Instruments Connected Directly to Battery?

[andyo]

Hi - I am "tidying" the wiring in my old Westerly Konsort and amongst other idiosyncrasies have found a number if items connected directly to the battery bank. In particular, I'm looking at the instrument panel above the chart table. I have a Standard Horizon chart plotter, VHF radio and FM radio. The plotter and VHF are connected to the 1-2-both-off rotary switch, the FM radio directly to the domestic battery bank (2*110 Ah). All are fused correctly.

If I tidy these up, is there any advantage (or otherwise) of having them connected directly to the batteries? The only thing I can think of is if there was a fault in the rotary switch, I would still have the VHF radio and plotter, so could call for help, etc.

All thoughts appreciated.

Andy

 

[prv]

The FM radio is probably directly connected as it's a car unit that needs a constant trickle of power to remember its radio station presets. With non-volatile memory technologies routinely available for at least the last couple of decades it's crazy that they still need this, but apparently even new ones still do. Personally I'd ditch the '90s car audio stuff entirely and use something more appropriate for 2015, but it's your choice

Don't connect the VHF and plotter directly to the batteries; your 1-2-both switch isn't going to fail. Far more likely is a fault somewhere else in the system and when that happens you'll be glad that your isolator really does isolate everything.

(If the switch did die somehow, it would be easy to just swap all the wires on the back of it to one terminal, thus bypassing the switch.)

Pete

 

[Kurrawong_Kid]

Always the danger that stray 12v. currents will start up electrolytic actions and decay anodes/fittings if left always on.

 

[lpdsn]

Don't connect the VHF and plotter directly to the batteries; your 1-2-both switch isn't going to fail. Far more likely is a fault somewhere else in the system and when that happens you'll be glad that your isolator really does isolate everything.

One reason for connecting the VHF directly is that any noise it produces on the power wiring goes directly to the battery and is less likely to affect other circuits. This is sometimes misunderstood as a counter for the master switch failing in an emergency.

I don't think it is a strong argument for doing it (ferrules on the power wiring will limit noise) just including it here for completeness.

 

[[70521]]

I have everything going through the switch, so when I leave the boat everything is off; makes for a better sleep.

 

[prv]

One reason for connecting the VHF directly is that any noise it produces on the power wiring goes directly to the battery and is less likely to affect other circuits.

Do modern VHFs produce significant noise on their power lines? I wouldn't have thought so. And even if they did, I can't see that moving the connection point slightly (one set of closed contacts and a couple of feet of cable) is going to make much difference. It's all connected to the same battery terminal, and cable doesn't have one-way signs

Pete

 

[GrahamM376]

Only items I have connected directly to battery are the bilge pumps.

 

[jwilson]

Only items I have connected directly to battery are the bilge pumps.

I am not convinced about bilge pumps directly to the battery, unless you have a known minor leak such as a greaser/packing type sterngland or a keel-stepped mast that inevitably always lets some rainwater into the bilge. Permanently connected auto pumps can fool you into thinking there is no problem if a steady leak (eg sterngland) develops, and then run down the batteries if it gets worse or you happen to leave the boat unvisited for longer than usual.

 

[VicS]

There may be times when bits of gear need to be permanently connected.
Auto bilge pumps and memory circuits have already been mentioned. You might also add alarm systems.

It used to be advised that VHF RTs should be directly connected to the battery. Partly I believe in an attempt to obtain a clean, interference free, power supply and partly to avoid volts drop in inadequate or already heavily loaded wiring

Karawong Kid raises the possibility of this leading to electrolysis of underwater fittings

It is vital that "always on" pieces of equipment also have a good and direct connection to the battery negative. A negative isolation switch could spell disaster if this is not done. A return path via the common negative busbar, engine block, stern gear, the water and the anodes or shorepower earth would result in electrolysis where the current leaves to boat to enter the water. In this example the stern gear

 

[rob2]

...your 1-2-both switch isn't going to fail.

I appreciate that you qualified this tatement, but when I bought my boat the switch had ejected its internals (Plastimo). So I bought a direct replacement for ease of fitting - it exploded as I screwed it in! For a quarter of the price I bought a chunky, Chinese switch which can be stripped down for repair and alignment.

I find the big terminals of the switch useful for additional and priority wiring, including the output from the windgen. I believe some people direct wire the automatic bilge pump (or else it really isn't automatic...) and I use an old car radio which predates pre-sets, so no problem there! Those that do require a permanent feed have a secondary input for it, so long as this is fused close to the battery it shouldn't be of any concern.

Rob.

 

[lw395]

I used to have a GPS wired direct to a battery, to avoid it losing the plot when starting the engine with the other battery.
The starter motor would drag the volts down for a few seconds and the GPS would reset.
It's annoying when you start the engine as you approach port with a tricky bit of pilotage, and the GPS forgets where you are.....
That might be why it's done?

Other thing I've wired direct include timer for heater, Navtex, a light near the companionway, voltmeter, socket intended for anchor light.....

 

[prv]

It used to be advised that VHF RTs should be directly connected to the battery. Partly I believe in an attempt to obtain a clean, interference free, power supply and partly to avoid volts drop in inadequate or already heavily loaded wiring

Mostly the latter, I suspect. The power drawn by a transmitting VHF, especially a big old pre-computerised one, would once have qualified as a relatively large load on a small basic yacht. Attaching it via undersized cable to the typical bird's nest of inadequate wiring by the sort of electrical numpty all too common among yacht owners, may well have led to complaints of poor performance. The makers could reduce the risk of that by telling people to connect it direct to the battery with big cables. But this precaution is completely unnecessary if you have a sound electrical system and connect the VHF to it properly.

Pete

 

[Poecheng]

Diesel heater on mine bypasses the main switches - in order to permit it to go through the purging procedure without interruption.

 

[lpdsn]

Do modern VHFs produce significant noise on their power lines? I wouldn't have thought so. And even if they did, I can't see that moving the connection point slightly (one set of closed contacts and a couple of feet of cable) is going to make much difference. It's all connected to the same battery terminal, and cable doesn't have one-way signs

Pete

Sufficient for SH to recommend ferrules for the new VHF I fitted last year, however as I said above I don't think it is a strong argument (or put another way, some people think you should do it but I wouldn't).

Assumption is that the noise is absorbed by the battery so much less of it makes it onto the other wiring. Obviously, it's far more complex than that with some induction of noise in any cables running parallel etc. etc.

 

[andyo]

Many thanks everyone, sounds like I ought to leave the connections as they are. I will tidy the rat's nest, tho'.