Lead Acid - 1) Sulphation Rate? + 2) Cycles?

[Scooterman]

Hi, these two questions are something I've often wondered...

1) I'm guessing the deeper discharged a battery, the the quicker it sulphates. But how much faster than a shallowly discharged battery?

The reason I ask mainly relates to my scooters. As I'll often do say a 6 - 8 mile round trip to the supermarket, say around lunchtime. When I get home I think to myself, I doubt if I'll be using the scooter again that day so stick it back on charge as soon as I get home. But if say I leave recharging it to the evening (just in case I do want to use the scooter again that day), are the batteries sulphating very quickly? Even if the sulphation rate difference isn't that great I suppose it adds up cumulatively over the lifetime of a battery?

2) Cycles - Do both a deeply discharged battery recharge cycle, and a shallowly discharged battery recharge cycle, both count as 1 cycle?

Question number 2) is about lead acid batteries. But would the same apply to say LifePo4 and the lithium batteries used in gadgets such as smartphones?

[Burgerman]

1) I'm guessing the deeper discharged a battery, the the quicker it sulphates. But how much faster than a shallowly discharged battery?

A lead battery uses WATER + SULFURIC ACID mixed as its electrolyte. And lead plates.

A fully 101% charged battery has no sulfation. (lead sulfate coating the cells). ALL the lead sulfate has been returned back to the acid. As you discharge a lead battery, the Sulfuric acid in the electrolyte turns to lead sulfate and coats the battery plates, leaving a much weaker, almost water alone electrolyte at the point where the battery is fully used up. Lead sulfate at this point is not permenant. As you subsequently recharge the battery, all of the lead sulfate is returned back to the acid, and the plates are again. clean. In an ideal world. But many chargers do not completely charge the battery. So some small amount remains every cycle. This gradually builds up. After a period of time, this lead sulfate turns from a super fine white powder, into larger crystals.

These can never be removed in the future since they do not conduct electricity. How long does this take? It starts happening straight away. But its slow. So as long as you recharge as soon as possible after use you cant do any more. The longer you leave it, the warmer it is, the more sulfate there is to start with, the deeper its discharged, the faster it happens.

The reason I ask mainly relates to my scooters. As I'll often do say a 6 - 8 mile round trip to the supermarket, say around lunchtime. When I get home I think to myself, I doubt if I'll be using the scooter again that day so stick it back on charge as soon as I get home. But if say I leave recharging it to the evening (just in case I do want to use the scooter again that day), are the batteries sulphating very quickly? Even if the sulphation rate difference isn't that great I suppose it adds up cumulatively over the lifetime of a battery?

Yes, in simplistic terms. But you would be better charging straight away ESPECIALLY if going out again later, as this loweres the average depth of discharge and thats another thing that murders lead batteries!

2) Cycles - Do both a deeply discharged battery recharge cycle, and a shallowly discharged battery recharge cycle, both count as 1 cycle?

Yes, but you get 1000s of shallow cycles, and 10s of deep ones...

Question number 2) is about lead acid batteries. But would the same apply to say LifePo4 and the lithium batteries used in gadgets such as smartphones?

Absolutely the opposite!

Lithium likes to be between say 20% to 30% full, and 80% full. LESS, or MORE shortens their life! They love being in the middle.
This is he MAX usable that you can get from a lead, and a lithium battery. AVOID going anywhere near the orange shaded parts and they last a very long time.

[Scooterman]

Thank you BM a brilliant reply I've saved the page as a pdf and put it in my mobility folder.

The reason I ask mainly relates to my scooters. As I'll often do say a 6 - 8 mile round trip to the supermarket, say around lunchtime. When I get home I think to myself, I doubt if I'll be using the scooter again that day so stick it back on charge as soon as I get home. But if say I leave recharging it to the evening (just in case I do want to use the scooter again that day), are the batteries sulphating very quickly? Even if the sulphation rate difference isn't that great I suppose it adds up cumulatively over the lifetime of a battery?

Yes, in simplistic terms. But you would be better charging straight away ESPECIALLY if going out again later, as this loweres the average depth of discharge and thats another thing that murders lead batteries!

Re the last point, the reason I've never done (the above) is because the user manuals say don't top up the batteries (lead acid) during the day, always wait until evening then charge overnight (say a minimum of 8 hours). But I guess that the recharge time depends on how deeply discharged the batteries are? If the batteries are discharged only by say 20% then a recharge might not take ≥8hrs? And recharging them for several hours and then using the scooter later in the early evening is better for the batteries?

One final question if I may. I use the generic chargers that come with the scooters and powerchair. The two scooter chargers are 5A and 8A and the powerchair charger is the same as the generic one supplied with your salsa (I'm not sure of the amp rating). What does the green charged light indicate? It comes on quite quickly on the scooter chargers (depending on discharge state) but am I right in thinking (I think I read it somewhere) it's not a reliable indication of the battery charge state and charger should be left connected until scooter is next required (which is what I do).

https://www.discountscooters.co.uk/8-amp-24v-value-battery-charger

[LROBBINS]

Those instructions are designed to get you to buy batteries, or run out of juice on a busy day.

