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17 minutes ago, MtB said:

 

Surely avoiding this effect was the whole point of Tony1 installing his lithium battery bank.

 

 

 

 

Yes thats about it- as you'll know, you can leave them at 25%, 50% or 85%, depending on what the sun delivers that day, and they dont suffer any ill effects. 

 

Reading in the literature, I got an impression that charging was a continuous and repeatable process- bulk, absoprtion, float, etc etc.

But in reality its mostly bulk charging, whenever and wherever it comes from.

I set off cruising at lunchtime today, with the batteries at about 58%, and there wasnt a lot of solar, so I disconnected it via the app in order to monitor the engine charge alone (and promptly went into some bushes coming out of bridge hole, which served me right). So for a while it was a steady 40 amps or so of charge.

Then an hour or so in, the sun started to appear overhead, so I got the  solar going again (waste not want not, and all that), and for a while I had almost 60 amps of solar as well.

The lithiums just seemed to soak it all up, and the SoC rose rapidly. 

The MPPTs did actually go into float at about 80% SoC, but thats because I was fiddling with the charging voltage, and they were a bit premature. Its all a bit trial and error at the moment. 

 

So in reality, it can be very variable, with lots of solar one minute, very little the next. You just bung whatever charge you've got into them, whenever you can- and its nearly all bulk charging, I think.

 

ETA- and apologies for my meandering.  your main point: Yes, you stop the charging whenever you want or need to, thankfully no need for an 8 hour charge to top up that last 10%. You dont even want that last 10%, because we're told that will shorten the battery life.

I'm getting the impression that the practice of float charging is not necessary with lithiums, and maybe not desirable.

 

Edited by Tony1
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39 minutes ago, Tony1 said:

I'm getting the impression that the practice of float charging is not necessary with lithiums, and maybe not desirable.

 

Getting the impression? 

 

From my own reading on lithiums, float charging is a total and utter no-no, as on float charge the SoC will creep up to 100% then exceed it, destroying the cells in the process. 

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6 hours ago, MtB said:

 

Getting the impression? 

 

From my own reading on lithiums, float charging is a total and utter no-no, as on float charge the SoC will creep up to 100% then exceed it, destroying the cells in the process. 

It depends on the float voltage. If the float voltage is the same as the rested voltage of the batteries at their present SoC, they don’t realise they are on float and no current flows into them, but it means that any loads from the boat are supplied by the alternator/solar/mains charger, not by the batteries.

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44 minutes ago, nicknorman said:

It depends on the float voltage. If the float voltage is the same as the rested voltage of the batteries at their present SoC, they don’t realise they are on float and no current flows into them, but it means that any loads from the boat are supplied by the alternator/solar/mains charger, not by the batteries.

 

Well yes, but if the float voltage is lower or equal to the battery voltage, then I suggest the battery is not on "float charge".  

 

I propose a new term is found for the charge voltage being set to accurately match the cell voltage, in anticipation of a load pulling the battery voltage down a bit and the charger then delivering the load current.

 

"Standby charge" perhaps?

 

Edit to add:

 

Thinking about this some more, the term "float charge" is a term borrowed from LA battery management, and in older times used to be called "trickle charge". Once these terms are imported to LFP technology, the term "float charge" is being used differently from "trickle charge", it seems to me.

 

The problem with trickle charging a LFP cell is once it reaches 100% SoC, lithium ions can no longer be absorbed into the anode and lithium gets 'plated' onto the anode as metal. This causes a reduction in capacity. An effect known as "lithium plating", according to the Nordkyn site. 

 

Further, I often read that LFP batteries can absorb as much current as one's charge sources can deliver. Whilst this may be true, excess charge currents also cause lithium plating (as the lithium ions need time to migrate deep into the anode) leading to reduction in battery capacity. The maximum charge rate to safely avoid lithium plating is a surprisingly low 0.3C, again according to Nordkyn.

 

 

Edited by MtB
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7 hours ago, MtB said:

 

Getting the impression? 

 

From my own reading on lithiums, float charging is a total and utter no-no, as on float charge the SoC will creep up to 100% then exceed it, destroying the cells in the process. 

