Sterling-NASA -Victron

[nicknorman]

2 minutes ago, WotEver said:

 

1/, 2/, 3/, all make my point, and you agreed with me on all 3 points. 

I agree with you (in the main) on all 3 points but they don't make your overall point.

As I said, explain what happens to the electrons produced by the reaction that don't (according to you) make it to the terminals. Or if you prefer, where the chemicals go if they don't react.

if a battery has fundamentally and unrecoverably lost disproportionate charge due to a high discharge rate, either chemicals have been lost or electrons have failed to materialise. There can't be any other explanation.

[WotEver]

3 minutes ago, nicknorman said:

one should bear in mind that whilst the voltages involved are linearly variable, the charge is in increments of one electron. One electron has a specific fixed charge. Two electrons arise from the reaction of lead and acid. The lead and acid react, two electrons are moved. Or the lead and acid don't react, no electrons are moved. You can't partially move and Elton or have the chemicals reacting without the two electrons moving. There is no linear variation, it's binary.

Yes, precisely this. You can’t ‘slightly’ move an electron, it either moves or it doesn’t. If it does, we know the voltage. So how/why does a battery’s voltage vary?

Just now, nicknorman said:

if a battery has fundamentally and unrecoverably lost disproportionate charge due to a high discharge rate...

It hasn’t. I never said it had. I said that bit of charge was unavailable to the user and hence is ‘lost’ to him for that cycle. 

The fact that he could recover it if he rested his battery is immaterial because he can’t rest it. 

[nb Innisfree]

1 hour ago, WotEver said:

 

I think you’re both saying the same thing guys

Whilst on the subject, it’s often said on here that “many folk misunderstand the so called rule of 'don't discharge to less than 50% SoC' thinking that discharging to anything higher than 50% SoC is somehow in safe territory and will look after their batteries.” but I’m not sure that ‘many folk’ actually do think that, do they?

No idea really, though I suspect some do which is probably suspect in itself. 

[nicknorman]

Just now, WotEver said:

Yes, precisely this. You can’t ‘slightly’ move an electron, it either moves or it doesn’t. If it does, we know the voltage. So how/why does a battery’s voltage vary?

No. Fundamental point: electrons have charge they do NOT have intrinsic voltage. If electrons are pumped somewhere then a voltage arises. It depends on how hard the electrons are pumped as to what the voltage is. Since the reaction in a lead acid battery is more complicated than the superficial one oft quoted, it will depend on the balance between the different reactions.

i don't know if you've done any organic chemistry but there is a concept called a reversible reaction and it's equilibrium. Two countering reactions fight each other to reach some equilibrium.

In the case of the battery, there is an equilibrium between the reaction and the voltage. Otherwise, the voltage would rise without limit as more and more chemicals react and more electrons are pumped. At the appropriate voltage, the reaction stops - no more electrons are pumped, other than to replace the ones that may be taken as current from the battery. The point at which the equilibrium is reached will depend on some factors (not sure exactly what - it's complicated!) so that equilibrium is reached at different voltages depending on the strength of the remaining acid and possibly the ratio of lead to lead sulphate, temperature etc.

[WotEver]

8 minutes ago, nb Innisfree said:

No idea really, though I suspect some do which is probably suspect in itself. 

I suspect that your suspicions probably aren’t suspect at all

1 minute ago, nicknorman said:

Fundamental point: electrons have charge they do NOT have intrinsic voltage

Yes, I know that. I should have written “so we know the voltage of that reaction”. 

[WotEver]

Basically, it’s magic. 

[nb Innisfree]

Does  'movement' actually exist? Is it ultimately real?  

[WotEver]

2 minutes ago, nb Innisfree said:

Does  'movement' actually exist? Is it ultimately real?  

I believe it’s dependant upon the observer imbibing sufficient quantities of alcohol. 

[nb Innisfree]

Nurse! I'm confused... 

[nicknorman]

49 minutes ago, WotEver said:

Yes, I know that. I should have written “so we know the voltage of that reaction”. 

But that's the point, there is more than one reaction and they have different voltages. So it depends on the equilibrium between the reactions.

[cuthound]

9 hours ago, WotEver said:

Basically, it’s magic. 

It's not just any magic, it's BLACK magic.

9 hours ago, WotEver said:

I believe it’s dependant upon the observer imbibing sufficient quantities of alcohol. 

DT's?

9 hours ago, nb Innisfree said:

Nurse! I'm confused... 

My head hurts...

[Tony Brooks]

11 hours ago, dmr said:

You are of course absolutely correct but I think your views would not be believed by the majority of boaters (and lots of other people too). Even well known battery suppliers suggest that batteries will be Damaged if they are discharged below 50%.

