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36 minutes ago, Tony Brooks said:

 Not if the alternator is energising to the questioner's satisfaction its not - once the new bulb is fitted. However I think the OP said the new bulb will be of a lower wattage so a resister may still be needed at that point.

But if there was a need for the resistor in the first place, chances are there remains a need for the resistor. People generally don’t add resistors without need.

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why mess with with resistors which mean extra wiring connections to go faulty, like whats happened, when the bulbs are required anyway.W 5w bulbs should be sufficient. If needed just drill out oversize the facia holes for bigger more substantial bulb holders.

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Bulbs - haven't seen one of those for many a year in my youth I used to change those bulbs all the time I think I still have a tool for pulling them out from the front of the panel.

 

i think Biz is right it would be worth changing them out for a more modern fitting able to take a slightly larger bulb, typically around 2W or more and a damn sight easier (and cheaper) to get hold of.

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13 hours ago, Tony Brooks said:

 Not if the alternator is energising to the questioner's satisfaction its not - once the new bulb is fitted. However I think the OP said the new bulb will be of a lower wattage so a resister may still be needed at that point.

Yes, the new bulb has a lower wattage (1.2W instead of 2W). I will replace the resistor with a new 47 ohm one, not a 68-ohm one as I originally typed, although I think both would still pass enough current to energise the alternator?

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13 hours ago, nicknorman said:

But if there was a need for the resistor in the first place, chances are there remains a need for the resistor. People generally don’t add resistors without need.

Not my experience and not what we see on here occasionally. It only takes one bar room expert and some poor boater is likely to do what they say will cure their problem. However in this case the neat sleeving suggests that the panel maker probably thought one was required but based on what? We used to energise the ACRs with a 2.2 watt bulb without problem but once you add in things like cam shaft driven alternators, split charge relays and possibly hour counters that may not be enough but I would have thought 2 watts would be OK on most engines where it is just energising the alternator, be it with a bit of a rev to start charging. The only true bulbs that do not seem to energise the alternator without help are grain of wheat (dolls house) bulbs. Even 2 watt "push in bayonet" bulbs seem to work most of the time.

 

I am with Biz though. keep things simple and the component count down, fit a warning lamps that takes a higher wattage bulb.

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Ok, I will see how I get on with the low wattage replacement lap + resistor. Plan B will be to mount a higher power lamp and remove the resistor.

Is it always the case that once the alternator is energised, there should be no current through the bulb? I.e. if the bulb goes out (and is not blown) does this always mean the alternator is successfully energised, assuming the alternator isn't faulty itself..

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17 minutes ago, GrahamSop said:

Ok, I will see how I get on with the low wattage replacement lap + resistor. Plan B will be to mount a higher power lamp and remove the resistor.

Is it always the case that once the alternator is energised, there should be no current through the bulb? I.e. if the bulb goes out (and is not blown) does this always mean the alternator is successfully energised, assuming the alternator isn't faulty itself..

Yes & yes - until the brushes or slip rings wear.

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Slightly off topic with the alternator/tacho issues, but in the process of investigating, I've drawn up a wiring diagram.

I'm about to wire in a 12V fridge, so I want to be able to isolate the starter battery from the domestic ones.

There is a cable connecting the +ve of the starter battery with the domestic ones. It's a newer looking cable, and is bolted on top of all other cable terminals so to me it looks like a later addition. Maybe the engine alternator I've been trying to get energised (alt 2 in my drawing) wasn't charging the starter battery so the previous owner has just connected them all together..?

I want to remove this cable (the one with the ??? in my drawing) so I can isolate the starter battery, but of course I need to make sure the alternator is working.

Does this make sense?

 

wiring diagram.jpg

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Yes perfect sense. Get both alternator's working & simply discard that cable.

 

There might be an issue about energising the second alternator but another warning lamp and relay should sort that out. It all depends upon how the boat is wired. From the Photo the 47 ohm resistor plus 2 watt bulb makes mores sense if the one lamp is trying to energise two alternators. Not that one bulb  energising two alternators is ideal because it can produce fault finding difficulties.

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The BSS does require an isolator between alt 1 and the batteries.  But it is quite common to wire as yours is done, though an examiner ‘might’ pick it up.  It’s not normal to have a fuse between the alternator and batteries - alt1 & 100A fuse.

Edited by Chewbacka

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13 minutes ago, Chewbacka said:

The BSS does require an isolator between alt 1 and the batteries.  But it is quite common to wire as yours is done, though an examiner ‘might’ pick it up.  It’s not normal to have a fuse between the alternator and batteries - alt1 & 100A fuse.

No, but if wired direct to the battery as it is then it’s a good safety measure. 

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2 hours ago, GrahamSop said:

Slightly off topic with the alternator/tacho issues, but in the process of investigating, I've drawn up a wiring diagram.

I'm about to wire in a 12V fridge, so I want to be able to isolate the starter battery from the domestic ones.

