Galvanic isolators on positive side of 12V bus

[phorvati]

I am sorting out through high amperage 12V bus and trying decide what to throw away what to keep. Wiring on this boat is new to me. Ive owned the boat for 18 months and am yet to commission her. I am wondering if there are any reasons to have galvanic isolators on the positive side of 12V bus. I have 6 isolators total. Three are on the positive side. I have not managed to identify the wiring for the rest. I will be plugged into shore power for first few years. I also gave a northern lights 5kV genset which i will not put into service until I sort out the wiring.

I am finding that there are at least 2 generations of old unused wiring which I am taking out. Previous owners just kept adding wires. Nobody bothered to remove the old ones. That makes me think that some of the isolators might not even serve any function.

I would prefer to test them and put them on the ground side of AC.

[phorvati]

Actually now that I think of this, they are battery isolators. they have three terminals on them.

[billknny]

Galvanic isolators in the DC wiring? That's.... different.

A galvanic isolator is designed to block the flow of low voltage DC (<~~1 volt) and allow higher voltages to pass through. They serve no propose in your DC wiring other than adding un-needed voltage drop. I imagine somebody who was too clever by half could have thought they might solve a stray current problem. If there are stray current problems, fix the leak, don't do this. On a boat with wiring like you describe I'll be stray currents are running EVERYWHERE.

A boat needs ONE galvanic isolator in the shore power safety ground wire. No need for six at any time or place.

If what you are looking at truly are galvanic isolators, then all of the previous wiring was installed by someone who had no idea what they were doing--in addition to being sloppy and careless to leave obsolete wires in place.

Sounds like a real dog's breakfast!

[Andina Marie]

Originally Posted by phorvati

Actually now that I think of this, they are battery isolators. they have three terminals on them.

Correct, they are heavy current diodes to isolate batteries when charging is finished. They have been largely replaced by Combiners that have no voltage drop so your batteries get a full charge.

[sainted]

As Andina notes, battery isolators have generally be replaced by battery combiners on sail boats because they're more efficient. And it's great that you're ripping out abandoned wiring, which makes trouble shooting so much harder (not to mention the extra weight and mess).

However, before though get much farther in your electrical refit, you need to have a plan based on how you are going to use your boat and the electrical demands of the systems on you vessel.

Since you seem - no offense intended here - to be not too familiar with dc electrical components, you might do well to hire a marine electrician, at least to help you plan your system. Otherwise, you should grab one of Nigel Calder's books on the subject and study up.

It's not rocket science, but due care, thought and planning will ensure that you get the most out of your system.

[phorvati]

Originally Posted by sainted

As Andina notes, battery isolators have generally be replaced by battery combiners on sail boats because they're more efficient. And it's great that you're ripping out abandoned wiring, which makes trouble shooting so much harder (not to mention the extra weight and mess).

However, before though get much farther in your electrical refit, you need to have a plan based on how you are going to use your boat and the electrical demands of the systems on you vessel.

Since you seem - no offense intended here - to be not too familiar with dc electrical components, you might do well to hire a marine electrician, at least to help you plan your system. Otherwise, you should grab one of Nigel Calder's books on the subject and study up.

It's not rocket science, but due care, thought and planning will ensure that you get the most out of your system.

curious what made you think Im not too familiar?

[sainted]

Just that you appeared to confuse battery isolators and galvanic isolators, but of course, I really don't know anything about you.

All the best!

[phorvati]

Well I would probably be inclined to say the same if someone confused isolators and combiners. Ive been digging through a large mess of old mostly unused wires so its really hard to tell what they were during a brief moment of encounter. But they looked big, with large amperage terminals, and I know I will have to deal with them. Then i had to leave, and i figured i'd pop a question here earlier rather then later. Im yanking those out considering that a diode drop is not useful when sensing charging voltage. I just realized that I bought myself room for a starting battery within 2 feet of a starter motor. For my boat that is a heavy current load(Ford lehman 90HP). And old starter bank was at least 50 feet (round trip ) away. No wonder previous owner barely started the engine when i came to look at the boat. And he said those batteries were not even a year old.

[Mike Banks]

This is what I did. Whether or not it makes any sense to you is something else.

First, I went around to every piece of equipment on the vessel wired to anything, and labelled it and the voltage and current draw under full load required for everything. I marked the position of all of this stuff on a drawn up plan of the vessel.

