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Lee3
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Joined: 17/09/2014
Location: Australia
Posts: 57

Posted: 03:14am 27 Mar 2018

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I now have a 120Ah AGM in a portable battery box in the car for camping. I say portable, but at 42kg it will likely spend most of its life where it now is!
I have a Projecta IDC25 DC-DC charger wired up to it, which has a temp probe - the manual says to cut it off if you don't need it - which I did.
Should I maybe reconnect it and use it - given the temps the battery will likely reach inside a vehicle, will temp compensation make much difference?
Thanks in advance.... Lee

Alastair
Senior Member

Joined: 03/04/2017
Location: Australia
Posts: 161

Posted: 12:26am 28 Mar 2018

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Lee,
yes I would reconnect it.

AGM batteries generally have a lower charge current because they need to absorb and recombine the gas produced as part of the lead/acid process. In a fluid filled battery it can just bubble off. In the AGM which has gel between the plates rather than fluid then it takes time to absorb. If you charge too fast then the gas causes the battery to expand and distort the case and internal structure. Heat makes this worse so a charger with an AGM setting and temperature compensation will do this best and give the battery a chance for a long life.
Edited by Alastair 2018-03-29

Cheers, Alastair

Lee3
Regular Member

Joined: 17/09/2014
Location: Australia
Posts: 57

Posted: 12:49am 28 Mar 2018

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Thanks, I will.... I'll just have to incorporate a plug/socket into the cable to keep the battery pack portable. Looking at Projectas info for the charger, their standard charge voltage for AGM is 14.4V, which, according to Fullrivers specs, is what they suggest at 38 deg C anyway....
If stuck I could probably just set the charger to 'Gel' mode - 14.1V ??

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 03:55pm 28 Mar 2018

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for 12 volt systems

it is going to be approx -0.3 volts for every +10 degrees Celsius (-30mV per degree)
or -3 to -5 mV per cell per degree.
reference zero point is 25 C

managing heat by restricting voltage when it is above 25 degrees is worth 15-20 % extra lifetime capacity for lead cells.

I'm confused, no wait... maybe I'm not...

Lee3
Regular Member

Joined: 17/09/2014
Location: Australia
Posts: 57

Posted: 08:53am 07 Apr 2018

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I reconnected it today, the battery is inside a box (Projecta Power Hub), so in order to keep it portable had to drill it for a socket for the temp probe. I fired the charger up and immediately saw the float voltage being reported on the box as 13.5V rather than 13.6V (the box seems to show about 0.1V lower than my Agilent multimeter) its been doing without the probe, must be doing something.....
Thanks for the advice....
Lee

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