Great, short, discussion on Depth of Discharge

[DLTooley]

There's a great thread over on Expedition Portal regarding total Ah's generated under various depth of discharge scenarios, the argument being that total amp hours generated is roughly the same when DoD is calculated across cycle life.

https://expeditionportal.com/forum/threads/lead-acid-50-dod-limit-rule-or-myth.194682/

 

[Trebor English]

1000 cycles of 30 amp hours is 30,000.  400 cycles of 80 amp hours is 32,000.  

The big problem is the 100% recharge that lead acid require.  The last 10% of an 80 amp hour discharge is deep below the surface of the lead.  It will take higher voltage and more time to finish getting that buried sulfur out.  Given a sufficient solar array that will work.  Two hours of generator run or two hours of driving will not do the job of finishing that charge.

 

[Weight]

That unsubstantiated post by a self appointed expert goes contrary to 100's of years experience by every battery manufacturer there has ever existed. And also contrary to any seriously researched battery information available for the same 100s of years.

 

[highdesertranger]

I am a member over there too. what you need to remember is that the majority of the people posting over there are weekenders. most of them replace their house battery(s) every 2 years weather they need it or not. also a majority of the members have more money then sense, don't believe me look at the Snow Peak Addiction thread. they are real big on fads over there and there seems to be a competition to have the latest greatest gadget. I have seen terrible advice given over there for electrical and solar set ups. however after talking all this smack if you weed through the crap you can get some good info from their forum. highdesertranger

 

[DLTooley]

I've designed for roughly a 20% depth of discharge - that puts me around 50% on the third cloudy day, maybe a bit lower. Most days I reach 100% recharge.

 

[John61CT]

Great for full-timing longevity, but on a big bank (800+AH) that would be carrying around **a lot** of extra weight unnecessarily.

It really is not a bad strategy, if "no surprises" reliability is the main goal, to replace on a schedule.

With quality batts that could be say every five years.

Since **if** well coddled they might last 8-10, bringing them down below 50% a minority of cycles may well still be fine.

If you drive a lot, have mains available sometimes or carry a gennie, no need to plan for 3 day cycles, that's a strategy for mostly solar setups.

So many variables, everyone's setup is unique, better to know the principles, collect real data for your setup and decide for yourself.

But rules of thumb guidelines are useful in the meantime, doesn't mean they are dogmatic "rules" to be followed slavishly.

 

[Ticklebellly]

The total AH delivered across life works best in low drain situations and is just another approach to resolving the "when is a cycle a cycle"? question. Is one or two 80% DOD incidents equal to 3 or 4 40% DOD incidents or maybe 4 or 8 20% DOD cycles? A weekend only camper will need 6.7 years to get 400 really deep cycles out of a specified Deep Cycle battery. A deep discharge cycle of two days spreads 400 cycles over just more than 2 years. There are too many variables in the practical use of any charge/discharge and daily management strategies to get too anal about predicting cycle life. I argue that concentrating on keeping a battery near its full charge numbers is a good place to start if concerned about cycle life or just how many AHs a battery will theoretically supply over its life.

 

[John61CT]

A good quality bank properly cared for can last 5-8 years routinely, and often 12+.

Just a data point for each person to do with what they will.

In case some think 3-4 is a long lifespan. . .