Originally Posted by tankcj
Ok, so now that I have my new AGM batteries, I'm about ready to reconfigure (at least on paper) my MC-RC controller but have some questions. My batteries are (4) Crown 6v AGM 220ah @ 20hrs
1) The absorption time seems to have a fairly wide range (2-4) hours for AGM batteries depending of DOD, charge rate, etc. I understand that too little time and the batteries will not reach a complete recharge. Correct? If I set the time too long, will the BTS adjust the voltage and/or amps so as not to overcharge? For my AGMs, they say the time should be 2.5 - 3 hours.
2) For my AGMs, the recommended charge rate is 10% of the C/20 with a max of 25%. The recommended rate would be 44 amps and the max would be 110 amps. My ME2012 has a 100 amp charger. So I should be able to set the Charge rate to 100% which is still less than the 110 max. Correct?
As you mentioned depending on how far your battery bank has been discharged the Absorb time can be a variable. The Absorb time is also affected by the charge rate. The higher the charge rate the lower the Absorb time could be.
With your setup I would set the Absorb time to 2 hours (to start with) and a charge rate of 90%. With the above Absorb time monitor the amps going into the batteries just before the end of the 2 hour period. Try to have other DC loads shut off when checking the amp load to get a more accurate indication of what is going to the batteries. If the charge amps has dropped to about 1% of your capacity which would be 4.4 amps then your batteries are 100% charged. If the charge amps are consistently higher than the 4.4 amps near the end of the 2 hour Absorb period then increase your Absorb time by 30 minutes. If the charge amps are consistently less then reduce your Absorb time slightly.
The Magnum inverter if worked hard will create lots of heat at the transformer and the FET boards. Can be seen under the TECH button and then select temperatures. Charging at 90% helps a little with the heat generated and still gives you a decent rate of charge which is within the recommended settings from Crown batteries.
Your battery temp sensor (BTS) adjusts the charge voltage based on temperature. If the temperature at the batteries is above 77F (25C) the charge voltage will be less than what is set in the charge profile. If the temperature is colder then the charge voltage will be higher. Unless grossly mis-set having a slightly longer Absorb time will not adversely affect your batteries or overcharge them. As the batteries reach full charge internal resistance goes up and charge current goes down so an extra few minutes at the Absorb voltage is fine. More batteries fail prematurely from under charging than from a slight over charge.
One other note, if your Magnum remote is capable of setting Final Charge (SET 9) then set this to Float to keep your AGM battery bank fully charged when sitting on shore power. The only exception to this would be if you had an extensive solar array (something greater than 200W) then set Final Charge to Multi.