Optimal Charging Regimen - Wet Cells

[akio.kanemoto]

Originally Posted by btrayfors

The problem with US Battery's charging recommendations is that they are geared to shore-based situations (like solar) and not to boats. They are totally impractical for boats, IMHO. Like, who's going to take 7 hours to charge a battery during the bulk and absorption phases? And, are you really going to charge an AGM battery at only 10% of its C/20 rate? Then why buy AGM batteries?

I would NOT equalize the batteries with every cycle.

I would NOT worry about current during the periodic but infrequent equalization treatments....the batteries are going to accept what they're going to accept and that will be totally limited by the voltage applied.

While yours may be showing 50A at the beginning of a 15.5VDC applied charge, that will quickly decrease.

Charge 'em at 14.7-14.8VDC bulk and absorption phases. Float 'em at 13.6-13.8VDC.

Only equalize them infrequently and when you have reason to believe they need it. They'll last a long time. IMHO, Bill

Got it. Settings fiddled, 14.8 bulk, 14.8 abs, 13.8 float.

Dumb question: the chargemaster changes from bulk to abs mode when abs voltage is reached. Us battery recommends bulk voltage of 14.8 but abs voltage of 15.5 or so. If I set these in the charger, the batts will never leave bulk mode right? (since the input voltage of 14.8 will never get the batts to 15.5?) ... am I missing something?

Also - just out of curiosity - when a charger with "equalization capability" is in eql mode - we know it cranks up the voltage, but does it also limit current? Or again, does it let the batts suck whatever they want to at the higher voltage?

[akio.kanemoto]

Originally Posted by mitiempo

I think you read it wrong. They recommend equalization

"for 1 to 3 hours after normal charge cycle (REPEAT EVERY 30 DAYS)"

In the graphs shown they state "equalization after every 30 cycles"

I doubt you will be totally cycling them once each day - using then to 50% state of charge - so the 30 cycles may well take 60 days or more.

And even that is a lot because equalization too often will shorten the life of a battery.

Originally Posted by goboatingnow

I read the US battery specs, Id be very careful as to the interpretation of equalization. There recommendation is based on following their regime. Thats not the way batteries are used on boats.

The say that equalization is required regularly. Thats a length of string. Flooded lead acid in good condition maintained and recharged, even if not quite to 100% do not need equalization.

dave

Both good points, I'll relax a bit and see how these go!

[btrayfors]

Originally Posted by akio.kanemoto

Got it. Settings fiddled, 14.8 bulk, 14.8 abs, 13.8 float.

Dumb question: the chargemaster changes from bulk to abs mode when abs voltage is reached. Us battery recommends bulk voltage of 14.8 but abs voltage of 15.5 or so. If I set these in the charger, the batts will never leave bulk mode right? (since the input voltage of 14.8 will never get the batts to 15.5?) ... am I missing something?

Also - just out of curiosity - when a charger with "equalization capability" is in eql mode - we know it cranks up the voltage, but does it also limit current? Or again, does it let the batts suck whatever they want to at the higher voltage?

US Battery recommends an absorption voltage of 14.4. They then talk about a "finish charge" of about 15.3V, same as their recommendation for an equalization voltage.

In practice, what will happen is determined by the properties of the charger -- and it's internal design and algorithms -- and the size, chemistry, and physics of the battery bank under charge.

Would that it were less complicated and that a simple answer were possible :-)

Chargers differ one from another in their behavior. Many modern multi-stage chargers have:

1. a "bulk phase" during which they allow the voltage to rise up to a certain level (the "absorption level") and pump out lots of amps while doing so;

2. when this absorption level voltage is reached -- often in the neighborhood of 14.4VDC -- they then hold the voltage constant and allow the battery to take whatever amperage it will accept. This is the so-called absorption phase, and it can be terminated in one or another of several ways. There's usually a time limit, but also some modern chargers calculate acceptance against time and voltage, and move onto the next "float" stage when they determine the battery to be near full.

3. an equalization phase for flooded batteries. This differs considerably from charger to charger, and it's important to know how your charger behaves before trying this phase.

The batteries themselves will determine how much charge (amps) they'll accept at any given state-of-charge (SOC) and applied voltage. So long as you don't let the voltage exceed a given level, there's no way the batteries will accept more current. In other words, you can't have a charger which is "too large", though you can have one which is too small and unable to deliver all the amps the battery would like to accept.

For reference, I measured the acceptance in amps of a pair of brand new, fully-charged Trojan T-105 deep-cycle flooded batteries at various elevated voltage levels. Ambient temp was 65F. The results are shown in the attached graph.

In blue, the maximum initial acceptance in amps is shown for each applied voltage level from 13.2 to 17.0VDC. If voltage were left at any given level for several minutes, the amps acceptance would drop, often dramatically. For example, at 16.0 volts applied the batteries initially accepted about 8 amps, but quickly dropped to less than 3 amps.

Interesting also is the fact that it was impossible to get the voltage above 17.0 and the amperage above about 17, even given a power supply capable of putting out up to 50 volts @ 20 amps.

The batteries will accept what they're going to accept. Period.

