ignition switch mystery

[Scholar Gypsy]

Thanks to Alan & Tony for their comments, which should help me next weekend.

 

I did have the situation (just before crossing from Salters Lode to Denver Sluice) where the engine started but the water & oil gauges did not work, and the alternator produced nil amps. A gentle tap on the panel brought it all back to life.

 

My rev counter has been stuck on 1,200 for about 15 years - although the integral hour meter works well - so I might get to fix that as well....

[Scholar Gypsy]

Thanks to Alan & Tony for their comments, which should help me next weekend.

 

I did have the situation (just before crossing from Salters Lode to Denver Sluice) where the engine started but the water & oil gauges did not work, and the alternator produced nil amps. A gentle tap on the panel brought it all back to life.

 

My rev counter has been stuck on 1,200 for about 15 years - although the integral hour meter works well - so I might get to fix that as well....

 

Well I took the multi-way connectors to pieces yesterday, all five of them, gave them a good clean with WD40, and found one spade clip that had worked half-loose. All seems to work fine now, and I am now half way to being able to produce a decent wiring diagram. The hour-meter has been the most erratic over the last couple of weeks.

 

It was interesting to finally work out which circuits are fused (fuel pump, horn etc) and which are not (engine start and stop solenoids, oil and water temp gauges.)

[Scholar Gypsy]

 

Well I took the multi-way connectors to pieces yesterday, all five of them, gave them a good clean with WD40, and found one spade clip that had worked half-loose. All seems to work fine now, and I am now half way to being able to produce a decent wiring diagram. The hour-meter has been the most erratic over the last couple of weeks.

 

It was interesting to finally work out which circuits are fused (fuel pump, horn etc) and which are not (engine start and stop solenoids, oil and water temp gauges.)

 

And here is the wiring diagram (PDF version, produced in powerpoint). A bit more to do on:

• the connections to the Adverc (I have the manual);
• the large number of wires attached to the alternator - linked to previous point;
• the various gauges, sensors and alarms, not least as a lot of the wires behind the panel seem to have no useful function - but maybe the switches are supposed to light up in the dark, if so then I have a bit more work to do;
• working out exactly which wires go through the five connectors on the main wiring loom. Some guesswork so far.

but it might be helpful to others trying to understand how boat electrics work. I think what I have is a fairly standard/typical set up, though there are some personal additions over the years!

[by'eck]

 

And here is the wiring diagram (PDF version, produced in powerpoint). A bit more to do on:

• the connections to the Adverc (I have the manual);
• the large number of wires attached to the alternator - linked to previous point;
• the various gauges, sensors and alarms, not least as a lot of the wires behind the panel seem to have no useful function - but maybe the switches are supposed to light up in the dark, if so then I have a bit more work to do;
• working out exactly which wires go through the five connectors on the main wiring loom. Some guesswork so far.

but it might be helpful to others trying to understand how boat electrics work. I think what I have is a fairly standard/typical set up, though there are some personal additions over the years!

 

Neat wiring diagram. One issue mentioned several times above sticks out though - the single isolator in the negative. Although a popular concept in the past requiring only one isolator, its not a good idea for several reasons (not all specific to your installation):

 

Your high current starter motor connection is permanently live to battery positive.

Combined battery load is fed through a single isolator which may not be up to taking the current safely now or in the future when further additions are made.

How can you be sure that any item wired directly to the battery negative doesn't provide a bypass to this switch for other devices (bilge pump, heater timer, alarm etc.).

A path via dampness is possible.

These stray paths are often through tenuous connections or thin cables, increasing the likelihood of something melting, fire or extra corrosion.

If as you should, have battery negative connected to the hull via a single strap, the likelihood of stray paths increases enormously. In any case its very difficult to absolutely avoid some sort of connection from battery negative to hull unless you have a completely dry plastic boat. There are too many engine and other ancillaries that have a negative return through their casing which may be bolted to the hull or engine crankcase.

 

Having isolators in each of the battery positive feeds allows each set to be turned off independently making electrics safer to work on. It also splits the load between several isolators so reducing the likelihood of overloading any one.

