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Old 07-27-2019, 10:08 AM   #1
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Float Charge Voltage

I just redid the house bank in the boat with 1200 A/hr of Lifeline AGM and installed a Balmar SG2000. The bank is charged while at dock with a magnum 2818 inverter charger. configured for AGMs and also a dedicated smart charger.



Lifeline specs float charge when the temp is 77 degrees at 13.3 volts. The magnum will achieve the voltage and turn off and turn back on when the battery voltage falls to some level at around 12.8 volts. The current when in Float mode is never more than 15 amps... So with just the inverter/charger the battery voltage fluctuates between 12.8 and 13.3 volts.... If I turn on the the battery charger it will allow the float voltage to go up to 13.5 volts and holds it there but the net current into the battery bank is 1 to 2 amps....



CMS says that for Lifelines 13.4 Vdc is fine.... My question is with the low current flowing into the bank does it hurt the battery bank to allow the FV to go to 13.5 to 13.6 Vdc or is it best to shut down the charger and let the inverter charger cycle between 13.3 and 12,8Vdc....
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Old 07-27-2019, 10:25 AM   #2
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It may be fine either way but the correct answer is to do what Lifeline says to do.

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Old 07-27-2019, 11:42 AM   #3
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My reply got lost apparently. Trying again.

Iirc, Lifeline gives a range of 13.2-13.4v for float at 20 degrees C. I set my Magnum at a float voltage of 13.4 as I have two banks and my non-Lifeline batteries was 13.4v at float. My Magnum 2812 will put out a lot more amps at float to maintain that 13.4v depending on what 12v loads there are. If there are no 12v loads (very rare for me) then after 4 hours at the float voltage it will shut down until the voltage drops to 12.6v then go into float again and when the 13.4v is reached, maintain that for another 4 hours. I rarely see this.

Right now the Magnum is putting out 0 amps to maintain the 13.4v since my solar (on this very cloudy and rainy morning) is sending 2 amps to the battery to maintain that 13.4 and I’m only drawing using 1.1 amps (holding tank aerator).
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Old 07-27-2019, 07:22 PM   #4
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Quote:
Originally Posted by Ka_sea_ta View Post
The bank is charged while at dock with a magnum 2818 inverter charger. configured for AGMs and also a dedicated smart charger.

Lifeline specs float charge when the temp is 77 degrees at 13.3 volts.
My question is with the low current flowing into the bank does it hurt the battery bank to allow the FV to go to 13.5 to 13.6 Vdc or is it best to shut down the charger and let the inverter charger cycle between 13.3 and 12,8Vdc....

"Configured for AGM's" covers a lot of territory. It's way too broad. You need to configure the chargers for YOUR BANK. Yes, your bank happens to be AGM, but there's too much variation in AGM profiles to set it at that and leave it. For the Magnum, go into the custom profile and set the voltages at what Lifeline recommends. IIRC, the setting is for standard temps, the temp sensor (you do have a temperature sensor, right??) will correct the voltage for different temperatures. If your non-magnum smart charger can't be set for the custom profile, then it's not really so smart, and I'd figure on turning it off unless you're bulk/absorb charging and the voltage isn't as critical. When it's close to float I'd let the Magnum with a custom profile finish up.


If you're charging with a Balmar regulator, program it to the battery bank's profile, don't use the presets. Pay special attention to the SLP or slope setting. It's not well documented, but it important to set it to match the bank profile for temperature vs. voltage. An incorrect value can result in inadequate charging when the battery temps rise. Particularly notable if the bank is in the engine room as many are.



I killed an expensive Lifeline bank through chronic inadequate charging. Months at anchor, would shut the genset down when SOC reached 90%, my charging underway rarely brought the system up to full charge. A high output alternator corrected that, and solar has enabled me to reach 100% SOC every cycle unless the sun's not shining. Those Lifelines are a great battery, and expensive. Protect that investment by insuring your system is up to the task of bringing them up to a full charge on a regular basis!
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Old 07-28-2019, 12:49 AM   #5
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Quote:
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"

I killed an expensive Lifeline bank through chronic inadequate charging. Months at anchor, would shut the genset down when SOC reached 90%, my charging underway rarely brought the system up to full charge. A high output alternator corrected that, and solar has enabled me to reach 100% SOC every cycle unless the sun's not shining. Those Lifelines are a great battery, and expensive. Protect that investment by insuring your system is up to the task of bringing them up to a full charge on a regular basis!


