Charging house bank from 12v And 24v Alternators?

[Dockhead]

Where on Earth do you get this from ? It's just utter nonsense.

Car type, bus type, huh ?

How do you imagine my puny 12v alternator charges my domestic bank, which is larger than the OPs ?

How do you imagine all of the other boats, also fitted with normal everyday 12v alternators do the same ?

Further words fail me

Oh, brother.

Instead of spluttering in amazement and outrage, at being faced with facts of which you are simply unaware, you might do some reading on the subject.

MaineSail is a great source and a good place to start:

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

A car-type alternator, 65 amps, can be expected to produce about 30 or maybe 40 amps more or less continuously. A 400 amp/hour lead-acid battery bank can accept 100-150 amps of current with no problem, AGM batteries much more. Such an alternator will struggle to get a decent charge on a bank that size -- see MaineSail's article.

A large frame alternator of say 160 amps, on the other hand, will produce 160 amps 24/7/365, because it's designed to do that.

My own second alternator, a 110 amp Leece Neville (@24v) will not only charge the large battery bank, it will run whatever AC gear on board through the inverter, whenever the main engine is running. Including the washer/dryer, electric cooking, whatever. Don't try that with a car alternator!

The point is that the OP has nothing to gain, by trying to add current from the puny standard alternator. Let the big one do its job and be happy that the starting system is entirely separate and not vulnerable to being run down by being connected with the house system.

 

[geem]

Oh, brother.

Instead of spluttering in amazement and outrage, at being faced with facts of which you are simply unaware, you might do some reading on the subject.

MaineSail is a great source and a good place to start:

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

A car-type alternator, 65 amps, can be expected to produce about 30 or maybe 40 amps more or less continuously. A 400 amp/hour lead-acid battery bank can accept 100-150 amps of current with no problem, AGM batteries much more. Such an alternator will struggle to get a decent charge on a bank that size -- see MaineSail's article.

A large frame alternator of say 160 amps, on the other hand, will produce 160 amps 24/7/365, because it's designed to do that.

My own second alternator, a 110 amp Leece Neville (@24v) will not only charge the large battery bank, it will run whatever AC gear on board through the inverter, whenever the main engine is running. Including the washer/dryer, electric cooking, whatever. Don't try that with a car alternator!

The point is that the OP has nothing to gain, by trying to add current from the puny standard alternator. Let the big one do its job and be happy that the starting system is entirely separate and not vulnerable to being run down by being connected with the house system.

I always find is amusing when people say how much their high output alternator can put out. Unless you have a massive battery bank they never produce anything like their rated output. The battery bank hits the limiting voltage of the regulator so quickly that most alternators put out a trickle of amps unless the battery bank is huge or the small battery bank is flat. A smart regulator can help with the absorbtion process once the limiting voltage has been met but this is about regulators not high output alternators. We have 1000 amp hr of domestic battery capacity and 120 amp alternator (converted to 12v-its actually a 24v system) but we never see more than 50 amps output from the alternator as the limiting voltage is reached in a few minutes. We used to have a smart regulator fitted but I removed it to gives the batteries a less harsh charging regime. The alternator brings the batteries up to 13.8v and the solar reg and towed generator reg bring the batteries up to full charge on passage. Once the solar reg is satisfied the batteries are charged it goes in to float mode and the alternator then keeps the batteries at 13.8v. Kinder on the batteries in my opinion than heavy over charging on a long trip.

 

[Dockhead]

I always find is amusing when people say how much their high output alternator can put out. Unless you have a massive battery bank they never produce anything like their rated output. The battery bank hits the limiting voltage of the regulator so quickly that most alternators put out a trickle of amps unless the battery bank is huge or the small battery bank is flat. A smart regulator can help with the absorbtion process once the limiting voltage has been met but this is about regulators not high output alternators. We have 1000 amp hr of domestic battery capacity and 120 amp alternator (converted to 12v-its actually a 24v system) but we never see more than 50 amps output from the alternator as the limiting voltage is reached in a few minutes. We used to have a smart regulator fitted but I removed it to gives the batteries a less harsh charging regime. The alternator brings the batteries up to 13.8v and the solar reg and towed generator reg bring the batteries up to full charge on passage. Once the solar reg is satisfied the batteries are charged it goes in to float mode and the alternator then keeps the batteries at 13.8v. Kinder on the batteries in my opinion than heavy over charging on a long trip.

