Charging house bank from 12v And 24v Alternators?

[Dockhead]

Carbon pile testers would normally be used for load testing starter batteries, not for capacity testing.

I wouldn't want to take my batteries down to 1.75v per cell, that's flatter than flat. There would be many, otherwise serviceable, batteries that would struggle to recover from such a dramatic discharge. A safer, simpler, cheaper and more meaningful capacity test would be to apply a specific load to a fully charged and rested battery and measure how long it takes to get down to your desired max state of discharge. This will give you your usable ah. A simple bulb will suffice for the load.

If the battery has sufficient usable capacity for your needs there is no need to replace it, simple. To quote an arbitrary figure, such as 80% is nonsense, although that is an "industry standard figure". It cannot sensibly be applied to all batteries or all circumstances. A correctly spec'd, dedicated, starter battery will generally start the engine at up to 40% capacity, but if the engine is mission critical, you wouldn't want to get to those levels. If it was on your ride on mower it probably wouldn't hurt to wait until the battery actually gives up.

For the domestic batteries on a boat there are a few factors to consider. How important is the leisure bank ? If you're planning a blue water voyage and will be depending on the electrics, you might be wise to have the best batteries possible. For the average yacht owner the question is, will the capacity we worked out earlier be sufficient for our needs ? If the answer is yes, there's no point changing the batteries.

The other pint to consider, when thinking about that 80% figure is this, if the batteries are basic SLA batteries you won't want to discharge them less than 50% (max), so you usable capacity is what it takes to get down to 50%. If you have true deep cycle that can, for instance, be discharged to 20%, the two capacity figures will be very different for, say, the same size battery bank.

Theories, formulas and most of all, web sites, don't always agree with the real World.

Well, as I said, there are different methods of measuring capacity, but the carbon pile works, and is probably the most common method. It's much better than a simple bulb because it can be easily adjusted to a specific percentage of C. There is another method using a carbon pile tester which infers the capacity from a shorter test, not taken down to zero. Carbon pile testers can also be used on starter batteries, but that is a completely different test, which measures the voltage sag rather than time to discharge.

Discharging to zero once in a while -- to dead flat -- and then immediately recharging lead batteries is actually beneficial and can help to partially reverse sulfation. This works with lighter duty "leisure" batteries as well as deep cycle batteries. But with "leisure" batteries you are not likely to care enough to go through this business anyway -- they are more disposable, and so you just toss them when they stop performing as you expect. They don't last enough years for logging capacity changes to be meaningful.

As to 80% -- as I said, this is the industry-standard definition of end of life, for deep discharge batteries. It is quite meaningful, actually, because this is the point in the life cycle when capacity falls off rapidly. That is not to say that all batteries become unusable at that point, but there is little point in stretching it much past there because in any case, total failure will occur fairly soon. You can push it further with really good heavy duty batteries which are less prone to structural failure so long as you don't care so much about the reduced acceptance rate, but with cheaper batteries this is really a bad idea because of the risk of a shorted cell from the accumulation of shed material or mechanical failure of a cell grid. A boat left on shore power in a marina with the not on board can burn down from this -- a battery with a shorted cell will show low voltage to the charger, which will pour power in to try to bring the voltage up, and if there is no temperature regulation, the battery can boil out and even catch on fire. Don't ask me how I know this -- it's an unpleasant memory!

 

[PaulRainbow]

Well, as I said, there are different methods of measuring capacity, but the carbon pile works, and is probably the most common method. It's much better than a simple bulb because it can be easily adjusted to a specific percentage of C. There is another method using a carbon pile tester which infers the capacity from a shorter test, not taken down to zero. Carbon pile testers can also be used on starter batteries, but that is a completely different test, which measures the voltage sag rather than time to discharge.

