Setting your Trace Auto Gen Start Parameters

[davidbrady]

AGM lifespan is inversely related to the number of discharge cycles. Fewer cycles, longer lifespan, so pole to pole camping is very easy on batteries. The other thing that messes them up is deep discharge to like 0% state of charge. I try not to go below 50% depth of discharge. Also, discharging them and then putting them on a shelf in a discharged state messes them up.

If you're boondocking, then you need to be careful to fully top-up your battery bank to over 100% of it's capacity during each charging cycle; otherwise, the batteries will "walk down" over time and fail. Over 100% is indicated by an absorption charge amperage of less than .5% of the battery bank capacity.

My coach has 8 4D's, of course wired in a 24V bank, which provides a 840Ah capacity. Lifeline says my charging current should be at least 0.2C which for me is about 170A. Our inverters control charging current based on AC amperage, so divide 170 by 4 to get 42A of AC charging current. We divide by 4 because of losses in the Trace chargers. Now, we have two inverter/chargers, so divide by 2 again to get your "Set Max Charge Amps AC" in menu 10 "Battery Charging". This tells me to set my inverter charging amps to 21A AC on each inverter.

If I do this, then I need the following amount of time to charge my 50% depleted battery bank back to 100%. (Remember my DC charging current is around 170A):

840 * 50/100 / 170 + Absorption Time = 2.5 hrs + 3 hrs = 5.5 hours

For boondocking, where I'm going to be doing this for day after day, there's a couple of things to pay attention to:

(1) I can shorten my charging time by increasing my Trace charger output. When my generator is running I want to use it to it's maximum, so I'll reach in and I'll increase the "Set Max Charge Amps AC" to 30. This will bring the Bulk (constant current) phase of the charge cycle down from 2.5 hours to: 840 * 50/100 / 240 = 1.75 hours, adding in 3 hours of Absorption time brings my charge time down from 5.5 hrs to 4.75 hrs.

(2) I need to make sure I'm spending enough time in Absorption. Remember what I said earlier about the batteries "walking-down" as the days wear on if I'm not topping then up to over 100%. (Lifeline says 102% to 110%). The only measure we have of this is the "Inverter/Charger Amps AC" in the Meters menu (Menu 4). Inverter/Charger amps can be (+) or (-). (+) means the inverter is charging, and (-) means the inverter is powering loads. To make it more confusing the inverter can be powering loads even though the red "Bulk" led is on indicating charging. Then, I also get into the case where one inverter is in Bulk and the other is in Float. So, to read this meter both inverters should be in Bulk and both should be showing a (+) value. In any case, Lifeline says the Absorption time is complete when the charging current reduces to 0.5% of the battery bank capacity.

In my case, with my 840Ah battery bank, this would be 4.2A DC. Dividing by 4 gives me about 1A AC, and dividing by 2 again for the two inverters gives me( around 0.5A per inverter of charging amperage at 120VAC. (In reality, one inverter is bound to dominate so you'll like read a larger value on one inverter and closer to zero on the other). So you can see the Absorption time is difficult to determine based on charger 120VAC Amps, but if you have an amperage anywhere above 0.5A AC then it's not complete and you need more time in Absorption.

For a DOD of over 50% Lifeline recommends an Absorption time of 4 hours. For a DOD of between 30 to 50% Lifeline recommends 3 hours, but the real time required is how long it takes to reduce Absorption amperage to less than 0.5% of the battery capacity. This parameter can be fine tuned - see "Set Absorption Time" in Menu 10, "Battery Charging".

In short, when the generator is running and when it's pretty much dedicated to charging my AGM's, I increase my charging amperage to 30, and I make sure I don't walk-down the battery bank as the boondocking days wear on by staying in Absorption long enough. Stay in the Absorption period for long enough to bring the battery bank back to 102 to 110%! Not doing this is probably the number one reason folks don't get years out of their AGMs.