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Old 18-08-2018, 13:03   #61
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Re: Practical Questions about LiFePo4 Power Systems

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interconnect the two banks with a battery-to-battery charger. That way the house loads would be run from the lithium bank until that was switched off for whatever reason (either manually or in an undervoltage situation), then the lead would take over automatically and instantly -- making a highly reliable power supply, a definite plus. Also the lead would practically extend the usable battery capacity, and maybe I wouldn't need as much lithium.

This would have some pretty big advantages, but would be getting borderline ridiculous, what concerns complexity.
There you go.

And to me much simplified not more complex by the B2B.

If you want complicated, grok this:

When your normal routine isn't getting your lead to 100% Full, turn the B2B around, use your LFP as the "long tail" charge source to do so.

Yes theoretically inefficient, but basically eliminates the need for solar to maximize lead bank longevity.

My thinking is Firefly bank for Starter/Reserve, LFP for Main/House.

Crazy I know. . .
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Old 18-08-2018, 13:13   #62
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Re: Practical Questions about LiFePo4 Power Systems

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An alternator setup to output high amps, precise voltage, proper staged profile is a lot of very expensive work

not saying not worth it, but

If you have inexpensive lead on board, then whatever existing alternator setup can be leveraged for the LFP

with a DCDC charger, e.g. Sterling BB series.

And once you have that, it can become the **only** charge source that touches the LFP.

No need for special fancy mains charger, even solar controller can route through the DCDC.

Since your well-coddled LFP bank will last longer than your boat, or when you move into an off-grid home or buy an RV

you are never upgrading any charge sources anywhere, just use whatever's there.

In effect you get all the benefits of "drop-in" without their limitations.

Not a panacea for all use cases maybe, but one idea worth considering.

OK, that sounds reasonable. Hmmm.


My alternator setup at present consists of a 110 amps * 24v Leece Neville schoolbus alternator, regulated by an Adverc regulator, which is a bit of an odd bird of a regulator which alternates high and low voltages to break up sulphation but stopping before the eletrolyte starts to boil.



I will probably replace it with a Balmar or Sterling regulator, and I guess there's no reason not to set it to deal correctly with the lead and then power the Sterling B2B charger from that. Sterling make a 70 amp version which should be about right.



But then what about when I am consuming power rather than charging? If the loads are connected to the lithium, then I guess I can transfer power out of the lead bank using the same B2B charger.



But what if the loads are connected to the lead bank? Then I'll need a SECOND B2B charger to get power from lithium to lead? How do I interconnect the two banks?


I guess I could have a switchover to simply switch over the house bus between lead and lithium so I could choose which bank to tap. I guess I'll need this in any case if I want to use the lead bank to power loads with the lithium knocked out of action by the BMS.



I'm trying hard to see an elegant and straightforward way to do this.
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Old 18-08-2018, 13:16   #63
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Re: Practical Questions about LiFePo4 Power Systems

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.. .
When your normal routine isn't getting your lead to 100% Full, turn the B2B around, use your LFP as the "long tail" charge source to do so.
.

Ha, ha. Believe it or not, I had actually thought of this. And I don't actually think it's so crazy.


An even less efficient but very straightforward way to do this would be to simply power the lead bank's battery charger via the inverter. For a low intensity tail charge -- I don't actually think that would be so stupid.
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Old 18-08-2018, 13:44   #64
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Re: Practical Questions about LiFePo4 Power Systems

Heresy! 8-D
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Old 18-08-2018, 13:55   #65
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Re: Practical Questions about LiFePo4 Power Systems

My Main/Reserve scenario means Reserve is kept for that, not regularly cycled. No dedicated starter batts, helps to justify carrying the dead lead.

Cranking can A/B switch, basically a regular health test for Reserve.

Of course, you could adapt the two banks to a windlass / high-load scenario, but personally unless wire gauges go too crazy, I prefer one big bank (Main), and if that is LFP, I like a lead one for a Reserve.

I would not advocate routine B2B transfers except while a charge source is active.

2 step, into the bank, then off to run loads.

If I were flowing B2B in both directions, I would be doing it rarely enough,

prefer to just set up reliable manual method to swap wires, not rigging a DPST switch or something to automate it.

