Engine interfering with depth readings

[Gixer]

For a while now every time I switch my engine on my depth sounds goes haywire. The thing is it’s been happening for so long I can’t remember when it started happening…
Everything else works fine and when the engine is off there’s no issues, it’s a 1GM10.

Any ideas?

 

[KevinV]

Vibration, or the alternator? Can you run the engine with the alternator belt off to see if that changes anything?

 

[William_H]

As said if it is not vibration it must be alternator interfering electrically. An alternator with a failed diode can cause a lot of interference as output is disjointed wavefrom wise by loss of diode. Often not noticed because you do not demand a lot from alternator and regulator forces enough charge. As said try running without alternator or with wiring disconnected. If that fixes problem then get alternator checked for full output capability. In some case a good alternator can cause interference. (not often)
Try if you can running sounder off an isolated (from engine) battery. If that fixes problem then try a filter in battery supply to sounder. Ferrite choke and electrolytic capcitor bypassing to ground at sounder side of choke might be a start. ol'will

 

[dslittle]

For a while now every time I switch my engine on my depth sounds goes haywire. The thing is it’s been happening for so long I can’t remember when it started happening…
Everything else works fine and when the engine is off there’s no issues, it’s a 1GM10.

Any ideas?

Any ideas would be very welcome.

For some obscure reason, our depth has just started counting down to 0.8m and then counting back to the ‘real’ depth again at random times. At first I thought that it might have been some submerged object but it goes down to 0.8m and then back even in deep water. This has happened both when under engine AND when sailing so it’s definitely not our alternator.

I do feel that it is probably an electrical issue though?

 

[Gixer]

Thanks guys, i'll try the alternator disconnected and see what happens. My engine and all other electrics are separate but charging is done though a battery combiner.
Quick question on the Ferrite choke mentioned, there is one on the cable that goes from the sounder to the unit but not on the power supply. could one on the power supply help?

 

[Graham376]

You could try adding a smoothing capacitor to the alternator to supress RF interference.

 

[Gixer]

You could try adding a smoothing capacitor to the alternator to supress RF interference.

Thats outside of my skill set but will look into it if the other suggestions fail, thanks.

 

[Milgrip]

Have you checked for corroded wiring connections?

 

[Jmc1764]

Ive just had similar issue, the depth display is going way above what it really is, ( NASA Clipper ) so I checked the water in the inside pot where the transducer is, no difference. Bought a new transducer and no difference, assumed the display unit was duff then checked the connection to it, found it was corroded, so cleaned it and did everything I could, tried again and no difference....Then I had a light bulb moment and plugged the transducer direct into the display and it worked perfectly....I have an extension cable that runs around the engine to get to the display. I fished it out and found it had been squashed when I refitted some interior wood during the winter clean up ! So check all the connections first before spending money !

 

[William_H]

Thanks guys, i'll try the alternator disconnected and see what happens. My engine and all other electrics are separate but charging is done though a battery combiner.
Quick question on the Ferrite choke mentioned, there is one on the cable that goes from the sounder to the unit but not on the power supply. could one on the power supply help?

The choke may help if problem is interference coming in to the sounder via the power cable. ie from alternator. The ferrite increases the inductance of the ire. So can be in the form of a torroid around the cable but is far more effective if the cable or additional wire is wound around the ferrite rod or through the torroid multiple times. Each turn multiplying the inductance. The inductance acts like a resistor or blockage to high frequency pulses. It is used in conjunction with an electrolytic capacitor and a ceramic capacitor to bypass the pulses to ground. The capacitor acts like a tiny battery charging on the pulse rise and discharging so filling in when pulse goes negative or down. The elctrolytic capacitor of about 220 micofarrads has some indctance in itself which slows down it's reaction. So a ceramic capacitor of about 1000picofarrads is placed in parallel (to ground) to soak up really high frequency (rapid ) pulses. Both capacitors on the sounder side of the inductance so inductance tends to block pulses while capacitors bypass what gets through.
220uF 25VDC Electrolytic RB Capacitor | Jaycar Electronics
Search Ferrite torroid | Jaycar Electronics
Or if you have an old transistor radio you can use the ferrite rod antenna by wrapping the deed wire around many times or add extra wire around the ferrite and insert in feed circuit. Note the extra wire must be able to carry the sounder current without loss. Or old computer equipment often has ferrite torroids ol'will

 

[justanothersailboat]

I had this exact problem. Turned out to be a dodgy connection. Interference is perfectly possible, but loads of depth sounders work fine with no special attention to interference protection so I think it less likely.

