Battery status- What’s broken

[tjbrace]

Whilst motoring home yesterday my Garmin 4012 started reporting ‘low voltage’ , threshold set to 9volts. The warning became increasingly frequent. This was confirmed by the monitor which was fluctuating between 12.5 and 7 volts with similarly silly charge/discharge rates. To preserve battery power, I switched off the fridge, auto pilot, and the 4012 and carried on. I know my batteries are now old, but with the engine running I thought this would provide sufficient power for these units.
Is it possible for bad batteries to affect alternator output?
Here is a list of what’s installed:

• 2 paralled domestic batteries, 110 ah each.
• 1starter battery, ah forgotten
• All batteries are Alphaline from 2014.
• VSR from KDD of this forum
• Yanmar 3gm30f (1991) with alternator.
• Sterling mains charger. 3 outputs with 2 clamped together.
• Eclectic Energy D400 wind turbine and PWM controller with 2 outputs.
• NASA bm2 monitor.
  
  
  the only charge source was the engine alternator as the wind turbine was stationary. Any advice very welcome!​

 

[VicS]

Bad connection somewhere
or bad battery isolation switch ?
Don't ignore the negative connections

 

[Caladh]

Check earths and output from the alternator and to the batteries with engine running.…..at least to start with.

 

[TernVI]

It is possible for failed batteries to pull the volts down, but that would require drawing a lot of current from the alternator and things would be warming up.
The battery monitor would show charge going into the batteries.
A fluctuating voltage suggests a bad connection, which may be getting hot.

 

[Refueler]

Boats can suffer same as cars where the negative lead needs removal ... clean up and put back ... alternator connections same ...

Some boats like mine tap main power of the starter relay for domestics - that can need cleaning and put back.

Basically my first action would be follow leads from the batterys and then check connections ... similarly from your switch system to control power to the boat. It can be a real pain but follow the leads and check ... not unusual to do this ... and cure the fault - but still be wondering what really was cause !

It may be an idea to have your alternator checked as well .. you may have problem there ...

As to batterys ? Here I will take the risk of flak ... but YES a bad battery can cause all sorts of woes ... depends on how you have system set up.

 

[tjbrace]

Thanks for your replies, lots to check which I can’t do until next week.
Refueler, thanks for risking the flak. Looks like you’ve escaped it this time?

 

[[70521]]

What did your multimeter read?

 

[tjbrace]

What did your multimeter read?

haven't tested yet, that will be next week. With the wind turbine tethered there is no charging happening so the batteries will have plenty of time to settle.

 

[tjbrace]

I think it is solved. When back on board I found the alternator drive belt so stretched that the alternator could be easily turned with one hand!
Belts now replaced and all seems ok again.
The rested batteries showed 12.95v domestic and 13.21v engine start. Wind turbine has been reactivated and the batteries are charging well.

 

[Refueler]

Magic ... glad it was a simple fix ...