What you are seeing is a function of either regulation, or else your bank is heavily sulfated. A healthy 1000 a/h bank is no way limited to 50 amps and in fact it is unhealthy to charge it at that rate -- it needs at least 0.1C or 100 amps. If it suits you -- fine. But normal FLA batteries are capable of absorbing at least 0.25C and AGM much more -- but the regulator needs to provide the corresponding voltage, and the alternator needs to be capable of dissipating the heat generated in the process of producing that much power.

My alternator produces its full output from about 2300 RPM (this is just a function of pulley sizes) and produces about 90 amps (@24v) from 1600 RPM. I monitor the current from my alternator with a shunt and ammeter. My 420 a/h bank (@24v) will take the full output of the alternator (or 90 -- 100 amps if the main engine is running slower) during the whole bulk phase -- roughly two hours from 50% SOC. At 85% or so, the process reaches absorption voltage and the acceptance rate tapers off.

If your batteries are only accepting 50 amps, then you have a problem. Flooded lead acid batteries have an acceptance rate of about 0.25C; AGM about 1C. If your bank is flooded lead acid, it should accept up to 250 amps during the bulk phase and NEEDS at least 100 amps.

 

[PaulRainbow]

Meanwhile, back on planet Earth...........................

 

[noelex]

A car-type alternator, 65 amps, can be expected to produce about 30 or maybe 40 amps more or less continuously. A 400 amp/hour lead-acid battery bank can accept 100-150 amps of current with no problem, AGM batteries much more. Such an alternator will struggle to get a decent charge on a bank that size -- see MaineSail's article.

This relatively low output of the 12v alternator is the crux of the problem. The 30A or maybe 40A @ 12v becomes 15-20A @ 24v. This is assuming 100% efficiency in the conversion process. The start battery will also require some of the output so in practice the OP will only gain about 10-15A into their house bank.

The conversion would require equipment such as a 12 to 24v battery charger which is expensive. It needs to be wired to automatically disconnect the battery charger when the engine is stopped.

The existing simple, foolproof system where the house and start batteries are completely seperate is lost with the conversion and the start alternator will be running at its peak capacity for long periods.

It is a complicated and expensive system that makes the start system less reliable for only a small gain in charging.

 

[Dockhead]

This relatively low output of the 12v alternator is the crux of the problem. The 30A or maybe 40A @ 12v becomes 15-20A @ 24v. This is assuming 100% efficiency in the conversion process. The start battery will also require some of the output so in practice the OP will only gain about 10-15A into their house bank.

The conversion would require equipment such as a 12 to 24v battery charger which is expensive. It needs to be wired to automatically disconnect the battery charger when the engine is stopped.

The existing simple, foolproof system where the house and start batteries are completely seperate is lost with the conversion and the start alternator will be running at its peak capacity for long periods.

It is a complicated and expensive system that makes the start system less reliable for only a small gain in charging.

Indeed. And the gain will be even smaller than that because of the inability of that type of alternator to produce its rated power continuously.

As to the guy with the 1000 amp/hour bank which will only accept 50 amps of charge --

He needs to do a 20-hour capacity test. I will bet 3 pints in the Solent pub of his choice, that those batts are heavily sulpahted and are down to less than 50% of their original capacity (and lead batts should be scrapped after 80%). And how did they get that way?

https://marinehowto.com/automotive-a...cle-batteries/

 

[PaulRainbow]

Indeed. And the gain will be even smaller than that because of the inability of that type of alternator to produce its rated power continuously.

Make your mind up. In post #21 you said

A car-type alternator, 65 amps, can be expected to produce about 30 or maybe 40 amps more or less continuously.

Now you're saying it will be even less ? Hardly seems worth fitting an alternator.

