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Over-charging batteries


Col_T

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We have 5 x 110Ah batteries, fitted late 2014; 300-ish wats of solar, fitted late 2018; a BM1 battery monitor, fitted middle-2020; use the boat mainly 3 or 4 weeks at a time; usually cruise 5 hours a day; boat left on hook-up, batteries trickle charging, when in a marina until we fitted the solar panels. 

 

The BM1 usually shows 12.9 or 13.0v when we retire, and 12.8 or 12.9 when we rise next morning, with outnight consumption about 25Ah - 12v fridge left on. Happy to concede the consumption may be a little iffy, as I don't recall if I connected both alternators to the bus-bar fitted when I installed the BM1, so the engine start battery may have an alternator connected. However, that shouldn't affect the voltage readings.

 

My interpretation of the above is that the battery bank is, effectively, spending it's whole life at 100% + surface charge. 

 

Is this correct, and will it damage the batteries at all?

 

 

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I think that after six years I would want to keep a closer eye on the electrolyte levels or the relative temperature of the batteries as they come off charge in case a cell starts to short. At least keep a mental log of the battery voltages and thus the state of charge so you can identify when they start to discharge more than usual and take longer to recharge.

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30 minutes ago, ditchcrawler said:

I guess the sun is up before you

Yup, even in winter?

 

The bit I didn't mention is that they are sealed lead acids, so no checking electrolyte levels on those, unfortunately, which is one reason why I'm 'curious' about damaging them. Lady wife is unimpressed, as she reckons I've gone from 'turn that off, we mustn't use too much electricity' to 'no, leave it on, we need to run down the batteries a bit' in a matter of minutes!

 

It's a dogs life, eh!? 

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2 minutes ago, Col_T said:

Yup, even in winter?

 

The bit I didn't mention is that they are sealed lead acids, so no checking electrolyte levels on those, unfortunately, which is one reason why I'm 'curious' about damaging them. Lady wife is unimpressed, as she reckons I've gone from 'turn that off, we mustn't use too much electricity' to 'no, leave it on, we need to run down the batteries a bit' in a matter of minutes!

 

It's a dogs life, eh!? 

In that case the morning voltage will be the charging voltage and they would have been lower in the dark

 

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13 minutes ago, Col_T said:

Yup, even in winter?

 

The bit I didn't mention is that they are sealed lead acids, so no checking electrolyte levels on those, unfortunately, which is one reason why I'm 'curious' about damaging them. Lady wife is unimpressed, as she reckons I've gone from 'turn that off, we mustn't use too much electricity' to 'no, leave it on, we need to run down the batteries a bit' in a matter of minutes!

 

It's a dogs life, eh!? 

 

I suspected as much which is why I suggested an occasional feel of each battery to assess temperature after charging.

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Yup, I had guessed that, so to-days little experiment is to isolate the panels so that I can see what the voltage really is when we rise. Isolating the panels is easily done, as we have an isolation switch between the panels and the solar controller.

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They can get a thing called positive grid corrosion but I don't really understand it. I think is is may depend on the solar controller. A PWM controller will overcharge, a MPPT less so, As I turn everything off when I leave the boat on it's mooring I have a 7 day time switch and a relay in the panel feed to the controller, (Do not fit in the controller to battery lead) thus I set the panels to be connected two days a week, one in summer. 

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As long as the float charge voltage is around 13.2 volts (2.2 volts per cell) they will come to no harm.

 

Many batteries used for standby power spend their entire lives on float at 2.2 vpc, just waiting for the mains to fail so they can do some work.

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14 hours ago, Detling said:

They can get a thing called positive grid corrosion but I don't really understand it. I think is is may depend on the solar controller. A PWM controller will overcharge, a MPPT less so, As I turn everything off when I leave the boat on it's mooring I have a 7 day time switch and a relay in the panel feed to the controller, (Do not fit in the controller to battery lead) thus I set the panels to be connected two days a week, one in summer. 

 

That is why lead acid batteries are floated at 2.2 volts per cell - to minimise grid (plate) corrosion.

 

The corrosion is worse on batteries with alloyed plates with a high calcium content, particularly if the plates join a pure lead group bar and the battery has been kept in a high temperature environment.

 

As always with batteries, the various charge voltages and enviro ment temperatures are a compromise between performance and maximising life.

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43 minutes ago, Col_T said:

FWIW - this morning their at 12.8v at 09:30.

I'll check, and alter if required, the float voltage on the solar charge controller.

 

Thanks for all contributions.

But they wern't on float at 9-30 they were charging. What is the voltage at say 4 pm on a sunny afternoon after they have been charging all day. Your snip shot voltages mean nothing. If they never get above 13 volts you are undercharging your batteries, we also really need some amps as as well as volts taken at the same time

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Confirming what Brian says. I would expect the solar charging voltage to get up to 14V+ before the controller dropped into float although as with chargers its likely to drop into float before the ideal. To test this when it drops to float start the engine and run at 1200 rpm and see what the charging voltage is. If its in excess of about 14.2 then the solar probably did not drop to float too soon. If less it probably did.

 

I find a lot of people are being mislead by the solar voltage first thing in the morning. This is why I always checked the voltage last thing at night and also as part of the night time wander routine.

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6 hours ago, Tony Brooks said:

I find a lot of people are being mislead by the solar voltage first thing in the morning. This is why I always checked the voltage last thing at night and also as part of the night time wander routine

 

As I have to walk past my Smartgauge to do my night time wander,  I press the button on the SG it gives just enough illumination for me to find my way ;)

 

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41 minutes ago, Loddon said:

 

As I have to walk past my Smartgauge to do my night time wander,  I press the button on the SG it gives just enough illumination for me to find my way ;)

 

My cheapo meter is already illuminated in the engine room so I dont have to stumble that far when I do my walk.

 

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On 11/09/2020 at 10:23, ditchcrawler said:

But they wern't on float at 9-30 they were charging

On 10/09/2020 at 17:01, Col_T said:

so to-days little experiment is to isolate the panels so that I can see what the voltage really is when we rise.

So the 12.8v at 09:30 was with neither solar controller nor alternator charging. Also, this . . . 

On 11/09/2020 at 09:37, Col_T said:

I'll check, and alter if required, the float voltage on the solar charge controller.

was in response to . . . 

On 11/09/2020 at 07:58, cuthound said:

As long as the float charge voltage is around 13.2 volts (2.2 volts per cell) they will come to no harm.

 

Finally, the BM1 was showing 1.9A at 14.5v when we moored to-day, after a 4 hour cruise.

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On 14/09/2020 at 07:56, jenevers said:

So what damage can happen if it's 14.4V?Trojans btw?

 

Plate and sometimes, depending on plate and group bar materials, group bar corrosion.

 

The former shortens battery life by a little, nowhere near as much as sulphation from undercharging. The latter causes the battery to fail spectacularly when one for more plates drop off their group bar and short the battery out.

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