

 

[bedouin]

I've certainly extended mine - I do this using solder connections, each insulated with adhesive heatshrink, with an additional layer of adhesive heatshrink covering the whole.

I would expect a little signal degradation with that approach but nothing that would matter for a log transducer

 

[Norman_E]

The problem with mine is that the copper is almost black. I have (just) managed to get a good connection, but I discovered that the more I cut the cable back towards the transducer, the worse it became. If the joint fails again it looks as if the only options will be a new transducer, or cut the old one open to solder in new wires made of tinned copper. I enquire whether anyone has done that, and am annoyed that the manufacturers do not use the correct cable in the first place.

 

[bedouin]

The copper oxide does not affect the ability of the conductor to pass current - just your ability to make good connections - so if the conductor is sealed in then it should not be too much of an issue.

It is possible to clean up oxidized copper to make a good connection using either brasso type cleaners or wire wool/emery paper

 

[jonathankent]

Fergus / Norman_E.... without being offensive, I suppose this is why they say not to cut/shorten the cables at all. If left as originals, there wouldn't have been any exposed wire to be coroded.

 

[bobgosling]

This may sound odd but believe me it works. Coat the blackened wire ends with HP brown sauce and leave it overnight before wiping off. I now eat bacon butties without brown sauce after seeing what it does ...

 

[Stemar]

I suspect vinegar would do the same job!

It's only for depth transducers that they say you mustn't cut them. IIRC, this is because it's a tuned circuit and the length is relevant, but cutting and reconnecting the cable won't cause the arrival of Armageddon and the rise of the Antichrist. I had to do so with mine - I used a bnc connector - and it works fine.

I'm thinking of putting a connection in my log impellor cable so I can remove the impellor and wash it in the sink to remove mud and critters. It lives in a relatively clean and dry (except when I pull the impellor!) bit of the boat, sealed from the rest of the bilges, so I don't anticipate too may problems with corrosion, but I think I will use gold plated connectors, which should also reduce signal attenuation. Again, I think male/female BNC would be favourite.

 

[Norman_E]

Cutting the cable was not the problem. As the corrosion gets worse the closer you cut to the transducer it is clear that moiture is getting in from the transducer and corroding the cable from that end. It would not have been a problem if the manufacturers had used tinned cable. When I bought the boat there was about three feet of log transducer cable, joined to a longer piece which goes to the master log instrument.

 

[Stemar]

In that case, I would suggest a new transducer. If moisture's getting through the transducer up to the cable from outside, then failure can't be far away. I'd keep the old one as a plug when scrubbing off or when laid up for the winter.

 

[William_H]

Before you throw the transducer away... I had a Smiths paddle wheel log which failed. I dug away all of the sealer etc where the cable goes in. Inside was a small reed switch which was easily replaceable along with new wire all sealed up again. I did this several tinmmes over the years until the magnet seemed to get weak. I replaced the reed switch with a Hall effect sensor. Like a tiny transistor which changes conductivity with magnetic field. That worked better but required 2 wires and an earth and a single transistor amplifier to imitate the original switch. PM me if anyone wants more details. But do explore that transducer before you throw it way...... olewill PS I finally got wise and threw the whole system away and use GPS the crustaceans are just too enthusiastic in our warm waters.