DiploStrat
Expedition Leader
If you have a lead acid battery with a true resting voltage of 13.8v, patent it immediately! 13.5v is simply amazing as well.
Just another battery voltage drop question!
- Thread starter Grenadiers
- Start date
If you have a lead acid battery with a true resting voltage of 13.8v, patent it immediately! 13.5v is simply amazing as well.
Grenadiers
Adventurer
I've been running the Waeco fridge for two days and voltage stays around 25.1, about 9 amps of solar for a few hours to help. The SoC though is stuck on 64%.
Grenadiers
Adventurer
Fridge pulls about two amps when running.
dwh
Tail-End Charlie
12v lead-acid batteries don't rest at 13.5v or 13.8v. The (fully 100% charged) resting voltage will be between 12.6v (old and worn out battery) to 12.9v (new high quality AGM battery).
Most have a full charge resting voltage of 12.8v.
Times two if wired in series.
To read the true resting voltage, allow the batteres to sit for several hours (4) without *any* charging or discharging taking place.
SoC readings are dodgy because the meter can't actually tell what the SoC is - it has to guess based on what size battery bank it was programmed to, combined with recorded numbers of amp*hours in/out through the shunt.
As time goes by and the battery capacity goes down, the SoC reading gets more and more inaccurate - until it ends up wildly inaccurate.
Where are you getting this SoC reading?
Most have a full charge resting voltage of 12.8v.
Times two if wired in series.
To read the true resting voltage, allow the batteres to sit for several hours (4) without *any* charging or discharging taking place.
SoC readings are dodgy because the meter can't actually tell what the SoC is - it has to guess based on what size battery bank it was programmed to, combined with recorded numbers of amp*hours in/out through the shunt.
As time goes by and the battery capacity goes down, the SoC reading gets more and more inaccurate - until it ends up wildly inaccurate.
Where are you getting this SoC reading?
Grenadiers
Adventurer
From the Steca PR-3030 battery controller installed in the unit.
dwh
Tail-End Charlie
Yea, that charge controller has no idea what the actual state of charge is because it can't measure what went in/out of the battery.
It can measure how much went in from solar, but doesn't track what goes in from other sources, such as an alternator or shore power charger.
It can measure what went out of the battery through the charge controller's load terminals, but doesn't track what goes out of the battery without going through the charge controller load terminals.
If the only power going into the battery is from solar *and* the only power going out of the battery goes through the charge controller load terminals - then yea, it could tell you state of charge. Otherwise, no way. It can't even make a reasonable guess.
It can measure how much went in from solar, but doesn't track what goes in from other sources, such as an alternator or shore power charger.
It can measure what went out of the battery through the charge controller's load terminals, but doesn't track what goes out of the battery without going through the charge controller load terminals.
If the only power going into the battery is from solar *and* the only power going out of the battery goes through the charge controller load terminals - then yea, it could tell you state of charge. Otherwise, no way. It can't even make a reasonable guess.
dwh
Tail-End Charlie
To get a proper state of charge, you need a meter (amp counter) with a shunt at the battery. All power that goes in/out of the battery gets measured. A meter like that is programmable - you tell it how many amp*hours capacity the battery bank has.
Bogart Trimetric and Xantrex LinkPro are popular and good quality. Since I have a Victron charge controller and MPPT controller/meter already, I've been thinking of adding the Victron BMV-700 battery monitor/amp counter, which has bluetooth built-in to use the Victron app.
https://www.amazon.com/gp/aw/d/B00M...ds=victron&dpPl=1&dpID=51mfuHsG-kL&ref=plSrch
Meter:
Shunt (required for amp counter meters)
Bogart Trimetric and Xantrex LinkPro are popular and good quality. Since I have a Victron charge controller and MPPT controller/meter already, I've been thinking of adding the Victron BMV-700 battery monitor/amp counter, which has bluetooth built-in to use the Victron app.
https://www.amazon.com/gp/aw/d/B00M...ds=victron&dpPl=1&dpID=51mfuHsG-kL&ref=plSrch
Meter:
Shunt (required for amp counter meters)
Grenadiers
Adventurer
I think you're correct on the charge controller's limitations. After downloading the manual, it clearly states it cannot 'read' the battery if there are outside, direct-connected items on the battery. I know of two, the Waeco fridge, and the 2000w 24v/110v inverter I installed.
dwh
Tail-End Charlie
Those are battery outputs, drawing from the battery. What about inputs directly connected to the battery, like alternator or shore charger?
It can't track those either, so it doesn't actually know what went in and what went out. Without that information, it's clueless.
Grenadiers
Adventurer
We have a German-made LEAB LPC-2425 25a 850w battery charger (connects to generator or shore power) next to the battery bank in the 'garage' of the cabin. The 'current' model of this is the ABC-2425. Two leads connect to the battery, and one somewhere upstream. Other side of wall, is the Phoenix inverter, and in front, is the Steca controller. The controller does indicate the battery charge voltage (usually in the 27-28 volt range) when the charger is on. My concern, is that this charger is 20+ years old, looks new of course, and the two little 'light' indicators, one shines green and the other, a half red light, indicating a problem with the battery. However, the batteries are taking a charge, the SoC is up to 65 from 64 yesterday.
dwh
Tail-End Charlie
To get a 24v lead acid battery fully charged, you need to get it up over 28v (14v x 2) and hold it there for enough hours for the battery to absorb to 100%. My AGMs have to get to 29.4v (14.7v x 2) and be held there for hours.
Just depends on the ultimate voltage it puts out. A) Will it get the battery to a high enough voltage? B) Will it run long enough to get it done?
No, the SoC went from a completely incorrect reading of 64 to a completely incorrect reading of 65.
Whatever SoC the charge controller is telling you is gibberish nonsense totally divorced from reality.
dwh
Tail-End Charlie
For example: The charge controller sees some power from solar flowed to the battery...let's say 100w for example.
What it didn't see was the 150w that went out of the battery to the fridge.
So it tells you SoC went up - even though the truth is SoC actually went down.
Forget the SoC reading from the charge controller. It's worse than useless - it actually lies.
What it didn't see was the 150w that went out of the battery to the fridge.
So it tells you SoC went up - even though the truth is SoC actually went down.
Forget the SoC reading from the charge controller. It's worse than useless - it actually lies.