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Old 01-24-2023, 02:39 PM   #81
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There are two challenges with LFP. The first is not burning out the alternator. Derating solves for that.

The second issue is properly setting up the system to handle a LFP battery failure. I'm motivated to look for alternatives in order to allow more flexibility in choosing the battery and BMS. To my mind taking the alternator out of the LFP loop solves for that.

Basically I think that lots of our thinking is based on the needs and capabilities of LA batteries. Going to LFP allows a rethink of that.
With the exception of charging abuse, I haven't heard much about LFP failures. Perhaps because they rarely occur, or perhaps because they are, in addition to BMS protection, correctly fused. Beats me, but of the systems I worry about, the LFP I've been using for years isn't very high up on the list.
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Old 01-24-2023, 02:44 PM   #82
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With the exception of charging abuse, I haven't heard much about LFP failures. Perhaps because they rarely occur, or perhaps because they are, in addition to BMS protection, correctly fused. Beats me, but of the systems I worry about, the LFP I've been using for years isn't very high up on the list.
Yes, I agree. I currently am charging LFP with my alternator, and don't lose sleep over it. But I recognize the concern, and am thinking of alternatives.
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Old 01-24-2023, 02:53 PM   #83
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Yes, I agree. I currently am charging LFP with my alternator, and don't lose sleep over it. But I recognize the concern, and am thinking of alternatives.
On reflection my view is shaped by the fact that I generally only charge the LFP underway from the alternator and when full, disconnect the LFP and direct alternator current to the LA start batteries. At anchor, I recharge the LFP from the genset. I think your concern about alternators stems from the usual attempt to want to treat LFP the same as LA in the sense that having the LFP constantly connected to the alternator creates a risk. I avoid that by only charging one bank at a time, which means the LFP is generally offline when underway or at the dock. In that state, I run off the LA starter bank. Problem solved.
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Old 01-24-2023, 03:06 PM   #84
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I think your concern about alternators stems from the usual attempt to want to treat LFP the same as LA in the sense that having the LFP constantly connected to the alternator creates a risk. I avoid that by only charging one bank at a time, which means the LFP is generally offline when underway or at the dock. In that state, I run off the LA starter bank. Problem solved.
That makes sense. There are differing approaches. I'm questioning the always-on alternator that in practice does most of the heavy lifting. It's often not needed for many people.
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Old 01-24-2023, 05:33 PM   #85
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I should add that one of my original motivations for going to a large alternator and good regulator was handling routine AC needs like cooking through the inverter when underway without running the genset.

I now recognize that lithium is an incredibly good buffer between supply and demand. It'll happily belt out a couple of kw for an hour and there is no urgency to replenish, assuming big storage. I don't really care whether my alternator is idling or belting out 2 kw during all this.

So why do I need to rapidly pay back that 2 kwh?
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Old 01-24-2023, 06:40 PM   #86
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Let's put more context around that. For someone with a genset, it may be that running the genset for dinner is more than enough to pay for the lunch deficit.
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Old 01-24-2023, 07:09 PM   #87
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Those are definitely valid points. But there's also the other side of the coin: a couple days of crappy solar production, so the batteries are low. You're moving the boat anyway. Big alternator lets you pull some power off the main while moving rather than putting extra hours and wear on the genset. And depending on the boat (helm placement and noise level) or when you would have done that generator run to help catch up on power, it might save some noise too.
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Old 01-24-2023, 08:59 PM   #88
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Those are definitely valid points. But there's also the other side of the coin: a couple days of crappy solar production, so the batteries are low. You're moving the boat anyway. Big alternator lets you pull some power off the main while moving rather than putting extra hours and wear on the genset. And depending on the boat (helm placement and noise level) or when you would have done that generator run to help catch up on power, it might save some noise too.
In that case you turn on charging from the operational side provided by the dc-dc charger. So current is limited. But again, what's the rush?
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Old 01-24-2023, 09:18 PM   #89
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I'm referencing all of this back to my use case.

If I travel 8 hours per day and limit house charging from the alternator to 30a, that gives me 240 ah daily, which roughly matches daily house needs.

I'm trying to get rid of my generator. That's a done deal in my mind.

I have installed solar that produces about the same on fair days. Even on a rainy day it's rare to get less than 1 kwh.

Operational needs are 100% met by the alternator (future state).

What's my motivation for high charging to house from the alternator? Pretty low, especially with 2 days reserve capacity.

Edit to add: my house needs are also variable. I can live on sandwiches and reduce house needs considerably if need be.
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Old 01-24-2023, 09:33 PM   #90
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I'm referencing all of this back to my use case.

If I travel 8 hours per day and limit house charging from the alternator to 30a, that gives me 240 ah daily, which roughly matches daily house needs.

I'm trying to get rid of my generator. That's a done deal in my mind.

I have installed solar that produces about the same on fair days. Even on a rainy day it's rare to get less than 1 kwh.

Operational needs are 100% met by the alternator (future state).

