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Firstly, thanks to everyone that has replied on this.
The explanation of the bi-metalic switch sounds very sensible to me and also explains the red warning light on the helm control panel - the purpose of which I hadn't worked out either!
Ellaboat wrote: >Whatever happened to AndyH who asked the question >that prompted all this?
Yes apologies for not following up - I was away on the boat for more that a week - then spent a week catching up with all sorts of things
This leads me to another question I'm afraid....
I've now noticed that when the batteries are charged the ammeter, rather than ramping down to a low charging current, "pulses" between 0 and (about) 30A. I'm thinking this indicates the 4TR is faulty. Any views?
On a healthy (but discharged) battery, the 4TR regulator will maintain a constant output from the alternator, but when the batteries have taken sufficient charge for the terminal voltage to rise above a preset level it will start pulsing as you describe.
The 4TR is just a voltage dependent switch and relies on the time it takes for the battery terminal voltage to rise and fall coupled with the time it takes for the alternator's magnetic field intensity to establish and collapse to prevent it switching far more rapidly.
This simple system works well enough (eventually) but you can get a higher charge into your batteries (and quicker too) by fitting one of the new alternator charge controllers on the market.
There's no need to disconnect the 4TR if you do fit a "smart" charge controller. The only real issue is maintaining sufficient airflow around the alternator to keep it from overheating in a hot engine compartment (when it's working harder than before) but "smart" charge controllers take this into consideration by incorporating a rest period into the charge sequence. This rest period is important for the batteries too.
Cheers,
E/boat Steve
This message was edited by Ellaboat on Jul-26-08 @ 2:39 PM
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Ellaboat
Jul-23-2008 @ 9:53 PM
for more that a week - then spent a week catching up with all sorts of things 
