depth gauge electrical interference

[mikewade]

I have a nasa clipper depth gauge installed which when the engine (a vetus M4.14) is running goes crazy, OK when engine stopped. I have re-routed the cable away from the engine as much as possible but little improvement. Nasa can't help suggesting I talk to Vetus.
Does anyone have an email or telephone number for Vetus technical, and does the panel have any other suggestions to shield the sounder cable. Would a snap on ferrite give any improvement. I have twin alternators - any suggestions as to suppressors on the alternators and how would I go about this, where do I install
Need to sort it as I am sailing back to the UK in May as were getting bored in Gran Canaria and coming past the Thames entrance, I would like to have a stable reading.
Thanks for any advice

 

[nimbusgb]

I think the problem is emanating from the alternator / regulator circuit.

Try running the depth sounder off a separate 12v battery for a while with the engine running. If the problem goes away its definitely not interference in the signal cable rather the supply.

If this is a new development I'd get the alternator checked out properly then I'd look at your earth / ground return lines.

A 20 000 ufarad cap across the depth sounder supply lines as close to the instrument head as possible might help.

A car type suppressor on the alternator might help too. Screwed to casing ( provided your block is earthed ) and connected to the output terminal.

Check block earthing and other system bonding in the boat.

 

[hubert]

Electrical noise on power lines rarely causes problems with modern sounders. If you disconnect the transducer you will find it reads "out" meaning it is not receiving anything. The problem will be direct pick up on the transducer cable. While the cable is shielded it will still pick up interference if the level is high enough. Moving cables rarely works as alternator interference is conducted all over the boat through the wireing system. With electrical interference the rule is you must surpress it at source.

 

[hightech]

Your alternator is starting to failand needs an overhaul, likely one or more of the diodes has failed and you are getting an AC ripple on your supply. Do you get any noise on long wave AM radio signals (off tune is sometimes better) that are proportional to engine revs, if you do then there is your answer

 

[mikewade]

sorry for the late reply Guys and thanks for the indicators. I havent tried the FM radio scenario but I will. Interestingly we have just found that one of the alternators needs work doing on it and this is happening now, so it will be interesting to see what happens when it goes back on. If there is little improvement I'll also try supression at source and maybe wrap a ferrite round the depth cable.
thanks once again