 

Yes, I must admit that 'getting the impression' does rather understate my own level of conviction on the issue there, but to tell the truth I am a bit wary of making declarative statements about any of this, having quite limited understand of electrics as a whole, and only having 6 months day-to-day usage experience within a very limited CCing context. 

 

The management of lead acid batteries has developed over decades into a well-understood and precise body of information, about which there is very little dispute.

But the management of lithium batteries is still developing, and in my case one of my chief sources of info is here, from people like Nick, Peter, Ian, and several other very helpful and well informed contributors.  

 

 

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3 minutes ago, Tony1 said:

 

The management of lead acid batteries has developed over decades into a well-understood and precise body of information, about which there is very little dispute.

But the management of lithium batteries is still developing, and in my case one of my chief sources of info is here, from people like Nick, Peter, Ian, and several other very helpful and well informed contributors.  

 

 

I'm inclined to disagree. LFP batteries in particular (there are loads of types of lithium batteries other than LFP) have been around for decades and the technology of managing them is broadly mature and well understood. They need very different management from LA batteries though and it is the understanding amongst boaters and leisure users that is still developing. I strongly recommend spending a few dozen hours reading the (completely new and updated) LFP pages on the Nordkyn site to gain a good basic understanding of LFP batteries. 

 

Start here I suggest:

https://nordkyndesign.com/lithium-battery-banks-fundamentals

 

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1 hour ago, nicknorman said:

It depends on the float voltage. If the float voltage is the same as the rested voltage of the batteries at their present SoC, they don’t realise they are on float and no current flows into them, but it means that any loads from the boat are supplied by the alternator/solar/mains charger, not by the batteries.

 

There seems to be a general agreement that lithiums are least stressed around 50% SoC, and my rather primitive deduction from this was that they will last longer if they spend more time closer that level than if they spend the majority of their time at say 85% SoC.

So my general approach is not to let them sit above say 70% SoC for too long, but rather to stop any charging at all, and allow them to offload some of their charge to the boat systems.

 

This is why I set up the 80-85% SoC charger disconnect using the BMV, rather than allowing the 'float' phase to happen. I didn't want the MPPTs to replace any used charge immediately, but rather to get them charged, and then to stop, and thus allow the batteries to discharge down to say 60% before any charging restarted. 

 

 

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1 hour ago, MtB said:

 

Well yes, but if the float voltage is lower or equal to the battery voltage, then I suggest the battery is not on "float charge".  

 

I propose a new term is found for the charge voltage being set to accurately match the cell voltage, in anticipation of a load pulling the battery voltage down a bit and the charger then delivering the load current.

 

"Standby charge" perhaps?

 


Although it seems to be, the concept isn’t really any different in principle. When we leave our boat it’s on shore power via the Combi. When we had LA batteries the float voltage (to which the charger switched after the batteries reached 100% SoC) was 13.25v. On returning a week/month later, the indicated current into the batteries would be zero within the accuracy of measurement.

Now the float voltage is 13.15v and on arriving back at the boat, the indicated current into the batteries is zero, but of course the SoC is around 50% rather than the 100% for LA. So a similar voltage, same current, different SoC.

 

Really the only major difference is the time it takes for the current to settle at zero. Probably several days for LA, just a very short time for Li

 

Incidentally ive set the Combi to “forced float” so that the charge voltage is fixed (at whatever I’ve set it to) and there are no longer the bulk and absorb phases on the charger display, it is always in float mode even if it happens to be charging at 100A.

 

Edited by nicknorman
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Many of us are still using much the same technology - lead acid batteries- that have been used for a century or so and still charging them in much the same way but with an alternator instead of a somewhat more primitive car dynamo.  There is a case for managing peoples expectations here as well. Most boats have more miles of wiring than an early airliner and many builders cram in everything from home cinemas to heated slippers (I made that bit up but you see what I mean) Look at the boats that are reviewed in Waterways World, full of stuff. Battery banks like a submarine, hundreds of amps and nothing special in the way of charging except a second alternator on the poor old engine. You can take all those amps out remarkably quickly but next day it will take a very long time to put them back so use them very carefully.

