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Old 10-07-2020, 22:58   #1
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The numbers don't add up (?)...

Hello all. So I finally was able to come back to my (new to me) boat after 7 months sitting on the dry, only to find no electrical systems were working at all.. hmm.. I checked the batteries and voltage on the terminals and it was 4V (!) .. Ok.. time to do my part for the economy and get new batteries. They were indeed old anyway (I just bought the boat last year and the previous owner had no idea how old they were).

Nevertheless I was a bit ticked. I mean, I have got solar and wind.. I figured that would take care of the batteries during my absence. But ok, they were old, a cell died, what do I know. Move on with life.

I got new batteries installed a couple of days ago. I am still on the dry trying to get ready to launch so I am connected to power and of course my solar panel and wind generators are running.. I kept my eye on the voltage and most of the time it fluctuates between 13.2 and 13.8V .. so I figured batteries are charging. I would like to see the charger getting closer to 14.2V since I read that near the end of the charging process, this kind of extra tension is required to be able to squeeze in those last electrons (or is it to take OUT those last electrons :-) .. but ok. I assumed all is well.

Last night I wanted to do a test. I disconnected shore power so the only thing generating anything would be the wind generator. It wasn't particularly windy so I basically left the batteries carry the load overnight. My small fridge was running (EDIT: and my AIS transmitter which you can't really switch off) but that was about it. When I went to sleep, voltage read 12.8V .. which as far as I understand constitutes a "fully charged battery".

This morning I wake up 8 hours later to find the voltage at 12.2V which according to my readings is about 50% charge gone, and the point where most people say "time to charge those batteries again" to take good care of the batteries long term.

So I am thinking.. I have got 480Ah combined (2 x 240) .. You mean to tell me my fridge and AIS ate 240A over 8 hours? It is a really small unit (albeit old). I really had nothing else running overnight, not that I can think off. Am I right to be concerned something here is draining my batteries, to the point where it is conceivable that solar and wind (in Greece) wouldn't be able to keep them charged over the mild winter?.. that would explain the battery failure in the first place (compounded by the age of the batteries of course). Or am I overthinking this?

EDIT: I just did another test and cut off the switches and the voltage immediately jumped up from 12.19V to 12.34V ... that's a biggish jump isn't it? the fridge was already off .. hmm..
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Old 10-07-2020, 23:19   #2
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Re: The numbers don't add up (?)...

Maybe some panel wiring is corroded and causing a lot of resistance?
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Old 11-07-2020, 00:51   #3
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Re: The numbers don't add up (?)...

Just to confirm that you actually have 2 x 240AH @ 12V batteries and not 2 x 6V in series: What batteries?
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Old 11-07-2020, 03:09   #4
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Re: The numbers don't add up (?)...

Install a correct battery monitor with a shunt so you know the Ah going out at night and stop guessing based on voltage alone.
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Old 11-07-2020, 03:45   #5
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Re: The numbers don't add up (?)...

It is difficult to predict the SOC of the batteries with the type of voltage readings you are measuring. Nevertheless, 12.2v in the morning is much lower than I would expect from your description.

The most likely explanation is that you have a load that you are not aware of. Sometimes this type of load can come from defective equipment such as an alternator drawing power when off.

There are many other possible explanations. The first step in troubleshooting is to measure the current moving in and out of the battery. This is easily done with a clamp on multimeter (make sure it reads DC current via the clamp). These are not expensive, easy to use and a really essential tool for boat owners.
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Old 11-07-2020, 03:58   #6
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Re: The numbers don't add up (?)...

Quote:
Originally Posted by crankysailor View Post
. I kept my eye on the voltage and most of the time it fluctuates between 13.2 and 13.8V .. s

When I went to sleep, voltage read 12.8V .. which as far as I understand constitutes a "fully charged battery".

This morning I wake up 8 hours later to find the voltage at 12.2V which according to my readings is about 50% charge gone,

EDIT: I just did another test and cut off the switches and the voltage immediately jumped up from 12.19V to 12.34V ... that's a biggish jump isn't it? the fridge was already off .. hmm..
1. the batteries probably were not fully charged, may not mean anything for this "problem"

2. 12.V to 12.34V when you removed the load would indicated a fairly large current. Short resting voltage suggests 70% charged. If you had been fully charged that would be a 17A load all night. What was the amp draw before you turned off everything? I think something else is drawing power that you aren't thinking of.
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Old 11-07-2020, 04:11   #7
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Re: The numbers don't add up (?)...

It is just guesswork until you can read the amps, a battery monitor is about ~$100 - $150, quite easy to install.
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Old 11-07-2020, 06:30   #8
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Re: The numbers don't add up (?)...

Quote:
Originally Posted by StuM View Post
Just to confirm that you actually have 2 x 240AH @ 12V batteries and not 2 x 6V in series: What batteries?


Yes, I meant two 240Ah 12V each connected in parallel.. I just bought them a few days ago so I am pretty sure
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Old 11-07-2020, 06:33   #9
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Re: The numbers don't add up (?)...

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Originally Posted by sailorboy1 View Post
1. the batteries probably were not fully charged, may not mean anything for this "problem"



2. 12.V to 12.34V when you removed the load would indicated a fairly large current. Short resting voltage suggests 70% charged. If you had been fully charged that would be a 17A load all night. What was the amp draw before you turned off everything? I think something else is drawing power that you aren't thinking of.


