Alternator Interference

[Gixer]

I know there are threads on here about this and I've read though them but am still not clear on the answer.

My alternator on my 1GM10 causes my depth to go haywire when the engine is running, it’s 100% the alternator as running the engine without the belt solves the issue. Its been like this since I rewired the boat but its now getting on my nerves.

I've fitted a Ferrite core to the depth cable and it hasn’t solved the issue. I've read about fitting a suppressor, is this the kind of thing?
Car Radio Noise Buzz Interference Alternator Suppressor 2.2 Uf - Classic Vintage 5081946680889 | eBay
Odd thing is nothing else seems to be affected, radio is fine, etc.

Is it worth fitting a ferrite core elsewhere on the electrical system?
Would fitting a suppressor just be masking an issue, am I better off getting the alternator looked at incase its a diode?

Thanks

 

[Boater Sam]

Fit a suppressor as you say. But I suspect that the wiring is in too close proximity to the depth gauge wiring. The alternator frequency is too low for ferrite beads to be successful.

 

[Gixer]

Fit a suppressor as you say. But I suspect that the wiring is in too close proximity to the depth gauge wiring. The alternator frequency is too low for ferrite beads to be successful.

Thanks, that a good point. Its a bit of a faff but do you think moving the wiring for the depth away from the other wiring could make a difference?

 

[Alex_Blackwood]

Thanks, that a good point. Its a bit of a faff but do you think moving the wiring for the depth away from the other wiring could make a difference?

Very much, more than likely especially if the wiring runs side by side. Separate by at least 50 mm or if the wires have to cross make sure it is at right angles.
I would very much recommend trying the wiring before fitting suppressors especially as nothing else is affected.

 

[Martin_J]

High resistance in any of the charging wires between the alternator and battery could also induce noise... Check the thick wires for corrosion, nicks and good end terminations..

Maybe disconnect, clean and reconnect the battery terminals as well.

Is the battery good... a dying battery might fail to absorb any ripple from the alternator.

One last thing. Could a failed diode in the alternator cause too big an AC ripple for the battery to easily absorb? Test with an oscilloscope (or maybe multimeter on AC setting) and look for less than 50 mV.

 

[Gixer]

This is great information thank you.

I know the wires for the depth run for quite a length with all the other cables, i'll correct this the weekend and see if it makes a difference.

Martin_J - I rewired the whole boat a year or so ago so all the connectors and cables (tinned) are brand new. I do have a multimeter so can test, do I do this on the battery terminals?

 

[William_H]

One thing to check is to ensure alternator is capable of near full output current. If a diode fails in alternator then it will still charge but at a much lower max rate. (hence you may not notice the failure) The loss of a diode gives a very ragged output waveform which can cause interference.
The suppressor in link is just a capacitor. Which may fix the problem at the alternator. An inductor would be better if coupled with capacitors both small ceramic capacitor ie 100 to 2000pf in parallel with larger 2 to 50 microfarrad. Mount on alternator body to give very short earth connection.
However suppressors on alternator are not usually needed.
One trick OP could try is to arrange to run sounder on a separate 12v supply to ships battery with alternator charging. This will confirm if interference is coming to sounder via 12v supply or via induction into transducer wiring. If interference stops on alternative battery supply then yes more suppressors needed. If interference still there on alternative supply then try moving transducer wiring and check the earth of the shield (braid) of transducer wiring. ol'will

 

[Alex_Blackwood]

Whilst the comments from Martin J and William H are theoretically sound they don't take into account that it is only the depth reading affected. Most of the suggestions would cause interference throughout. The suggestion from WH for separate supply is possible, if everything else is powered up as normal! However I would still suggest separation before getting more complicated.