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9 hours ago, TheBiscuits said:

 

Well yes, but you wouldn't have working lights or water except for the first two days on a new set of batteries.

 

If you recharge them until they die you have working services every day.

 

There's a balance to be struck though.  The electrical experts on this forum advocate charging daily until a tail-current of 1-2% of capacity is reached.  The problem with that is that the last few percentage points takes up about half of the overall charging time.  So you may be paying £3-4 just to get from a 5% tail current to a 1.5% tail current, every time you do it.  If you don't bother doing this last bit (or only do it occassionally), your batteries lose capacity.  Somewhere there's a sweet spot in all this but I don't have the patience to do the maths to work out exactly where that sweet spot is.  So I go by my own hunch, and this is what I do:

 

1.  Buy 3 x bog-standard 110ah leisure batteries.

2. Trust my solar to pickup most of my needs for about 7 month of the year.  Run a genny when my consumption is high or it's very gloomy out.

3. Come early October, start paying more attention to what my batteries are doing.  Especially what charge they're at first thing in the morning.  Run genny accordingly, when needed for a couple of hours or so.  Make sure I charge up everything while the genny is on.

4.  Come November-ish, turn the fridge off and switch to outside cool-box.  Start running genny more days than not, as needed.  Once a week or so, run the genny for 4-5 hours.

5.  Expect to replace batteries every 3 years or so. (£250-ish)

 

Note:  I work from home and have a laptop and connected monitor running for approx 8 hours a day.  When the fridge goes off, that's by far my highest power draw.

 

Now I could fork out a huge sum on fancy deep cycling batteries, but that would only be worthwhile if I was going to charge them properly.  That would mean something like 3 times the engine or genny running for half the year, which would also cost me a lot of extra money in fuel, servicing and wear and tear.  A very quick sum in my head tells me that it would come to a load more than £250 every three years.  I also get the benefit of less annoying engine noise and pollution for me and other boaters nearby.

 

Lithium is a different ball-game, and I may go that way at some point.

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14 minutes ago, MtB said:

 

I get the feeling that soon, LA batts will feel desperately old fashioned....

Only for those that rarely move their boats a decent amount and don't reap the benefit of charging on the move 😉

For many boats LA is a perfectly good solution. My batteries never drop below 75% and that's not even moving every day so spending a grand or so on lithiums just doesn't seem a good use of any spare cash I might have😎

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3 minutes ago, MtB said:

 

I get the feeling that soon, LA batts will feel desperately old fashioned....

 

I joke about being a lithium snob, but my personal view is that we aren't quite there yet, in terms of lithium being an 'easy' replacement option for lead acid.

 

We are half way there, at least. The lithium batteries are now cheap enough that if they do in fact last for the 7-10 years that people say they can, then they are certainly cheaper than lead acid.

 

But where I feel the real complication and expense arises is in the charging and management/protection systems.

And until simpler, more integrated systems become available, I suspect that many boaters will steer clear of lithiums.

 

Once you get lithiums, you suddenly have to consider issues like alternator overheating, high/low voltages killing the batteries, avoiding high stress situations like high or low SoC- there is a lot to think about, and I quite understand that many people prefer to keep things simple, and live with the known limitations of lead acids.  

 

 

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16 minutes ago, Tony1 said:

Once you get lithiums, you suddenly have to consider issues like alternator overheating, high/low voltages killing the batteries, avoiding high stress situations like high or low SoC- there is a lot to think about, and I quite understand that many people prefer to keep things simple, and live with the known limitations of lead acids.  

 

I agree, complexity accumulates really quickly with LFP batts but the points I highlighted are covered and dealt with by a well-designed battery management PCB. Similarly, if charged mainly by solar, the solar controller (probably) does not care about being unexpectedly disconnected, and nor does the alternator if the crude protection method of bunging an old LA batt in parallel is employed. 

 

I'm intrigued by the idea of using a B2B charger to protect the alternator from high voltage disconnection instead, and also from high current overheating, but haven't thought it though yet in any detail.

 

 

 

 

 

22 minutes ago, Loddon said:

Only for those that rarely move their boats a decent amount and don't reap the benefit of charging on the move 😉

 

 

Quite so, which probably comprises the majority of CCers so a pretty big sector. 