As to the guy with the 1000 amp/hour bank which will only accept 50 amps of charge --

He needs to do a 20-hour capacity test. I will bet 3 pints in the Solent pub of his choice, that those batts are heavily sulpahted and are down to less than 50% of their original capacity (and lead batts should be scrapped after 80%). And how did they get that way?

https://marinehowto.com/automotive-a...cle-batteries/

Ah, you've read a website, you clearly must know all about the subject then :encouragement:

Edit, hope you battery knowledge is better than your link posting

 

[geem]

What you are seeing is a function of either regulation, or else your bank is heavily sulfated. A healthy 1000 a/h bank is no way limited to 50 amps and in fact it is unhealthy to charge it at that rate -- it needs at least 0.1C or 100 amps. If it suits you -- fine. But normal FLA batteries are capable of absorbing at least 0.25C and AGM much more -- but the regulator needs to provide the corresponding voltage, and the alternator needs to be capable of dissipating the heat generated in the process of producing that much power.

My alternator produces its full output from about 2300 RPM (this is just a function of pulley sizes) and produces about 90 amps (@24v) from 1600 RPM. I monitor the current from my alternator with a shunt and ammeter. My 420 a/h bank (@24v) will take the full output of the alternator (or 90 -- 100 amps if the main engine is running slower) during the whole bulk phase -- roughly two hours from 50% SOC. At 85% or so, the process reaches absorption voltage and the acceptance rate tapers off.

If your batteries are only accepting 50 amps, then you have a problem. Flooded lead acid batteries have an acceptance rate of about 0.25C; AGM about 1C. If your bank is flooded lead acid, it should accept up to 250 amps during the bulk phase and NEEDS at least 100 amps.

I dont have a problem with my batteries. The ability to take the charge depends on the voltage on the batteries when you first start the alternator running. Since my batteries dont drop below 25.4v over night, my alternator hits the limiting voltage of the regulator very quickly so I dont see large amps at my alternator. If you are cycling you battery bank to low voltage levels then you will see the alternator putting it back. Dont have that senario with my installation.

 

[VicS]

Make your mind up. In post #21 you said Now you're saying it will be even less ? Hardly seems worth fitting an alternator.



Ah, you've read a website, you clearly must know all about the subject then :encouragement:

Edit, hope you battery knowledge is better than your link posting

Unkind!

The link as originally posted in #21 works just fine !

Not read it though so dont know if its relevant

 

[William_H]

Indeed. And the gain will be even smaller than that because of the inability of that type of alternator to produce its rated power continuously.

As to the guy with the 1000 amp/hour bank which will only accept 50 amps of charge --

He needs to do a 20-hour capacity test. I will bet 3 pints in the Solent pub of his choice, that those batts are heavily sulpahted and are down to less than 50% of their original capacity (and lead batts should be scrapped after 80%). And how did they get that way?

https://marinehowto.com/automotive-a...cle-batteries/

"Lead acid batteries should be scrapped if less than 80% of their capacity." NOOOOO Much depends on how the batteries are tested but I reckon even new batteries may not test 80% of claimed or rated capacity if discharged from a typical load and current. There is no reason to scrap any battery unless it fails to do the job you ask of it. ie start the engine or provide enough Amp hours to meet your needs ina typical live aboard senario. ol'will

 

[matthewriches]

Just seen this thread. So what gear to you have fitted to your boat Pau Amma? What prompted your question to ask for "I would like to get more efficient charging into the batteries". Are you finding you have issues? If not, don't fix what's not broken? Have you found a charge deficiency? Is that why you're currently replacing your battery bank? Is someone trying to sell you something?


Not directly relevant.....

What Dockhead has spoken about is very real (although maybe not relevant to this topic), certainly from a pleasure boat point on Grand Banks, Nordhavn and other large motorboats ordinarily stemming from the US. Can't speak for sailing vessels as I try to avoid them. Also very relevant on small commercial tugs, pilot launches, etc. An alternator on each engine for separate engine start banks, then a huge socking alternator (or more) for ships load, domestic load, etc.

I did mention on here once before about the Hitachi alternators for instance; they're rubbish at powering a medium sized single engine motorboat for example. Go out on anchor overnight, have a good usage (TV, fridge, lights, etc), turn engine on in the morning after a late breakfast and see how quickly the alternator limits itself. I only found this out after extensive testing for a customer with a nearly new boat which ruined 2 battery banks in less than 4 months because the batteries were never being charged sufficiently. Luckily only cheap LA batts. River mooring, no shore support for charger, no solar, etc...

