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Old 09-02-2020, 12:14 PM   #1
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Battery Discharge Level

I recently converted from two 12v batteries to two 6v Trojan T105 batteries. And yesterday I installed a volt meter so that I can see actual voltage rather than looking at the 4 red lights on the control panel. So now that I can monitor voltage I am looking for some wisdom from those of you who understand these 6v batteries as to what level of discharge is reasonable without damage to the batteries. I've found a couple of charts that show 11.81 (across both batteries) as "yellow/caution" and 11.51v as "red/danger". Is this a realistic guideline or does your experience show something different? How far down to you feel comfortable running your 6v batteries?
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Old 09-02-2020, 12:25 PM   #2
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It's my understanding led acid batteries should not be discharged below 50%. I have my AGS set at 12.2 volts.
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Old 09-02-2020, 12:27 PM   #3
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See attached chart
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Old 09-02-2020, 12:31 PM   #4
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Reading volts is tricky. The reading will varry depending on the load on them at the time or if no load, how long they have been resting.

You don't want to drop down in the red zone with no load, that's when things can go bad.

Many folks are going to tell you that going into the yellow, actually below 50% charge, will " Damage " your battery but that's not true.

In the long run, the battery will last longer, about twice as long, drawing down to 50%, then 20%, but then you need to recharge it sooner and more often.

If you hit the red zone with a load, its time to get it charging.
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Old 09-02-2020, 02:28 PM   #5
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What Twinboat said..I myself don't like to see mine down past 12.2v I want to get as many years service out of them as I can.

Keep in mined, those 6v like a high volt for bulk charging. Mine want to see 14.8 v for bulk...yours are going to be 14.7v I believe, Trojan (the batteries) has a good website for info.

https://www.trojanbattery.com/tech-s...y-maintenance/
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Old 09-02-2020, 04:01 PM   #6
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Good info. Hadn't even thought about different readings depending upon load or no load. This is new territory for me and this will give me some decent guidelines to go by. Thanks much.
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Old 09-02-2020, 04:16 PM   #7
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Quote:
Originally Posted by twinboat View Post
Reading volts is tricky. The reading will varry depending on the load on them at the time or if no load, how long they have been resting.

You don't want to drop down in the red zone with no load, that's when things can go bad.

Many folks are going to tell you that going into the yellow, actually below 50% charge, will " Damage " your battery but that's not true.

In the long run, the battery will last longer, about twice as long, drawing down to 50%, then 20%, but then you need to recharge it sooner and more often.

If you hit the red zone with a load, its time to get it charging.
This^^^^

Also remember that lead acid batteries should be recharged all the way to 100% after each cycle, not charging them back to 100% will also reduce your lifecycles very much in the same way that taking them below 50% does......it's all about sulfation on the plates
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Old 09-02-2020, 05:14 PM   #8
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I'm with Twinboat and Paul... There is no precipitous "failure" or "damage" that occurs magically at 50% DOD. If there was the batty mfg charts for life would "drop off" drastically beyond the 50% DOD. I have yet to see anyone promoting the 50% myth that can provide charts & data that support it. I'm open to counter arguments where real data vs opinion is included.

Here is my summation of how I interpret the facts, data & info provided by batty mfg. Nothing wrong with limiting DOD to a max of 50% but you will either need to recharge more frequently and/or install larger batty banks.
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Old 09-02-2020, 05:24 PM   #9
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Very interesting life cycle chart!
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Old 09-02-2020, 05:39 PM   #10
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Quote:
Originally Posted by fisher99 View Post
Very interesting life cycle chart!
Many other Mfg charts available but they are similar and haven't seen ANY that don't continue beyond 50%. Take a look at & read thru the attachment to see what a couple leading batty mfg have to say about it... but I'm sure the nay-sayers will chime in.
The difficulty is accurately determining DOD!
as twinboat mentioned V charts are often quoted but depend a LOT on the conditions - time since charge / discharge - load / no load - etc, etc
See -
https://marinehowto.com/under-load-b...oltage-vs-soc/


Unfortunately no easy answer or at least I'm not aware of it other than batty monitoring systems and they have their shortcomings as well.
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Old 09-02-2020, 07:48 PM   #11
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check out Handy Bob, he's a wealth of information

https://handybobsolar.wordpress.com/...ging-puzzle-2/
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Old 09-03-2020, 12:13 PM   #12
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Quote:
Originally Posted by fisher99 View Post
Good info. Hadn't even thought about different readings depending upon load or no load. This is new territory for me and this will give me some decent guidelines to go by. Thanks much.
The end of twinboat's sentence is also important ".... how long they have been resting."

Batteries voltages will usually slowly rise for some time after all loads are removed, and will slowly drop after charging stops.

If you have a digital voltmeter, you can get a feel for how close you are to resting voltage by monitoring the 1/100's digit.
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Old 09-03-2020, 05:45 PM   #13
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Hi Neighbor! Here's some more source information for you from "Battery University".

Good luck in your quest!

Bob
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Old 09-03-2020, 05:57 PM   #14
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If I only take my car on 20 mile trips, it will last for twice as many trips as it would if I only take it on 40 mile trips.


(That's why we don't measure a car's life in trips. We use miles. Like we should use "AmpHours extracted" for batteries instead of cycles. If you take a FLA battery down 75% instead of 50%, you'll get fewer cycles, but just as much power delivered by the time it dies.)
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