Does absorption time depend on % DOD?

[kateonmars]

Hi there,

I have a question about absorption time on the Kid: namely, should it vary by season, since my DOD varies by season?

I have an off-grid solar set-up which includes the Kid, four Rolls AGM 6v batteries set up for 12V, a MMS-1012 Pure Sine Wave Inverter, and two 250W Hanwah panels. The absorption time for this battery set-up, according to Rolls, is about 11 hours for 50% DOD. However, in summer, my daily DOD is much lower than this because it's naturally light almost all the time (I live at 60 degrees N), and in winter, it is much higher because I'm using LED lights etc for far longer. Given this, my solar installer suggested I change the "absorption time" on the Kid seasonally, to reflect these different DODs.

Does this make sense? Or does the Midnite Sun Kid gauge how charged the batteries are, and adjust the absorption time accordingly? For example, if the batteries have only been discharged 80%, shouldn't the Kid's absorption time required change accordingly -- ie. the charge controller shouldn't blindly run the full absorption time of 11 hours. Is that how the Kid works?

If anyone can help clarify this for me, I would greatly appreciate it.

Many thanks,
Kate

[Vic]

Hi Kate,

YES,  the required Absorption time for Lead Acid batteries does depend upon the DOD in the previous discharge of the battery.

One good way to accomplish this,   is to use End Amps,  which the Optional WhizBang Jr accessory will allow the KID to use.  The EA setting is customarily about  1 - 3% of 20 Hour Capacity.

AGM batteries often require L O N   G  Absorb stages,  and your stated 11-hour Absorb seems long,  indeed.

I have no experience with AGM batteries as an off-grid battery.   

If you choose to not use the WBjr current monitoring device with your KID,  you should probably manually change the length of your Absorb stage.

What brand of AGM batteries are you using?
FWIW,   Good Luck,   Vic