I discharged mine to just below 40% recently and am now so worried that I have needed to drink a bottle of Henry Westons 8.2% cider every day to calm my nerves.

It is clear that the deeper you discharge the more of the cyclic life you "use up". That is a natural part of battery behaviour and not damage in the normal sense of the word but it is a good word to use when trying to explain to less battery aware people.

As others have said the 50% "rule" is no rule at all its just guidance to get optimum battery life. In view of some posts over the last couple of years (and more so now solar is so much more prevalent) I think we should add "and try to recharge  every day as much as possible.

 

I also have problems with people who say if you "fully" discharge a battery it will be destroyed. Experience shows it is simply not true UNLESS its left like that for a long time. Think back - those who can - to when we had to park with the side and tail lamps on. How often did we come back to a flat battery and then push start the car and carry on. On my own boat I have twice had both battery banks totally flattened by the yard who worked on the boat and left the master  switches turned on. The domestic bank because they also left the radio on and the engine battery because they did not turn the ignition off properly. In both cases I was back within a week, jump started the engine, and recharged the batteries as fully as I could. On both occasions there seemed no appreciable loss of cyclic life but there must have been a loss of capacity but it left plenty for normal use.

Fully discharging the batteries just once or twice will not damage them to a significant extent in my view unless they are already on their last legs. Leaving them like it or not fully recharging them WILL damage them by sulphation.

Such arguments as there may be are really about what "shorthand" one uses to try to make it simple for the less knowing to optimise their battery life and therefore it leaves room for people to argue over the advice and also parrot it as the full and total truth - not helpful in my view.

[cuthound]

How many times a battery can be fully discharged depends very much on how it is constructed.

In the early years of my career telephone exchanges were powered  by "cells No.2". Large lead lined wooden boxes, filled with acid and plates, which were held apart by glass separator rods and covered in glass splash plates. They were topped up weekly with bucket loads of de-ionised water.

These batteries were fully discharged every other year, to assess their capacity, yet had lives in excess of 25 years.

Modern leisure batteries are poorly constructed to keep costs low and thus will not survive being completely discharged many times.

[mrsmelly]

So there we have it. In reality you buy cheap batteries, discharge them as little as possible and recharge them as quickly as possible and they last until they are knackered and then you replace them. Simples.

[Tony Brooks]

But Cuthound's batteries were almost certainly recharged almost a soon as the full discharge had taken place so hardening sulphate had little time to establish itself.

I also suspect the cell groups could be lifted out, the acid emptied, the sediment washed out and the groups and acid replaced. That would also help top extend life.

However not so sure you can equate telephone exchange batteries with a boat's domestic bank that has a huge inverter connected to it. The discharge profile and I suspect charge profile would be very different. However the fact remains the better constructed the battery the longer its cyclic life is likely to be.

 

 

 

 

[Dr Bob]

13 hours ago, nicknorman said:

For 2/, the chemicals (simplistically, lead and sulphuric acid) react together to produce lead sulphate for each molecule, an electron is liberated (or is it 2, can't be bothered to check!). But the reaction isn't instantaneous and relies on the two chemicals being able to come into intimate contact. To start with, lead on the surface of the plate and sulphuric acid adjacent, is free to react swiftly. But later once those chemicals have been exhausted, lead deeper in the plate and sulphuric acid further away, need to react to pump the electrons round. It takes a while for the chemicals to diffuse towards each other and so the reaction slows, the terminal voltage decreases. The faster one tries to discharge the electrons the faster the chemicals have to react and so, due to the time it takes for the chemicals to migrate to each other, the lower the terminal voltage.
 

Going back to the discussion between Nicknorman and Wotever, I concur that you are saying the same thing about 'charge' being lost – one of you saying it is time dependent and the other saying it is lost in that cycle.

I think Nick's description in post 38 is a really good way to describe what is likely happening (snipped above) and doubt if there is a simpler way to put it. The outstanding issue then is to answer Tony's question of why 12.7V is higher than the theoretical output. I've got a PhD in Chemistry and I dont understand so what hope have we got here!

I think we have it right that the generation of electrons is binary, it happens or it doesn't. I never really got to grips with electrons moving –  they just transfer their charge to the next atom not actually move. Dont forget volts are just the potential – not the current. The potential will be limited by the chemistry ie the lead/lead oxide / H2SO4 equilibrium (as Nick says). That potential should set up an upper limit which cant be exceeded. At the upper limit of potential, the potential will stop further electons being formed by reversing the equilibrium. If demand, ie current draw is high, lots of sites will convert lead/lead oxide to lead sulphate and current flow will be high. Likely this will reduce potential as the chemistry reaction tries to keep up with demand. This 'sort of' explains why voltage drops with load but not why we get the 12.7V. Perhaps the 12.7V is a surface effect – ie why is my battery showing 13V+ just after the battery charger is turned off? Shouldnt it immediately go back to its theoretical maximum potential? I think the chemistry is far too complicated for us here.

