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Posted: Tue Apr 10, 2012 9:03pm

Post Subject: red ing/battery light

on returning from our first outing this year the red warning /ing light stayed on from minutes to continuous over a 5 hour period.the isuzu 42engine is fitted with 1 lucas 80ah & 110ah alternator.we quickly checked all belts and these were in good condition and at the correct tension.the voltmeter continued to display in its normal charge position and our led battery condition, read 13.2 to 13.5 charge on engine & domestic batteries at end of journey.the bow thruster worked as normal with no loss of power.i am at a loss as to why the red light stays on and any help would be much appreciated, many thanks rob.


Posted: Tue Apr 10, 2012 9:25pm

Post Subject: red ing/battery light

First of all with 2 alternators my view is that you really should have two warning lamps although far too often only one lamp is used. This has a number of effects such as requiring the engine to be revved more than normal to energise the alternators, false failed alternator warnings caused by poor connections or faulty batteries and, more to the point, making the diagnosis of which alternator is faulty difficult. You do not tell me what the voltmeter actually registered or which battery bank it is monitoring. You also do not tell me which battery bank the LED "battery condition" is monitoring. However I can tell you that at the end of a 5 hour cruise both the voltmeter and "battery condition" should read between 14 and 14.5 volts. In my view one of the alternators has failed. However if you are saying the "battery condition" reading was taken as soon as the engine was shut down then the readings reflect surface charge and can not be relied on for diagnostic purposes. Put a multimeter set to 20 volts DC across the engine battery, start and rev the engine. The meter should jump up and after half an hour or so should read 14 to 14.5 volts. Repeat with the domestic bank. The same applies BUT this time it could take a couple of hours or more for the meter to reach 14 to 14.5 volts. This shoudl give you some idea about which alternator might be faulty, however with just one warning lamp you need to rule out bad connections between both alternators, their batteries and ignition switch. Also repeat for the negative circuit from battery neg to alternator neg. Look for a large multi-way connector on the main wiring harness that runs from engine to control panel. These are known to work lose and develop dirty contacts. Tony Brooks

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