Edited by MtB
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34 minutes ago, MtB said:

 

I agree, complexity accumulates really quickly with LFP batts but the points I highlighted are covered and dealt with by a well-designed battery management PCB. Similarly, if charged mainly by solar, the solar controller (probably) does not care about being unexpectedly disconnected, and nor does the alternator if the crude protection method of bunging an old LA batt in parallel is employed. 

 

I'm intrigued by the idea of using a B2B charger to protect the alternator from high voltage disconnection instead, but haven't thought it though yet in any detail.

 

 

 

I think what deters people from adopting lithiums is also their lack of certainty over the final cost for the battery management systems. 

 

My own B2B-based solution isnt the best, if I'm honest.

Its probably the simplest to install, if you have to do the job with no professional help, and if you're ok with a fairly modest output of about 45 amps.

 

But those Sterling BB1260s are about £300 a pop, and I normally get about 45 amps from them (which I think means the alternator is putting about 55-60 amps into them)

For less than the price of two of those units you could get a pro like Ed Shiers to fit a mastervolt regulator, which will do a far more efficient charging job, and it also includes features like alternator temp monitoring (so it will throttle back at your set 'warning' temp), precise control over the current output at various rpms, and a safe stopping of the charge process, rather than an abrupt disconnection.  You can really fine tune them to get the most from your alternator. Not to mention much simpler wiring etc.

Those regulators even work with BMV712s, so I could even control the regulator based on parameters like SoC. 

 

But I feel like I'm kind of stuck with the B2B method, having invested so much in it, and to be fair it does work if you need a cheap quick fix, and can accept the limitations.

As you say, the lead acid source battery gives you a buffer to cope when the B2B stops its charging, and the B2B controls the current very well. 

But its a minefield- you dont know for sure that your typical alternator on a 38hp engine is going to be able to cope even with the B2B output. Some of the smaller/cheaper ones might overheat even giving out 45 amps, and by that time you've already shelled out the cash on the B2B....

 

I think the biggest disappointment for me was the alternator itself, and finding out that once my batteries were drawing a continuous steady  current from the alternator, it overheated.

It seems that my 100 amp alternator is only good for 100 amps for a few minutes, but on a continuous basis it can only deliver about 50-55 amps before overheating.

 

 

Edited by Tony1
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6 minutes ago, Tony1 said:

 

I think what deters people from adopting lithiums is also their lack of certainty over the final cost for the battery management systems. 

 

My own B2B-based solution isnt the best, if I'm honest.

Its probably the simplest to install, if you have to do the job with no professional help, and if you're ok with a fairly modest output of about 45 amps.

 

But those Sterling BB1260s are about £300 a pop, and I normally get about 45 amps from them (which I think means the alternator is putting about 55-60 amps into them)

For less than the price of two of those units you could get a pro like Ed Shiers to fit a mastervolt regulator, which will do a far more efficient charging job, and it also includes features like alternator temp monitoring (so it will throttle back at your set 'warning' temp), precise control over the current output at various rpms, and a safe stopping of the charge process, rather than an abrupt disconnection.  You can really fine tune them to get the most from your alternator. Not to mention much simpler wiring etc.

Those regulators even work with BMV712s, so I could even control the regulator based on parameters like SoC. 

 

But I feel like I'm kind of stuck with the B2B method, having invested so much in it, and to be fair it does work if you need a cheap quick fix, and can accept the limitations.

As you say, the lead acid source battery gives you a buffer to cope when the B2B stops its charging, and the B2B controls the current very well. 

But its a minefield- you dont know for sure that your typical alternator on a 38hp engine is going to be able to cope even with the B2B output. Some of the smaller/cheaper ones might overheat even giving out 45 amps, and by that time you've already shelled out the cash on the B2B....

 

I think the biggest disappointment for me was the alternator itself, and finding out that once my batteries were drawing a continuous steady  current from the alternator, it overheated.

It seems that my 100 amp alternator is only good for 100 amps for a few minutes, but on a continuous basis it can only deliver about 50-55 amps before overheating.