Nick's explanation on time dependency raises other issues for me. If we assume the lead/lead oxide buried deep in the plates takes time to react then we can paint the picture where a site say 50% deep in a plate will only offer up its electrons and convert to lead sulphate when the SoC is 50% ish. OK so far? Now when we put the battery on charge, the sites that will be converted back to Pb/PbO will be the ones on the outside of the plate and if we only achieve 95% SoC on recharge, our 50% site will still be PbSO4. Next time we discharge we go to 60% charge and recharge to 98%. That 50% site is still PbSO4 and so on. In a few weeks of this, if we never achieve 100% SoC, then that site will still be sulphated (although I have no idea how long to that remaining permanent). It really is important to get that last bit of charge to 100%. Bottom line, the last sulphated Pb/PbO sites to be converted back to Pb/PbO will be the most difficult to get to (for the acid) and not 'first in- first out' as the layman might think.

My head is starting to hurt now.

[cuthound]

58 minutes ago, Tony Brooks said:

But Cuthound's batteries were almost certainly recharged almost a soon as the full discharge had taken place so hardening sulphate had little time to establish itself.

I also suspect the cell groups could be lifted out, the acid emptied, the sediment washed out and the groups and acid replaced. That would also help top extend life.

However not so sure you can equate telephone exchange batteries with a boat's domestic bank that has a huge inverter connected to it. The discharge profile and I suspect charge profile would be very different. However the fact remains the better constructed the battery the longer its cyclic life is likely to be.

 

 

 

 

Yes they were recharged immediately after each discharge.

They were huge, the attached image is the closest I can find to what they actually looked like.

They were topped up weekly with several buckets of de-ionised water to each cell.

The largest 2 volt cells had a capacity of 15,050 Ah and were about 4 feet high, 4 feet long and 6 feet across. Lower capacity ones had fewer plates in parallel, so we're less than 6 feet across.

Plates were separated with long glass rods and covered with glass splash plates to keep the acid within the cells when charging.

We had a dealing stick, a sword like tool to remove growths between plates which shorted plates out and reduced capacity. You could pump out the acid to remove sediment, but as the plates were 6 inches off the bottom of the cell it was very rarely necessary.

Individual plates could be cut out and new ones lead welded back in if necessary.

They were designed to provide one hours autonomy at full load, so a more extreme load than most boat batteries. As previously stated, they were fully discharged every 2 years at the 10 hour rate to assess capacity. A 20% loss of capacity over 25 years was deemed acceptable.

A handful of major exchanges used these batteries to power motor alternator sets to provide uninterruptible 240 volt mains power, an early type of inverter, like a large Rediline investor as used on boats in the 80's to provide limited mains power.

In the early 1980's digital exchanges came in. These were much less power hungry and supplied from multiple  VRSLA batteries with a capacity of 100 Ah each, which obviously were maintenance free.

Edited October 5, 2017 by cuthound
Clarification

[WotEver]

1 hour ago, Dr Bob said:

Perhaps the 12.7V is a surface effect – ie why is my battery showing 13V+ just after the battery charger is turned off? Shouldnt it immediately go back to its theoretical maximum potential?

Yes it should

Why it doesn’t is one of life’s many mysteries and my (quite extensive) Googling research suggests that it isn’t fully understood by anyone. Unless someone can find a paper that offers an explanation?

[dmr]

3 hours ago, cuthound said:

It's not just any magic, it's BLACK magic.

 

Not sure that sort of language is allowed anymore, and anyway you are totally wrong. For many years I worked with a motor mechanic who referred to anything electrical as WHITE  Mans magic.

......................Dave

[cuthound]

Dr Bob,

It is surface charge. It disperses as the highly charged surface of the plate (because it is in contact with the electrolyte,  unlike the centre) charges the less charged centre of the plate. When the surface charge has dispersed the entire plate is evenly charged.

I agree with WotEver, no one can fully explain everything that happens with lead acid batteries.

 

Edited October 5, 2017 by cuthound

[nb Innisfree]

4 hours ago, Tony Brooks said:

Think back - those who can - to when we had to park with the side and tail lamps on. How often did we come back to a flat battery and then push start the car and carry on.

Jump starting also was easier in then. Also parking light with one bulb that fitted on a window were handy. 

[Dr Bob]

1 hour ago, cuthound said:

Dr Bob,

It is surface charge. It disperses as the highly charged surface of the plate (because it is in contact with the electrolyte,  unlike the centre) charges the less charged centre of the plate. When the surface charge has dispersed the entire plate is evenly charged.