A simple load test with a known load is simple, anyone can do it without buying expensive testers. It provides real World results, as in "how much power my battery delivers before it reaches my chosen SOC"

Discharging to zero once in a while -- to dead flat -- and then immediately recharging lead batteries is actually beneficial and can help to partially reverse sulfation. This works with lighter duty "leisure" batteries as well as deep cycle batteries. But with "leisure" batteries you are not likely to care enough to go through this business anyway -- they are more disposable, and so you just toss them when they stop performing as you expect. They don't last enough years for logging capacity changes to be meaningful.

Anyone starts discharging my batteries to dead flat and they better be good swimmers. My batteries never get to 50%, rarely bellow 80%.

As to 80% -- as I said, this is the industry-standard definition of end of life, for deep discharge batteries.

Where are you getting this from, particularly in relation to the current subject matter ?

I suspect your just quoting IEEE figures you read on a website somewhere.

It is quite meaningful, actually, because this is the point in the life cycle when capacity falls off rapidly. That is not to say that all batteries become unusable at that point, but there is little point in stretching it much past there because in any case, total failure will occur fairly soon.

Batteries don't get to 80% then just die. As i said repeatedly, depends on the application. If it's a small yacht, minimal electrics, used for day sailing from a marina with shore power, 80% isn't going to be an issue. If it's on a fully loaded blue water cruiser, different story.

 

[Dockhead]

A simple load test with a known load is simple, anyone can do it without buying expensive testers. It provides real World results, as in "how much power my battery delivers before it reaches my chosen SOC"

Sure. No argument there. I think that's a perfectly valid approach.

Anyone starts discharging my batteries to dead flat and they better be good swimmers. My batteries never get to 50%, rarely bellow 80%.

A controlled discharge to 0% followed by immediate controlled charging at about 0.1C is very different from just letting the batteries go flat in use. This is a well known and very good technique for reviving sulphated batteries, recommended by Nigel Calder, just to name one.

This can be combined with the most accurate possible capacity test say once a year -- it's good for your batteries. This procedure is used for managing lead-acid standby power banks in the telecomms and data center industries.

Where are you getting this from, particularly in relation to the current subject matter ?

I suspect your just quoting IEEE figures you read on a website somewhere.

Batteries don't get to 80% then just die. As i said repeatedly, depends on the application. If it's a small yacht, minimal electrics, used for day sailing from a marina with shore power, 80% isn't going to be an issue. If it's on a fully loaded blue water cruiser, different story.

Where I get this from is from years of using and studying lead acid batteries, and from reading the technical literature on renewable energy systems, where the life cycles of lead acid batteries are studied in depth. I humbly offer the results of this study to the forum, for anyone who is interested. For those who are happy with what they already know -- well, that's fine!

I already explained the significance of 80% capacity. It is accepted throughout the industry that the end of life of lead acid batteries is defined as capacity decline to 80%. All the published cycle life charts and so forth are based on this definition of end of life.

As I said, reaching this definition of end of life does not necessarily mean the battery bank is unusable -- it depends on what people expect their banks to do. But if you read enough cycle life charts, you will see that in nearly all cases the curves turn down sharply around that point -- which is no doubt why 80% was chosen. So your batts might still be working more or less at 80%, but they are in any case not likely to work for much longer.

Don't believe me if you don't want to; the information is widely available from other sources. Some cites:

"The end-of-life of a lead-acid battery is typically taken to be when one (or both) of the power or energy capacity has fallen to 80% of its initial value. Beyond this point, lead-acid batteries tend to fail imminently, and so an 80% state-of-health (SOH) indicates that replacement is required."

ITP Renewables.

https://batterytestcentre.com.au/project/lead-acid/

"If properly designed, built, and maintained, a battery can provide many years of reliable service. A new battery might not initially provide 100% capacity. The capacity typically improves over the first few years of service, reaches a peak, and declines until the battery reaches its end of life. A reduction to 80% of the rated capacity is usually defined as the end of life for a lead-acid battery. Below 80%, the rate of battery deterioration accelerates, and it is more prone to sudden failure resulting from a mechanical shock (such as a seismic event) or a high discharge rate."

http://www.power-thru.com/documents/The Truth About Batteries - POWERTHRU White Paper.pdf

"What happens at the end of a battery’s life?