Under charging is not the issue, I'm concerned about over charging the bank because the float voltage is about .15 volts higher than lifeline recommends but the current at that voltage is typically 1 to 2 amps. lifeline defines a fully charged bank as the input current is equal to .05 of total bank capacity so in my case when the float current is 6 amps or less the bank is considered fully charged.... So my question is it best to let the magnum cycle between 12,75 volts and 13.3 volts or just let the not to smart battery charger maintain a float charge up to 13,5 volts with 1 to 2 amps of input current. when I turn off the charger the bank voltage will quickly drop down to under 13 volts and within a few hours with no load the bank voltage will drop to 12.75 which will cause the magnum to charge in float mode till the banks voltage reaches 13.3 Vdc then the inverter charger shuts down and the bank voltage slowly returns to 12.75v
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Old 07-28-2019, 06:04 AM   #6
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I would just call Concord and ask them. Their techs are very helpful. One suggestion, and you probably already do this, but if you are fine tuning, you need to put a meter directly on the batteries and not rely on any remote voltage reading. Second, as M already said, if you do not have a temp sense on the battery, feeding a controller that adjusts per the Lifeline guidelines, then don’t even bother fine tuning float.
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Old 07-28-2019, 08:15 AM   #7
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Follow Maerin's advice on adjusting the Magnum to
Concord Lifeline's specs (I trust you are using the remote with temp sensor as noted). If you don't have one, get their Battery Monitoring Kit. Among many other things, it will give you an accurate voltage reading just as it you put a multimeter on the terminals (which is actually what you are doing with one).
Not sure I understand having another standard battery charger involved.
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Old 07-28-2019, 09:00 AM   #8
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I think I can clarify my question, Once 100% SOC is achieved, is it best to let the magnum provide the float charge. The way the magnum works is once the bank reaches 13.3 volts it shuts off, in the course of a few hours with no load on the batts the voltage will decay to about 12.7vdc then the magnum turns back on and will provide the float charge necessary to reach cutoff voltage.... So in effect the battery bank voltage when in float mode with just the magnum cycles between 12.75 and 13.3 vdc


With the other charger it does not cycle on and off it will maintain the voltage at a constant 13.5 volts and drop the current to 1 to 2 amps
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Old 07-28-2019, 09:25 AM   #9
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Quote:
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With the other charger it does not cycle on and off it will maintain the voltage at a constant 13.5 volts and drop the current to 1 to 2 amps

Use the Magnum.

Turn the 2nd charger off unless you're recharging from SOC less than 90% or so- while you're bulk/absorb charging, the voltage isn't likely to climb higher than the profile voltage, so the net result is a bit shorter duration with both chargers on line. If the 2nd charger can be customized, then simply set the float voltage a couple of tenths lower than the Magnum's float, then as it approaches float, it will automatically defer to the Magnum that has the better maintenance charging sequence.
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Old 07-28-2019, 01:17 PM   #10
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Internal resistance of a battery is part of the picture and might help make sense of the other measures.
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Old 07-29-2019, 05:54 AM   #11
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The big hassle is a not too smart charger that sees operation of a DC electric device like a TV, fan, bilge or FW pump as a slightly discharge batt and will charge it full tilr , and finally switch back to a lower float voltage.

This does not seem to harm the batt , but may require far more frequent water service.
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Old 07-29-2019, 08:22 AM   #12
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I think we make too much out of the proper float voltage.

Once a battery is fully charged, ie all of the lead sulfate has been converted to lead and sulfuric acid then a voltage of 12.7-14 volts will keep it stable. On the higher end of that range you will disassociate a little of the electrolyte (boil in the common vernacular) and that will require adding water more frequently. On the lower end of that range you risk leaving lead sulfate in solution which can precipitate out and ultimately short the plates.

So keep your float voltage at about 13.5, check the water regularly- I check mine every 2-3 mo, and err on the high side. As long as you don't let the water level drop below the plates, you will do no harm.

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Old 07-30-2019, 03:19 PM   #13
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I think we make too much out of the proper float voltage.

Once a battery is fully charged, ie all of the lead sulfate has been converted to lead and sulfuric acid then a voltage of 12.7-14 volts will keep it stable. On the higher end of that range you will disassociate a little of the electrolyte (boil in the common vernacular) and that will require adding water more frequently. On the lower end of that range you risk leaving lead sulfate in solution which can precipitate out and ultimately short the plates.

So keep your float voltage at about 13.5, check the water regularly- I check mine every 2-3 mo, and err on the high side. As long as you don't let the water level drop below the plates, you will do no harm.

David
For flooded cells, that makes sense. The OP has AGM and should follow the manufacturer's voltage recommendations as closely as possible for the best possible life span.
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Old 07-30-2019, 06:01 PM   #14
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This does not seem to harm the batt , but may require far more frequent water service.

Remember, the OP is working with Lifeline AGM's. Watering service isn't in the equation. Overcharging certainly won't make AGM's very happy, neither will undercharging, for that matter.

I prematurely killed an expensive bank if 6-L16-2V Lifelines through chronic poor charging. I'd advise anyone considering Lifelines to make certain their system is capable of maintaining the bank BEFORE dropping those expensive units into place. Granted, they're great batteries. Maintained per the manufacturer's specific profile (and fully charged regularly), they'll last a long time. If not, you're wasting your money.
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