Bizarre voltage drop

[Peregrine1983]

Curious if anyone can shed some light on this issue...

We recently replaced our Raymarine autopilot computer because the old one was fried.

This morning while underway under sail we had the autopilot steering for about 5 hours in about 20kts of wind. I then noticed that our Vesper XB8000 AIS wasn’t transmitting or receiving.

I went below, checked connections, looked OK. Breaker not tripped. Volt meter on panel showing around 12.3v in the batt bank. I ended up pulling the power wires from the ais unit and testing with a voltmeter - the voltage was fluctuating from 12.x down to 2-3 volts every couple of seconds. It seemed to correspond with the autopilot drive unit engaging. Time to shut off the autopilot.

Thinking this meant the autopilot had basically drained our house battery bank (600ah golf cart batts), I had my wife hand steer and turned on the engine to charge them up. I figured our 300w of solar would not be enough to charge them up in any reasonable amount of time if they were so low that the autopilot drive was causing such a huge voltage drop.

With the autopilot off and the engine on the power wires to the AIS now say about 13.8x. I reconnect them to the ais, but the unit won’t power on. When I stick the voltmeter probes into the butt connector connecting the ais unit to the power wires it shows that same low voltage of 2-3v, but now constant at just 2-3v.

I remove the butt connectors and disconnect the ais, check the power wires again coming direct from the panel and they read 13.8x. Reconnect to the ais, the ais wont turn on and the same wires show 2-3 volts.

I’m super confused. Any ideas what is happening here? Now I’m concerned that some sort of power issue fried our old autopilot and is on track to fry other gear.

[jamhass]

I would suspect a bad connection at the other end of the power cable. Don't forget to check both positive and negative leads, could be on the ground side.

[Peregrine1983]

Thanks jamhass. Will check that and report back.

[DeepFrz]

Sounds like you have a bad connection or wire to the AIS. Also maybe your batteries are weak. Just guessing because you haven't given us much to go on like battery age, usage, charging regime, etc.

[Peregrine1983]

Originally Posted by DeepFrz

Sounds like you have a bad connection or wire to the AIS. Also maybe your batteries are weak. Just guessing because you haven't given us much to go on like battery age, usage, charging regime, etc.

Thank you. I do not think the batts are weak. Performance has been fantastic. Topped them all off with distilled water just a few weeks ago. They are 4xDuracell 6v golf cart batteries in two 12v pairs. 2017 vintage. Charging is through 300w of solar into a Victron 15/75 charge controller and from the motor through a 150 amp alternator through a Aqualine Plus marine regulator. Batteries have seen heavy use over the past 4 weeks due to a long cruise, but I'm inclined now to think this may be a negative/ground connection issue. I need to wait until we stop to take the panel apart, but will report back.

[boatbod]

You have a bad connection somewhere in the wiring. When the AIS is not operating there is no current draw so no voltage drop. Diagnosis is simple... make sure current us flowing in the power wires and use you meter to check the voltage at each end and at any splices that exist in the wiring.

[barnakiel]

To me sounds like something shorted on the ais unit pcb.


If I read you post right.


b.

[Peregrine1983]

Promised I would report back on this fwiw... turned out to be a bad breaker. The terminals on the back were loose and every other rock back and forth of the boat was causing the voltage to drop on the positive. I’ll likely be replacing my breaker panel this winter as it’s the original Marinetics.