Connecting batteries

[S/V Adeline]

Automatic charger will supply amperage as long as a battery will accept it. Significant A/H difference can cause the smaller battery to be continually overcharged while the larger battery is being 'topped up'. That will shorten the life of the smaller battery.

[DanaTucker]

Originally Posted by YANDINA

Male bovine excrement.

Yep, that one is going in the books! By the time they figure out what it means, I will have been long gone. That is just about as the politest way as it can be said. Ya made my day!

[markcouz]

HaHa, cool pic - I am going to save it for future use.


Give it a go and tell us the result after a few months, it will be an interesting experiment to carry out on someone else's boat.

[YANDINA]

For anyone still following this thread, here is a copy of a PM I received that invites further discussion.

Originally Posted by john61ct

If this interests you, I'd be curious what you might have to say, either there or here
https://endless-sphere.com/forums/vi...14687#p1514687

If you want to respond in public not on that ES thread but on CF, feel free to repackage it as you see fit as a new thread

The contention here is that if you parallel 12 volt batteries, for example, that only the ends of the series chain are at the same voltage and that there may be variations in the charge level of individual cells.

While it is true that the voltage of the individual cells will differ this has nothing to do with being connected in parallel with another battery. The imbalance of cells will be found in every battery, paralleled or not. If there was a need to have cell voltages matching it would be just as important in every battery.

The charge level of a battery and each cell of a battery is measured in AMP-HOURS (that is how many amps can it supply for a given amount of time). It doesn't matter exactly what the individual cell voltage is, because all the current must go through the cell since it has nowhere else to go, there is only one connection in and one connection out.

This means that each cell gains or loses charge (amp hours) exactly equally independent of what the actual cell voltage may be and when discharging, the battery will fail when the WEAKEST cell becomes tragically discharged.

This process, however, breaks down when a battery cell is fully charged and has run out of electrolytic material to move to the other plate. At this stage putting in more current cannot increase storage so the energy is dissipated in "boiling" the electrolyte and creating bubbles. While this is happening other cells will be receiving charge while the bubbling cell(s) remain at full charge. This is what happens when you run an "equalizing" session on a battery long enough for all cells to become fully charged and all making bubbles.

With the arrival of Lithium batteries, however, there are catastrophic consequences to over charging or over discharging and balancing cells is crucial. Good Lithium battery managing controls do monitor the voltage of individual cells and bypass current through cells as needed to maintain balance.

[S/V Adeline]

Originally Posted by YANDINA

For anyone still following this thread, here is a copy of a PM I received that invites further discussion.




The contention here is that if you parallel 12 volt batteries, for example, that only the ends of the series chain are at the same voltage and that there may be variations in the charge level of individual cells.

While it is true that the voltage of the individual cells will differ this has nothing to do with being connected in parallel with another battery. The imbalance of cells will be found in every battery, paralleled or not. If there was a need to have cell voltages matching it would be just as important in every battery.

The charge level of a battery and each cell of a battery is measured in AMP-HOURS (that is how many amps can it supply for a given amount of time). It doesn't matter exactly what the individual cell voltage is, because all the current must go through the cell since it has nowhere else to go, there is only one connection in and one connection out.

This means that each cell gains or loses charge (amp hours) exactly equally independent of what the actual cell voltage may be and when discharging, the battery will fail when the WEAKEST cell becomes tragically discharged.

This process, however, breaks down when a battery cell is fully charged and has run out of electrolytic material to move to the other plate. At this stage putting in more current cannot increase storage so the energy is dissipated in "boiling" the electrolyte and creating bubbles. While this is happening other cells will be receiving charge while the bubbling cell(s) remain at full charge. This is what happens when you run an "equalizing" session on a battery long enough for all cells to become fully charged and all making bubbles.

With the arrival of Lithium batteries, however, there are catastrophic consequences to over charging or over discharging and balancing cells is crucial. Good Lithium battery managing controls do monitor the voltage of individual cells and bypass current through cells as needed to maintain balance.

While I agree with the individual points in the summary, it seems to suggest that a weak cell in a battery or a smaller weaker battery in a parallel setup is ok.
True, all cells are individual, but if one is measurably weaker it degrades the entire battery. Repeated hard charging (boiling) a battery reduces the overall life and capacity. If 5 cells boil while the weak cell is charged, they are being damaged. Same goes for the *small* battery that boils all cells while the large battery is being fully charged. (All references are to 6 cell batteries)

Back in they day we used to install *loaner* batteries in a vehicle while their battery was charged and tested. Salespeople described it as a deep charge but technicians called it a hard charge. I was in charge of a 48 battery manual charging rack (all in parallel). The customer battery gets hooked in, and hard charged for 72 hours. I don't remember the amperage involved but a manual charger capable of 48 12v batteries at once is awesome. If a brand new battery was accidentally left on for an extra day or two usually it would fail load testing. Many batteries ruined because a salesman decided to hook up a new one and it never got documented to be removed on time.
My current manual charger has settings for 12, 24, 36, 48, 60, and 72 volts, but only pumps a maximum of 10 amps so it takes a couple hours to start boiling a decent battery. A 100amp alternator can boil a small battery dry while charging a large one.