t@b400 battery - when to charge?

AMac

Hi all - I've looked in owner's manual, at battery maker's website (Discover), and on this forum, and I can't seem to find an answer to a basic question about the t@b 400 AGM battery:  how low can we safely discharge the battery (voltmeter reading) before we should recharge it? (Currently, voltmeter reads 11.86 and t@b battery monitor panel shows 3 of 4 lights lit).  Battery is Discover AGM EV4DA-A.

Sharon_is_SAM

Generally accepted if you want to prolong the use of your battery, do not routinely discharge below 50%.  In a 12 volt battery that is no lower than about 12.1 volts.

AMac

@SAM - I remembered @ScottG 's post and took voltmeter reading with all draws off (except for CO detector) and reading was 12.01 volts.  Based on table above, this would mean we need to charge the battery now.  But the reading on the t@b battery monitor panel shows 3 of 4 lights lit, which would seem to mean that the "3/4" of the battery's use remains....While camping we would like to be able to rely on the battery monitor panel (rather than having to turn everything off and take a voltmeter reading) in order to know when we need to start conserving use or need to hook up to shore power, but I remain uncertain about whether we can rely on the monitor panel.  Can someone from nucamp weigh in on this?  

Roamey

Keep an eye on this thread:

http://tab-rv.vanillaforums.com/discussion/5878/400-is-not-operating-at-all-on-battery-power#latest

AMac

Roamey said:

Keep an eye on this thread:h

http://tab-rv.vanillaforums.com/discussion/5878/400-is-not-operating-at-all-on-battery-power#latest

Yes, I started that thread but thought it might be good to split out this specific question - what do you think? 

Roamey

Oops, I think I wasn't paying attention. 

Sharon_is_SAM

Too bad.  The SeeLevel monitor in the newer 320s shows voltage.  It is not an exact measurement (you can get close to the same number if you use a 12 volt outlet tester) as it is located beyond the battery, but it is better in precision than your 4 color coded lights.  The lights obviously have a range of power that they reflect.  I see you have a volt meter - assume you are testing at the battery.  Go get an outlet tester - they are easier.  Also Karen and Steve discussed the Tab 400 lights.  I will see if I can find the thread.

Sharon_is_SAM

This is from @skwhee on October 15th at the end of your thread titled Battery monitor panel 400:  basically there is not any information posted / discovered yet regarding correleation of the lights with ACTUAL charge.

 

Here's what we learned from nüCamp:
C - Charged
G - Good
F - Fair
L - Low

So far we do not know how any of that relates to voltage or depth of discharge. 

in a 400 with the solar package the solar controller monitors the voltage and is bluetooth capable. Although it is located under the bed the smartphone app is easy to use. For more information on that here's a link to a relevant forum discussion:
http://tabforum.nucamprv.com/#/discussion/comment/78113

If your unit did not come with the solar package, Michigan Mike's suggestion of a voltmeter that plugs into the 12V (round) receptacle to the left of the kitchen window is the simplest solution.

Hope this helps. If we learn more, we'll certainly share. 

Happy Trails!
Steve & Karen 

Steve and Karen Cullowhee, North Carolina 2008 Ford F150 --2018 T@B 400

AMac

Thanks for the recap @SAM; no solar, we have been testing with voltmeter at 12v outlet per suggestions. My question relates to the fact that my voltmeter reading is 12.01V with a corresponding "good" readout on the monitor, but this thread seems to indicate that I should be charging the battery at this point since a reading less than 12.1V apparently means my battery is 50% discharged. Our dealer scared the bejezus out of us about discharging the battery too much, and I still don't know how to figure out whether I'm 'there' yet. I'm and engineer and my husband is a former mechanic so maybe we are overthinking this...

ScottG

@AMac, keep in mind you don't need to turn everything off to take a voltmeter reading, just big stuff like lights, fan, and water pump. The little LEDs and other phantom drain whatnots don't make that big of a difference. Regardless, I would still put more stock in an actual voltage reading than what some blinking lights suggest. 

I just leave my meter plugged in full time (except when I'm sleeping--dang that thing is bright!) and monitor my voltage on an ongoing bases. If you do this, you will quickly get a sense of the state of your battery (as well as the effect of turning on high power appliances).

Sharon_is_SAM

Cheap and easy way is the plug-in voltmeter that you are using.  I wonder if theTab 400 battery monitor inaccuracy is unique to your unit.  If it is widespread, I would think there will be a number of owners overly discharging their batteries as they have trusted the accuracy of the monitor.  

skwhee

@AMac
Remember that in our 400s that we have an AGM battery which has 80% depth of discharge capability. According to the the manufacturers brochure: http://discoverbattery.com/product-search/view/EV4DA-A
the voltage at 80% DOD is 11.4V. 

Since we personally rely on the bluetooth solar controller for our battery readings we had not paid enough attention to the relationship between the readings on the panel and the voltage readouts, but it sounds reasonable for the panel to read G-Good at 12.01V for the AGM battery. 

It would be true that if you had a wet cell lead acid battery, the type that most dealers supply in the T@B-320s that you would need to be charging at 12.01V. That's one of the advantages of the sealed or AGM battery in the 400. 

That said, our practice usually is to begin charging by the time the battery gets in the range of 12V or so. 

If you are planning on camping off-grid a fair amount, at some time in the future you might consider getting the bluetooth monitor. We definitely prefer it to the plug-in voltmeter.


Hope this helps.
Steve & Karen

AMac

@skwhee thank you so much! This makes a lot of sense. 

skwhee

@AMac You are welcome!

Sharon_is_SAM

http://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html#AGM,%20or%20Absorbed%20Glass%20Mat%20Batteries

@AMac

Northern Arizona Wind and Sun does a nice job of explaining depth of discharge and battery.  The concorde Lifeline Battery they refer to is an AGM, also.  The Discover battery charts indicate that at 25 degrees C  and a 50% depth of discharge, you will have a lifespan of about 1200 cycles relative to less than 800 at 75% depth of discharge.  So, the same holds true for AGM, not just regular flooded batteries.  Yes, the AGM can be discharged to 80% and recover, but routine discharge like that will limit the battery life.  The real benefit in the 400 is being able to house it inside (no off gas), essentially no maintenance, and AGMs as a whole charge faster than flooded batteries (less resistance).  

Cycles vs Lifespan

A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. However, there are often ratings for other depth of discharge cycles, the most common ones are 10%, 20%, and 50%. You have to be careful when looking at ratings that list how many cycles a battery is rated for unless it also states how far down it is being discharged. For example, one of the widely advertised telephone type (float service) batteries have been advertised as having a 20-year life. If you look at the fine print, it has that rating only at 5% DOD - it is much less when used in an application where they are cycled deeper on a regular basis. Those same batteries are rated at less than 5 years if cycled to 50%. For example, most golf cart batteries are rated for about 550 cycles to 50% discharge - which equates to about 2 years.

Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50%. Obviously, there are some practical limitations on this - you don't usually want to have a 5 ton pile of batteries sitting there just to reduce the DOD. The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor. Also, there is an upper limit - a battery that is continually cycled 5% or less will usually not last as long as one cycled down 10%. This happens because at very shallow cycles, the Lead Dioxide tends to build up in clumps on the the positive plates rather in an even film. The graph above shows how lifespan is affected by depth of discharge. The chart is for a Concorde Lifeline battery, but all lead-acid batteries will be similar in the shape of the curve, although the number of cycles will vary.