Not sure if any of that helps your concerns, not like I can really say KISS at this point 8-D
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Old 19-08-2018, 06:11   #66
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Re: Practical Questions about LiFePo4 Power Systems

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There you go.

And to me much simplified not more complex by the B2B.

If you want complicated, grok this:

When your normal routine isn't getting your lead to 100% Full, turn the B2B around, use your LFP as the "long tail" charge source to do so.

Yes theoretically inefficient, but basically eliminates the need for solar to maximize lead bank longevity.

My thinking is Firefly bank for Starter/Reserve, LFP for Main/House.

Crazy I know. . .


ThatĎs exactly our approach. The LA starter battery is charged primarily from the LiFePO4 house bank via a Sterling B2B charger. The B2B Charger is behind a timer relay (set to 30 min minimum, retriggerable) which is triggered by the Ignition switch or the BMV 700 relay which is monitoring starter battery voltage and SoC. This is working brilliantly.
(Secondary charge source is a small Charger which is directly connected to shore power inlet and is only used for LA charging during prolonged absence from the boat.)

By connecting the charge sources to the LiFePO4 bank we get the benefits of virtually unlimited charge acceptance rate.

Yes, charging the LA batt from the charge sources and then have a B2B charger feeding the LiFePO4 bank is much simpler engineering-wise but requires a very powerful B2B charger, otherwise the benefits of the LFP go out of the window.
I like our approach (documented here: https://www.entropypool.de/2015/05/1...system-design/)
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Old 19-08-2018, 07:31   #67
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Re: Practical Questions about LiFePo4 Power Systems

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That‘s exactly our approach. The LA starter battery is charged primarily from the LiFePO4 house bank via a Sterling B2B charger. The B2B Charger is behind a timer relay (set to 30 min minimum, retriggerable) which is triggered by the Ignition switch or the BMV 700 relay which is monitoring starter battery voltage and SoC. This is working brilliantly.
(Secondary charge source is a small Charger which is directly connected to shore power inlet and is only used for LA charging during prolonged absence from the boat.)

By connecting the charge sources to the LiFePO4 bank we get the benefits of virtually unlimited charge acceptance rate.

Yes, charging the LA batt from the charge sources and then have a B2B charger feeding the LiFePO4 bank is much simpler engineering-wise but requires a very powerful B2B charger, otherwise the benefits of the LFP go out of the window.
I like our approach (documented here: https://www.entropypool.de/2015/05/18/designing-a-lifepo4-battery-system-part-3-system-design/)

That's a very interesting design, which has given me a number of ideas.


But one thing which bothers me -- the loads will be disconnected from the alternator, and not just from the lithium bank, in case of a LVC event, and the alternator will be disconnected from the lead bank as well. The alternator will be completed isolated in case of a LVC, which does not seem to me to be an inherent requirement. Why did you design it that way? Seems to lose the big advantage of having lead in the system -- you could disconnect the lithium without risk of damaging the alternator and without shutting down the loads, if you leave the alternator connected to everything except the lithium bank.


Risk of sudden shutdown of the electrical system due to a BMS automatic decision seems to me to be a huge disadvantage of lithium, something actually dangerous in some cases. A starter battery would give you a bit of time, but if the alternator is working, why would you want to disconnect it?


Likewise, it looks like a HVC event would NOT disconnect the alternator from the lithium bank -- isn't that a risk?
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Old 19-08-2018, 07:54   #68
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Re: Practical Questions about LiFePo4 Power Systems

I like the simplicity of the alt output going directly to lead, no need to ever isolate that connection, controls for alt output are upstream as they should be.

I also don't mind buying a high-amp B2B charger to put on the LFP, long-term amortization, eliminates a lot of expensive futzing around with regulation of the other charge sources.

Since my lead bank is Reserve/Starter, not usually cycled at all, keeping it topped up is usually not much of a challenge, not worth jumping through lots of design / expense / complexity hoops.

The idea of putting the B2B to use for that purpose does not mean it needs to "be wired" for that use.

If catastrophe strikes my Main bank, to the point I need to fall back to actually cycling Reserve, I don't mind stepping through a checklist of tasks to make the transition manually.