 

 

The ocean paddlers with pots of cash and crew use water cooled alternators.  perhaps this is the way to go with lithium?

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2 minutes ago, Tony1 said:

 

I think what deters people from adopting lithiums is also their lack of certainty over the final cost for the battery management systems. 

 

My own B2B-based solution isnt the best, if I'm honest.

Its probably the simplest to install, if you have to do the job with no professional help, and if you're ok with a fairly modest output of about 45 amps.

 

But those Sterling BB1260s are about £300 a pop, and I normally get about 45 amps from them.

For less than the price of two of those units you could get a pro like Ed Shiers to fit a mastervolt regulator, which will do a far more efficient charging job, and it also includes features like alternator temp monitoring (so it will throttle back at your set 'warning' temp), precise control over the current output at various rpms, and a safe stopping of the charge process, rather than an abrupt disconnection.  You can really fine tune them to get the most from your alternator. Not to mention much simpler wiring etc.

Those regulators even work with BMV712s, so I could even control the regulator based on parameters like SoC. 

 

But I feel like I'm kind of stuck with the B2B method, having invested so much in it, and to be fair it does work if you need a cheap quick fix, and can accept the limitations.

As you say, the lead acid source battery gives you a buffer to cope when the B2B stops its charging, and the B2B controls the current very well. 

But its a minefield- you dont know for sure that your typical alternator on a 38hp engine is going to be able to cope even with the B2B output. Some of the smaller/cheaper ones might overheat even giving out 45 amps, and by that time you've already shelled out the cash on the B2B....

 

I think the biggest disappointment for me was the alternator itself, and finding out that once my batteries were drawing a continuous steady  current from the alternator, it overheated.

It seems that my 100 amp alternator is only good for 100 amps for a few minutes, but on a continuous basis it can only deliver about 40-45 amps before overheating.

 

 

I realise that your system “evolved”  but you’ve spent £300 x 2 on B2Bs (or maybe x3). For that money yes you could have had one of the fancy alternator controllers, the Mastervolt or Wakespeed ones for example. Yes they do need to be connected to the internals of the alternator and I think that is the stumbling block for many, but the reality is it isn’t hard to get rid of the built in regulator and connect the alternator brushes to the controller plus a phase (W) wire.
 

So to be brutally honest and with the benefit of hindsight I think that would have been your better tactic, but of course it’s easy to be wise after the event! And not just you, you’ll recall that Dr Bob declined one of my home made alternator controllers in favour of the B2B approach because he didn’t fancy invasive surgery on his shiny new 240A alternator.

 

But eventually I think the alternator controller method will prevail and of course Ed is leading the charge on doing that commercially.

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27 minutes ago, Tracy D'arth said:

The ocean paddlers with pots of cash and crew use water cooled alternators.  perhaps this is the way to go with lithium?

 

I do think that as and when lithiums batteries become more popular, there will be a growing focus on the issue of alternator charging- especially if diesel prices increase.

People will resent having to run their engine for 3 hours to obtain 100Ah or so, when a better alternator could give them that same charge in an hour or less. 

 

You dont even have to go water cooled as such, I think. There are alternators that will put out a continuous 100 amps or more, but they often need things like poly V belts to drive them properly- which arent that straightforward to fit onto the smaller engines like my canaline 38. 

 

 

 

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31 minutes ago, nicknorman said:

I realise that your system “evolved”  but you’ve spent £300 x 2 on B2Bs (or maybe x3). For that money yes you could have had one of the fancy alternator controllers, the Mastervolt or Wakespeed ones for example. Yes they do need to be connected to the internals of the alternator and I think that is the stumbling block for many, but the reality is it isn’t hard to get rid of the built in regulator and connect the alternator brushes to the controller plus a phase (W) wire.
 

So to be brutally honest and with the benefit of hindsight I think that would have been your better tactic, but of course it’s easy to be wise after the event! And not just you, you’ll recall that Dr Bob declined one of my home made alternator controllers in favour of the B2B approach because he didn’t fancy invasive surgery on his shiny new 240A alternator.

 

But eventually I think the alternator controller method will prevail and of course Ed is leading the charge on doing that commercially.

