Absorb charging voltage for AGM concern

[Tinman]

I just changed my batteries to 4 Lifeline GPL 6CT connected series/parallel to give me a 600 amp 12 volt battery bank. I went through the wizard and changed the setting to AGM but I now see an absorb charge rate of 14.8 volts which even temperature adjusted is too high. What gives?

According to the CC' the battery temp is 11 (Celsius I guess, no way to change it, I tried) so converted that is 51.8 F. The absorb voltage should be 14.72.

Voltage at the batteries is 14.9 so I know something is off. I checked the setting in the "charge" menu and it is 14.3.

Very concerned here as batteries are new and the last thing I need is surpassing Kn GAMe or incorrect charging voltage.

[Tinman]

Seems to be the temperature sensor and how it attaches to batteries. I did some checking and found that without the double-sided tape on the sensor holding it onto the battery, the reading on the CC was 2 degrees Celsius higher. That is a 3.6 degree F difference and quite a bit. My test method was as follows:

Sensor in place with the double sided tape holding it to battery. Take reading. 11°C
Sensor in place, no tape held to battery by insulated weight so as not to transfer heat from weight. Take reading - 13.5°C. I figure a fudge factor for the 1/2°.

I allowed the sensor to adjust for about 10 minutes but it reacts much faster so 10 minutes should be adequate.

The CC then immediately adjusted the charging voltage for absorb and went to float.

I have another temp sensor which uses a battery terminal, connection and it too shows a higher temp that the Midnight sensor.

I then ran a third test with two very small of very thin 3M VHB (thinnest they make) attached to only the two lengthwise borders of the sensor. Take reading - 13.2°.

So it would seem that an alternative sensor attachment method is in order, using only my cursory tests. The most accurate appears to be with the sensor held on the battery by insulated weight (not much, just a few ounces). Next, I will test the battery temp using a direct heat measurement to verify if any of this is correct but one thing is certain, removal of the tape changes the temperature reading the sensor gives to the CC.

[boB]

Usually, just putting the temp sensor near the batteries should be close enough.  I like
to just wedge the temp sensor in-between two batteries and call it good.

Mounting a temp sensor to the terminals can show a temperature that is too hot because
of the heating due to resistance of the battery cable connection to the battery post.

11 degrees C, if just the air around the batteries, will certainly raise the charge voltage
and will usually be fine.  But it's probably better to get the sensor on the battery side or top.
A couple of degrees C should  make too much difference.

Higher charge voltage isn't a problem, especially if you just watch the electrolyte level to make
sure it covers the plates and then some.

If you are using VRLA sealed batteries and would like to limit the absolute highest and/or
lowest charging voltage, go to the LIMITS menu and adjust the MAX and MIN charge
voltage to your liking.  Realize though that if the batteries are cold and that voltage
limit is too low, you can sulfate the batteries early.

boB

[Tinman]

Usually, just putting the temp sensor near the batteries should be close enough.  I like
to just wedge the temp sensor in-between two batteries and call it good.

Mounting a temp sensor to the terminals can show a temperature that is too hot because
of the heating due to resistance of the battery cable connection to the battery post.

11 degrees C, if just the air around the batteries, will certainly raise the charge voltage
and will usually be fine.  But it's probably better to get the sensor on the battery side or top.
A couple of degrees C should  make too much difference.

Higher charge voltage isn't a problem, especially if you just watch the electrolyte level to make
sure it covers the plates and then some.

If you are using VRLA sealed batteries and would like to limit the absolute highest and/or
lowest charging voltage, go to the LIMITS menu and adjust the MAX and MIN charge
voltage to your liking.  Realize though that if the batteries are cold and that voltage
limit is too low, you can sulfate the batteries early.

boB

These are AGM batteries Bob, no fluid level to check and AGMs charge at lower voltages than flooded batteries. If they out gas there is no way to put fluid back in.

I see today a very different charging voltage in absorb. I didn't need to mess with limits, just mount  the sensor in a better way than the tape. The tape as it comes is in between the sensor and the battery. It made quite a difference and using the charge voltages from the battery manufacturer no reason for not getting accurate temps. The batteries cost a lot more than the Midnight 150 so taking best care of them is taking best care of me.

It was a simple fix but after all I've put into this system, just okay wasn't good enough. If a battery goes south, there will be no question as to how, when and quality of maintenance.

[boB]

OK, that's great.

I would still look at the specifications for those AGMs and set the maximum voltage in the charger menu limits just to
be safe.  That's what those maximum and minimum voltages are for.   Good thing these batteries have that
recombination chemistry in them !!

boB