"Reaching end of life (EoL) does not necessarily mean that a battery will no longer function; in fact, it may still be usable, albeit in a diminished capacity. For most (but not all) types of batteries, end of life agreed to be the point at which the a battery will hold only a set percentage of its original storage capacity (‘retained capacity’). This gradual degradation is known as ‘capacity fade‘.

"In addition to the reduced ability to hold a charge, reaching end of life may also be associated with other markers of decreased performance: a poorer ratio of ‘energy in’ to ‘energy out’ (round-trip efficiency) and in some batteries an increased risk of other malfunction that could render them unusable or unreliable.

"For example, end of life for a lead-acid battery is usually 80% – so once a lead-acid battery bank with an original capacity of 10 kilowatt-hours (kWh) of energy reaches the end of its life, it will only be able to store 8kWh."

What is battery ‘end of life’? by James Martin II

https://www.solarchoice.net.au/blog/battery-end-of-life-explained

 

[pvb]

This is a well known and very good technique for reviving sulphated batteries, recommended by Nigel Calder, just to name one.

It's best to remember that Nigel Calder is primarily a journalist, rather than an engineer, and has made a good living from re-hashing information into readable books. But he isn't always right; he once wrote that stainless steel washers shouldn't be used in bolted high current cable connections, because they'd overheat and could cause a fire! Obviously nonsense, but someone must have told him it was true.

 

[PaulRainbow]

A controlled discharge to 0% followed by immediate controlled charging at about 0.1C is very different from just letting the batteries go flat in use. This is a well known and very good technique for reviving sulphated batteries, recommended by Nigel Calder, just to name one.

The problem with reading websites relating to industrial/domestic solar power, telecoms, UPS systems etc, is that none of them are fitted to boats. We mostly use lead acid starter batteries or "leisure" batteries. It really isn't good practice to discharge these to nothing, by any means. The really well known and very good techniques for dealing with sulphation definitely don't involve totally discharging batteries. As for Mr Calder, i imagine i've dealt with a few more batteries than he has, probably this year alone lol

The 80% IEEE figure actually relates to fixed installations. The IEEE actually state "This standard defines terms currently in use in the field of stationary batteries. This standard does not include terms specific to battery manufacturing activities or to non-stationary battery applications such as motive, portable, marine, or other such applications"

An 80% figure is certainly a good indication that the batteries aren't performing at their best, as would be a 90% figure, even a 95% figure. But it still does not mean they have to be arbitrarily replaced, as i keep saying, depends on use and circumstances.

You simply cannot read a few random websites, that mostly deal with different industries and technologies and unilaterally apply the theories and practices to every application.

 

[Dockhead]

The problem with reading websites relating to industrial/domestic solar power, telecoms, UPS systems etc, is that none of them are fitted to boats. We mostly use lead acid starter batteries or "leisure" batteries. It really isn't good practice to discharge these to nothing, by any means. The really well known and very good techniques for dealing with sulphation definitely don't involve totally discharging batteries. As for Mr Calder, i imagine i've dealt with a few more batteries than he has, probably this year alone lol

The 80% IEEE figure actually relates to fixed installations. The IEEE actually state "This standard defines terms currently in use in the field of stationary batteries. This standard does not include terms specific to battery manufacturing activities or to non-stationary battery applications such as motive, portable, marine, or other such applications"

An 80% figure is certainly a good indication that the batteries aren't performing at their best, as would be a 90% figure, even a 95% figure. But it still does not mean they have to be arbitrarily replaced, as i keep saying, depends on use and circumstances.

You simply cannot read a few random websites, that mostly deal with different industries and technologies and unilaterally apply the theories and practices to every application.

80% capacity as end of life is not specific to any industry. It is the standard used everywhere and by all the makers. The chemistry is the same and even many of the actual batteries are the same.