As opposed to the greater complexity involved in setting everything up so it's a matter of just flipping a couple of switches.
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Old 19-08-2018, 12:27   #69
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Re: Practical Questions about LiFePo4 Power Systems

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I like the simplicity of the alt output going directly to lead, no need to ever isolate that connection, controls for alt output are upstream as they should be.

I also don't mind buying a high-amp B2B charger to put on the LFP, long-term amortization, eliminates a lot of expensive futzing around with regulation of the other charge sources.

Since my lead bank is Reserve/Starter, not usually cycled at all, keeping it topped up is usually not much of a challenge, not worth jumping through lots of design / expense / complexity hoops.

The idea of putting the B2B to use for that purpose does not mean it needs to "be wired" for that use.

If catastrophe strikes my Main bank, to the point I need to fall back to actually cycling Reserve, I don't mind stepping through a checklist of tasks to make the transition manually.

As opposed to the greater complexity involved in setting everything up so it's a matter of just flipping a couple of switches.

I don't mind manual operating procedures, but the only problem with a manual switchover is what happens in a crucial navigational situation and a sudden automatic shutdown. It's also why I might not want to rely on just a starter battery, but that wouldn't be my problem in any case because both start batts are 12v completely separated from house and from each other, with their own dedicated 12v alternators and chargers, and house system is 24v.


I'm still trying to think my way through this into something with reasonable elegance and economy, but I have to admit that just replacing the battery boxes in order to be able to fit T-105's is starting to look more appealing, despite a few problems with that setup in my particular case.
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Old 19-08-2018, 15:21   #70
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Re: Practical Questions about LiFePo4 Power Systems

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what happens in a crucial navigational situation and a sudden automatic shutdown.
I just meant the charging reconfiguration.

An Essentials circuit could easily have an A/B switch on it.

Really, how failsafe are most boats?

I just want to compensate a bit for the (maybe imaginary) added risk of LFP.

The "BMS cutting off loads" protects the bank. Without it the same thing would happen anyway just a bit later.
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Old 19-08-2018, 16:45   #71
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Re: Practical Questions about LiFePo4 Power Systems

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I just meant the charging reconfiguration.

An Essentials circuit could easily have an A/B switch on it.

Really, how failsafe are most boats?

I just want to compensate a bit for the (maybe imaginary) added risk of LFP.

The "BMS cutting off loads" protects the bank. Without it the same thing would happen anyway just a bit later.

I understand, but it won't happen with lead until much later -- when the bank has been completely killed, after lots of warning. Not in a blink due to an automatic decision of the BMS, which might even be a malfunction. This is a serious issue which shouldn't be underestimated.


I could set up an "essentials load bus", but that is definitely a bridge too far for this boat. The boat already has a very nice set of busses and panels and I'm not going to rip them out and reconfigure them.


No, I think I would need the whole supply backed up. Perhaps running the loads bus off the lead and charging it via the lithium via a B2B charger might be the way to go. In normal conditions, the loads will be powered directly by the lithium bank. If that drops out for any reason, the lead takes over seamlessly, and I have about 100 amp/hours @ 24v of reserve power on tap (even more if I think I can discharge the lead below 50%) out of a 220 amp/hour @ 24v nominal bank.


So lithium directly powering the heavy technical loads (winches, windlass, thruster) through the existing bus for that, and indirectly powering the house loads via B2B charger on the lead bank. That's starting to sound more reasonable. Very easy to disconnect the lithium without causing a navigational crisis, and minimal reconfiguration of existing gear.



That just leaves the alternator to puzzle over. But maybe that's not such a big deal -- just connect it to lithium and create some other kind of protection for the flyback current. I bet I can find a BMS which wouldn't do the high voltage cutoff instantaneously -- would give a second or two for the alternator to power down after cutting the field current. And the cost of the problem is not that great -- a couple of alternator diodes -- not the most expensive electrical components on board, and I carry a complete spare alternator on board.