The green light just means that the constant voltage bulk charge stage has finished and it's gone to float (or just shut off on older type chargers). That is not fully charged (it's at about 90%) and if you just charge to this point and stop the life of the batteries will be seriously compromised. Unless it had been hardly used at all, it will take a good 8-12 hours at float to really bring it to full charge. You don't have to let it float that long all the time, but at least once a week or so a good long soaking float will help keep lead sulfate crystals from growing to where they can't be converted back to lead + sulfuric acid.

[Burgerman]

Re the last point, the reason I've never done (the above) is because the user manuals say don't top up the batteries (lead acid) during the day, always wait until evening then charge overnight (say a minimum of 8 hours).

Its because:
1. they think that the user will just keep topping up, and never do a full overnight charge and that will ruin the battery. You MUST STILL do a full overnight charge... Topping up for a couple of hours during the day is a great way to keep the level of average discharge low. So they never get discharged deeply. Keeps them outof that orange bit above. That alone will double the life of the battery at least.

2. some generic chargers do not sense current at all. They just charge at 14. something for 8 hours regardless. And then go a) 0ff. b) FLOAT often at too high 27.6V. And some DO sense termination current and go off completely, or to float, but do so LONG before the battery is full. So you get a green light about 4 or 5 hours too soon and the battery isnt full. And so I dont realy know what each charger that you have will do...

But I guess that the recharge time depends on how deeply discharged the batteries are? If the batteries are discharged only by say 20% then a recharge might not take ≥8hrs? And recharging them for several hours and then using the scooter later in the early evening is better for the batteries?

Yes. And as long as it also gets a full overnight charge as well as lots of short top ups.

The sunrise orange one was quite good from what I remember, but its ights tell you its done and its still charging regardless... So it lies.

[Burgerman]

Lenny beat me too it!

[Scooterman]

Those instructions are designed to get you to buy batteries, or run out of juice on a busy day.

The green light just means that the constant voltage bulk charge stage has finished and it's gone to float (or just shut off on older type chargers). That is not fully charged (it's at about 90%) and if you just charge to this point and stop the life of the batteries will be seriously compromised. Unless it had been hardly used at all, it will take a good 8-12 hours at float to really bring it to full charge. You don't have to let it float that long all the time, but at least once a week or so a good long soaking float will help keep lead sulfate crystals from growing to where they can't be converted back to lead + sulfuric acid.

Thank you, I understand now

[Scooterman]

Re the last point, the reason I've never done (the above) is because the user manuals say don't top up the batteries (lead acid) during the day, always wait until evening then charge overnight (say a minimum of 8 hours).

Its because:
1. they think that the user will just keep topping up, and never do a full overnight charge and that will ruin the battery. You MUST STILL do a full overnight charge... Topping up for a couple of hours during the day is a great way to keep the level of average discharge low. So they never get discharged deeply. Keeps them outof that orange bit above. That alone will double the life of the battery at least.

2. some generic chargers do not sense current at all. They just charge at 14. something for 8 hours regardless. And then go a) 0ff. b) FLOAT often at too high 27.6V. And some DO sense termination current and go off completely, or to float, but do so LONG before the battery is full. So you get a green light about 4 or 5 hours too soon and the battery isnt full. And so I dont realy know what each charger that you have will do...

But I guess that the recharge time depends on how deeply discharged the batteries are? If the batteries are discharged only by say 20% then a recharge might not take ≥8hrs? And recharging them for several hours and then using the scooter later in the early evening is better for the batteries?

Yes. And as long as it also gets a full overnight charge as well as lots of short top ups.

The sunrise orange one was quite good from what I remember, but its ights tell you its done and its still charging regardless... So it lies.

Thank you once again, I do understand all that, yourself and LROBBINS has made it very clear

[ex-Gooserider]

BM is better about posting exact graphs and such, but if you look through some of the technical docs for batteries that he posts sometimes, you will find a graph showing the number of charge cycles the battery will last through, vs. the average depth of discharge.... The typical manufacturer claim of '500 cycles' or such, is normally based on an 80% depth of discharge (use of the available current stored in the battery)....

However if you look at the graph, it shows a gradually sloping line from zero to about 50% depth of discharge, with 50% still in the THOUSANDS of cycle range... The curve then gets much steeper until you are down to only 500 or so cycles at 80%.... After 80% the curve starts falling off a cliff, until at 100% you are looking at 10's of cycles or less....

In practical terms, this means that a battery that is never discharged below say 20% or so will last almost indefinitely compared to one that is regularly discharged deeply....

Granted my current chair is on the emphatically weedy side, even after upgrading the controller to an 80A Pilot+, but I try not to let the "charge LED's" ever lose more than one or two greens for any length of time. I not sure I've ever actually gotten it down into any of the red LED's and rarely hit the first orange. My Odyssey rebrand batteries seem to not have lost any noticeable power, and go about as far before I start losing LED's as they did when new.... I normally charge every night using an Invacare branded charger, but in addition, if I know that I've done more running around than usual, especially if I've lost ANY LED's I will plug into my van (using a BM-style wire setup so I'm charging off the alternator) for the 30-40 minute drive home....