 

One of the many pluses of the controller route is that you dont lose energy in the same way as a B2B. My B2B units take in 60 amps but I rarely see more than 45-50 amps from them, so I'm looking at a 15-20% loss.

Whatever your alternator can put out, you will pretty much get into your batteries.

 

Problem is that there are not too many marine electricians around, and even fewer with the knowledge and skill to install a controller, whereas even a DIYer can install a B2B- so there will always be a few people who like the look of that option. 

 

In my case I thought I'd be ok with 45 amps of charge, but I didnt think it through, and in practice I'm not. I was moored in a green tunnel with almost no solar not long ago, and I think I ran the engine for 3 hours that day- and I just dont think thats a good long term proposition. 

 

I thought one B2B was ok, then I got two, and now I find myself with four of the things.

To paraphrase Macbeth, I am in B2Bs so far stepped, that it would be more tedious to return than to continue!

 

 

 

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6 hours ago, Tony1 said:

 

There seems to be a general agreement that lithiums are least stressed around 50% SoC, and my rather primitive deduction from this was that they will last longer if they spend more time closer that level than if they spend the majority of their time at say 85% SoC.

So my general approach is not to let them sit above say 70% SoC for too long, but rather to stop any charging at all, and allow them to offload some of their charge to the boat systems.

 

This is why I set up the 80-85% SoC charger disconnect using the BMV, rather than allowing the 'float' phase to happen. I didn't want the MPPTs to replace any used charge immediately, but rather to get them charged, and then to stop, and thus allow the batteries to discharge down to say 60% before any charging restarted. 

 

 

 

The LiFePO4 cell/battery manufacturers who provide data are now pretty much saying that so long as you stay between 10% and 90% SoC what you do in between doesn't really matter, in the sense that total capacity over lifetime (in MWh) is hardly affected -- this is in the guarantee terms of manufacturers like BYD where the BMS is part of the battery and controls charging. This makes sense because if you look at the charge/discharge curves the voltage is a gentle slope in this region and then curves up about 90% and down below 10%, implying that the chemical reaction internally is changing.

 

Nothing wrong with using tighter limits if you want to, but this does reduce the usable capacity and almost certainly doesn't increase total energy stored over lifetime, you just have to charge more often -- for example cycling between 30% and 70% the lifetime in cycles roughly doubles compared to 10% to 90% -- which sounds good! -- but then you need about twice as many cycles, so the battery lifetime in years is the same. Of course if the charge zigzags up and down on a daily basis (e.g. charge from solar, discharge from domestic loads) it'll change by however much the load and battery size determine, and in this case keeping it roughly centred on 50% is best for obvious reasons. If the charge is coming from a generator then there's no problem using the full 10%-90% range and running the generator less often but for longer periods instead of every day if that's what you want to do -- unless it also heats hot water in which case you probably want to run it daily for as long as necessary.

 

The point is that unlike lead-acids the charging regime with LiFePO4 is no longer determined by the need to treat the batteries in a particular way, you can choose how you use them to suit other aspects of your lifestyle -- together with no need to run for long times to fully charge, this is the biggest advantage of LiFePO4, you can do what you want with them.

 

As always these numbers are not exact, but any lifetime differences with charging regime inside the 10%-90% limits are small. Going down to 0% and up to 100% occasionally and for limited time periods is also OK (e.g. when you really need to do it), but shouldn't be done routinely or for any significant length of time.

Edited by IanD
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3 hours ago, Tony1 said:

 

I do think that as and when lithiums batteries become more popular, there will be a growing focus on the issue of alternator charging- especially if diesel prices increase.

People will resent having to run their engine for 3 hours to obtain 100Ah or so, when a better alternator could give them that same charge in an hour or less. 

 

You dont even have to go water cooled as such, I think. There are alternators that will put out a continuous 100 amps or more, but they often need things like poly V belts to drive them properly- which arent that straightforward to fit onto the smaller engines like my canaline 38. 

