Charging batteries on shore power

[lawrence_craig]

Hello all.

I have a pretty new set of Bosch 12v batteries onboard. Bought in August last year, used for about 60 cycles max, not dropping below 60% charge.

I have since been living onboard connected to shore power with a Victron Centaur charger.

Normally, the voltage from the charger sits around 13.5-13.6 volts. I assume this voltage is coming from the charger to keep the batteries topped up whilst we use the 12v services.

However, today, whilst doing some work on the 230v system, the batteries dropped to 12.4V. This suggests to me that there is either a problem with the batteries (losing charge quickly) or with the charger (not charging the batteries correctly).

Has anyone had a similar experience? Any advice?

Thanks,
Lawrence

[StuM]

You don't say:
How large the battery bank is (how many Ah)
What was the average power draw while the 230V was not connected (A)
How long before it dropped to 12.4V
What was the power draw at the time it dropped to 12.4V (A)

WIthout those details, it's impossible to say whether you have a problem or not.

[lawrence_craig]

Battery bank is 450ah.

Amperage draw was about 10a max for like 20 minutes. Thats how long the 230V was off. I then looked at the panel and was thinking "why is my leisure battery at 12.4v?"

Turning the main load off (fridge, freezer), voltage went up from 12.4v to 12.5V.

[Sailmonkey]

Originally Posted by lawrence_craig

Battery bank is 450ah.

Amperage draw was about 10a max for like 20 minutes. Thats how long the 230V was off. I then looked at the panel and was thinking "why is my leisure battery at 12.4v?"

Turning the main load off (fridge, freezer), voltage went up from 12.4v to 12.5V.

Are you getting this voltage from a panel meter, or from a battery monitor?

[lawrence_craig]

Originally Posted by Sailmonkey

Are you getting this voltage from a panel meter, or from a battery monitor?

From the panel meter.

[Sailmonkey]

Originally Posted by lawrence_craig

From the panel meter.

I would repeat the experiment with a multi meter. Measure the voltage at the battery terminals.

Panel meters are either notoriously in accurate, or suffer from small wire voltage drop.

[sailorboy1]

it could just be normal. Turn off the battery charger for a day and see what happens. My batteries under load in the morning will read 12.3 at 80% state of charge.

[YANDINA]

The peril of batteries short cycling on shore power. Shore power keeps the batteries between 98 and 100% and cycling JUST in this range dozens of times a day. So while the lower 98% has had minimal use you have worn out your 2,000 recharges in the top 2%.

See this article on defining the problem and a solution.

[facciatosta]

Originally Posted by lawrence_craig

Normally, the voltage from the charger sits around 13.5-13.6 volts. I assume this voltage is coming from the charger to keep the batteries topped up whilst we use the 12v services.


Thanks,
Lawrence

Presumably 13.5-13.6 is float voltage. In general voltage drop to 12.4V with charger disconnected is not a problem as long as it stays at the same or even slightly lower level for expected time which depends on the battery capacity.

What is the battery capacity and type?

[guyrj33]

Originally Posted by YANDINA

The peril of batteries short cycling on shore power. Shore power keeps the batteries between 98 and 100% and cycling JUST in this range dozens of times a day. So while the lower 98% has had minimal use you have worn out your 2,000 recharges in the top 2%.

See this article on defining the problem and a solution.

Much of the advice given on the referenced web page encourages more questions than answers. I think the battery short cycling while on charger advice is particularly naive.

At rest 12.4v is about 80%, and that's at rest. Under load 12.4v could be seen on a panel meter with a fully charged battery.

[stormalong]

The battery voltage is only an approximation of battery charge unless the batteries have not been charged or discharged (rested) for 24 hours.

Measuring the voltage at a breaker panel, remote from the batteries and after going through fuse(s) circuit breaker(s) and multiple connections would not be accurate. It needs to be measured at the batteries with a good quality digital multimeter..

[StuM]

Originally Posted by YANDINA

The peril of batteries short cycling on shore power. Shore power keeps the batteries between 98 and 100% and cycling JUST in this range dozens of times a day. So while the lower 98% has had minimal use you have worn out your 2,000 recharges in the top 2%.

See this article on defining the problem and a solution.

Could you please explain the physics and chemistry behind these claims: "This short cycle, always at the same place on the battery plates can produce a layer which can materially reduce the capacity of your expensive battery bank and shorten its life drastically."

[YANDINA]

Originally Posted by StuM

Could you please explain the physics and chemistry behind these claims: "This short cycle, always at the same place on the battery plates can produce a layer which can materially reduce the capacity of your expensive battery bank and shorten its life drastically."

The process of charging and discharging a battery is accomplished by electrolytic transfer of metal between the anode and cathode. When it is replaced during charging the uniformity of the layer is never as precise as the original casting resulting in the creation of random hills and valleys.

If the depth of discharge on the next cycle is greater, then the level of the non-uniform hills and valleys of the previous cycle, all get transferred and a fresh surface corresponding to that particular depth of discharge is exposed so the disruptive pattern of hills and valleys of the previous cycle get absorbed or diluted in the total mass transferred.

However if the depth of discharge is precisely the same as would happen on repetitive discharges such as flushing a toilet or pressurizing a water pump, the random defects are compounded on each cycle rather than being removed entirely which promotes non uniform current flow across the surface until the build up can bridge the anode and cathode shorting it out which either melts the bridge or discharges the cell.

Electrolyte absorbed in a glass matte rather than liquid between the plates provides a level of protection but eventually a hot spot will plate through it and your battery dies.

By breaking the repetitive cycle you move the plates to fresh surfaces and prolong battery life.

[smac999]

Do a c20 load test. It’s the only way to know the condition of the batteries.

[StuM]

Originally Posted by YANDINA

The process of charging and discharging a battery is accomplished by electrolytic transfer of metal between the anode and cathode.

So let's just be clear about this. You are saying that lead moves from one plate to another during discharge and back again during charging. Do I have that right?

And that this lead can grow out of one spot on one plate across to the other plate?


(I won't use the words anode or cathode, since strictly speaking, it is the direction of electron flow which determines which is which and that changes between charge and discharge)