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float current too high?

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Posted by Robert Morein on July 26, 2004, 4:47 am
The battery bank consists of four Concorde Lifeline AGM 6V 220 ah batteries
in series parallel to make a 440 ah 12 bank, model GPL-4C (see
http://www.lifelinebatteries.com/marine.asp )
The relevant charging specs are:
Bulk: 14.2-14.4 V
Acceptance: 14.2-14.4 V
Float: 13.2-13.3V

This is a brand new installation. Before installing the batteries, I
measured the open circuit voltage of each. Three were above 6.40V, and one
was 6.35V. All these reading correspond to 100% SOC.

I'm using an Outback MX-60 charge controller, which has a very nice display
of voltage, mode, and current. With the approval of Outback, it is hooked up
to a 24V DC supply, to make a complete AC charging system.

Last night, the MX-60 LCD display indicated "FULL", meaning that no current
was being supplied to float the batteries. However, 24 hours later, I
noticed the AC supply fan was running. The MX-60 now indicated "FLOAT",
meaning that the charger was now active.

The MX-60 amp reading now indicated 2 amps. I thought I might have heard
something like a faint Bronx cheer (battery venting?), and in a panic pulled
the plug on the supply. I plugged and unplugged several times, with the
ammeter indicating as high as 7 amps, but mostly, 2 or 3. I checked the
voltage with a multimeter, and obtained 13.18 volts. I did not check the
amps independently, but the power supply fan had been running, and the PS
case warmed up a bit.

I reduced the MX-60 float voltage to 13.0V, below the Concorde
recommendation. After about an hour, the MX-60 again indicated "FLOAT", and
the ammeter indicates 1 amp.

With $00 invested in these four batteries, I'm worried. Is 2 amps a
reasonable float figure? Intuitively, it doesn't seem reasonable to pump 24
watts into a sealed battery on a continuous basis. The Concorde website
indicates that boost charging is to terminate when the amperage drops to 0.5

Therefore, it puzzles me that the float current I'm observing is double

Posted by Robert Morein on July 26, 2004, 7:14 am
Additional info:
At 13.0 volts, the float current was 1a.
At 12.9 volts, it was .5a
At 12.8 volts, the MX-60 entered sleep mode, meaning that it was not
supplying charge current.




Posted by Ron Rosenfeld on July 26, 2004, 10:52 am

You should have the Battery Temperature Sensing option.

Sounds like pretty normal behavior.  After the MX60 finishes it's ABSORB
state (which is determined by a timer -- not by current flow), it'll go
into BAT FULL until the voltage drops below the FLOAT voltage.

And what was the battery temperature when you measured that voltage?

The lower the voltage from the MX60, the less current you will put into the

If the current of a fully charged battery, at float (temperature
compensated) voltage is supposed to be less, than probably your batteries
are not fully charged.

Boost charging is not the same as float.

See above.

And also, check with the Concorde tech support folk.  It is likely they
know more about their product than I do.

-- ron  (off the grid in Downeast Maine)

Posted by no useful info on July 26, 2004, 3:08 pm



I do, but the batteries are installed in a temperature regulated location.

Posted by Robert Morein on July 26, 2004, 6:29 pm
  "no useful info" <not for you> wrote:

Are they in a wooden battery box? Have you ventilated it properly? Is it
NEC compliant?

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