As I said, it doesn't mean that between 81% and 80% every lead acid battery crosses a hard line between fit for service and dead, but have you done any actual study of this question? 80% of capacity, more or less, corresponds to a sharp acceleration of loss of capacity and greatly increasing risk of failure. It is not at all the same as 90%, which is in the middle of a battery's lifetime with no big acceleration of loss of capacity coming.

Of course if you're using disposable "leisure" type batteries you don't need to delve this deeply into it. Just chuck 'em as soon as they don't do what you want them to, and forget about it.

But for those who spend weeks or months at a time off shore power, this information can be valuable.

As to full discharge and immediate recharge as a method of correcting sulfation -- I'll refrain from further comment. You consider all experience in other applications to be irrelevant, and you know more about batteries than Nigel Calder, so there's nothing I could say which could be of interest to you.

 

[Dockhead]

It's best to remember that Nigel Calder is primarily a journalist, rather than an engineer, and has made a good living from re-hashing information into readable books. But he isn't always right; he once wrote that stainless steel washers shouldn't be used in bolted high current cable connections, because they'd overheat and could cause a fire! Obviously nonsense, but someone must have told him it was true.

Of course you are right.

But he is incredibly knowledgeable, and you can find errors in anyone's work. I'm personally quite a fan of his -- I don't actually think anyone has done as much as he has, to bring deep understanding of all the different technical aspects of our sport. His "big smart book", as it's jokingly called, is the basic technical reference manual on board many long distance cruising boats.

 

[matthewriches]

There is some truth in that, in high current applications, stainless washers between conductors on posts for example can cause a high resistance which can generate a good amount of heat. An American blogger conducted some research regarding this a while ago but cannot put my hands immediately on it.

And if I apply that to any DNO connections or industrial gensets I do, all the switchgear and connection points definitely do not use stainless, even in outdoor sheds.

He once wrote that stainless steel washers shouldn't be used in bolted high current cable connections, because they'd overheat and could cause a fire! Obviously nonsense, but someone must have told him it was true.

 

[pvb]

There is some truth in that, in high current applications, stainless washers between conductors on posts for example can cause a high resistance which can generate a good amount of heat. An American blogger conducted some research regarding this a while ago but cannot put my hands immediately on it.

And if I apply that to any DNO connections or industrial gensets I do, all the switchgear and connection points definitely do not use stainless, even in outdoor sheds.

No, if you calculate the potential watts of heat likely to be generated in the worst circumstances on a leisure boat, it's an insignificant amount. Do the calculations yourself. I did.

 

[PaulRainbow]

As to full discharge and immediate recharge as a method of correcting sulfation -- I'll refrain from further comment. You consider all experience in other applications to be irrelevant, and you know more about batteries than Nigel Calder, so there's nothing I could say which could be of interest to you.

How much practical experience do you imagine Mr Calder has ?

 

[matthewriches]

I said in high current applications. But your calculations would be welcomed for the nice viewers.

No, if you calculate the potential watts of heat likely to be generated in the worst circumstances on a leisure boat, it's an insignificant amount. Do the calculations yourself. I did.

 

[pvb]

I said in high current applications. But your calculations would be welcomed for the nice viewers.

And I said on a leisure boat. As for the calculations, you're probably better to do them yourself if you're to believe them.

 

[pvb]

I said in high current applications. But your calculations would be welcomed for the nice viewers.

Out of idle interest, I Googled and found the original thread on Scuttlebutt. You'll see that Nigel Calder replied, with more fake facts he'd heard from someone and hadn't bothered to check!

http://www.ybw.com/forums/showthread.php?5074-Oi!-Nigel-Calder!-NO

 

[lw395]

Mr Calder is not alone in disliking ss washers in electrical circuits.
Stainless works by having a fast-forming oxide coating. Which is an insulator.
Remove the oxide layer and you can get some odd corrosion effects with other metals.
Where the washer is actually in the circuit, it would be normal practice to use a plated washer of brass, steel or copper.
You don't see stainless in professional electrics much. I can't recall any connector product which puts stainless in a high current DC path. It does get used in RF, but normally gold or silver plated?

