Understanding intelligent chargers

[tanglewood]

This may be beating a dead horse, but the OP doesn't seem to understand the basic dynamics between the charger and battery. I don't mean that as a criticism - after all, we aren't born knowing this. So let me take a crack at it.


All a charger does to try to attain, and then maintain a certain output voltage. It does this by regulating it's output current.


A battery "resists" the charger's attempt to attain it's desired voltage, more so when it's at a low SOC, and less so as it becomes full.


That's the basic dynamic.


Looking a little more closely, while the charger is trying to attain a certain voltage, but not succeeding, it is putting out it's maximum amperage capacity. It's try as hard as it possibly can to raise the battery voltage, but not succeeding. This is what we call "Bulk" charging because the charger is outputting max current.


During this stage, the battery is soaking up all the power that the charger is throwing at it, and as it's SOC raises, the voltage also works it's way up.



As soon as the charger finally attains the target voltage, it now maintains it by regulating how much current it outputs. This is the "absorption" stage of charging. This cross over point is reached when the battery is sufficiently charged to reach the desired voltage with less than the chargers max current capacity. As the battery's SOC continues to climb, it takes less and less current to maintain the target voltage. This declining current is called the "acceptance" current, or "acceptance" rate.


When the current required to maintain the target voltage drops to a certain level, the battery is considered charged and the charger stops. Since this is often hard/impossible to measure by the charger, charging often stops based on a simple timer - the so-called "egg timer" referred to previously.


Now, throw in a second charger.


If the target voltage hasn't been reached, which means the first charger is outputting max current trying it's darnedest, but not yet succeeding (aka Bulk mode), the second charger will also start outputting current attempting to raise the battery voltage. Now you have the full output of both chargers trying to raise the battery voltage. The battery will charge faster, the voltage will rise faster, and the target voltage will be reached sooner. But both chargers will operate at max capacity with no conflict, and unaware of the other chargers presence.


Once the target voltage is reached, but chargers will now regulate their current output to maintain the voltage. It is very unlikely that both will contribute equally or proportionally to the task, but it doesn't matter. As long at the battery voltage is being maintained, both chargers and the battery will be happy.


As the battery reaches full charge, each charger will independently decide when it thinks the battery is full, and will stop charging. This will almost never be at the same time, but again, it doesn't really matter. You basically will get the longest charge time of your different chargers. And lead batteries are very tolerant of longer absorb times, and often benefit from it, so certainly no harm is likely.


Hopefully that helps your understanding of who's doing what to whom, and how everything is responding.

[john61ct]

Great writing there, all the same information, but

perhaps that phrasing will give the OP his "realization Aha moment" of the fundamental process.

[Wotname]

While not all battery chargers are the same, all the ones I'm familiar with work a little differently than what is posted below. The differences I'm aware of are shown below in red.

Originally Posted by tanglewood

This may be beating a dead horse, but the OP doesn't seem to understand the basic dynamics between the charger and battery. I don't mean that as a criticism - after all, we aren't born knowing this. So let me take a crack at it.


All a charger does to try to attain, and then maintain a certain output voltage. It does this by regulating it's output current. voltage. It's current is limited to it's maximum current at first by it's design (during "bulk") and then later by the charge acceptance of the battery chemistry (during "absorption")


A battery "resists" the charger's attempt to attain it's desired voltage, more so when it's at a low SOC, and less so as it becomes full.
Sort of, really at a low SOC, at any given charging voltage, the battery chemistry will accept a higher charging current than what it will accept at a high SOC. It is the battery chemistry that determines the acceptance rate, not the charger.


That's the basic dynamic.


Looking a little more closely, while the charger is trying to attain a certain voltage, but not succeeding, it is putting out it's maximum amperage capacity. It's try as hard as it possibly can to raise the battery voltage, but not succeeding. This is what we call "Bulk" charging because the charger is outputting max current.

During this stage, the battery is soaking up all the power that the charger is throwing at it, and as it's SOC raises, the voltage also works it's way up.
Yes

As soon as the charger finally attains the target voltage, it now maintains it by regulating how much current it outputs.
It is the battery chemistry that is limiting the current during the absorption stage, the charger maintains a constant voltage at this time.

This is the "absorption" stage of charging. This cross over point is reached when the battery is sufficiently charged to reach the desired voltage with less than the chargers max current capacity. As the battery's SOC continues to climb, it takes less and less current to maintain the target voltage. This declining current is called the "acceptance" current, or "acceptance" rate.
Yes

When the current required to maintain the target voltage drops to a certain level, the battery is considered charged and the charger stops. Since this is often hard/impossible to measure by the charger, charging often stops based on a simple timer - the so-called "egg timer" referred to previously.
Yes


Now, throw in a second charger.


If the target voltage hasn't been reached, which means the first charger is outputting max current trying it's darnedest, but not yet succeeding (aka Bulk mode), the second charger will also start outputting current attempting to raise the battery voltage. Now you have the full output of both chargers trying to raise the battery voltage. The battery will charge faster, the voltage will rise faster, and the target voltage will be reached sooner. But both chargers will operate at max capacity with no conflict, and unaware of the other chargers presence.


Once the target voltage is reached, but chargers will now regulate their current output to maintain the voltage. It is very unlikely that both will contribute equally or proportionally to the task, but it doesn't matter. As long at the battery voltage is being maintained, both chargers and the battery will be happy.


As the battery reaches full charge, each charger will independently decide when it thinks the battery is full, and will stop charging. This will almost never be at the same time, but again, it doesn't really matter. You basically will get the longest charge time of your different chargers. And lead batteries are very tolerant of longer absorb times, and often benefit from it, so certainly no harm is likely.


Hopefully that helps your understanding of who's doing what to whom, and how everything is responding.

I repeat that not all chargers act the same way.

[john61ct]

There were no conflicts there, what you both wrote is correct.

Just see it as a "black box". When it needs to limit voltage to not rise above the setpoint, that is what it does.

How the sausage is made internally is irrelevant, info overload, just a distraction at this level of discussion.

[Jlp0217]

Originally Posted by medsailor1

I too would love to understand more , as I just don't grasp half of what I should know .
Here my example . To day we started off with an 12.5 v ( SOC 70%) the battery bank is 450AH , we had no wind so we had to motor for 10hours and 10 mins ,
at the same time over that time our solar panels (200w) put in 780wh or so my Mppt says , and the max V reached 14.26 .
The Victron is set to Absorption at 14.8 at one point amps drop to 2A with both the alternator and the panels .
What I don't understand motoring for that time plus what the panels where putting in why didn't the voltages reach 14.8 and the Victron entered Absorption stages .Attachment 180390

There's not enough information here to tell what's going on. In particular we need to know:
All charging sources, and their voltage setpoints and amperage.
Loads, refrigeration?, autopilot?, radar?, pumps?, AC? especially any older electronics as they use much more power than newer ones.
Alternator and rating and whether internally or externally regulated.

Max V of 14.26 seems low unless you have sensitive AGM or GEL batteries, or it is very hot in your battery/mppt area. And the 14.26 is the max voltage produced by either the alts, or solar which ever is set higher.
Also, the 780 Wh of solor is only 54.9 amp hours, while your batteries were down 315 amp hours. That would only bring them up to 82%, just enough to begin limiting current. Then if your alts setpoint were lower than solar setpoint, they'd stop producing when/if voltage got to the setpoint.