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Old 03-01-2020, 12:32   #1
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0.5% X 20C for 100% SOC - myth?

I've read it here lots of time and accepted it and even repeated it.

Batteries aren't really 100% charged till they will only accept 0.5% of the 20C capacity at absorption voltage, measured as amps.

Who can provide a link to a battery manufacturer or similar that says this?

Trojan says 1-3%. Victron in my battery monitor directions say 4%. Battery University says 3-5%.

My batteries (T105s) have been at 14.8V for 2 hours accepting 2.2% steady. Am I charged? Trojan also says to not do more than 4 hours at absorption, if I'm still at 2% at end of that should I keep charging at absorption voltage?

I'm only using my batteries as an example, the real questions is - Who can provide a true technical reference that says 0.5% of the 20C AH capacity as as an amperage for 100% state of charge?
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Old 03-01-2020, 12:58   #2
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Re: 0.5% X 20C for 100% SOC - myth?

Ahh, the trap of battery chemistry. Here is a Trojan reference that says 0.5%.

Quote:
Phase 2: Constant voltage absorption charge
A constant voltage equal to 2.35-2.45 V/cell is applied as the current slowly declines. The absorption phase ends when the current stabilizes at a low value of approximately 0.005 x C20.
It applies to AGM/Gel batteries. Trojan and Rolls recommend ~2% (with a range) for FLA. Deka uses a different approach, they say that if the charging current (at absorption voltage) does not change by more than 0.1A in an hour then you're done (by that criteria sounds like you are, also by the 2% rule - with wiggle room).

Trojan's recommendation on FLAs is a finish current of 1-3% until they bubble.
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Old 03-01-2020, 13:14   #3
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Re: 0.5% X 20C for 100% SOC - myth?

so per Trojan - approximately 0.5% for agm/gel (I never have read the agm/gel as it didn't matter to me) and 1-3% for flooded

yet I'm pretty sure people throw the 0.5% around as applying to flooded also, do they have a reference

For info I can do the 0.5% on my T105s IF I've been on shore power for days . The acid flumes quickly result in me turning down the solar setpoint. I've only seen this 3 times in 4 years.
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Old 03-01-2020, 13:27   #4
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Re: 0.5% X 20C for 100% SOC - myth?

Crossposting https://www.sailnet.com/forums/showt...p?p=2051644992
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Old 03-01-2020, 13:29   #5
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Re: 0.5% X 20C for 100% SOC - myth?

> absorption phase ends when the current stabilizes at a low value of approximately 0.005 x C20

aka 0.005C

is a better (standard) phrasing to use than 0.5%
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Old 03-01-2020, 13:38   #6
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Re: 0.5% X 20C for 100% SOC - myth?

From my notes after talking to Trojan engineer, was about equalizing, but that affects the Absorb setpoint, principal for termination point is the same. Note this case the adjustable PSU used for 6V was low power, maybe 10A only:

Charge at 12V (14.7) until trailing amps falls to between .01 - .005C. This is the normal charge to Full (whenever possible) for daily cycling.

Then separate into 6V and

(optional) do that again but using 7.35V

reason is the remote possibility the string(s) were so unbalanced that one may demand (accept) a higher current at EqV than you want to inflict on your smaller 6V charger.

If you want, use a hydrometer for following the Specific Gravity specs, otherwise

set Eq V to 8.1 and start, noting max amps accepted in the first seconds. Run until trailing amps falls to around 0.005C, at least below 0.01C or

stops falling for an hour, or

you hit 4 hours


Resting V (and/or SG) after isolating 24+hrs should be very close on all batteries.

if not, parallel pairs and run the Eq cycle again, doing that in the first place next time would be fine long as max amps accepted were well within the small chargers limit.
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Old 03-01-2020, 13:57   #7
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Re: 0.5% X 20C for 100% SOC - myth?

The .5% applies to my knowledge only to Lifeline batteries, it may apply to others by chance.
Many if not most battery manufacturers just don’t supply such information, Lifeline is rare in that they have a very good manual. It’s my belief that due to it being such an informative manual, people have a tendency to try to apply what it says to batteries in general, and maybe you shouldn’t do that.
However for what it’s worth over time even my 5 yr old Lifeline bank goes well below the .5% which in my case is 3.3 amps, but if I hold absorption voltage longer, it will continue to drop to about .2 amps.

When I’m equalizing, my bank very quickly tops out and stops accepting much charge at all and only a fraction of an amp actually goes into the bank, assuming th shunt will measure such small current accurately.
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Old 03-01-2020, 13:59   #8
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Re: 0.5% X 20C for 100% SOC - myth?