Note that your mileage may vary considerably due to differences in battery chemistry and construction, SOC, age, contamination, sulfation, stratification, plate damage, etc., etc. This picture only applies to these two brand new (factory coded Feb 2012) fully charged T-105s in series.



Bill

[Maine Sail]

Originally Posted by btrayfors

US Battery recommends an absorption voltage of 14.4. They then talk about a "finish charge" of about 15.3V, same as their recommendation for an equalization voltage.

In practice, what will happen is determined by the properties of the charger -- and it's internal design and algorithms -- and the size, chemistry, and physics of the battery bank under charge.

Would that it were less complicated and that a simple answer were possible :-)

Chargers differ one from another in their behavior. Many modern multi-stage chargers have:

1. a "bulk phase" during which they allow the voltage to rise up to a certain level (the "absorption level") and pump out lots of amps while doing so;

2. when this absorption level voltage is reached -- often in the neighborhood of 14.4VDC -- they then hold the voltage constant and allow the battery to take whatever amperage it will accept. This is the so-called absorption phase, and it can be terminated in one or another of several ways. There's usually a time limit, but also some modern chargers calculate acceptance against time and voltage, and move onto the next "float" stage when they determine the battery to be near full.

3. an equalization phase for flooded batteries. This differs considerably from charger to charger, and it's important to know how your charger behaves before trying this phase.

The batteries themselves will determine how much charge (amps) they'll accept at any given state-of-charge (SOC) and applied voltage. So long as you don't let the voltage exceed a given level, there's no way the batteries will accept more current. In other words, you can't have a charger which is "too large", though you can have one which is too small and unable to deliver all the amps the battery would like to accept.

For reference, I measured the acceptance in amps of a pair of brand new, fully-charged Trojan T-105 deep-cycle flooded batteries at various elevated voltage levels. Ambient temp was 65F. The results are shown in the attached graph.

In blue, the maximum initial acceptance in amps is shown for each applied voltage level from 13.2 to 17.0VDC. If voltage were left at any given level for several minutes, the amps acceptance would drop, often dramatically. For example, at 16.0 volts applied the batteries initially accepted about 8 amps, but quickly dropped to less than 3 amps.

Interesting also is the fact that it was impossible to get the voltage above 17.0 and the amperage above about 17, even given a power supply capable of putting out up to 50 volts @ 20 amps.

The batteries will accept what they're going to accept. Period.

Note that your mileage may vary considerably due to differences in battery chemistry and construction, SOC, age, contamination, sulfation, stratification, plate damage, etc., etc. This picture only applies to these two brand new (factory coded Feb 2012) fully charged T-105s in series.

Attachment 37363

Bill

Bill,

Excellent illustration of "voltage is pressure".....

[goboatingnow]

Interesting also is the fact that it was impossible to get the voltage above 17.0 and the amperage above about 17, even given a power supply capable of putting out up to 50 volts @ 20 amps.

Yes because the input impedance of the battery is so low, compared to the output impedance of the charger.IE the battery determines everything really/ At 17 amps , the charger is close to its limit, hence it can't raise the voltage anymore.

[akio.kanemoto]

Greetings Folks,

Thank you for the detailed explanations. So I'm understanding that within reason - current doesn't really matter as the battery will take whatever it wants to take, so I shouldn't worry too much about it.

So in terms of settings, when I want to equalize, I'll set the float voltage to 15.5, charge to full and leave it at "float" for an hour or so and let it pull as much as it can/wants to.

On this note - I've just noticed that I'm showing that the bank is discharged down only 83.7Ah (from 675AH capacity) on my Linkpro, but the voltage is down to about 12.4V.

83.7AH is approx 13% DoD, but 12.4V means that it's 50% (no other loads at the moment).

Does this sound like a loss of capacity requiring an equalization?

Thanks!

[S/V Antares]

I would like to thank all in this thread for the great info. I just used a toothpick to to push the switch on my xantrax Truecharge 40+ to start an equalize on my t105's. First time since I installed them 3 years ago. I have had no issues with the charger but have heard plenty here and other sites about the inability to contact Xantrax.

[btrayfors]

Originally Posted by akio.kanemoto

.....
On this note - I've just noticed that I'm showing that the bank is discharged down only 83.7Ah (from 675AH capacity) on my Linkpro, but the voltage is down to about 12.4V.

83.7AH is approx 13% DoD, but 12.4V means that it's 50% (no other loads at the moment).

Does this sound like a loss of capacity requiring an equalization?

Thanks!

12.4VDC is 25% discharged, not 50%. 50% is 12.2VDC.

No, that's not necessarily an indication of the need to equalize the batteries or of a loss of capacity. Why? For one thing, your Link may not have been calibrated correctly. For another, the batteries may not have been really fully charged to begin with. Other factors are important, too, like temperature, rate of discharge (Peukert's), whether batteries have been "broken in" yet by several rounds of deep cycling, etc., etc.

I wouldn't worry about them for the moment. Use 'em awhile, including in deep discharge applications (down to 50% SOC or 12.2VDC resting overnite with no loads or charging). See how they perform.

Bill