Unisolated services on domestic batteries. Advice please.

[frderek]

My recently-purchased Westerly Merlin 28 is having problems with the domestic batteries discharging. Today I identified the culprit: the autohelm sockets, and they have been disconnected pending investigation and repair.

But that got me thinking. I have two manifolds on each of the positive and negative terminals of the domestic bank (2 x 130 Ah) each with 4 spade terminals to feed electrics NOT isolated by the domestic isolator switch.

Some of these I have identified, some still to be investigated.

So far I have found the following NOT to be isolated: solar panel input (makes sense), VHF radio (possibly makes sense in an emergency), navtex, autopilot, gas alarm plus two others yet to be identified.

My question: which services would YOU think need to be permanently 'on' despite the battery isolation switch? N.B. I have two isolation switches: one for the engine battery and one for the domestic bank, not a 1,2,both switch. My intention is to move as many as possible to the far side of the domestic isolator. Why, for example, would I need the autopilot when the rest of the instruments etc. are isolated?

many tia

Derek, 'Lisia', St. Aubin Harbour, Jersey.

 

[prv]

Sounds like the standard spaghetti wiring problem in a middle-aged boat with a less-than-meticulous former owner. Applied to both the boats we've bought, and both of them I have rewired.

The only things I have connected upstream of the isolator are the mains charger and the Smartgauge state-of-charge monitor. If I had a solar panel, then obviously that would be connected full-time too. Nothing else.

I doubt your autopilot was deliberately designed to be un-isolated, just that the person who installed it found that an easier place to make the connection.

Pete

 

[KellysEye]

We had switch panel that turned the majority of things off. The exception was the wind generator which had it's own off switch and the smart charger for the batteries which had no off switch. The gas alarm should have no off switch, VHF, Navtex and autopilot should have off switches. You haven't mentioned other things but if it isn't safety kit like a gas alarm it should have an off switch.

 

[Bru]

The only items I would have on the battery side of the main services isolator, and I would still have a separate "Pumps" isolator so that they could be isolated for maintenance etc,, would be the automatic bilge pumps.

You could add intruder alarm (if fitted), gas alarm (likewise) and of course any solar or wind charging would need to be permanently connected

 

[JumbleDuck]

Only my solar panels feed in before the isolator switch, and even they are attached on the switch side of the 250A breakers which come between batteries and switch.

 

[Robin]

Sounds like the standard spaghetti wiring problem in a middle-aged boat with a less-than-meticulous former owner. Applied to both the boats we've bought, and both of them I have rewired.

The only things I have connected upstream of the isolator are the mains charger and the Smartgauge state-of-charge monitor. If I had a solar panel, then obviously that would be connected full-time too. Nothing else.

I doubt your autopilot was deliberately designed to be un-isolated, just that the person who installed it found that an easier place to make the connection.

Pete

+1

our last UK boat used to lose battery volts gradually on the engine bank with all the isolators 'off', eventually traced (by me with a multimeter and some applied logic) to the alternator charge warning light being wired to it before the isolator switch. Adverc's man at LBS suggested it was probably done to provide some permanent excitation to the alternator, got me excited that was for sure and it all worked fine when disconnected . The other and main culprit was a permanently wired gas alarm ( current draw measured 0.5A, no need to leave that permanently 'on' surely when nobody there to hear it? That boat had been professionally rewired and solar and wind chargers, extra alternator and smart regulators added as well as a SSB radio all work done for the previous owners, prior to them doing an AZAB TWo Up Race and embarking on a subsequent longterm Med cruise , Once we corrected all the nonsense wiring logic and incorrect wiring we had a very powerful charging and DC power system that really worked.

 

[rosssavage]

I have a hot battery bus that is not isolated, but is PROTECTED by a 50a fuse. It is fed from the engine bank. It feeds engine space bilge pump, lower helm vhf and lower helm plotter - everything else is isolated and fed from the domestic bus.

The gas alarm and auto shut off solenoid are fed from the domestics. I have a gas switch next to the cooker that is always off unless the cooker is in use. This isolates the gas six inches downstream of the bottle connection, within the confines of the overboard-vented gas locker. The solenoid is power off = gas off, hence Domestics off / fault = gas off.

Reasoning is essential services back up in the case of catastrophic domestic system failure.

Hot battery bus is fine, but it must be protected (fuse or cb) as close to the battery as possible.

 

[frderek]

Thanks. Actually the gas alarm and navtex do both have their own 'on/off' switches and the VHF set, obviously, can be turned off by the volume control. The Autopilot sockets don't have switches: I suppose the reasoning is that if it ain't plugged in it's not going to draw power. What seems to be happening (and I've yet to investigate) is that one or both of the sockets is (at least partially) shorting the +ve to the -ve, possibly due to ingress of sea-water or breakdown of insulation. What I would prefer is not to have to check 101 'off switches' but to throw the isolator knowing that that really did isolate the batteries from drain (charge is another matter, of course )

 

[frderek]

Pleased to say that my gas solenoid is exactly like yours. Plus a tap where the copper pipe joins the rubber underneath the cooker. I have no electric bilge-pumps and seem not to need them, she's a very dry boat. Each of the 'hot-bus' wires has its own in-line fuse but I still think most of the connections should be moved to the other side of the isolator (easily done as the 'manifolds' or 'buses' can be attached to the switch output as easily as to he +ve terminal - they are only six inches apart).