 

 

 

 

Those really big alternators (multi-kilowatt) are also often *very* expensive (e.g. Balmar, anything up to £2000 each). I looked at this intensively a couple of years back, and it was a lot cheaper (for a new engine) to use a couple of the biggest standard low-cost alternators with an external controller if your engine supports that, as well as being supported by the engine manufacturer -- for example a Beta 43 can have 2 175A 12V alternators fitted (poly-V belt to each) for less than half the cost. On an existing engine if you have to start replacing/adding crank pulleys (assuming they can be fitted) it could get expensive.

 

Alternatively if you have an inverter/charger that supports it (e.g. Victron Quattro) you could fit a Travelpower and connect it to one of the AC inputs, this is likely to be possible on a wider range of engines. It has the advantage of being more efficient than 12V alternators so doesn't run as hot, but is also not exactly cheap -- but then, neither is a lithium battery bank...

 

Still doesn't get round the problem that running a (40bhp?) propulsion diesel for hours while putting out maybe 5bhp to charge batteries (or generate AC) while moored is horribly inefficient and increases wear and tear 😞

Edited by IanD
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1 hour ago, IanD said:

 

The LiFePO4 cell/battery manufacturers who provide data are now pretty much saying that so long as you stay between 10% and 90% SoC what you do in between doesn't matter, in the sense that total capacity over lifetime (in MWh) is hardly affected -- this is in the guarantee terms of manufacturers like BYD where the BMS is part of the battery and controls charging. This makes sense because if you look at the charge/discharge curves the voltage is a gentle slope in this region and then curves up about 90% and down below 10%, implying that the chemical reaction internally is changing.

 

Nothing wrong with using tighter limits if you want to, but this does reduce the usable capacity and almost certainly doesn't increase total energy stored over lifetime, you just have to charge more often -- for example cycling between 30% and 70% the lifetime in cycles roughly doubles compared to 10% to 90% -- which sounds good! -- but then you need about twice as many cycles, so the battery lifetime in years is the same.

 

As always these numbers are not exact, but any lifetime differences with charging regime inside the 10%-90% limits are small. Going down to 0% and up to 100% occasionally and for limited time periods is also OK (e.g. when you really need to do it), but shouldn't be done routinely or for any great length of time.

 

Thanks Ian, I'll probably stick with 85% SoC as a general 'soft' guideline, but I wont worry too much about going up to 90%. 

In fact just yesterday I let them get up to almost 90% since I was cruising, and it looked like today would be mainly overcast, and I wasnt sure I'd be able to find a mooring spot with half decent solar. 

As it turned out I found a spot that was reasonable, and in just a few hours intermittent sun this afternoon they've gone up to 80%.

 

So for me personally, whether I go to 80, 85 or 90 depends on the context. If I know tomorrows sunny and I have a reasonably clear view of the sun, I'll stop charging at 80%. 

And conversely, as the days get shorter, if there is a chance to get a good blast of solar I'll probably take it, even if it means going up to 90% SoC, because I know the following days wont be as fruitful.

 

I only have about 400Ah, (three with 135Ah each) and that does limit your wiggle room in making these decisions. Another 135Ah would have been great, and I remember Peter urging me to think long term and get as much capacity as I could- but I hesitated, which in hindsight was a mistake.

I know in theory I can let them go down to 15% (and maybe less), but you do find this inner doubt creeping in, because you know that if something malfunctions with the charging, your batteries are already very low and you have no contingency power to tide you over- so I have this subconscious aversion to letting them go much below 50%. Its illogical, because the chances of both engine and solar charging going down are very slim. 

 

There was one morning in May when I was woken at 5am by the beeper on the BMV712. I had very bravely decided to let the charge go down past my usual 50%, but I left something switched on overnight and the batteries got down to 25%, which was the point I had set for the low SoC alarm. 

Needless to say, I soon lowered that setting.  

 

I havent yet done enough monitoring of my batteries at low SoC, so I dont have a good feel for where the 'knee' is, when the voltage starts to drop more quickly. 

Before I let the batteries go down below say 30% overnight, I want to do a trial run of that happening in daylight, so I can do any recharging that might needed immediately. 

 

But when you are trying to let the batteries run down, and you look out and see all that lovely solar, its hard to avoid the urge to capture some of it. I think I have solar greed syndrome. 