I agree with WotEver, no one can fully explain everything that happens with lead acid batteries.

 

Thinking about this, it is likely that as Nick says - it is about the equilibrium reaction. Tony said "Add the two voltages (for each reaction) together and we get 2.041 volts. That is the natural voltage of that cell.  6 cells gives us 12.246V. " I am not sure where you got that from but lets go with it (can you post the link?). I would guess this is the absolute voltage that the chemical reaction going from Pb/PbO to PbSO4 generates in isolation - ie one atom generating 1 (or is it 2?) electrons. We know the reaction goes in the reverse direction when a voltage over 13V+ is applied and goes to completion (100% of sites) when up over 14V (albeit over an extended time period). I would think it therefore very likely that the position of the equilbrium (ie does the reaction go towards PbSO4 or towards Pb/PbO?) will be dependent on the voltage potential in the system. The 'forward' reaction of Pb/PbO to PbSO4 will generate the potential and that potential will rise until it is high enough to permit the reverse reaction and then the potential will drop. Therefore although an individual atom can only produce the 2.041 volts, a whole trillion or so sites will produce higher potential to the point where that starts the reverse reaction. Therefore the 12.246V may only be a theoretical value and not a 'in practice' value (hence interested to see Tony's link). Highly likely this is a surface effect. I may be talking a load of bol****s as although I am well up on equilibrium reactions involving hetrogeneous materials (solid/liquid interfaces) my knowledge of electrochemisty is pretty poor.

[nicknorman]

4 hours ago, Dr Bob said:

 

Nick's explanation on time dependency raises other issues for me. If we assume the lead/lead oxide buried deep in the plates takes time to react then we can paint the picture where a site say 50% deep in a plate will only offer up its electrons and convert to lead sulphate when the SoC is 50% ish. OK so far? Now when we put the battery on charge, the sites that will be converted back to Pb/PbO will be the ones on the outside of the plate and if we only achieve 95% SoC on recharge, our 50% site will still be PbSO4. Next time we discharge we go to 60% charge and recharge to 98%. That 50% site is still PbSO4 and so on. In a few weeks of this, if we never achieve 100% SoC, then that site will still be sulphated (although I have no idea how long to that remaining permanent). It really is important to get that last bit of charge to 100%. Bottom line, the last sulphated Pb/PbO sites to be converted back to Pb/PbO will be the most difficult to get to (for the acid) and not 'first in- first out' as the layman might think.

This is definitely born out by my practical observations. If we stop for lunch, on restarting the engine the initial charge current may be over 100A even though the SoC might be 98%. But of course very rapidly the current falls off. The chemicals very near the surface have reacted to keep the boat going for an hour or so, and now the same chemicals very near surface react the other way.

If we discharge overnight to say 75%, of course we get a high charge current to start with and this tails off gradually but is still quite significant at say 90%.

If we discharge to 50% same high initial charge current but by 90% the charge current is very low and it takes ages to fully charge the batteries. If we stopped at 4% tail current it would probably only be 95% SoC. This last very slow stage is of course due to the need for the chemicals buried deep within the plates to react.

[WotEver]

1 hour ago, Dr Bob said:

am not sure where you got that from but lets go with it (can you post the link?)

I can’t recall where I first learned this, it might have been Gibbo, but if you Google “2.041 volts” you will see many references to it including “Art in Chemistry, Chemistry in Art” and many others. 

In fairness, this reaction is generally referred to as the ‘basic reaction’ which suggests (as we know from observation) that there are other, secondary reactions going on, hence the fact that the battery voltage varies. 

Whether the lead oxide is deep within the plate or on the surface can only affect the speed of the conversion and hence the current. The voltage is dictated by the basic reaction which as we’ve previously agreed is binary - it either happens or it doesn’t. 

Gibbo once told me of an occasion that he took a sample of electrolyte from a battery which was being hard charged from 50% SoC and gave that sample to a Dr Hewitt PHD (Chemistry) and Dr Hewitt found chemicals there which had no right to be there and he couldn’t offer an explanation for their existence. However he noted that those chemicals would be effective in removing hardened sulphate, which Water and H2SO4 cannot do. So nobody truly understands where these compounds come from but it’s a good thing that they do or a LA battery would never work - it would be totally sulphated after a handful of cycles. 

So, like I said earlier in this thread - it’s magic. 

[Tony Brooks]

I agree. For the majority of us experience based on empirical observations plus the "rules" that seem to fit those observations will do well enough for us to look after our batteries. To be honest after a certain depth of discussion I could not giver a flying fig - it produces nothing practically useful.