Alternator Question

[wooslehunter]

I have a really simple set-up.

The alternator is an old Fiesta 1100 unit. It's connected through an isolator switch to the battery. The field winding's connected through the charge lamp & starter switch to the isolator/battery.

The system seems to work OK but reacts strangely when loaded more than normal. Normal load is GPS, VHF, tillerpilot etc - fairly low load & charge lamp off as expected. When I switch on the nav lights, the charge light starts to glow. No prob with the battery either.

I had the alternator tested by Lucas & it's good for 30A so no prob there.

Anyone got any ideas?

 

[fireball]

If your alternator and battery are ok (how did you check the battery?) then it is down to the equipment and/or wiring ....

Have you tried turning off the GPS, VHF & Tillerpilot etc and just turning on the nav lights?
If the charge lamp comes on then you'll need to check the cabling for wear that could be shorting out.
Otherwise could it be some dodgy wiring between the isolator switch and the battery? Easy one to check - replace with a jump lead!

 

[wooslehunter]

Same problem with a new battery. Hence assume battery is OK. Wiring is new also.

Battery does remain charged but that's because most of the time spent motoring is during the day time with minimal load. If I had to motor all night I may have a problem.

 

[VicS]

Its almost certainly a poor connection somewhere. With only a light load there is only a small voltage drop across it but when you increase the load somewhat the volts drop increases and then there is sufficient difference across the warning light (rememeber one end is at alternater output potential) for it to glow.

I had this some years ago on the car when driving back from holiday through the night. It this instance the light glowed when the turn indicators were on! Fortunately I found an AA man in the Motor way service area who checked that the alternator was charging OK and suggested a poor connection. In this case it turned out to be a bad contact between a fuse and its holder.

You will have to look at those parts of your wiring which are common to the warning light and the load which causes the symptom to occur.

 

[William_H]

Connect a wire temporarily from the nav lights to the battery terminal. Nav Lights should be on. With engine charging I am guessing the charge light won't be on. If it is I dunno. If charge light is not on them work your way through the system with the wire that was on the battery. ie to the battery switch There will probably be a point where the problem reoccurs isolating the area of problem. Probably switch or fuse contacts. good luck olewill

 

[sailorman]

the lamp is fed by 2 wires ( Live when engine running ) that should be of equal power out-put, ie. say 13.2 v each,when the engine is running. if there is a poor connection on one of them the out-put will be lower than the other wire therefore the bulb will glow to a greater or lesser amount.

 

[wooslehunter]

Thanks All,

I'll check all connections as soon as the boat's back in the water next week.