 

Edited by Tony1
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5 minutes ago, IanD said:

 

Those really big alternators (multi-kilowatt) are also often *very* expensive (e.g. Balmar, anything up to £2000 each). I looked at this intensively a couple of years back, and it was a lot cheaper (for a new engine) to use a couple of the biggest standard low-cost alternators with an external controller if your engine supports that, as well as being supported by the engine manufacturer -- for example a Beta 43 can have 2 175A 12V alternators fitted (poly-V belt to each) for less than half the cost. On an existing engine if you have to start replacing/adding crank pulleys (assuming they can be fitted) it could get expensive.

 

Alternatively if you have an inverter/charger that supports it (e.g. Victron Quattro) you could fit a Travelpower and connect it to one of the AC inputs, this is likely to be possible on a wider range of engines. It has the advantage of being more efficient than 12V alternators so doesn't run as hot, but is also not exactly cheap -- but then, neither is a lithium battery bank...

 

Still doesn't get round the problem that running a (40bhp?) propulsion diesel for hours while putting out maybe 5bhp to charge batteries (or generate AC) while moored is horribly inefficient and increases wear and tear 😞

 

I think Nick has got it spot on- a large and capable alternator that will give all the charge he needs in an hour or so.

Some people might say even an hour of engine running per day is too much, but you also need hot water, so you're going to be running it for say 30 mins anyway on most days. 

 

For me, with the extra solar, engine charging has become a winter-only issue, and I think that limits how much I can justify spending on the solution. 

And any charging solution that is not going to pay for itself over say a ten year ownership, its less appealing to me personally. 

 

I've ended up contemplating a half way house approach- so a bigger alternator, but not that big. One that will still run on a V belt, for example. 

I got a quote for the parts to convert my canaline 38 to take a poly V pulley, and it was well over £500. And thats before you buy the alternator itself, or the controller, or the numerous hours of labour that would be needed to do the fitting to a smaller engine.

If I'd had an engine with a poly V pulley already in place it woiuld have been loads cheaper and easier, but c'est la vie.

If I ever sell this and buy a new boat, one of the big issues I'll be looking at (and something that never even crossed my mind originally) is how big and capable the alternator is, because that can be a major limiting factor and a n extra cost, if/when you want to upgrade the charging. 

 

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1 hour ago, Tony1 said:

 

I think Nick has got it spot on- a large and capable alternator that will give all the charge he needs in an hour or so.

Some people might say even an hour of engine running per day is too much, but you also need hot water, so you're going to be running it for say 30 mins anyway on most days. 

 

For me, with the extra solar, engine charging has become a winter-only issue, and I think that limits how much I can justify spending on the solution. 

And any charging solution that is not going to pay for itself over say a ten year ownership, its less appealing to me personally. 

 

I've ended up contemplating a half way house approach- so a bigger alternator, but not that big. One that will still run on a V belt, for example. 

I got a quote for the parts to convert my canaline 38 to take a poly V pulley, and it was well over £500. And thats before you buy the alternator itself, or the controller, or the numerous hours of labour that would be needed to do the fitting to a smaller engine.

If I'd had an engine with a poly V pulley already in place it woiuld have been loads cheaper and easier, but c'est la vie.

If I ever sell this and buy a new boat, one of the big issues I'll be looking at (and something that never even crossed my mind originally) is how big and capable the alternator is, because that can be a major limiting factor and a n extra cost, if/when you want to upgrade the charging. 

 

 

I'd be very surprised if 30 mins or so engine running will heat the hot water enough, in my experience on various boats it takes a lot longer than that. Dave Jesse measured that his generator puts just over 1kW into the calorifier coil, which isn't much -- depends on the size of the calorifier, a big one (55l) will heat up by about 16C per hour (8C in 30mins), the same as using a 1kW immersion heater -- a smaller one will obviously be faster.

 

https://www.perseverancenb.com/post/how-to-measure-the-calorifier

 

Ironically, heating the hot water with the engine works better with lead-acid batteries where you need to run for hours to fully charge them, with lithiums the engine running time is much lower so less good for hot water...

Edited by IanD
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