Slowly discharging lead acid batteries

[GeorgeF]

A question about lead acid battery

Why do you need thicker plates for daily cycle use and can a high cranking (float use) battery like Northstar Telecom UPS
batteries, which can be fast and deeply discharged with high amperage, not be used for slow and deep discharge?

Why do you need thicker plates for this?

Can anyone explain me please.

[Mike90250]

Welcome. First - the title of this thread, LA batteries have a slow self discharge and should be topped off at least monthly with a charger.

a gross explanation:
As the battery is "used" the plates "dissolve" and combines with the sulfur in the acid, creating lead sulfate and the acid slowly gets weaker
Thin plates in starter batteries only discharge for few seconds and then are quickly recharged, deep discharges damage the plates beyond the rebuilding that happens when a battery is recharged, sulfur driven back into the acid and this is the basis of the Hydrometer measurement, as the acid strength is a reliable indicator of the state of the battery charge.

[GeorgeF]

Thanks moderator for your explanation. So, it is impossible to use a second hand high cranking NorthStar BTS Telecom battery with a (home) solar system and have a daily DoD of 50% for more than let say 2 years+, especially if you only charge with solar panel(s) which never can be "fully saturated" to Full State of Charge during peak hours. Their specs can be a bit misleading for those who are not familiar with the term "deep cycle".

[Mike90250]

There is no such beast as a 2nd hand Cranking Telecom battery.

Deep cycle batteries are rated for a 20-30% daily discharge, followed by a recharge. The longer the battery sits at a lower state of charge, the harder the sulfite crystals become, and after 48 hours, the crystals are pretty well hardened and become locked in and unable to easily be re-dissolved. This is known as " walking the battery capacity down" or "chronic undercharge". Within a couple weeks, you have a totally discharged, sulfated battery.

With an expected daily recharge, even going to 50% will have a huge impact on the lifetime of a deep cycle rated battery, and having it last even 2 years would be spectacular.

Look for the Discharge Depth vs Cycle Life chart for your batteries, that's the best predictor of life. Your mileage may vary.

DoD_vs_CycleLife.gif

[GeorgeF]

Thanks again for your reply. I did post this thread because utilities "dump" their batteries, like NorthStar Red and Blue series after a certain period, and some are trading those second hand bateries claiming even to run 2 aircons in the evening with a predicted lifetime of 5 years, proven by themselves. I suppose this can be considered as hoax and sneeky way to promote their secondhand batteries. I've read also some replies in other subjects from another moderator or member Sunking about those BTS thin plates batteries. I consider it as gambling if I would buy those second hand batteries, right? Btw, are you using NIFE? Are you satisfied?

[Mike90250]

...... about those BTS thin plates batteries. I consider it as gambling if I would buy those second hand batteries, right? .....

Not much of a gamble with 2nd hand Telecom batteries, It's nearly a sure thing they are fine till the 2nd deep discharge, then you get to pay for the hazmat disposal. ( depends on then labels on the batteries, if they are recyclable or haz waste )

But it's a sure thing Float duty batteries won't last long in cycle service.

And they are being rotated out for new ones, just because they are nice people and will sell the batteries to you , cheaper than hazmat disposal will cost them.

And Yes, I am running a NiFe bank, did an electrolyte change this summer, and should be good for another 10 years. Pretty darn happy, other than they use a lot of water.

[GeorgeF]

Nice to hear that your NIFE did not disappoint you. I suppose you have no grid connection, do you need a genset to (re)charge a bit in the evenings? It is hard to reach Full State of Charge with only solar panels if you cycle on a daily basis, even in the summer, is this correct? Also if one uses AGM CC @ 14.4v and C/4 ?

[Mike90250]

Summer, I only fire up the genset for testing. Winter, I'm running it 90 min morning and 90 min evening, so I get rid of my stale fuel that didn't get used in the tractor.




CloudCover_11-2018.gif

Generator :

IMG_20160217_082900710.jpg