Then I drew in red pencil all of the current draws in excess of or up to 100 amps but exceeding 15 amps. That was the anchor windlass and the cables for sail and dinghy handling--even though most would not draw more than fifty amps except for the anchor windlass. On the plan I drew this wire as heavy tinned cable--and that would run from the anchor windlass to a pony battery (a large one) situated abaft of the chain locker in a sealed water-resistant fibreglass box with a lid that was easily removed, but strong enough to have some light equipment stowed above it as needed on a temporary basis. Into this heavy cable I placed a 100 ampere overload switch. It is better to have that inconvenience of re-setting the switch than replacing a burned out anchor windlass motor, if the anchor is jammed. For the other loads, fit overloads as required. If the expected draw is 30 amps max, fit a 40 or 50 amp overload. If your budget does not run to overloads--use ceramic cartridge fuses and carry spares.

All of the heavy amperage cables are tinned copper cables ex-aircraft quality and acquired from military surplus. If you can not get access to this sort of cable second hand--welding cable for welder's 200 amp leads is good enough.

Almost every other load on the vessel is less than fifteen amps, except for the charging current to the pony battery. Because I run the anchor windlass only with the engine running, and gain another fifty possible amps from the alternator, I also run the heavy cable from the engine start battery to the pony battery. This way I bypass the regulator system for the main house battery bank, and just deliver as much as the alternator can put out to augment the pony battery. After hoisting the anchor, I usually run the diesel for a half hour or so afterwards as I motor out of the anchorage and set sail when the wind rises. The pony batrtery is also charged by the solar array and house battery system, but I fit a blocking diode, so thet using the windlass does not draw down on the house batteries or burn out the charging 6mm tinned twin charging lead from the solar array and house batteries charger--which is also a mains powered charger for use in a marina as well as being able to be connected to a gen-set if required to be..

The problem now becomes a lot simpler. You will need a roll of 6 mm tinned DC twin cable. You will also need a few lengths of open-able square conduit, some round conduit (all PVC) with angles and inspection ports on some of the angles and a couple of packets of countersunk stainless steel posi-drive screws. I know some people think stainless steel staples are adequate. I am not among them.

Next you will need some cartridge fuses, ten, fifteen and some even larger. Automotive fuses can work here if you can keep them in a dry environment.

From here there are two schools of thought. One school uses two bus-bars, and an earth heavy cable but one kept separate, which also runs the length of the vessel. The bus bars carry the main supply of all DC to all equipment, lights, gas detector etc. Moire on the earth later

The individual equipment is locally switched, (or permanently wired ON via a removable fuse). Equipment is locally fused, and the large and complex switchboards and excess metres of duplicated wires to and from remote switches are not used--just a few small circuit switches for nearby equipment, the master charging regulators for the house battery and all of the isolator switches for the bilge-pump float switch over-ride switches, as well as any meters that one may feel are required for monitoring equipment or the main bus-bars or house batteries.


The earth cable links everything metal on the vessel EXCEPT for the radio and Radar equipment which has a separate earth plate outside the hull. The other earth system is part of the lightning protection and is NOT connected to the negative rail of anything. On a boat, everything must have two wires and a fuse, preferable a flame-proof fuse. The earth linking cable just links anything metal and conductive and connects it to an external lighting earth--but NOT electronics equipment which has its own entirely separate earth plate.

Then there is the school that wants everything double-switched, one at the equipment, the other at a master panel. Lotsa luck--you wire everything in the same way except there are few if any local fuses--and all fuses are set into the long and wire-consuming positive legs of the DC supply in the panel itself, and they are usually those crappy glass fuses set into a spring loaded socket. Their only advantage is speed and ease of replacement, and they are no better than a plug-in automotive fuse--and may in fact be inferior.

I run all of my wires in conduits, waterproof ones set through watertight bulkheads using epoxy bog, or the re-enterable square ones with two channels for the bus bars, and smaller square re-enterable ones for the take-off's to individual equipment. When one takes off a wire from a bus bar, strip some insulation, take two turns of 6 mm core tinned around the wire and solder. To the other end of this wire where it reaches youyr equipment, fit a cartridge sealed fuse. The only exception is in the bilges. Always fuse any circuits to bilge pumps well clear of the bilge itself--just in case there are any fumes present and the gas detector has not picked them up. ALL BILGE PUMP CONNECTIONS MUST BE SOLDERED. Cover the soldered joints with heat shrink tubing, and ideally, the bilge pump wiring should be in circular conduits specifically for the purpose. A trough-hull and some non-tocic PVC hols wioll do to get the wires out of the bilge as tidily as possible, and from there the square conduit can take the wires to the bus bar or master switch panel. Small re-enterable conduits can hold about two or three circuits--but they seldom hold more than two. Larger re-enterable conduits can hold a whole bunch of circuits very neatly, and if one has labelled the cables as one inserted them, it is easy to isolate them later for further testing or additions.

Bilge ventilation is another topic.