The guy who posted his design a few posts up didn't have any such protection for the alternator at all.
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Old 19-08-2018, 16:55   #72
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Practical Questions about LiFePo4 Power Systems

On aircraft, itís called the emergency bus.
Not too hard to do really, but once you add up all the work and fiddling and reconfiguring that may be required plus essential backups.
Is it worth it? Many times things are done not out of necessity, but because they can be.
Whenever you start designing s system, there is always limits where you reconsider and start the design process over, cause you see a better or more elegant way to accomplish something.
In aircraft design I call it creeping elegance, if you donít put a handle on it, nothing will ever be built and or you will have a super elegant design, but it will be so expensive and complex that it just isnít practicable.

Before you redesign to fix something, you really ought to back up and decide if itís really broken or are you enticed by the neatness of a new toy?

Iím as guilty or moreso than anyone, I bet I have one of the most over engineered 30 yr old 38í boats with multiple redundancies and backup systems.
My reason was I was waiting, still working and had excess money and was trying to get everything right before we left.
Well I find myself way more than prepared, but still waiting, now for a Hurricane season, but we needed to have left a year ago.

Sometimes good enough, is well good enough, and for me lead acid is good enough. Of course there is better, there is always better but is it needed?
How about hydrogen fuel cells? Iím only partially kidding
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Old 19-08-2018, 17:19   #73
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Re: Practical Questions about LiFePo4 Power Systems

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On aircraft, itís called the emergency bus.
Not too hard to do really, but once you add up all the work and fiddling and reconfiguring that may be required plus essential backups.
Is it worth it? Many times things are done not out of necessity, but because they can be.
Whenever you start designing s system, there is always limits where you reconsider and start the design process over, cause you see a better or more elegant way to accomplish something.
In aircraft design I call it creeping elegance, if you donít put a handle on it, nothing will ever be built and or you will have a super elegant design, but it will be so expensive and complex that it just isnít practicable.

Before you redesign to fix something, you really ought to back up and decide if itís really broken or are you enticed by the neatness of a new toy?

Iím as guilty or moreso than anyone, I bet I have one of the most over engineered 30 yr old 38í boats with multiple redundancies and backup systems.
My reason was I was waiting, still working and had excess money and was trying to get everything right before we left.
Well I find myself way more than prepared, but still waiting, now for a Hurricane season, but we needed to have left a year ago.

Sometimes good enough, is well good enough, and for me lead acid is good enough. Of course there is better, there is always better but is it needed?
How about hydrogen fuel cells? Iím only partially kidding

Well, as I explained above, I would not be considering this if it were not for certain systems architecture problems I have with the existing system. I don't have space to accommodate a single bank with lead, and my boat was designed with two separate banks, so separate busses for technical and house loads.



I will only do this if a really straightforward solution can be found which reuses most of the really excellent electrical installation I already have, and which well solves the existing problem.



Creeping elegance is not much of a threat because I still hope to start building a new boat in the next year or two, so whatever I build in now in this boat will be sold on to someone else who will pay nothing for it. That's quite an effective disincentive.



And no, it's not entirely broken. I could get by with changing the battery boxes, installing T-105's in place of the 27TMX's I have now, and muddling along with two interconnected banks. It would not be the end of the world, but I need to probe further and see if lithium might solve these configuration problems and give me a significant improvement in functionality, before I make the final decision.
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Old 19-08-2018, 17:44   #74
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Practical Questions about LiFePo4 Power Systems

Why not run the generator more often? Itís probably got thousands of hours left in it, and you only need it for another year, maybe two, you will likely not put a significant number of hours on it in two years, not enough to justify Lithium anyway.
Especially if your going to do a new build in a year or so.
Like I said, I was only partially kidding with a hydrogen fuel cell. Itís my opinion that electric cars are a stepping stone, hydrogen fuel cell cars will be what they become.
Except for the availability of fuel, itís easy to get in industrialized areas, probably not in the boonies though
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Old 19-08-2018, 17:53   #75
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Re: Practical Questions about LiFePo4 Power Systems

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Why not run the generator more often? It’s probably got thousands of hours left in it, and you only need it for another year, maybe two, you will likely not put a significant number of hours on it in two years, not enough to justify Lithium anyway. . . .

That was always my solution. The theory was I can hardly hear the gnerator running; I don't care whether it's running or not, and it's a prime power unit rated for 10,000 hours and I only have 2,000 on it.


But I simply got sick of it this summer. That's all there is to it.
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