Received from Sean Breheny at 02/10/2014 18:34 UTC: >In my experience, it is primarily the _change_ in state of charge which=20 >causes permanent wear on batteries. So, in terms of cycle wear,=20 >charging/discharging repeatedly between 80% and 100% is the same as=20 >charging/discharging repeatedly between 40% and 60%. This may be true for some chemistries, but for lead acid cycled as you=20 describe you will achieve failure due to chronic undercharging long before= =20 you could ever hope to prove your hypothesis. It's untestable because the= =20 battteries will fail for reasons other than cycle wear. > There is nothing magical in lead acid batteries about the 50% point (the= re=20 > is in some other chemistries such as some variants of LiFePO4). The=20 > difference between the top 20% of SOC range and something lower-down is n= ot=20 > about whether you go there but about how much time you spend there before= =20 > you come back up to 100%. Anything below 100% converts some lead and lead= =20 > dioxide to lead sulfate, and further down converts more. By itself, this = is=20 > not a problem. However, the longer the lead sulfate remains, a process=20 > known as Ostwald Ripening slowly converts it to a different crystal=20 > configuration which is less permeable and therefore less able to take par= t=20 > in the charge/discharge reactions and more insulating. > >Cycle wear comes from the fact that the charge/discharge reactions involve= =20 >removal of material from the plates and deposition of other material, whic= h=20 >causes a change in the average particle size on the plates as well as=20 >mechanical swelling and shrinking of the material attached to the plates,= =20 >leading to voids and even complete detachment of active material. Just lik= e=20 >metal fatigue, this process is much worse as the amount of change per cycl= e=20 >increases. > >Sean Exactly. And that means longer life for a battery cycled to 40%, 50% or 6= 0%=20 or even 80% depth of discharge vs one cycled to 90% or 100%. There will be= a=20 marked difference in cycle life for sets of batteries cycled to 80% vs 90% = vs=20 100%. Even more so to only 50%. JimH >On Mon, Feb 10, 2014 at 11:17 AM, Jim Higgins KB3PU wr= ote: > > > > > Yes, mostly. But that wasn't the point. The point was that shallower > > 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 c= ar > > battteries when run to 90% DoD. But neither were the point being discu= ssed > > 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 voltage = for > > a > > > long period of time. An automotive battery is designed to deliver a l= ot > > 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 short > > > order. A golf cart battery is recharged over a long time period. If y= ou > > try > > > to quick charge it, it will over heat and the plates will buckle and = then > > > they will short out. Neither battery type should be left in a dischar= ged > > > state for a long period of time as the plates will become sulfated an= d > > 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 > > 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 i= s to > > > >> avoid draining them beyond 50%. > > > > > > > > YES! and especially true of thin plate batteries like golf car bat= ts. > > > > > > > > JimH --=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 .