Quote:
Originally Posted by sailorboy1 View Post
I've read it here lots of time and accepted it and even repeated it.

Batteries aren't really 100% charged till they will only accept 0.5% of the 20C capacity at absorption voltage, measured as amps.

Who can provide a link to a battery manufacturer or similar that says this?

Trojan says 1-3%. Victron in my battery monitor directions say 4%. Battery University says 3-5%.

My batteries (T105s) have been at 14.8V for 2 hours accepting 2.2% steady. Am I charged? Trojan also says to not do more than 4 hours at absorption, if I'm still at 2% at end of that should I keep charging at absorption voltage?

I'm only using my batteries as an example, the real questions is - Who can provide a true technical reference that says 0.5% of the 20C AH capacity as as an amperage for 100% state of charge?
Once off the charger and back on solar what voltage do you show ?

I have T105's and they sit at 13.2.Vdc.
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Old 03-01-2020, 14:04   #9
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Re: 0.5% X 20C for 100% SOC - myth?

To continue, logic would say that it’s full when the charge acceptance rate stops dropping, if your at 2% and it’s no longer dropping, then you won’t ever get to .5%.

I believe that normal aging meaning sulphation will slowly over time increase that current that the bank will stop at, so a brand new bank you may get .5%, one a few years old, maybe only 1-2% etc.

That’s why I think the statement of when the current doesn’t drop for an hour you’re done is a very logical statement, and maybe add if it’s a higher number than it used to be, an equalization May be in order to attempt to reverse some sulphation.
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Old 03-01-2020, 14:35   #10
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Re: 0.5% X 20C for 100% SOC - myth?

Quote:
Originally Posted by Dave_S View Post
Once off the charger and back on solar what voltage do you show ?

I have T105's and they sit at 13.2.Vdc.
The 14.8 was on solar. I have float set to solar 13.4 so i don't drop below that till batteries start discharging in the afternoon.
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Old 03-01-2020, 14:40   #11
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Re: 0.5% X 20C for 100% SOC - myth?

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Originally Posted by a64pilot View Post
To continue, logic would say that itís full when the charge acceptance rate stops dropping, if your at 2% and itís no longer dropping, then you wonít ever get to .5%..
But they get to 0.5% and i already so. They did it regularly jst this last Oct as shore power and charge kept the batteries charged and solar during the day would ramp up to absorption with less than 0.5% acceptance. I had to turn the absorption time down or the flumes would chase me out.

But thats really thread drift. The question is to provide links to manufactures or technical type papers. Not to repeat what one has heated or been told.
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Old 03-01-2020, 15:29   #12
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Re: 0.5% X 20C for 100% SOC - myth?

Quote:
Originally Posted by a64pilot View Post
Many if not most battery manufacturers just donít supply such information, Lifeline is rare in that they have a very good manual
On the contrary, every maker whose true deep-cycling product is worth buying not only publishes their detailed specs, but has technically competent CS staff available to discuss the details with customers.

If they don't you should avoid purchasing their product.

Yes Lifeline may be better than most.

The 0.005C number is common for FLA, but yes a bit stringent for VRLA types where you don't want to overcharge and lose electrolyte.

Going longer results in a higher level 100%, while stopping earlier (higher C rate) will not fight sulfation as well.

For FLA measuring specific gravity with a hydrometer is an alternative to using the endAmps spec.
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Old 03-01-2020, 15:35   #13
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Re: 0.5% X 20C for 100% SOC - myth?

Quote:
Originally Posted by sailorboy1 View Post
The question is to provide links to manufactures or technical type papers.
Which ones specifically are you having trouble verifying?

As I said, just contacting their tech support is also usually easy.
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Old 03-01-2020, 15:40   #14
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Re: 0.5% X 20C for 100% SOC - myth?

If you are trying to point out that there is no endAmps spec that covers all batts, as stated that is 100% true.

You should use the one spec'd by the maker.
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Old 04-01-2020, 10:30   #15
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Re: 0.5% X 20C for 100% SOC - myth?

sailorboy1. Can you list the parameters you've set your Victron BM to? We also use T-105s (6 total-arranged into 3 "batteries"-for our house use), and have a Victron BM and Victron Solar Controller. As one not so knowledgeable in all matters LA battery, I'd like to see/compare your settings to what we use. We also have a SmartGage BM (different logic, good to compare), but they almost never agree!
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