Wiring of Alternator Warning Lamps

[RichLech]

On my Barrus Shire I've got two alternators, one for the starter batt (50A) and one (110A) for the domestic bank). The two work independently and have separate warning lights on the Deluxe Panel.

 

The 12V feeds for both alternator warning lights are from the ignition switch ie. from the starter battery. This is reflected in the wiring diagrams so was obviously deliberate.

 

Other than the fact that it would be more logical so use a feed from the leisure batteries for the domestic alternator warning light, is this going to cause any problems?

 

I've seen reference to this in past posts but it is unclear whether it is actually a problem. In my limited understanding this 12V feed is only used to "kick start" the charging and once that is done plays no further role.

 

Any comments will be much appreciated.

[nicknorman]

On my Barrus Shire I've got two alternators, one for the starter batt (50A) and one (110A) for the domestic bank). The two work independently and have separate warning lights on the Deluxe Panel.

 

The 12V feeds for both alternator warning lights are from the ignition switch ie. from the starter battery. This is reflected in the wiring diagrams so was obviously deliberate.

 

Other than the fact that it would be more logical so use a feed from the leisure batteries for the domestic alternator warning light, is this going to cause any problems?

 

I've seen reference to this in past posts but it is unclear whether it is actually a problem. In my limited understanding this 12V feed is only used to "kick start" the charging and once that is done plays no further role.

 

Any comments will be much appreciated.

Some installations use the leisure batteries to feed the leisure alternator's warning lamp, but for that a relay is required to switch on that feed when the engine electrics are switched on, which is an added complication (ie something more to go wrong). So sometimes the engine battery is used for both. Normally this doesn't cause s problem although I suppose if the batteries were at very different states of charge (eg engine battery full, leisure batteries flat) it might cause the warning lamp to glow dimly for a while but that is not really a big deal.

[OldGoat]

Umm - the lamp only indicates that the alternator is charging - not the state of charge of the ultimate battery and only draws a small current - so a common feed would be adequate?

[by'eck]

Umm - the lamp only indicates that the alternator is charging - not the state of charge of the ultimate battery and only draws a small current - so a common feed would be adequate?

 

Nevertheless there would be a small potential across the bulb of the domestic warning light equivalent to the difference between starter and domestic battery voltages, which I suppose could give rise to a faint glow, although unlikely.

 

Having said that I have a similar arrangement with both (LED paralleled with 47 ohm resistor) warning lights fed from starter battery feed. Works fine excepting that larger alternator shuts down completely with warning lamp illuminating when regulator voltage reached, leaving smaller one to complete charging.

[Tony Brooks]

Therein is the problem. Both you and Nick know how the systems work and interact so are not concerned on the odd occasion the lamp glows but I suspect the majority of boaters such occurrences would worry them. In my view safer and less worrying to fit a relay and keep both systems separate. Having a common feed can also make easily identifying a faulty alternator that still has some output more difficult.

[by'eck]

Therein is the problem. Both you and Nick know how the systems work and interact so are not concerned on the odd occasion the lamp glows but I suspect the majority of boaters such occurrences would worry them. In my view safer and less worrying to fit a relay and keep both systems separate. Having a common feed can also make easily identifying a faulty alternator that still has some output more difficult.

 

I was just pointing out both sides of the coin, although I think I may have misled you. The reason one of my alternators shuts down and so allows warning light to illuminate, is nothing to do with sharing the same excitation feed - see similar issue in thread here

 

On balance my own view is that the hassle of adding a relay to avoid sharing the excitation source is not worth the trouble,.

[RichLech]

Thanks for your replies people. While I was further investigating my high charging voltage yesterday (see my other post for (lack of) progress on that one) I did actually temporarily re-wire the domestic light to the domestic bank.

 

As you suggested, it did not make any difference to the charging issue.

 

Thanks again.