[Shop-talk] Float chargers

[Pat Horne]

Sounds like a question for interstate. 

Peace,
Pat

Pat Horne 
We support Habitat for Humanity


> On Apr 7, 2020, at 9:34 AM, Jimmie Mayfield via Shop-talk <shop-talk at autox.team.net> wrote:
> 

The recent discussion about solar-powered float chargers has reminded me of an issue that I've yet to understand or resolve...

I have a Battery Minder 12248 (12V 2/4/8A) charger/de-sulfator with temperature compensation sensor.  While I've never been able to appreciably restore a dead UPS battery using the de-sulfation mode, it seems to work fine as a slow charger.  It has several modes -- gel-cell, AGM or flooded -- which, near as I can tell, adjusts the threshold voltage at which the charger switches from bulk-charge mode to float-charge/de-sulfation mode.

Every 12V battery that I've ever connected to the charger, even the old AGM batteries taken out of my UPS units, eventually reached the threshold voltage and switched over to float mode (usually within 30-45 minutes for a nearly-fully-charged battery).  Except one.

About 2 years ago I installed an Interstate battery from Costco (size 27F, 890CA, 710CCA) in my truck.  It's a flooded battery and if I understand Interstate's spec correctly, its capacity works out to around 100Ah.  The battery has a resting voltage of 12.6V so it doesn't appear to have any shorted cells and has no trouble starting my truck.  So it seems to be a normally healthy battery, right?

Thing is...I've never seen my charger go into float mode when connected to this battery even when it was nearly new.  With the recent pandemic stay-at-home orders, yesterday I decided to connect my truck to the charger to stave off parasitic drain (measured to be 20-30mA) that may have accumulated over the past week of inactivity.  I'm currently at 16 hours (@4A) and it still seems to be in bulk-charging mode.  I have difficulty believing that the battery needed 50+ Ah.

So what's going on here?  This is the only battery that I've come across that behaves like this.


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