First Post - ROLLS AGM S6-275

The date code on both Rolls batteries show   K154104  H  5N  ...Oct 7 2015

I charged the batteries again. It took 25min at 51amps for the charger to reach full 15.1 charge voltage @ 64F today. 

After 1 1/2 hours on the charger the temperatures on the sides of the batteries where all within 0.5 degrees.


Next I used the Pronautic set to AGM Profile #2 to charge a brand new Northstar NSB-AGM27 that is 91AH.

http://buy.northstarbattery.com/p/nsb-agm-27m-battery

The charger was disconnected when the outputw as 0.5A.

Five minutes after disconnecting the charger the Northstar voltage was 13.2V

A hour after the charger was disconnected the voltage was 12.86V.

The LED light bar was connected (nothing else connected to the batteries) and the voltage dropped to 12.22V.
1 hour later the voltage was 12.19V
2 hours later the voltage was 12.08V
3 hours later the voltage was 11.89V - the light bar was disconnected

The Nothstar has been charged twice. Essentially it is not formed as much as the Rolls that have been charged 14 times

The Rolls are being charge at 15.2V bulk while at the same temperature the Northstar is 14.5V bulk...that is a big difference.

Mystifying how the same load can draw 250Ah down to 50% in the same time that 91Ah is drawn down to 40%.

zoneblue said:

Im not sure that im following your situation exactly, but AGM capacity anxiety is common.  While AGMs are well suited to RV applications (although lithium is rapidly taking over), the trick to sanity there is a) knowing that youve fully charged them regularly, and b) employing some kind of coulomb counting based state of charge monitoring.

Fixed absorb times are difficult to work with, can over charge or undercharge. A charger with true end amps will help a lot there. You dont want to under charge them because you create a spiral of reducing capacity each time you do it. You dont want to overcharge them because youll wear out the catylyst and pop the vents releasing gas that can not be replaced, causing the battery to fail early.

A battery monitor like the victron/bogart's or the one built into the midnite classics will help give a reasonable estimate of SOC, but perhaps mroe usefully it also allows you to monitor in real time what is going into and out of the battery, thus allowing you to trace unusual loads.

Over time you will learn how your particular batterys rest voltage maps to SOC, but for now it sounds like you need better information before worrying too much.

Thank You Zoneblue

I have 2 - 6V S6-275 Rolls in series that are suppose to have 250Ah. I only seem to be getting 36Ah.

The charger is left to run each time until the output is .0.5A . I don't know if this is what you would call a charger with true end amps?

I have a battery monitor. It was going to be installed along with the rest of the system....instead the time has be diverted to problem solving the Rolls batteries.

I have everything on a bench so as a final double check today I'll rig up the battery monitor and give things a go.

Take Care
John

BB. said:

From what you have posted, I do not see you doing anything wrong (especially in terms of under charging).

The batteries are ending the charge with high voltage and low current. Whether automatically terminating or you stopping at low amps (down to 0.1% or below 2.5 amps), it does not explain your poor bank performance (unless you took the batteries to dead and sat for 1+ weeks uncharged, or the batteries were delivered dead to you).

One question, that you may have missed of mine (or I missed your answer), what is the voltage of each 6 volt battery during loads+ charging. Are the voltages very close or are they >>0.01 volts different.

Looking to understand if you have one failing battery or two failing batteries.

At least, one failing battery would be easier to attribute to mfg/not your problem.

-Bill

Thanks for the reminder Bill.....after you asked I checked.....then forgot to post the results.

I don't remember what the number are but every time I've checked (4-5 times now) the voltage on both batteries is identical to .01V.

I've had the capacity issue since day 1. First trip out I got my ear burned off by the dear wife after spending $$$ on the Rolls only to have them last less time than the Group 27 that was there before......it gets worse my other ear keeps getting smacked because I have to run the generator (Honda 3000is) 2 times day and last trip had to make a special trip out to buy more gas. Before the generator only ran once a day or every 2nd day.

If I did do something to the batteries then I sure like to know so I don't screw up again...my ears are very sore.

The only thing I can think of now is that I've been assuming 50% capacity is 12.1V. Do you know what it should be?

Thanks
John

 


 
 

westbranch said:

is that 12.1 V been measured at rest or under load?  There is a big difference...

The 12.1V has been measured under load but the loads varied from 1 amp to 12 amps.  I've considered the 1amp ghost load that the trailer draws to be resting.

This is the test I did on Friday...after going down to 12.09V an hour later it returned to 12.32V

Yesterday we charged the batteries (using the temp sensor) for 6 hours @ 15.2V bulk and 14.1 float.  Five minutes after disconnecting the charger the voltage was 13.0V
 7:15AM this morning the resting voltage was 12.82V.
The 12amp light bar was connected (nothing else connected to the batteries) and the voltage dropped to 12.33V.
1 hour later the voltage was 12.32V
2 hours later the voltage was 12.25V
3 hours later the voltage was 12.16V
3 1/2 hours later the voltage was 12.09V - the light bar was disconnected
4 1/2 hours later with no load on the batteries the voltage was 12.32V

Today the ambient is temp is 74F.

 The batteries where fully charged at 14.8V bulk & 13.8V float. The charger finished charging and went into standby mode.

Battery monitor was set up and then turned the light bar on.

The monitor shows load from the light bar at 11.9 amps and the battery temp at 71F.

 After 3 1/2 hours with the light bar connected the monitor alarm set at 12.1V went off.

The S6-275AGM 20 hour rate is 12.5amp to 10.5V

 http://www.rolls-battery.com/pdf/s6-275agm.pdf

This became even more puzzling....this morning I took the batteries to be test.

They put 400amp load on each battery for 2 seconds then put 100amps on for 10 seconds.

Both batteries tested good.

The needle on the battery tester was on the low side of the range for being good so I don't know if that means anything.
 

BB. said:

It does take several dozen cycles +/- (deeper than 75% state of charge) to full form plates.

-Bill

Thank You Bill

The last thing I want to do is return the batteries but I need batteries that last longer than 3 1/2 hours with a 12 amp load.

As the plates form do you see the capacity going from 3 1/2 hours at 12amps to being close to the 20 hours at 12.5 amps that the batteries are rated for?

Take Care
  John