Take my Volvo alternators for instance, twin engines, each with a 12v 100 amp alternator, they're bloody massive in comparison to an 80-110 amp alternator as fitted to some Beta, Sole, Shire etc. They're massive because they're designed to do something day in, day out as opposed to just for a short while so are designed to work therefore much larger windings + bigger everything. The Volvo's would be happy to run and produce charge if required, all day every day. A little Barrus offering will not, and would end up limiting, shutting down or burning up if it was asked to charge maybe 800Ah battery bank from flat. Much the same as our crane, it has a starter alternator then a bloody great alternator for maintaining usage all day, every day.

It all comes down to design. Many older boats have insufficient charging systems as 30 years ago, electricity whilst not underway was a luxury. Batteries were nothing like they were now and vastly more expensive for a, by todays standards, feeble offering. It is possible for people to just bolt on lots more batteries to a 30 year old system that has not also had a parallel upgrade..... of course you're asking for trouble.

One of my customers on the Medway did it exactly that. 40 year old sailing boat. Old original Volvo engine, pre-dates me. The guy had put on 6x huge gel batteries which were fine with shore charger but when sailing and anchoring, which is his thing, he had issues after about 5-6 days. Back on shore power, they were fine. Long and short was the alternator was putting out less than 20 amps, averaging 11 amps over a couple of hours watching. Fitted a 2nd hand alternator from an old donkey engine = 65 amps averaging 50 amps. And it didn't do what I thought it was going to do and load the engine too much. Just purely technology has moved on.

Of course you could fit a generator of many thousand kva but we don't know if you have a little bathtub or the Titanic.

 

[Dockhead]

"Lead acid batteries should be scrapped if less than 80% of their capacity." NOOOOO Much depends on how the batteries are tested but I reckon even new batteries may not test 80% of claimed or rated capacity if discharged from a typical load and current. There is no reason to scrap any battery unless it fails to do the job you ask of it. ie start the engine or provide enough Amp hours to meet your needs ina typical live aboard senario. ol'will

Well, 80% is the industry standard for end of life of deep cycle batteries, but you are right that it's not necessarily the CLAIMED capacity -- it's best to measure against the measured stabilised capacity after a certain number of initiation cycles shortly after new.

There are a few different ways to measure capacity of lead acid batteries, but the simplest way is to use a carbon pile battery load tester set to 0.2C and measure the time it takes to get to 1.75v per cell.

You can use them beyond 80% if they are still doing what you need, but by that time they will be accepting much less charging current, and you are running a risk of a shorted cell, which can cause a fire, so 80% is a good time to get rid of them.

 

[PaulRainbow]

Just seen this thread. So what gear to you have fitted to your boat Pau Amma? What prompted your question to ask for "I would like to get more efficient charging into the batteries". Are you finding you have issues? If not, don't fix what's not broken? Have you found a charge deficiency? Is that why you're currently replacing your battery bank? Is someone trying to sell you something?

<snip>

Of course you could fit a generator of many thousand kva but we don't know if you have a little bathtub or the Titanic.

I asked this in post #2 Matt, but nothing has been said. Doesn't stop the suggestions for all sorts of alterations.

 

[lw395]

What it all comes down to is that recharging batteries takes both current and time.
If the alternator is current limited to a low value, you will need more time.
On a sailing boat which actually sails, engine hours can be quite low.

You need to work out what charge is required.
Allow for the inefficiency of charging.
Then look at the engine hours available.

If you want to push in a high current, you will need an aggressive charging voltage, not the default 14V of older basic alternators.

Alternators on the main engine are basically a poor means of charging the house batteries on a sailing yacht. A decade ago, a generator was preferred. These days most people are using solar. Shore power is always nice to have, and many yachts rely on it happily.

The other side of the equation is to limit the power you use. Back in the day, a 10W lamp to read a book by for a couple of hours was a luxury....

 

[PaulRainbow]

There are a few different ways to measure capacity of lead acid batteries, but the simplest way is to use a carbon pile battery load tester set to 0.2C and measure the time it takes to get to 1.75v per cell.

Could you explain in more detail how you would do this please ?

What tester would you recommend ?

 

[Dockhead]

Could you explain in more detail how you would do this please ?

What tester would you recommend ?

Testing capacity, and logging the results, is a very useful thing to do. It's actually essential if you are using an amp-counting battery SOC meter and want to get any useful information out of it.

