Batteries accept amps from solar even when 100% full?

[john61ct]

Originally Posted by redpointist

I have a bogart engineering trimetric 2030 battery monitor and matching bogart engineering sc-2030 charge controller.

The batteries are 6v Duracell GC2 wet cells from Sams club wired into a 12v system.

0.5% of 600ah would mean at 100% full they should only accept about 3 amps at 14.4 volts once fully charged?

The trimetric has a lot of settings to play with, but I think it was indeed switching to float prematurely. I suspected it may be, so tempararily increased float voltage to 14.4 volts (from 13.5) to see how long it would accept charge at the full rate, and over the course of a few days it seems to added 20% capacity to the bank even though the charger thought it was at 100% already. Even now it's still accepting almost 1.5% of capacity.

Since I'm using the batteries every day and unlikely to ever have them fully topped off for long (if ever), does it make sense to permanently ignore lowering voltage for float and just let them charge daily at 14.4 volts for as long as the sun is up? The batteries get a break from the 14.4 volts every night when it drops down to 12.6-13 depending on how much load I'm using.

Yes, but only for while you're on solar only and actively cycling.

To me, that means No.

The "gotcha" phenomenon root cause is the SC basing its algorithm off measuring its amps **output**, a fatal flaw. Since your SC is using the actual amps **accepted by the battery** at the shunt, it should be pretty easy to get the Trimetric adjusted to work properly.

Setting FloatV = AbsorbV is to me just a kludge workaround for those with less accurate monitoring gear.

But in the end the TM **will** drift if you're not getting to 100% most cycles, besides the bank longevity hit.

In that scenario consider using a SmartGauge to be able to cross-reference, if the extra cost is not an issue.

You state - and seem willing to accept - that your bank is rarely actually getting to true 100%.

So using that workaround, as noted you will need to manually change the TM settings in order to get a proper safe float when your bank actually does get to Full, not least when sitting on shore power and/or not cycling.

I think personally the goal of a good setup should be to actually get to 100% as often as possible, even if that requires a little genny run in the morning, ideally while doing other things like charging the freezer, doing dishes, laundry, making water etc.

But even if that's not often possible, try to get to Full often enough to help the Bogart to be accurate, and especially as it is your solar controller - do what it takes to tweak the settings to ensure it transitions to FloatV only **after** the bank is truly full.

[thomm225]

If you don't have an amp meter installed, you can always just check the voltage on the panel side of the controller.

When the batteries are about fully charged you will read almost max voltage out of your panels on a sunny day which on mine is 20 volts plus.

[john61ct]

That tells you more about what's going on with the controller than inside the battery.

The fundamental problem is that with lousy non-adjustable controllers, or even good ones left at factory settings, the SC drops to Float voltage long before the bank is truly full.

In general, never assume a charge source knows the SoC of your batts, you need to teach it how to make that call accurately, and verify anything the charge source is telling you with independent known-accurate tools.

If you can't/don't want to do that yourself, pay a pro to help.

[billknny]

Something I am surprised nobody has mentioned, there is a scenario where a battery will accept amps "forever" even when fully charged. That is if a cell is internally shorted.

The easiest way to determine if this is the case is to disconnect all the batteries from charging sources, and each other, and then test terminal voltages. If you see <11 volts you know that battery is bad and needs to be removed from the system or you risk a thermal runaway.

On flooded batteries you can check specific gravity of each cell, or note if one cell (or more!) is using more water than others.

[a64pilot]

Originally Posted by john61ct

I'm confused. What about SmartGauge?

Are you saying you need to regularly use endAmps to manually reset the Full point on your SG as AH-counting BMs require?

The Smart Gauge can’t be relied upon during the charge cycle, if you watch it, sometimes it will sit at the same SOC% for hours during charging, making you think your bank is not being charged.
No you don’t reset it, it somehow catches up during the discharge cycle, in fact it will catch up and read 100% eventually on its own even with the bank still being charged, just takes time, but it lags behind.
What you can’t do is watch the SOC% during charge to try to get an idea how long it will take to fully charge the bank.

To my knowledge if you have an AGM bank, they only way to determine if your fully charged is by watching acceptance rate at absorption voltage, when it reaches .5% for a Lifeline bank, they are full and its time to go to float. I don’t believe an extra hour or so at absorption voltage hurts.

[a64pilot]

Originally Posted by billknny

Something I am surprised nobody has mentioned, there is a scenario where a battery will accept amps "forever" even when fully charged. That is if a cell is internally shorted.



The easiest way to determine if this is the case is to disconnect all the batteries from charging sources, and each other, and then test terminal voltages. If you see <11 volts you know that battery is bad and needs to be removed from the system or you risk a thermal runaway.



On flooded batteries you can check specific gravity of each cell, or note if one cell (or more!) is using more water than others.

Yep, you right, and that bad battery will get hot to if its on shore power or other inexhaustible charge source, cause that power has to go somewhere.

[john61ct]

Originally Posted by a64pilot

The ONLY way to determine when my bank is fully 100% charged is by how much the bank is accepting at absorption voltage.

Ah I see, I did not realize you meant "while charging".

Just take the charge off the bank, shouldn't take more than a few minutes for the SG to read accurately?

Aren't your charge sources set up so that they automatically hold Absorb until endAmps is reached?