Yes.. this is what I am suspecting... I have no clue what could be sucking so many amps.. I am going back to the boat now and will start physically disconnecting everything and see what happens
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Old 11-07-2020, 07:32   #10
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Re: The numbers don't add up (?)...

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Originally Posted by noelex 77 View Post
The most likely explanation is that you have a load that you are not aware of. Sometimes this type of load can come from defective equipment such as an alternator drawing power when off.

.

Hmm I think you might have hit the nail on the head right in the first try! I came back to the boat and started chasing this and when I disconnect the motor (at least that's what the red switch suggests...remember this is a boat new to me) the voltage jumped up immediately from 12.2 to 12.8.. I started fiddling with the not so user friendly battery monitor and from what I gather, the engine is drawing 6A...and it is not like I am going anywhere while sitting on the dry .. combined with a fridge running overnight I would have about 10 to 12A which start making this puzzle fall into place. So I guess the alternator is as you say a prime suspect... hmmm

On top of that it would appear that the solar and wind aren't pumping anything into the system at all .. If I disconnect shore power and the engine, net current is around zero.. now it could be that turning off these battery switches disconnects solar as well, I am not sure of that, I need to open up stuff and follow the mess...
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Old 11-07-2020, 09:31   #11
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Re: The numbers don't add up (?)...

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Originally Posted by crankysailor View Post
Hmm I think you might have hit the nail on the head right in the first try! I came back to the boat and started chasing this and when I disconnect the motor (at least that's what the red switch suggests...remember this is a boat new to me) the voltage jumped up immediately from 12.2 to 12.8.. I started fiddling with the not so user friendly battery monitor and from what I gather, the engine is drawing 6A...and it is not like I am going anywhere while sitting on the dry .. combined with a fridge running overnight I would have about 10 to 12A which start making this puzzle fall into place. So I guess the alternator is as you say a prime suspect... hmmm

On top of that it would appear that the solar and wind aren't pumping anything into the system at all .. If I disconnect shore power and the engine, net current is around zero.. now it could be that turning off these battery switches disconnects solar as well, I am not sure of that, I need to open up stuff and follow the mess...
Turn the engine switch back on, wait an hour and put your hand on the alternator. If it is warm you have a wiring problem with the engine not being turned off correctly.

What do you mean that your AIS can't be turned off? Add a switch or circuit breaker. There is no need to run it while on the hard or when in a marina.
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Old 11-07-2020, 09:37   #12
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Re: The numbers don't add up (?)...

Quote:
Originally Posted by crankysailor View Post
......
Last night I wanted to do a test. I disconnected shore power so the only thing generating anything would be the wind generator. It wasn't particularly windy so I basically left the batteries carry the load overnight. My small fridge was running (EDIT: and my AIS transmitter which you can't really switch off) but that was about it. When I went to sleep, voltage read 12.8V .. which as far as I understand constitutes a "fully charged battery".

This morning I wake up 8 hours later to find the voltage at 12.2V which according to my readings is about 50% charge gone, and the point where most people say "time to charge those batteries again" to take good care of the batteries long term.

hmm..
Yep, You're in the ball park. With 3 batteries overnight, with the fridge on, I would have felt very lucky to be at 12.2 volts in the a.m. Often 11.5 volts! It's just not a linear scale on voltage depletion I think.
I never understood why it works that way. My boats were all engine charged batteries except one that had a wind gen to help.
As the voltage goes down, but the draw stays the same, does it deplete faster?
My batteries were often not fully charged though, but close. That last 5% of charging seems like unobtanium! I think part of the problem is the battery gets a surface charge that is higher voltage than the battery will be after sitting for an hour.
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Old 11-07-2020, 14:32   #13
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Re: The numbers don't add up (?)...

It is also important to realize that while we think in terms of 12.8 V being fully charged and around 11.7 being discharged (because things begin to stop working at lower voltages), battery manufacturers consider a battery to be discharged when it reaches 10.5 volts. All the ratings are based on that. Additionally, the charger should get to a solid 14.2 (absorption voltage) well before the battery is fully charged. The fluctuations make me wonder about both corrosion and poor connections.
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Old 11-07-2020, 15:22   #14
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Re: The numbers don't add up (?)...

If you attach new charged batteries and the voltage stays at 13.8v for more than an hour or so you have a charger fault or it is incorrectly set. This will kill your batteries in no time. FLA's need 14.6-14.8v to reach full charge, sealed cells 14.2 to 14.4v. 13.8 is the car/motor boat setting where there is a constant power supply and batteries only rarely cycle. Check the charger AND the alternator regulator to ensure they are set for the correct battery type. Same for solar and wind. This is very likely why the previouse bank went dead.
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Old 11-07-2020, 15:35   #15
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Re: The numbers don't add up (?)...

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I just bought them a few days ago so I am pretty sure
I noticed last year our new FLA Trojans needed a few cycles before they settled down to give the sort of capacity I was expecting. Initially they seemed to drop quickly, but after a few weeks of discharges and then fully charging everything has been fine.

But I think Roland's post above warrants investigation as well.

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