Batteries: more frequent, shallower cycling vs. less frequent, deeper cycling

[magictime]

22 minutes ago, Mike the Boilerman said:

 

But three of the major advantages of LC chemistry AIUI are that you can discharge them down to 20% with no ill effect, you can leave them part charged with no risk of sulphation, and you don't need to charge them to 100% once a week. 

 

Almost as different from LA as lithiums.

 

 

I don't think the 'no ill effect' is right. Leoch's data sheet for them has a graph plotting number of cycles against depth of discharge, and it tails off all the way down. I think they're more tolerant of higher DoDs than normal LAs, but they still 'prefer' shallower cycling. Also I don't think Leoch claim no risk of sulphation, just a much reduced risk. The need for regular full charges I'm less sure of; I should ask Leoch I guess. It was a bit of advice from Victron on their lead carbons that mentioned a full charge every 1-2 weeks. Anyway they should get a full charge at least that often by default just in the course of CCing, so it doesn't really matter if it's strictly necessary or not. My battery monitor(s) will probably appreciate regular full charges anyway.

[Iain_S]

7 hours ago, magictime said:

(snip)

I wonder how impressive that actually is, though. I mean, isn't 'end of life' usually defined as the point where a battery's capacity is down to 80% of the original figure? In which case yours might have hit it after maybe four years. 

"End of life" as far as we boaters is concerned is when the batteries are incapable of doing what they are supposed to. Most will happily use batteries that are down to less than 50% of capacity, although I get the impression that the deterioration accelerates towards the end.

[Richard10002]

7 minutes ago, Iain_S said:

"End of life" as far as we boaters is concerned is when the batteries are incapable of doing what they are supposed to. Most will happily use batteries that are down to less than 50% of capacity, although I get the impression that the deterioration accelerates towards the end.

As a battery killer extraordinaire, my experience, over 4 sets of cheap and expensive batteries over 9 years, has been that, once a bank gets down to 50% of capacity, it tends to stay there or thereabouts.

 

(Smartgauge and NASA BM2 enable me to estimate capacity very roughly).

[Alan de Enfield]

7 hours ago, Richard10002 said:

As a battery killer extraordinaire, my experience, over 4 sets of cheap and expensive batteries over 9 years, has been that, once a bank gets down to 50% of capacity, it tends to stay there or thereabouts.

 

(Smartgauge and NASA BM2 enable me to estimate capacity very roughly).

I bought a NB that had batteries with very poor capacity - in fact I could only use anything electrical (even turn one light on) if either the battery charger was on or the engine was running - in essence they had a capacity of zero and I was simply using the 'power supply' as the source.

 

On taking them out to replace I found they had a date on them which showed them to be 14 years old.

The starter battery was of the same age but still functioned quite well.

[Sea Dog]

11 minutes ago, Alan de Enfield said:

The starter battery was of the same age but still functioned quite well.

Easy life. It gets used for a few seconds, taking just a few percent of the charge, then the alternator flashes up along with the engine and puts absolutely all of it back.

(I know you know that Alan, but it goes back to the OP's original question).

[MtB]

8 hours ago, Richard10002 said:

As a battery killer extraordinaire, my experience, over 4 sets of cheap and expensive batteries over 9 years, has been that, once a bank gets down to 50% of capacity, it tends to stay there or thereabouts.

 

This is my experience too. Once you mess up a battery bank by not keeping it 100% charged 100% of the time, it plummets to about 50% capacity then stays there for years.

 

 

[cuthound]

9 hours ago, Richard10002 said:

As a battery killer extraordinaire, my experience, over 4 sets of cheap and expensive batteries over 9 years, has been that, once a bank gets down to 50% of capacity, it tends to stay there or thereabouts.

 

(Smartgauge and NASA BM2 enable me to estimate capacity very roughly).

 

1 hour ago, Mike the Boilerman said:

 

This is my experience too. Once you mess up a battery bank by not keeping it 100% charged 100% of the time, it plummets to about 50% capacity then stays there for years.

 

 

 

Maybe that exlains why my Lifeline AGM's are still going strong at 12 years! ?

