AGM Battery Charging THE PRIME DIRECTIVE

Smitty77 wrote:

Another fact I learned over the last few weeks is that the Magnum Charger portion logic has a significant design parameter problem for AGM's maintenance. When in storage for up 2-3 months at a time, we're plugged into a 15A outlet. We leave the MS2812 Inverter On (In case of power outages.), and the Charger On to maintain the batteries. Once the Magnum reached Full Charge via reaching 100% SOC (As displayed on Line 1 of the ARC-50 Remote Display.) - it will not go back into charge mode until after the voltage drops below 12.7V, so basically when it reaches 12.6V the charge will kick back on. But, it then kicks back on in Float Mode only, and only runs for 4 hours. From 12.6V level, Float mode for 4 hours will not bring the batteries back to Full Charge. The conclusion from talking to Magnum Tech Support, is that this contributed to my previous battery bank 'walking down', and sulfate build up.

The Magnum is actually a 4 stage charger by default but this can be changed:

03G Final Charge Stage – This setting determines what charge stage(s) occurs after the
Absorption Charge stage has finished.
Default setting: Multi
Range: Multi, Float, Silent

Multi does what you describe, and I have changed mine to Float to act like a 3 stage charger as I didn't like that behavior either, this is Magnums reasoning for multi:

Why should I use Multi? Multi is the most commonly used charge mode. It is suitable for most
applications and assures a full charge to the batteries, without overcharging. If there is another
alternate charge source charging the batteries (PV, wind or hydro), then Multi mode uses the
inverter/charger to complete a full charge. The inverter/charger transitions to Full Charge mode
and the alternate charge source then maintains the battery voltage. If the alternate source is unable
to maintain the voltage, the charger enters Float mode for another 4-hour period. The Full
Charge feature in the Multi mode also helps reduce water consumption in fl ooded batteries when
they are left in charge mode for extended periods, such as in a backup power application.

The Magnum manuals are very detailed and more completing than any I have seen from other competing product such as Victron. The only issue is the information is split between the inverter manual and the remote manual, most of the information on settings is in the remote manual, where the inverter manual is more about installation.

Smitty77 wrote:

So it seems to me the Absorb End - Amps value is best used, and would work well, for those who have everything turned off in their coach. No inverter or parasitic draws. Now if I was in the coach like when we're using it for months at a time. I could manually monitor the Amps via the BMK-Meter Amps display. But while in storage, I'm not in the coach daily... And as mentioned, the dang values used by Magnum to wake up the Charge cycle once Fully Charged value is reached, as well as the going into Float only, are not supportive of my Lifelines. (With the new bank, in testing, once I knew for certain I was at Fully Charged status on the battery. I monitored the SOC values daily over three days. I was down to 81% SOC, and the Voltage was still above the 12.6V needed to goose the Charger back on. So lots of up/down of battery usage, and then again, the Float for 4 hours would not get the bank back to full charge.....)

Again this is not my understanding, if you set done based on amps and you have a BMK installed it will be monitoring the shunt current not the charger current. This way loads will not effect the calculation. If you do not have a BMK it only knows the amps leaving the charger and cannot account for loads, in that situation they do not recommend using amps for done, also the DC amps leaving the charger are calculated from AC amps and not accurate below 1 amp ac / 10 amps dc, the BMK however is accurate to a tenth amp DC all the way to zero.