There are a number of different ways to do it, and I'm not familiar with all of them. The method I have used and seen used requires a variable resistive load, which can be provided either by a carbon pile load tester (like this one: https://www.sipuk.co.uk/sip-06446-carbon-pile-tester.html), or some people just use an inverter with some combination of loads on it, like heaters. You make sure the bank (or individual battery) is fully charged, then adjust the load to 0.2C, connect it, and measure the time it takes to reach 1.75v per cell (21v for a 24v bank). Multiply the time by the load in amperes and you have the precise capacity, measured directly.

 

[Dockhead]

What it all comes down to is that recharging batteries takes both current and time.
If the alternator is current limited to a low value, you will need more time.
On a sailing boat which actually sails, engine hours can be quite low.

You need to work out what charge is required.
Allow for the inefficiency of charging.
Then look at the engine hours available.

If you want to push in a high current, you will need an aggressive charging voltage, not the default 14V of older basic alternators.

Alternators on the main engine are basically a poor means of charging the house batteries on a sailing yacht. A decade ago, a generator was preferred. These days most people are using solar. Shore power is always nice to have, and many yachts rely on it happily.

The other side of the equation is to limit the power you use. Back in the day, a 10W lamp to read a book by for a couple of hours was a luxury....

Alternators on the main engine can be a very good way of charging the house batteries, under the right circumstances, and using the right equipment.

With lithium batteries, an alternator on the main engine can be an IDEAL way to produce power, and many people are going over to this. Lithium does away with the necessity to put a long finishing charge on the batteries, which is unhealthy for the main engine if it's not doing propulsion work at the same time. So with a large capacity alternator and lithium batteries, you can produce whatever amount of power you need, and shut down the engine, and be happy. I know a few different people who are building or who have built new boats who have cut the generator from the specification, in this way.

But even with lead batteries, a properly regulated heavy duty alternator can produce a great deal of useful power. It's a nice bonus that it is often produced incidentally to propulsion.

Solar is great if you can fit it, but I reckon less than 10% of UK yachts actually have any solar power, and much fewer still have enough solar capacity to supply all of their needs. So for the great majority of folks, understanding alternators and how to configure them properly is really useful.

I have a heavy duty low speed generator on my yacht, 6.5kW, but the alternator on the main engine STILL produces probably half of the power I use on board, which I don't get from shore power.

 

[pvb]

Testing capacity, and logging the results, is a very useful thing to do. It's actually essential if you are using an amp-counting battery SOC meter and want to get any useful information out of it.

There are a number of different ways to do it, and I'm not familiar with all of them. The method I have used and seen used requires a variable resistive load, which can be provided either by a carbon pile load tester (like this one: https://www.sipuk.co.uk/sip-06446-carbon-pile-tester.html), or some people just use an inverter with some combination of loads on it, like heaters. You make sure the bank (or individual battery) is fully charged, then adjust the load to 0.2C, connect it, and measure the time it takes to reach 1.75v per cell (21v for a 24v bank). Multiply the time by the load in amperes and you have the precise capacity, measured directly.

I guess you were thinking of an amp-hour counting battery SOC meter. With the method you've proposed, you'll get a precise capacity certainly, but it will be at the 5-hour rate, not at the 20-hour rate which is the general standard for quoting leisure battery capacities. Most battery SOC meters need the capacity to be programmed in at the 20-hour rate, so the results of your test method will need converting. As a rough guide, a typical 100Ah battery (capacity at the 20-hour rate) will only have a capacity of 75-80Ah at the 5-hour rate (depending of course on the battery's Peukert value).

 

[Dockhead]

I guess you were thinking of an amp-hour counting battery SOC meter. With the method you've proposed, you'll get a precise capacity certainly, but it will be at the 5-hour rate, not at the 20-hour rate which is the general standard for quoting leisure battery capacities. Most battery SOC meters need the capacity to be programmed in at the 20-hour rate, so the results of your test method will need converting. As a rough guide, a typical 100Ah battery (capacity at the 20-hour rate) will only have a capacity of 75-80Ah at the 5-hour rate (depending of course on the battery's Peukert value).

Sorry, you are correct! Brain fart. I should have said .05C not 0.2C!

You do want the 20 hour rate. Thanks for the correction.

 

[PaulRainbow]

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.