 

It will be interesting to see how they fair when I pick my boat up after its blacking and repaint as it hasn't been connected to shore power AFAIK during the works. Should have taken 6 weeks, currently in its10th week. Hopefully will be ready for collection in the next couple of weeks.

Edited October 27, 2019 by cuthound
To remove a letter masquerading as a space

[MtB]

4 minutes ago, cuthound said:

Hopefully will be ready for collection in the next couple of weeks.

 

Is that what they are telling you? 

[cuthound]

1 minute ago, Mike the Boilerman said:

 

Is that what they are telling you? 

 

That's why I said hopefully ?

[Dr Bob]

20 hours ago, magictime said:

To put this in it simplest terms: all else being equal, what's likely to last longer: a battery recharged from 75% to 100% every day, or a battery recharged from 50% to 100% every other day? (Or more realistically perhaps: 70% to 90% vs. 50% to 90%?)

 

Forgive me if I return to the orginal question. 50%-90% every few days or 70%-90% each day?

Well neither! You must get them to 100%. However I am strongly biased to having a bigger bank and avoiding these 50% excursions. For me, both the theory and experience supports it. This is for Lead acids not Lead carbons!

The theory first. If you look at the chemical reaction in the battery, aqueous ions react with the solid electrodes. Whilst the basic chemistry is simple, the actual reaction is complex due to Liquid/solid issues. The solid electrodes are made up with a complex pore structure and that introduces steric hinderance to the chemical reaction which in turn changes the activation energy for the reaction dependent on where in the pores the reaction is taking place. Lets look at a battery having a range of accessible sites. The most accessible at the outside of each pore will be the first to give up it's electrons when a 100% SoG battery has a load - on the discharge cycle. Lets call them the '100' sites. As the first 10% of sites give up their electrons, they will be the least sterically hindered. We then get down to the '90' sites. These will be sites a little down the pores and it is a little more difficult for the aqueous phase to get down there. We then discharge to the '50' sites, when we get down to 50% SoC and these sites will be significantly sterically hindered. Ok that is the discharge side.

Once we start charging and put our 14V on the system, the first sites to react are the ones with the lowest activation energy, ie the '100' sites at the end of the pores. The '90' sites charge next and finally the '50' receive enough energy to convert ...and crucially are the last to convert. If you only charge to 98% SoC then the 2% not charged are the 2% in the '50' sites ie ones that are very sterically hindered. These sites do need a good oooomph to get them to react......ie 14.5V+ ???? That is chemistry for you! If you only charge to 90% then that missing 10% of sites are buried deep in the pores..

For a reasonably discharged battery ie 50% discharge, you do need 14.4+V to get the charge in. If you dont then these sites due to the steric hinderance will sulphate easily as there will be little transfer of reactive reagents up those narrow pores. It may be these inaccessible sites will never receive enough charge to recover...ie why equalisation is needed.

The important thing then in assessing whether a LA battery will sulphate is to look at how deep the discharge is. I would argue that where an LA battery is only ever discharged to 80% then the prospect of sulphation is reduced as it is easier (chemically) to reverse as the activation energy for the reverse reaction is lower.

If the OP cycles between his 50-90% then those batteries will be killed in a year.

A good theory? My experience supports that theory. I had 3* newish flooded LA's when I bought the boat May 2017. Added 3 * sealed LAs. Ran 6 months with an alternator charging at 13.9V max. Put a Sterling AtoB on, which raised that to 14.1-14.4V and ALWAYS dropped down to float far too early. The solar MMPT also dropped to float. My batteries were never charged at over 14.4V and rarely went under 80% and never went under 75%. Before I put my Li's on at the end March this year (LAs 22 months old) my capacity was maybe 95% (conservative estimate). Very little sulphation.

A second observation is how my LAs now respond with my Li's. A few months back @nicknorman   @WotEver and @cuthound   all said I would have a problem keeping my LAs sulphate free as the Lithiums would only charge them at 13.4V (need at least 14.0+V). In the last few weeks I have been down in voltage around the 12.6V on discharge so the LAs have been discharging as well as the Li's. On charging at 13.5V the 30Ahrs discharged from the LA's were replaced very easily ( ie the top '100' sites) – I knew they were full as just after the recharge, I got onto shore power and with the Li's disconnected, the tail current fell on the battery charger to almost zero in a few minutes.