There is a cable connecting the +ve of the starter battery with the domestic ones. It's a newer looking cable, and is bolted on top of all other cable terminals so to me it looks like a later addition. Maybe the engine alternator I've been trying to get energised (alt 2 in my drawing) wasn't charging the starter battery so the previous owner has just connected them all together..?

I want to remove this cable (the one with the ??? in my drawing) so I can isolate the starter battery, but of course I need to make sure the alternator is working.

Does this make sense?

 

wiring diagram.jpg

With that wire in place you don't have separate starter and domestic battery banks, you have a single bank of three batteries. It would be very easy to run all three down to the point where you are unable to start the engine. Then what do you do? (Unless you have a hand start).

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I really would ditch the 100A fuse, or if you insist on having it make it 200A then it won’t be operating hot for long periods. If there is a cable short you will get way over 200A and the fuse will blow. Not that you will get a cable short if you install the cable properly.

 

Also I’d put the solar on the other side of the isolator (ie direct to the battery) with the fuse near the battery. That way the batteries will be kept charged even with the isolator off. Also, solar is a bit like an alternator, if you open the isolator when it’s working hard it can trash the solar controller.

Edited by nicknorman

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4 hours ago, nicknorman said:

Also, solar is a bit like an alternator, if you open the isolator when it’s working hard it can trash the solar controller.

I have a 50A circuit breaker between panels and controller, (not between controller and batteries), which I break occasionally if the solar is working, and I want to do something with the batteries. Could that trash the controller?

 

 

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5 minutes ago, Richard10002 said:

I have a 50A circuit breaker between panels and controller, (not between controller and batteries), which I break occasionally if the solar is working, and I want to do something with the batteries. Could that trash the controller?

 

 

No that is absolutely fine and a good idea. It is when you interrupt the connection between controller and batteries that it can cause disaster (depending on the specific controller).

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On the warning light subject. Warning lights were something we were used to from dynamos. In fact, early alternator systems had a separate unit purely to operate one. The next generation of alternators required a small initial current to get them going and it made sense to double task a lamp filament as a ballast resistor for that initial current. The thing is that this left the whole system vulnerable to complete failure because a lamp filament had burned out. This is the original reason for shunt resistors, CAV actually made a lamp holder incorporating one specifically for charge lights. The wheel long ago came full circle and many newer European and Japanese and nearly all American alternators no longer need that small current and go back to simulating the warning light but now with a transistor circuit which goes pop when people try to improve cutting in speed by adding shunt resistors. I did write a "how your alternator works" thing. I must see if I can find it.

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I have now replaced the blown charging lamp (with the new lower power one), and also replaced both the corroded resistors with new 47-ohm ones. I get two charging lamps at ignition, and they both go out once the engine is running. The tacho also now works nicely! So it appears all is ok. 

 

I have also swapped the solar +ve to the battery side of the domestic isolation switch, I agree this makes more sense. Re cutting the power to the solar controller while it's working hard - I can't see an obvious way to turn off the controller other than cutting the supply from the battery, although I haven't had a good look through the functions yet. I disconnected it in the evening when there was barely any power coming in, so it's ok but it's good to know about this potentially wrecking the controller.

 

Finally, I've removed the cable between the starter battery and domestic ones. I'm a lot happier now that I'll at least be able to start the engine if I drain the domestic batteries. Fridge has been running smoothly for 3 days now, on the 2 domestic batteries and no problems at all with healthy voltage even after the night. Although, it's been sunny so the solar has been helping a lot! Winter will be the real test!

 

Thanks again for all your help!

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16 minutes ago, GrahamSop said:

I have now replaced the blown charging lamp (with the new lower power one), and also replaced both the corroded resistors with new 47-ohm ones. I get two charging lamps at ignition, and they both go out once the engine is running. The tacho also now works nicely! So it appears all is ok. 

 

I have also swapped the solar +ve to the battery side of the domestic isolation switch, I agree this makes more sense. Re cutting the power to the solar controller while it's working hard - I can't see an obvious way to turn off the controller other than cutting the supply from the battery, although I haven't had a good look through the functions yet. I disconnected it in the evening when there was barely any power coming in, so it's ok but it's good to know about this potentially wrecking the controller.

 

Finally, I've removed the cable between the starter battery and domestic ones. I'm a lot happier now that I'll at least be able to start the engine if I drain the domestic batteries. Fridge has been running smoothly for 3 days now, on the 2 domestic batteries and no problems at all with healthy voltage even after the night. Although, it's been sunny so the solar has been helping a lot! Winter will be the real test!

 

Thanks again for all your help!

Excellent and thanks for reporting back. Regarding the solar, if you need to disconnect it from the battery you can either fit a switch/isolator between the panels and the controller, or simply cover the panels with blankets, duvets etc. Or only disconnect in the dark or in tunnels! Since it seems unlikely that you would want to turn it off more than very occasionally (eg when replacing the batteries) I suggest that the blankets/duvet/dark is a perfectly acceptable solution.

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