 

Other observations: the diode splitter will drop volts. Although this will be compensated by the Adverc controller sensing on the domestic bank, the starter battery will likely receive too higher charge voltage. Not sure why the radiator pump control is fed with direct alternator output as well as feed from diode splitter to domestic batteries, unless its to sense when engine is running.

[Scholar Gypsy]

 

Neat wiring diagram. One issue mentioned several times above sticks out though - the single isolator in the negative. Although a popular concept in the past requiring only one isolator, its not a good idea for several reasons (not all specific to your installation):

 

Your high current starter motor connection is permanently live to battery positive.

Combined battery load is fed through a single isolator which may not be up to taking the current safely now or in the future when further additions are made.

How can you be sure that any item wired directly to the battery negative doesn't provide a bypass to this switch for other devices (bilge pump, heater timer, alarm etc.).

A path via dampness is possible.

These stray paths are often through tenuous connections or thin cables, increasing the likelihood of something melting, fire or extra corrosion.

If as you should, have battery negative connected to the hull via a single strap, the likelihood of stray paths increases enormously. In any case its very difficult to absolutely avoid some sort of connection from battery negative to hull unless you have a completely dry plastic boat. There are too many engine and other ancillaries that have a negative return through their casing which may be bolted to the hull or engine crankcase.

 

Having isolators in each of the battery positive feeds allows each set to be turned off independently making electrics safer to work on. It also splits the load between several isolators so reducing the likelihood of overloading any one.

 

Other observations: the diode splitter will drop volts. Although this will be compensated by the Adverc controller sensing on the domestic bank, the starter battery will likely receive too higher charge voltage. Not sure why the radiator pump control is fed with direct alternator output as well as feed from diode splitter to domestic batteries, unless its to sense when engine is running.

 

Thanks very much - all very helpful. Moving to two isolators on the positive side may be my project for next winter - there would be quite a bit of cabling to replace to reach the sensible location for the new isolators.

 

I have been pondering these issues over the last few days, since I finally got around to putting this together, 20 years after installation. In particular I do need to add a fuse to the negative side of the Smartgauge circuit - that's the only item left on when the boat is unattended. It also seems rather odd that the various gauges and dials are not fused at all, while (for example) the fuel pump is.

 

On the radiator pump - you are right. Out of sight, there is a three way switch for the radiator pump - off, on (for testing), and auto (on when the engine is running).

 

The engine charge current drops to nil after about five minutes of running.

Edited May 14, 2014 by Scholar Gypsy

[by'eck]

Generally only the positive legs are fused on various circuits. Remember that battery negatives are (usually) strapped to hull so no chance of a short on negative returns through chaffing.

 

Its possible to go OTT with fusing especially on short cable runs. Better to spend time and money on mechanically good installations so no chance of chaffing etc.

[Scholar Gypsy]

Dear Richard

 

Many thanks - I take the point re fuses on the dials etc: any shorts on the much longer "downstream" cable runs will lead to false readings (eg the temperature alarm triggering when it shouldn't) rather than a risk of fire/melting etc.

 

What you say on strapping applies if the isolators are on the +ve side, of course: with the isolator on the neg side there is a theoretical risk of frayed insulation on the neg cable for "always on" equipment touching the hull, which could be interesting if you tried to start the engine with the (negative) isolator turned off.

 

For some reason I had it in my mind that the Smartgauge instructions recommended a fuse on both pos and neg cables, for this reason. But on checking I see that is not the case: one less thing to do. However the instructions for my VHF radio do reccomend double fuses - with a diagram showing the wires connected directly to the battery posts ...

[by'eck]

All I can say being an ICOM fan, is that the several marine HF and VHF radio's I have fitted have all had just one manufacturer supplied fuse in the positive leg. It may be that your radio's DC input assumes an isolated return (negative) system hence perceived need for two fuses.

 

As I alluded to in post above you can justify in your mind having fuses everywhere, but some moderation has to prevail else you end up with a system that creates more safety issues than it prevents.