I think the ohms are not the point. It could be a case of a 1V contact potential of some oxide or other compound.

 

[pvb]

Mr Calder is not alone in disliking ss washers in electrical circuits.
Stainless works by having a fast-forming oxide coating. Which is an insulator.
Remove the oxide layer and you can get some odd corrosion effects with other metals.
Where the washer is actually in the circuit, it would be normal practice to use a plated washer of brass, steel or copper.
You don't see stainless in professional electrics much. I can't recall any connector product which puts stainless in a high current DC path. It does get used in RF, but normally gold or silver plated?

I think the ohms are not the point. It could be a case of a 1V contact potential of some oxide or other compound.

And this would generate enough heat to start a fire, as Calder states in his book?

 

[lw395]

And this would generate enough heat to start a fire, as Calder states in his book?

Possibly.
Once a connection is poor, it can go 'bad' via several routes.
On a boat, corrosion is always possible.
Once the bits are warm enough for a bit of expansion, the hard stainless might fret the softer metals until the joint is slack.
There is usually no reason to have current going through a washer. If there is, why use a stainless washer?

I've seen melted and scorched plastic from various fairly low current circuits, due to poor connections.
Boat electrics these days are tending towards power levels which need to be treated with a bit of care, even if it's only 12V.

While Mr Calder's research and explanation may not be the greatest in this instance, I think the general advice not to put stainless in circuit is very sound.
Note 'in circuit', I will use a stainless washer on top of an eylet connector for instance, even a stainless bolt to hold and eyelet against a battery connector. But zinc plated steel would be better.

 

[PaulRainbow]

I've seen melted and scorched plastic from various fairly low current circuits, due to poor connections.
Boat electrics these days are tending towards power levels which need to be treated with a bit of care, even if it's only 12V.

That would probably be the cause of most fires. People thinking "it's only 12v" and wiring the bilge pump up with speaker wire and Screwfix choc blocks. i recently saw an undersized cable supplying an electric toilet (fitted by the owner, using choc blocks) completely burned through, it had been arcing and blown a section of conductor away. He ran another cable, in parallel (same undersize stuff, same choc blocks), which obviously left the burned out cable live from both ends and unprotected at the break. I see similar things on an all too regular basis.

Also recently, i had to sort out the wiring on a 45ft flybridge mobo there the engine wiring had melted due to the stop solenoid being engaged too long, This was primarily a bad design by Volvo, featuring a poor method of operation and inadequate wiring protection, such as a 2.5mm cable running around the engine, connected to the heavy starter cable at the starter solenoid, with no fuse ! I estimate the whole loom was seconds from catching fire when the owner turned the battery isolator off, The wiring was less than a foot from a 1000 litre diesel tank, which is linked to the 1000 litre diesel tank for the other engine.

Note 'in circuit', I will use a stainless washer on top of an eylet connector for instance, even a stainless bolt to hold and eyelet against a battery connector. But zinc plated steel would be better.

Duly noted I can't think of an instance where i've seen stainless washers between the connector and the device it's bolted to. Busbars often use stainless screws and washer, but the washer is supposed to be part of the retaining mechanism, not in circuit.

 

[Pau Amma]

Wow I’ve just logged back in to see any updates and see lots of kind input.
So here’s what I’ve done... so far... I have set up my Torqeedo batteries to charge from the 12v alternator with a voltage switch to protect the start battery and a 12v to 24v converter to get max charge into the Torqeedo batteries, works great.
NEXT UP I shall upgrade to Lead Carbon batteries and the 24v alternator (sadly small frame) will be converted or replaced and externally regulated with a Balmar MC. I can’t understand the obsession with Lithium when you take into account the voltage protection and costs the latest Carbon Foam AGMs knock it all into a cocked hat for cost / psoc / cycles..
Anyhoooooow thanks for all the input. I am reassured that it’s not a simple subject to tackle by the amount of opinions..