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<div> <font size="3">The way these multi-phase chargers work is they charge at constant-current (Bulk Mode) until a voltage threshold (~14.25V) is reached at which point it switches to constant voltage (Absorption Mode) until the current drops below a threshold where it switches to Float Mode. The data sheet doesn't talk much about this (or at all) but it is possible that this charger is calibrated for a 40 A-H battery </font><font size="3">more typical of what is found in private vehicles. It is possible that the absorption current on a much larger battery (100 A-H) never gets below this threshold so the charger never switches to Float. <br>
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<div><font size="3">But this is just speculation.</font></div>
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<div><font size="3">OTOH, I had a 5-year old Optima in my TR6 that displayed the same symptom. But on my car I can connect the charger in such a manner that I can monitor the charge current on the in-dash ammeter which never dropped below a few amps. In fact I first noticed the problem while driving as the ammeter was centered indicating zero amps early in the drive but when approaching the house the current was definitely in showing a few amps of charge which is not at all typical. <br>
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<div><font size="3">I took it to the shop specializing in batteries and they rolled out their tester and pronounced it "good." In my estimation, their test is not comprehensive and only checked for open and/or shorted cells and for current capacity. They were more than happy to take my money when I insisted that the battery was not going to last and I was happy with replacing the battery since it was at least five years old and had been abused (completely discharged at least once).<br>
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<div><font size="3">So, I guess the short answer is what is the current into the battery when the charger hangs in the Absorption Mode?<br>
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<div style="clear:both"><font size="4">Dave </font><br>
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<div style="font-family:arial,helvetica;font-size:10pt;color:black">-----Original Message-----<br>
From: Jimmie Mayfield via Shop-talk <shop-talk@autox.team.net><br>
To: shop-talk <shop-talk@autox.team.net><br>
Sent: Tue, Apr 7, 2020 9:34 am<br>
Subject: [Shop-talk] Float chargers<br>
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<div dir="ltr">The recent discussion about solar-powered float chargers has reminded me <br clear="none">of an issue that I've yet to understand or resolve...<br clear="none"><br clear="none">I have a Battery Minder 12248 (12V 2/4/8A) charger/de-sulfator with <br clear="none">temperature compensation sensor. While I've never been able to <br clear="none">appreciably restore a dead UPS battery using the de-sulfation mode, it <br clear="none">seems to work fine as a slow charger. It has several modes -- gel-cell, <br clear="none">AGM or flooded -- which, near as I can tell, adjusts the threshold <br clear="none">voltage at which the charger switches from bulk-charge mode to <br clear="none">float-charge/de-sulfation mode.<br clear="none"><br clear="none">Every 12V battery that I've ever connected to the charger, even the old <br clear="none">AGM batteries taken out of my UPS units, eventually reached the <br clear="none">threshold voltage and switched over to float mode (usually within 30-45 <br clear="none">minutes for a nearly-fully-charged battery). Except one.<br clear="none"><br clear="none">About 2 years ago I installed an Interstate battery from Costco (size <br clear="none">27F, 890CA, 710CCA) in my truck. It's a flooded battery and if I <br clear="none">understand Interstate's spec correctly, its capacity works out to around <br clear="none">100Ah. The battery has a resting voltage of 12.6V so it doesn't appear <br clear="none">to have any shorted cells and has no trouble starting my truck. So it <br clear="none">seems to be a normally healthy battery, right?<br clear="none"><br clear="none">Thing is...I've never seen my charger go into float mode when connected <br clear="none">to this battery even when it was nearly new. With the recent pandemic <br clear="none">stay-at-home orders, yesterday I decided to connect my truck to the <br clear="none">charger to stave off parasitic drain (measured to be 20-30mA) that may <br clear="none">have accumulated over the past week of inactivity. I'm currently at 16 <br clear="none">hours (@4A) and it still seems to be in bulk-charging mode. I have <br clear="none">difficulty believing that the battery needed 50+ Ah.<br clear="none"><br clear="none">So what's going on here? This is the only battery that I've come across <br clear="none">that behaves like this.
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