Jim, I have tested this hypothesis. I work for a company which uses valve-regulated lead-acid batteries in a partial state-of-charge regime by the thousands and we have done cycle testing and demonstrated thousands of such micro-cycles, at much less than 100% SOC, before failure. Sean On Mon, Feb 10, 2014 at 4:14 PM, Jim Higgins KB3PU wrot= e: > Received from Sean Breheny at 02/10/2014 18:34 UTC: > > >In my experience, it is primarily the _change_ in state of charge which > >causes permanent wear on batteries. So, in terms of cycle wear, > >charging/discharging repeatedly between 80% and 100% is the same as > >charging/discharging repeatedly between 40% and 60%. > > > This may be true for some chemistries, but for lead acid cycled as you > describe you will achieve failure due to chronic undercharging long befor= e > you could ever hope to prove your hypothesis. It's untestable because th= e > battteries will fail for reasons other than cycle wear. > > > > There is nothing magical in lead acid batteries about the 50% point > (there > > is in some other chemistries such as some variants of LiFePO4). The > > difference between the top 20% of SOC range and something lower-down is > not > > about whether you go there but about how much time you spend there befo= re > > you come back up to 100%. Anything below 100% converts some lead and le= ad > > dioxide to lead sulfate, and further down converts more. By itself, thi= s > is > > not a problem. However, the longer the lead sulfate remains, a process > > known as Ostwald Ripening slowly converts it to a different crystal > > configuration which is less permeable and therefore less able to take > part > > in the charge/discharge reactions and more insulating. > > > >Cycle wear comes from the fact that the charge/discharge reactions invol= ve > >removal of material from the plates and deposition of other material, > which > >causes a change in the average particle size on the plates as well as > >mechanical swelling and shrinking of the material attached to the plates= , > >leading to voids and even complete detachment of active material. Just > like > >metal fatigue, this process is much worse as the amount of change per > cycle > >increases. > > > >Sean > > > Exactly. And that means longer life for a battery cycled to 40%, 50% or > 60% > or even 80% depth of discharge vs one cycled to 90% or 100%. There will > be a > marked difference in cycle life for sets of batteries cycled to 80% vs 90= % > vs > 100%. Even more so to only 50%. > > JimH > > > > > > >On Mon, Feb 10, 2014 at 11:17 AM, Jim Higgins KB3PU >wrote: > > > > > > > > Yes, mostly. But that wasn't the point. The point was that shallowe= r > > > depth > > > of discharge results in much longer life. That is true regardless of > > > battery > > > design. What you're reminding me of is that golf car batteries are > > > designed > > > to last much longer when run to 90% DoD than an automotive battery is= .. > And > > > I'll mention that fork lift batteries will last much longer than golf > car > > > battteries when run to 90% DoD. But neither were the point being > discussed > > > at the time. All last much much longer if not discharged so deeply. > > > > > > JimH > > > > > > > > > > > > Received from Richard R. Pope at 02/10/2014 07:15 UTC: > > > > > > >Jim, > > > > Golf cart batteries are designed to be discharged as much as > 90% of > > > > their rated capacity. That is why they are called deep discharge > > > batteries. > > > > It is automotive batteries that are not designed to be deeply > > > discharged. A > > > > golf cart battery is designed to deliver a relatively steady voltag= e > for > > > a > > > > long period of time. An automotive battery is designed to deliver a > lot > > > of > > > > current for a short period of time and then to be quickly recharged= .. > If > > > you > > > > try to deep discharge an automotive battery you will ruin it in sho= rt > > > > order. A golf cart battery is recharged over a long time period. If > you > > > try > > > > to quick charge it, it will over heat and the plates will buckle an= d > then > > > > they will short out. Neither battery type should be left in a > discharged > > > > state for a long period of time as the plates will become sulfated > and > > > then > > > > it becomes almost impossible to recharge the battery. > > > >Thanks, > > > >rich! > > > > > > > > > > > > > > > >On 2/8/2014 8:17 PM, Jim Higgins KB3PU wrote: > > > > > Received from Peter Johansson at 02/09/2014 01:09 UTC: > > > > > > > > > >> On Sat, Feb 8, 2014 at 3:13 PM, Larry Bradley < > larry.bradley@ncf.ca> > > > wrote: > > > > >> > > > > >>> ability to handle deep discharge (80%) > > > > >> Just because you can discharge 80% doesn't mean you should make = a > > > > >> habit of it. The best way to prolong the life of your batteries > is to > > > > >> avoid draining them beyond 50%. > > > > > > > > > > YES! and especially true of thin plate batteries like golf car > batts. > > > > > > > > > > JimH > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .