Preparation for working on 12V High Amp circuits

[Gashmore]

Might want to go to your local Ace hardware and invest $40 in a GB Lan tracker. Disconnect a suspect wire at the breaker and attach the little transmitter then probe around the boat with the receiver listening for the signal. It has helped me figure out some weird old wiring in the past. Heck, it helps me figure out what I did yesterday. :-)

[MidLandOne]

Originally Posted by j-yelroc

We have a noisy hum in the VHF and tried a dedicated battery for power and it cleared it up.

If you don't want the trouble and expense of a separate battery, its charging system (which may introduce a hum itself if done off AC as AC chargers are a common source) and maintenance, then a 30 Amp noise filter as sold to go in the DC supplies to automobile audio systems will usually kill it both for Rx and Tx. 30 Amp seems an overkill for a 25 watt VHF radio but in my experience is best to use one of that rating to minimise voltage drop across it.

They are simple passive filters using an iron cored inductor and electrolytic capacitors, and very inexpensive.

[hellosailor]

j-y:
Since the hum in the VHF goes away with the dedicated battery source, that means it is coming in over your power lines not the antenna line. Hum usually is coming from an AC leak into the DC circuits, or being produced by something else, possibly a florescent light fixture with a bad ballast coil (transformer) in it.
If you have shore power, physically disconnect it, see if the hum goes away. An inverter? Disconnect it, see if the hum goes away. Shut down literally half the breakers, see if the hum goes away, if not try the other half. Keep shutting down circuits until it goes away, and the odds are you will be able to find it quickly. Something--a motor, a pump, a transformer, maybe an electric refrigeration system?--is making the hum and probably can be stopped with a simple noise filter added to the offending circuit.

What do you mena by "control circuits attached to the VHF? ? Wouldn't you run that as a separate circuit, directly through one breaker then to the battery switch?

[Rodz]

I am not sure but ......bus-tie circuit breaker = disjoncteur de couplage ..... rings the bell.

[j-ylwroc2]

Due to log-in password problems, I am now j-ylwroc2.

Thanks for the translation attempts for Servitudes, but let me be clear -- that switch is NOT a breaker. Its simply a DPST. Two set of contects which are open in one position and closed in the other - common red plastic body - I dont remember the manufacturer but it is well known.

Perhaps a more correct description would be a TIE SWITCH. I hope to get back to the boat to do further checking. I suspect it Ties port and stbd batteries (catamaran).

Gashmore, MidLandOne, hellosailer, Rodz thanks for your suggestions. The tracer sounds like a good idea as does the line filter. We are fairly sure the hum is coming from the inverter.

VHF control circuits are really accessory lines to GPS or other devices, not really control. Sorry to mislead. They are not being used so will make sure they are disconnected.

Thanks

j

[j-ylwroc2]

1. On the boat visit this past week determined that "Servitudes" labels the ON/OFF switch (DPDT) which Ties (connects) port start battery to the main dc bus. Both + and - are switched.

The port start battery also connects to the port engine run-enable ON/OFF switch (DPST) where both + and - are switched. The engine run-enable switch connects start battery to the starter solenoid and engine run time meter.

2. There is a 70mm2 cable from port start battery + to stbd side of boat and is labeled MOT TRI. Moteur is French for engine. Does TRI represent tribord (starboard)? Does this label mean "To stbd engine"? That seems reasonable.

3. The boat uses Blue Sea "ShorePower-Generator" change-over uses interlocked breakers to switch power sources. One of the 4 breakers is labeled Reverse Polarity (RP). From what I've read there should be an RP light which I don't remember seeing. Is it likely that what I think is an RP breaker is really an RP light?

Jess

[j-ylwroc2]

In my previous post item 1, switch is DPST (two circuit ON/OFF) not DPDT.