Before most of us went to Lithium, the constant message was "Charge early, charge often"....

ex-Gooserider

[Scooterman]

BM is better about posting exact graphs and such, but if you look through some of the technical docs for batteries that he posts sometimes, you will find a graph showing the number of charge cycles the battery will last through, vs. the average depth of discharge.... The typical manufacturer claim of '500 cycles' or such, is normally based on an 80% depth of discharge (use of the available current stored in the battery)....

However if you look at the graph, it shows a gradually sloping line from zero to about 50% depth of discharge, with 50% still in the THOUSANDS of cycle range... The curve then gets much steeper until you are down to only 500 or so cycles at 80%.... After 80% the curve starts falling off a cliff, until at 100% you are looking at 10's of cycles or less....

In practical terms, this means that a battery that is never discharged below say 20% or so will last almost indefinitely compared to one that is regularly discharged deeply....

Granted my current chair is on the emphatically weedy side, even after upgrading the controller to an 80A Pilot+, but I try not to let the "charge LED's" ever lose more than one or two greens for any length of time. I not sure I've ever actually gotten it down into any of the red LED's and rarely hit the first orange. My Odyssey rebrand batteries seem to not have lost any noticeable power, and go about as far before I start losing LED's as they did when new.... I normally charge every night using an Invacare branded charger, but in addition, if I know that I've done more running around than usual, especially if I've lost ANY LED's I will plug into my van (using a BM-style wire setup so I'm charging off the alternator) for the 30-40 minute drive home....

Before most of us went to Lithium, the constant message was "Charge early, charge often"....

ex-Gooserider

Thank you, I'm sorry I missed your reply previously, I was busy then doing mechanical mods on my chair.

So in economic terms it's better to pay extra and squeeze in as large a Ah battery as the compartment will allow, so the battery don't get as discharged and you get more cycles out of the battery.

The trouble with me and I think a lot of other laymen, is that we think of batteries as similar to automobile engines. In that it's better for the engine (and exhaust) for the vehicle to be used for lots of long runs, than lots of shorts runs. I remember de-coking my old a-series mini engine and re-lapping the valves, everyone used to do it. I don't know if it did any good? They always used to say to leave a small ring of carbon deposit at the top of the cylinder so you don't lose compression?

For lead 'Charge early, charge often' is a good mantra, I will remember that

[Burgerman]

Or...

For lead, throw straight in the bin cos they are garbage, fit LARGE lithium.

[ex-Gooserider]

Thank you, I'm sorry I missed your reply previously, I was busy then doing mechanical mods on my chair.

So in economic terms it's better to pay extra and squeeze in as large a Ah battery as the compartment will allow, so the battery don't get as discharged and you get more cycles out of the battery.

The trouble with me and I think a lot of other laymen, is that we think of batteries as similar to automobile engines. In that it's better for the engine (and exhaust) for the vehicle to be used for lots of long runs, than lots of shorts runs. I remember de-coking my old a-series mini engine and re-lapping the valves, everyone used to do it. I don't know if it did any good? They always used to say to leave a small ring of carbon deposit at the top of the cylinder so you don't lose compression?

For purely economic terms, best to go with Lithium....

If sticking with lead, its more complex... For first approximation, bigger is better, so go with the biggest case (Group) size that will fit, at least usually...

But in a given size, there is a balancing act between internal resistance, and other design issues that makes life more complex... There is a thing called the Peukert effect that essentially says the faster you discharge a given lead brick, the fewer Ah you get... The higher the internal resistance the worse the effect, so you can get some batteries that claim 100Ah in a Group 24 case, which might be true if you were just running a light bulb, but in a chair that draws much higher currents, they have such a high voltage drop that they stop working almost immediately...

So for a given size, internal resistance (lower is better) is almost more important than nominal capacity. This is so true that the much lower resistance Odyssey Group 34 size battery will often outlast the larger group 24 MK Gel in heavy use applications like wheelchair soccer chairs... (Group 34 has the same L x W as Group 24, but is shorter)

At any rate the ONLY two batteries WCD (and even the former not-so-lamented Junky Wheelchair site) has found to be worth purchasing are either the MK-Gel's (NOT the MK-AGM's!) or Odysseys.... In addition to the charge early, charge often rule, we also told people that they could not afford cheap batteries... (I went through a couple sets finding out the hard way how true this is...)

In terms of the engine rebuilds, it was a combination of things - the metals weren't as good (material science is an arcane and evolving art...) probably the gas was worse (the lead in it was there mostly to make up for metal wear) and carbs simply don't offer the same level of precise control over fuel metering that injectors do, so you had to run richer mixes to avoid cooking the engine...

The 'leave a ring at the top' is because the piston rings sit a little below the top of the pistons, so they never clean the top of the cylinder... There would eventually even be a bit of a layer of less worn metal at the top, plus the carbon buildup that formed a sort of 'extra' seal at the top of the compression stroke... In addition, I actually suspect that part of the logic was to keep you from scraping further down and damaging the part of the cylinder that actually did see the rings...

ex-Gooserider