I would certainly avoid a 50% discharge unless you can bang the voltage up and you must get back to 100% otherwise it will sulphate.

I wonder if Cuthound has some data to support the above info?

I cant comment at all about Lead Carbons...but if they do not sulphate like LAs then that is a huge plus.

[rusty69]

^^^^^Wot he said.Except for the steric hinderance bit,cos that is utter bollox,oh and the reactive reagents bit,cos he made it up.

 

Did you have a brief encounter with wikipedia this morning Doc?

[Tony Brooks]

I want to know how the basic lead carbon chemistry differs from the basic lead acid chemistry.  I don't see how the carbon can effect the basic chemistry but will have an effect on getting electrons into the depth of the plates. This will/should minimise the surface charge effect and arguably give faster charging but apart from the fact that in a given time the LCs should (in my view) "absorb" more electrons and thus be better charged I simply cannot see how the carbon can minimise sulphation of that part of the plates that is less well charged and standing.

[WotEver]

5 minutes ago, Tony Brooks said:

I simply cannot see how the carbon can minimise sulphation of that part of the plates that is less well charged and standing

Me neither, although that’s what all of the references I’ve read have stated. They simply don’t explain WHY. 
https://batteryuniversity.com/learn/article/new_lead_acid_systems

[Tony Brooks]

I would also extend this to AGMs as well.

[PeterF]

The scientific papers that I have briefly looked at state that the addition of carbon affects the surface of the negative electrode at the microscopic level which promotes the formation of smaller lead sulphate crystals during discharge and the smaller the crystals, the easier they are to convert back to lead during charging. By reducing the build up of large lead sulphate crystals, which are the ones which are harder to reconvert to lead, irreversible sulphation is reduced.

 

The reaction remains the same, the carbon appears to create a physical disruption to the surface which affects the crystal nucleation and growth which shows it is not all about the reaction only.

Edited October 27, 2019 by PeterF

[cuthound]

1 hour ago, Dr Bob said:

I cant comment at all about Lead Carbons...but if they do not sulphate like LAs then that is a huge plus.

 

Not really, in the critical power industry deep discharges were rare because  20-30 seconds after the mains electrical failure the gegenerators or DRUPS had usually started and taken the site load, so the batteries were immediately recharged.

 

Other than when batteries were being commissioned or capacity tested, I can only recall a handful of occasions when the batteries were deeply discharged, and as soon as power was restored they were charged back to 100%.

 

 

Edited October 27, 2019 by cuthound

[cuthound]

1 hour ago, Tony Brooks said:

I want to know how the basic lead carbon chemistry differs from the basic lead acid chemistry.  I don't see how the carbon can effect the basic chemistry but will have an effect on getting electrons into the depth of the plates. This will/should minimise the surface charge effect and arguably give faster charging but apart from the fact that in a given time the LCs should (in my view) "absorb" more electrons and thus be better charged I simply cannot see how the carbon can minimise sulphation of that part of the plates that is less well charged and standing.

 

I too share your concerns regarding carbon lead acid batteries.

 

Hopefully they will prove to meet the manufacturers claims regarding lower sulphation, but until they have been around for a while and abused by those who don't know how to look after batteries we won't know.

[ditchcrawler]

3 minutes ago, cuthound said:

 

Not really, in the critical power industry deep discharges were rare because  20-30 seconds after the mains electrical failure the gegenerators or DRUPS had usually started and taken the site load, so the batteries were immediately recharged.

 

Other than when batteries were being commissioned or capacity tested, I can only recall a handful of occasions when the batteries were deeply discharged, and as soon as power was restored they were charged back to 100%.

When I worked Offshore I had to run the 110 volt DC emergency battery bank for 24 hours on full rated load to prove to the Lloyds inspector it would do it. 

[cuthound]

1 minute ago, ditchcrawler said:

When I worked Offshore I had to run the 110 volt DC emergency battery bank for 24 hours on full rated load to prove to the Lloyds inspector it would do it. 

 

There's quite a low discharge rate. Most of the batteries in the places I worked were designed to last 1 hour, some only 10 minutes!

