DC ground leak


Alan Leslie
 

A week ago I operated the switch in the companion way and the Masse - lamp illuminated, but only just. The lense is missing and if it was in place, the illumination of the lamp is so weak, I doubt I would have noticed it.

Anyway, it went away after a day or so, and then suddenly today it's back

So, I have set about trying to find where the leak between ground and 24V-ve is. I've disconnected the negative leads on both head macerator pumps and the anchor wash pump, no difference. I looked at the fresh water pump, but the pressure switch switches both +ve and -ve so it can't be that.


Anybody with more experience with this that can give me some advice as to where and how to look for this leak ?


Thanks

Cheers

Alan

Elyse SM437, Koumac 

20 34.63S, 164 16.49E


rossirossix4
 

Hi Alan,
I hope you find the source.  We had a similar indication with intermittent low illumination of the Masse neg lamp.  We were wintering in an Italian marina and through observation of their electrician staff I had reservations about how the pedestals were wired and maintained (not sure if this was the problem).  We had a sailboat on our port side that was not plugged in and a slip on our right that was periodically used by various local boats.  Turned out that when certain boats were along side and plugged in the Masse Neg lamp would glow.  We decided that the common ground to the other boats that may have not have been protected or zinc'd well were causing the indication.  Our greater than normal zinc erosion that season seemed to confirm it..  The installation of a galvanic isolator solved it.  Without galvanic isolation, other nearby vessels that are under-zinced can use yours!  If you already have a gav isolater make sure it is wired before the gen/shore power--anywhere before the grounding stud in the gen/shore power box.
Bob KAIMI SM 429


Alan Leslie
 

Thanks Bob,
we do have a galvanic isolator wired into the ground wire that comes from the shore power cable, but this is happening while we are at sea!
We noticed that it seems to happen after using the washing machine, but that makes no sense at all....
when it happens again I will completely disconnect everything DC powered with a ground and hopefully find it.
Cheers
Alan
Elyse SM437


Walter
 

Hi Alan,
before going into AC I would check the DC connections - you mentioned the usual suspects (electric pumps) and the leak detector is for the DC-circuit.
Do you use a laptop and to which other devices is it connected (ssb, instruments ...)?

Kind regards,
Walter (Noa, SM2K 436)


Alan Leslie
 

Thanks Walter,
It came on again today when motor sailing but now at anchor its off again.
The SSB has an isolated power supply.
The laptop is powered from a Mastervolt inverter under the nav station.
It is connected to the SSB, GPS, AIS and a NMEA multiplexer...none of which have ground connections except the SSB, but the laptop is isolated from the DC circuit by its own power supply and the SSB also has an isolated power supply.
The leak is very small, barely noticeable on the lamp, so it must be some "device" that has both a 24V-ve and ground connection
I will try disconnecting things when the Masse- light comes on, but right now it's off.
Cheers
Alan
Elyse SM437
Ile Puen, Baie de St Vincent, New Caledonia
 


Walter
 

Hi Alan,
your SSB is probably connected to the laptop via pactor and seriell to usb converter.
What happens when you plug and unplug the usb cable at the laptop?
We experienced a leak/the lamp on - although the SSB has an isolation transformer. Difficult to explain (there is something "funny" with the usb shield) but we fixed it with a seriell optocoupler. It works like a galvanic seperation and seperates the computer from the SSB. You can get them as a seriell plug with male on one and female on the other side, so it fits between the seriell cable (from the SSB) and the "seriell to usb" converter cable from the computer.

Regards,
Walter (Noa, SM2K436)


Walter
 

Hi Alan,
to be more precise: the optocoupler is between the seriell cable from the pactor and the usb to seriell converter from the laptop. Our SCS Pactor III has seriell connections on both sides, SSB is an Icom 710. The standard setup for mail, fax, rtty.

Regards,
Walter (Noa, Sm2K 436)