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Old 19-10-2017, 10:21   #1
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Question Batteries accept amps from solar even when 100% full?

I'm pretty sure my batteries are currently 100% charged (but maybe not!), but they are still accepting 8 amps from the panels.

I have 6 golf cart batteries (about 600 ah) and 300w of solar. I can get about 14amps from the panels in full sun with normal conditions when the batteries aren't full.

I had heard that when the batteries are full they will stop accepting charge. The accepted charge seems to have lowered, but only by about 40%. Can I expect the amps to trail off to nothing, or will a 600ah bank accept 8 amps indefinitely, even when fully charged?
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Old 19-10-2017, 10:27   #2
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Batteries accept amps from solar even when 100% full?

I’m not sure about your batteries, but believe “full” is usually when a bank will only accept about .5% of their rated capacity at ABSORPTION voltage, not float.
It is very difficult to actually get there on Solar alone due to the time limit of available sunlight.
It’s been postulated that the majority of people think their bank is full when it is not as almost all chargers prematurely drop back into float voltage.
Don’t forget your house load too, if it’s 5 Amps, you have to subtract that number to get what the bank is accepting.

A way to determine is to get onto shore power and charge with your shorepower Charger, but hold it in float voltage. Sometime that means turning it off and back on, maybe several times, or some you can program to stay into float voltage, or program it temporarily to float voltage being at absorption levels.
Either way hold it at absorption voltage until your bank is accepting the rate that your manufacturer says is full, mine is .5%, yours may be more or less.
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Old 19-10-2017, 10:28   #3
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Re: Batteries accept amps from solar even when 100% full?

I hope your panels aren't just connected directly to the battery? You should have a controller or regulator between the panels and the batteries, or you very well may fry them.

If you do have a controller, what make / model?
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Old 19-10-2017, 10:31   #4
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Re: Batteries accept amps from solar even when 100% full?

If they were directly connected, how would he know how many amps the bank was accepting?
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Old 19-10-2017, 10:47   #5
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Re: Batteries accept amps from solar even when 100% full?

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.
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Old 19-10-2017, 10:56   #6
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Re: Batteries accept amps from solar even when 100% full?

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Originally Posted by a64pilot View Post
If they were directly connected, how would he know how many amps the bank was accepting?
Battery current monitor? Clamp-on ammeter?

Anyway, it turns out that the OP does have a controller. I suspect that the batteries weren't fully charged. Perhaps checking with a hygrometer or looking for outgassing might be appropriate. My boat has AGM batteries, so I can't do either of those things.
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Old 19-10-2017, 10:58   #7
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Re: Batteries accept amps from solar even when 100% full?

Quote:
Originally Posted by redpointist View Post
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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 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. >>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
You may not have seen this yet:

For everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Also read this one:

Programming a Battery Monitor (by Maine Sail)

Keeping Your Battery Monitor More Accurate Photo Gallery by Compass Marine How To at pbase.com
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Old 19-10-2017, 11:56   #8
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Re: Batteries accept amps from solar even when 100% full?

Thank you all, it looks like I'm looking for 0.5-1.5% of capacity going in to the battery to do a manual 100% reset.

It does look like I'm battling this "gotcha factor" that falsely sets to 100% and goes into float. I've programmed the gotcha factor out, but also wonder if in my situation it would make sense to program the lower float voltage out entirely too?

Since I'm discharging the batteries every day and they are really never fully charged, and they're only being charged on solar (~10 hours a day of charging with ~14 hours of no charge), does it really make sense to ever have it drop into float voltage while the sun is up, even if by amp counting the monitor thinks it's at 100%?
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Old 19-10-2017, 12:53   #9
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Batteries accept amps from solar even when 100% full?

From Maine Sails advice, I have programmed my Outback 80 so that float voltage is really absorption voltage. According to him, and my Smart gauge agrees with him, it’s unlikely that a boat being used will ever really truly get to a full 100% SOC on Solar alone, the danger of overcharging is almost nil.
Now that is for a Boat being used, don’t turn everything off and leave it on a mooring that way, you will overcharge your bank and boil off water and likely damage it.
My plan if I leave the boat with everything off, is to program the Outback 80 so that it never goes to absorption voltage, only float.
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Old 19-10-2017, 13:18   #10
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Re: Batteries accept amps from solar even when 100% full?

I'm afraid that many of these so-called "smart gauges" try to oversimplify lead-acid batteries, a well-characterized but fairly complex subject. I believe that anybody who depends upon them can benefit from spending the time to better understand them:


Charging Information For Lead Acid Batteries – Battery University
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Old 19-10-2017, 14:58   #11
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Re: Batteries accept amps from solar even when 100% full?

The ONLY way to determine when my bank is fully 100% charged is by how much the bank is accepting at absorption voltage.
It’s an AGM bank, and therefore specific gravity can’t be measured.
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Old 19-10-2017, 15:23   #12
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Re: Batteries accept amps from solar even when 100% full?

Here's a 400Ah bank of trojan L-16's after being fully charged then on float for a few days. At 14.4V they are accepting just 0.1A of charge current. They will keep accepting current but it will get very, very small to the point where your charger or charge controller may actually turn off for a few seconds, then blip back on, then turn off for a few seconds, repeat, repeat, repeat. 8A is not full but almost close enough for a "cruising full".

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Old 19-10-2017, 17:27   #13
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Re: Batteries accept amps from solar even when 100% full?

I had similar concerns. 15.1 volts and 8 amps after the sun broke through, following 24 hours of on grid charging with a ProNautic. MorningStar explained temperature sensing voltage increase because of low temperature and cold batteries.
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Old 20-10-2017, 07:13   #14
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Re: Batteries accept amps from solar even when 100% full?

Quote:
Originally Posted by TreblePlink View Post
I'm afraid that many of these so-called "smart gauges" try to oversimplify lead-acid batteries
The SmartGauge is a specific model battery monitor from Merlin. It is unique, not a category.

The site you link to is fine for DC electric 101 overviews, but is not comparable as a detailed learning resource to Maine Sail's.

http://www.pbase.com/mainecruising/smart_gauge
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Old 20-10-2017, 07:23   #15
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Re: Batteries accept amps from solar even when 100% full?

Quote:
Originally Posted by a64pilot View Post
The ONLY way to determine when my bank is fully 100% charged is by how much the bank is accepting at absorption voltage.
It’s an AGM bank, and therefore specific gravity can’t be measured.
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?
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