[Dr Bob]

1 hour ago, rusty69 said:

^^^^^Wot he said.Except for the steric hinderance bit,cos that is utter bollox,oh and the reactive reagents bit,cos he made it up.

 

Did you have a brief encounter with wikipedia this morning Doc?

Chemistry Rules!!!

Steric hinderance IS the dogs bollox. I did learn somett in my youff.

[WotEver]

2 hours ago, Dr Bob said:

A few months back @nicknorman   @WotEver and @cuthound   all said I would have a problem keeping my LAs sulphate free as the Lithiums would only charge them at 13.4V (need at least 14.0+V).

Are you sure I said that?  I’ve spent many an unhappy hour arguing the exact opposite on caravan forums in the past. Sure, if you have any Sulphation then 13.4V ain’t going to shift it, but if you’re consistently getting the LA’s to 100% then you won’t get the hardened sulphate crystals in the first place. 

[Richard10002]

2 hours ago, Tony Brooks said:

I want to know how the basic lead carbon chemistry differs from the basic lead acid chemistry.  I don't see how the carbon can effect the basic chemistry but will have an effect on getting electrons into the depth of the plates. This will/should minimise the surface charge effect and arguably give faster charging but apart from the fact that in a given time the LCs should (in my view) "absorb" more electrons and thus be better charged I simply cannot see how the carbon can minimise sulphation of that part of the plates that is less well charged and standing.

FWIW My lay mans perception is that Lead Carbon batteries are either AGM batteries with a new marketing name, or are constructed in the same way as AGM batteries. 

[MtB]

17 minutes ago, Richard10002 said:

FWIW My lay mans perception is that Lead Carbon batteries are either AGM batteries with a new marketing name, or are constructed in the same way as AGM batteries. 

The springing fully formed of a whole new type of battery onto the market does seem rather suspicious, dunnit!  
 

 

[Dr Bob]

20 minutes ago, WotEver said:

Are you sure I said that?  I’ve spent many an unhappy hour arguing the exact opposite on caravan forums in the past. Sure, if you have any Sulphation then 13.4V ain’t going to shift it, but if you’re consistently getting the LA’s to 100% then you won’t get the hardened sulphate crystals in the first place. 

In post 34 on this linked thread

 

You said

 

"WRT Nick’s post above, Gibbo once posted that 13.6V WILL fully charge LA batteries but...

1. It will take forever 

2. It will not counter sulphation and is so low that it will in fact permit sulphation to accumulate. 

 

So I believe that Nick’s points are valid. 

Particularly if we’re only talking about 13.1V. "

 

The discussion was Nick and Cuthound saying that my 13.4V was not enough to stop sulphation in my LA bank at <10% DoD......with the Li's sitting at 13.1 -13.4V above them. I disagreed but didnt have much data to support it. I'm pretty certain now from the data I am getting that if just the top 10% of LA capacity is used then it doesnt sulphate at thes low 'charging' voltages. With the sulphate at the accessible ends of the pores, it doesnt take much potential to make the reaction go.

I agree with your quote for DoD's > 10-20%.

[WotEver]

9 minutes ago, Dr Bob said:

In post 34 on this linked thread

 

You said

 

"WRT Nick’s post above, Gibbo once posted that 13.6V WILL fully charge LA batteries but...

1. It will take forever 

2. It will not counter sulphation and is so low that it will in fact permit sulphation to accumulate. 

 

So I believe that Nick’s points are valid. 

Particularly if we’re only talking about 13.1V. "

 

The discussion was Nick and Cuthound saying that my 13.4V was not enough to stop sulphation in my LA bank at <10% DoD......with the Li's sitting at 13.1 -13.4V above them. I disagreed but didnt have much data to support it. I'm pretty certain now from the data I am getting that if just the top 10% of LA capacity is used then it doesnt sulphate at thes low 'charging' voltages. With the sulphate at the accessible ends of the pores, it doesnt take much potential to make the reaction go.

I agree with your quote for DoD's > 10-20%.

Yes, I think the pertinent point in your scenario is that you’re not actually using the LAs. Not in any meaningful sense.