 

[Daydream believer]

Any ideas would be very welcome.

For some obscure reason, our depth has just started counting down to 0.8m and then counting back to the ‘real’ depth again at random times. At first I thought that it might have been some submerged object but it goes down to 0.8m and then back even in deep water. This has happened both when under engine AND when sailing so it’s definitely not our alternator.

I do feel that it is probably an electrical issue though?

Down to 0.8 .You are lucky. Here on the east coast it often starts at 0.8 & goes down hill from there. I find it more often when it is supposed to be 6+M deep.

 

[laika]

For some obscure reason, our depth has just started counting down to 0.8m and then counting back to the ‘real’ depth again at random times. At first I thought that it might have been some submerged object but it goes down to 0.8m and then back even in deep water.

ST50s by any chance?

See my thread from last year:
Depth reading wrong

Summary:
0.8m is (according to the person at the Service Centre who looked at my depth head unit) the min depth an ST50 (and maybe other?) will read. At first I assumed this was a transducer issue, bought a new transducer, shoved the bare wires into the head unit and dangled it over the side to test and it still said 0.8m (well...actually 1.5 but I have a 0.7 offset). SO I sent the head unit to the service centre who said no fault found. SO currently I'm back to the transducer but haven't got round to testing it yet. And if anyone knows the part number for the 2 pin plug (I think it's a switchcraft one) that would save me having to cut the plug off the old transducer....

Problem seems more likely to occur the lower the depth. Generally depth looks fine in deeper water but gets flaky where you need it <6m

 

[Gixer]

Note the extra wire must be able to carry the sounder current without loss. Or old computer equipment often has ferrite torroids ol'will

Funnily enough I was in the office yesterday and they had boxes of cables going to be recycled. I wasn't sure at the time but did see the ferrite torroids on them. When I go in tomorrow i'll liberate a few.

Thanks

 

[dslittle]

ST50s by any chance?

See my thread from last year:
Depth reading wrong

Summary:
0.8m is (according to the person at the Service Centre who looked at my depth head unit) the min depth an ST50 (and maybe other?) will read. At first I assumed this was a transducer issue, bought a new transducer, shoved the bare wires into the head unit and dangled it over the side to test and it still said 0.8m (well...actually 1.5 but I have a 0.7 offset). SO I sent the head unit to the service centre who said no fault found. SO currently I'm back to the transducer but haven't got round to testing it yet. And if anyone knows the part number for the 2 pin plug (I think it's a switchcraft one) that would save me having to cut the plug off the old transducer....

Problem seems more likely to occur the lower the depth. Generally depth looks fine in deeper water but gets flaky where you need it <6m

Hi.

It’s a ST60+. It worked flawlessly for years and I’m not sure that anything has changed…

It’s interesting that 0.8 is the minimum reading (I don’t use an offset so that is what it shows). I’m definitely thinking it’s electrical so I will go down the contact cleaning route to start. I do have a spare head unit so I can try that as well in due course.

As you’ve found, it only kicks off in shallower water which is not ideal !!!

Funnily enough (and almost as annoying as not working) it worked fine today in 3-5m of water. Arghhhh

 

[laika]

Funnily enough (and almost as annoying as not working) it worked fine today in 3-5m of water.

Is this “fine” for a definition of “fine” which looks roughly right but occasionally rapidly goes down and up again whilst moored? I seem to get that but it rarely registers anything other than 0.8+offset in that depth of water while sailing

 

[dslittle]

Is this “fine” for a definition of “fine” which looks roughly right but occasionally rapidly goes down and up again whilst moored? I seem to get that but it rarely registers anything other than 0.8+offset in that depth of water while sailing

No. Fine meant that it worked faultlessly for that trip in shallower water - only 30 mins.

The next trip brought us out I to 10m+ and it started counting down to 0.8m again intermittently. We are currently moored up in 6m and it’s gone up with the tide but no ‘strange readings‘ for the last 30 mins.

Very strange

 

[Bilgediver]

You could try adding a smoothing capacitor to the alternator to supress RF interference.

That is something I have done on cars. You can test for interference if you have an old tranny you can take to the boat. If you are lucky It will pick up the interference and you will hear it on the speaker