Many thanks to all who have helped so far!

 

[prv]

What I would prefer is not to have to check 101 'off switches' but to throw the isolator knowing that that really did isolate the batteries from drain (charge is another matter, of course )

Indeed.

Some people say that gas alarms should be connected 24/7, to prevent the situation where you come on board to a cabin full of gas (but no alarm sounding due to no power) and then ignite it from the spark of turning the isolator on. However,

1) If the boat's closed up and turned off, then the gas bottle is isolated in the locker
2) If a leak has been going on for some time, I'd expect to smell it on opening the hatch
3) My battery isolator is sealed and approved for explosive atmospheres anyway!

Pete

 

[frderek]

I have a hot battery bus that is not isolated, but is PROTECTED by a 50a fuse. It is fed from the engine bank. It feeds engine space bilge pump, lower helm vhf and lower helm plotter - everything else is isolated and fed from the domestic bus.

I'd be a bit worried about ANYTHING other than the starter-motor drawing power from the engine battery while I am sailing. Am I wrong/over-cautious? Bear in mind that I am a novice owner so this is a genuine question, not point-scoring

 

[prv]

I'd be a bit worried about ANYTHING other than the starter-motor drawing power from the engine battery while I am sailing. Am I wrong/over-cautious? Bear in mind that I am a novice owner so this is a genuine question, not point-scoring

The mention of a "lower helm" suggests that Ross has a motorboat . If I'm right, that issue obviously doesn't apply for him!

I adopt the same approach as you, only the engine (and its controls/gauges) is connected to my engine battery.

Pete

 

[JumbleDuck]

I adopt the same approach as you, only the engine (and its controls/gauges) is connected to my engine battery.

Me too. I've just separated the engine from everything else, with two completely separate (but linkable) 12V circuits.

 

[frderek]

The mention of a "lower helm" suggests that Ross has a motorboat . If I'm right, that issue obviously doesn't apply for him!

I adopt the same approach as you, only the engine (and its controls/gauges) is connected to my engine battery.

Pete

Light dawns! The lovely chap (YMI) who taught us how to sail and later sold us his boat had a wonderful saying which I now use on every trip. About 2 cables or so from the harbour/marina/mooring he would always say "NOW would be a good time to see if the engine will start". Great advice!

 

[Neil_Y]

MCA codeing requires gas alarms to be always on (as far as I understood the instructions)

We had a small 7Ah sealed battery in parallel always connected to the vhf, so it was still useable even if the main battery bank was underwater and fried, it would charge in parallel with the domestic battery. It always worried me after being on a yacht that was taking on water we had a few minutes to use the main vhf and call a mayday before the battery bank was under water. This meant that even if the main battery bank was off any one could fire up the vhf. I think this is very useful from the perspective of a guest having to use it in an emergency and maybe not knowing where the isolator is.

 

[frderek]

MCA codeing requires gas alarms to be always on (as far as I understood the instructions)

We had a small 7Ah sealed battery in parallel always connected to the vhf, so it was still useable even if the main battery bank was underwater and fried, it would charge in parallel with the domestic battery. It always worried me after being on a yacht that was taking on water we had a few minutes to use the main vhf and call a mayday before the battery bank was under water. This meant that even if the main battery bank was off any one could fire up the vhf. I think this is very useful from the perspective of a guest having to use it in an emergency and maybe not knowing where the isolator is.

I am SO glad I asked this question. What a good idea, a motorcycle battery on the shelf behind the VHF, a fathom above the main batteries! Could also feed the GPS so as to provide a fix for the DSC. What diodes would be needed?

 

[Hoolie]

What diodes would be needed?

Use Schottky diodes of suitable current rating as they have a lower voltage drop than standard junction diodes. Maplins or CPC-Farnell online.

 

[JumbleDuck]

Use Schottky diodes of suitable current rating as they have a lower voltage drop than standard junction diodes. Maplins or CPC-Farnell online.

I think I have just found a use for the small VSR I bought from eBay a while back!

 

[Richard10002]

On Rogue there was always a half amp draw with the battery isolators off and, try as i might, I couldnt find it.

after about 3 years of ownership, I traced it to the Navtex, which actually doesnt have an off switch, and was connected to the battery side of the isolators.

I cant recall how I found it, but I put a switch in its power supply, and all was well thereafter.

I dont know whether the later Navtex have on/off switches, and I dont know why the older models wouldn't have one. i dont think I ever used it in anger either... didnt really understand how to use it.

 

[rosssavage]

Oops, yes, guilty as charged!

Ok, so my setup is not such a good idea if you spend a lot of time under way with the engine off - my boat goes no where in that condition!

So, no, not such a good idea in your case, but I am a serious advocate of alternate power systems for essential services back up.

In your case that seems to be limited to the VHF set only, so maybe a simple change over switch to power the radio if you really need it, or the extra bike battery solution.