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Old 28-10-2016, 01:01   #1
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Baffled - battery charge rate all of a sudden cut in half??

Hope someone can shed some light on this!

Our house bank is 345 amp @ 24v AGM batteries (Sonnenschein). 8 years old, never discharged more than 30% to 70% SOC, about 100amps usage between charges. We've been charging batteries by running generator about 3 hours per day, first thing in the morning. The small solar array we have left (in the process of upgrading solar) just barely manages to supply our load during the sunlight hours.

The typical charge rates we've seen on startup bulk charge is about 55-60 amps in bulk load (via our Victron 70amp Multi). The charge rate then drops as the batteries take a charge into the teens in adsorption mode and so on. After 3 or so hours we are in the high 90s% SOC. Every 3 or 4 days we make water with our generator after loading our batteries, which provides us enough extra power (max 20 amps available to charge batteries while making water) to top the batteries to 100%. We have been living like this all summer with no problem.

Then all of a sudden, three days ago, I noticed the bulk charge rate had dropped exactly in half (25 - 30 amps).

The same 1/2 charge maximum seems to happen under engine alternator - was 80 - 90 amps on start-up bulk stage, now 40 - 45 max on start-up bulk.

It seems (this is only the third day so still observing!) that the 1/2 reduction is only in early bulk stage. The charge rate curve seems to catch up over time - so it is not taking twice as long to charge - just not as fast at the beginning (hope that makes sense!).

Nothing else seems to have changed. The daily loads are exactly the same.

Any ideas?
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Old 28-10-2016, 02:08   #2
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Re: Baffled - battery charge rate all of a sudden cut in half??

Bad connections in battery bank so only part of the bank is being discharged/charged?

Batteries losing capacity?
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Old 28-10-2016, 05:50   #3
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Re: Baffled - battery charge rate all of a sudden cut in half??

Bad cell in one battery? What's the voltage during bulk charge?
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Old 28-10-2016, 09:54   #4
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Re: Baffled - battery charge rate all of a sudden cut in half??

Show us a drawing of how your batteries are wired.
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Old 28-10-2016, 10:03   #5
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Re: Baffled - battery charge rate all of a sudden cut in half??

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Bad cell in one battery? What's the voltage during bulk charge?
I will check again tomorrow, but I believe it has not dropped, 28 something Volts.
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Old 28-10-2016, 10:09   #6
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Re: Baffled - battery charge rate all of a sudden cut in half??

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Originally Posted by DeepFrz View Post
Show us a drawing of how your batteries are wired.
Here's the wiring diagram from our ship's manual
Attached Files
File Type: pdf Manuel proCatana 50 fr 15 04 07 ind A_EN 41.pdf (41.6 KB, 34 views)
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Old 28-10-2016, 11:52   #7
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Re: Baffled - battery charge rate all of a sudden cut in half??

Measure drop between pos terminal of charger and pos terminal (touching lead) of a battery. Same for negative and report back. All this in early bulk.
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Old 28-10-2016, 12:29   #8
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Re: Baffled - battery charge rate all of a sudden cut in half??

Could be a bad battery or bad connection on the batteries. Could also be that you have been undercharging the batteries and they have sulphated but that would be a slow degradation, I would think.
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Old 28-10-2016, 12:35   #9
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Re: Baffled - battery charge rate all of a sudden cut in half??

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Originally Posted by svlamorocha View Post
Measure drop between pos terminal of charger and pos terminal (touching lead) of a battery. Same for negative and report back. All this in early bulk.
We have an 18 hour sail tomorrow - heading to a yard to do some other work, but have now put this on our priority list. I will do that asap.... Thanks
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Old 28-10-2016, 12:39   #10
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Re: Baffled - battery charge rate all of a sudden cut in half??

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Could be a bad battery or bad connection on the batteries. Could also be that you have been undercharging the batteries and they have sulphated but that would be a slow degradation, I would think.
I will check the connections first thing in the morning, but doubt that. And, we have never gone more than 3 or 4 days with a 100% charge on the bank, we make water using our generator about every 3rd day, which gives us an extra 3 hours of low charge adsorption time, and always gets to float levels, and we motor almost as much as a power trawler!!!

Thanks
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Old 02-11-2016, 17:48   #11
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Re: Baffled - battery charge rate all of a sudden cut in half??

It looks like the first answer is most likely,check all battery connections.I have 16 battires to worry about, feel for heat on all battery connections,and wiere runs.Have fun.Solar help
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Old 03-11-2016, 05:31   #12
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Re: Baffled - battery charge rate all of a sudden cut in half??

Sorry for delay in responding. We are now tucked into a marina for a few weeks, so back at this.

donradcliffe, & David Trupiano - No loose connections, no warm batteries, but they are fully charged now and on float, as we are connected to shore power.
boatbod - charge voltage is in 28v range, sometimes hits 29.
svlamorocha - have not done that yet! We are now in a marina on shore power. But I will try to test this over the next day or two...

I had someone tell me that means the batteries are giving up! ??

Thanks everyone...
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Old 03-11-2016, 05:56   #13
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Re: Baffled - battery charge rate all of a sudden cut in half??

It could also mean that something that was drawing power, no longer is.
Anything from fridge, Radar, Autopilot etc.
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Old 03-11-2016, 06:10   #14
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Re: Baffled - battery charge rate all of a sudden cut in half??

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It could also mean that something that was drawing power, no longer is.
Anything from fridge, Radar, Autopilot etc.

How would that effect the bulk charge rate? Our charge rate in early bulk phase has been very consistent (especially on generator since it has lots of excess generation capacity over and above the battery charger) - then all of the sudden from one day to the next, it drops to half. Even prior to the drop, the charge rate when on generator, ever changed, regardless of what load we had on the batteries.
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Old 03-11-2016, 06:19   #15
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Re: Baffled - battery charge rate all of a sudden cut in half??

If the shunt measuring battery current is installed such that it measures battery charge and discharge current (amp counting type) then if a load is present that will display on the amp meter as less charging current. It all depends on where the current measurement is done. The charger may be outputting the same current but the current used by house loads will be subtracted from the displayed charging current.

When things change by exactly half then I look for "simple" explanations like something could be wrong with the shunt or sampling wires.
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