What's my motivation for high charging to house from the alternator? Pretty low, especially with 2 days reserve capacity.
On an 8 hour travel day, high amp charging is pretty unimportant unless you have high power draws while underway. But having the ability to charge faster is nice if you sometimes make a short hop to the next destination that's only an hour or 3 away. Of course, whether it's worth it depends on whether the faster charging is easy to implement or if it adds too much complexity.
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Old 01-24-2023, 09:37 PM   #91
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On an 8 hour travel day, high amp charging is pretty unimportant unless you have high power draws while underway. But having the ability to charge faster is nice if you sometimes make a short hop to the next destination that's only an hour or 3 away. Of course, whether it's worth it depends on whether the faster charging is easy to implement or if it adds too much complexity.
Right. And how important more capacity is in the future. It's an odd way to think about it. The promise of a future charge is equivalent to a charge now, until you run out of buffer.
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Old 01-24-2023, 09:40 PM   #92
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On an 8 hour travel day, high amp charging is pretty unimportant unless you have high power draws while underway.
Nope. See my earlier post. Irrelevant.
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Old 01-24-2023, 11:41 PM   #93
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Hope my last comment made sense Rob.

In the real world, if I hit a six day patch of really gloomy weather at anchor and want to cook, I need to get traveling again, and not just across the bay.

I had one occasion last summer when I ran the engine specifically in order to charge. I had been at anchor a week or more on solar only, and was running low on juice. Gloomy dark weather late in the season. Rather than start the winterized genset I ran the motor for a couple of hours and was very thankful for the ability to charge at 130a.

But for me that's a highly anomalous situation. Normally if I pull anchor I'm putting in a long day. And if I end the day at 30% SoC I'm satisfied.

Edit to add: actually I've done that twice. Was at anchor in NS when the tail end of a hurricane blocked out the sun almost completely for 3 days.
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Old 01-25-2023, 04:50 AM   #94
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Of course, whether it's worth it depends on whether the faster charging is easy to implement or if it adds too much complexity.
And risk, I'd suggest. Not to mention cost.

Think through the failure case. BMS takes a wrong turn. Unrecoverable error.

If you've got your alternator hooked to the bricked battery it doesn't really matter whether it still works or not.

Assuming you've got operational needs covered, you carry on.

Now, if you have a generator you can support the operational side, assuming you have an AC 12v charger.

Solar is useless because it passed through house.

I'm not suggesting that this is a high likelihood event. TT has deep insight into the innards of his battery, and full failover capabilities. I want to use Chinese drop ins. Neither one of us is at particularly high risk.

I dunno. Seems like a no-brainer, for me at least.

This has been enormously helpful. Thanks to all.
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Old 01-25-2023, 05:20 AM   #95
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Edit to add: actually I've done that twice. Was at anchor in NS when the tail end of a hurricane blocked out the sun almost completely for 3 days.
But that was pre-lithium, so it doesn't count :-)
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Old 01-25-2023, 06:31 AM   #96
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We have a pair of externally regulated 175 amp 24v alternators. Way more capacity than our batteries or hotel loads ever need or use. Iíve found that using our small generator instead of the alternators under way uses less fuel and keeps our engine room temp ten to fifteen degrees cooler. I pulled both alternators for rebuild at the 8000 hour mark just because. Not going to think about them ever again.
I remember you mentioning this here a long time ago. At the time I was more Huh than Hmm. I get it now. Do you have lithium, or just run the generator all the time?
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Old 01-25-2023, 08:06 AM   #97
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And risk, I'd suggest. Not to mention cost.

Think through the failure case. BMS takes a wrong turn. Unrecoverable error.

If you've got your alternator hooked to the bricked battery it doesn't really matter whether it still works or not.

Assuming you've got operational needs covered, you carry on.

Now, if you have a generator you can support the operational side, assuming you have an AC 12v charger.

Solar is useless because it passed through house.

I'm not suggesting that this is a high likelihood event. TT has deep insight into the innards of his battery, and full failover capabilities. I want to use Chinese drop ins. Neither one of us is at particularly high risk.

I dunno. Seems like a no-brainer, for me at least.

This has been enormously helpful. Thanks to all.

I figure in the worst-case scenario like that, I re-configure things a bit to keep the important DC loads powered, and most likely crank up the generator and point the bow towards somewhere with shore power and the ability to get parts so I can get the system working again.

Thinking about the cloudy weather case, I think that becomes less of an issue as the boat gets bigger. Larger boats can often carry disproportionately more solar and battery, so it takes more cloudy days to become a problem.

For us, for example, we've got 820 watts of solar. Until the day comes that I ditch the bimini for a hard top, that's all we get as we're out of space to mount panels. It's enough in decent weather, but not when it gets really cloudy. And we still cook on generator power, as we don't have enough battery or solar to support using the stove on battery power full time (we can and at some point will add more battery).
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Old 01-25-2023, 08:32 AM   #98
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Yeah, I could probably get up to 3+ kw without really giving anything up. It's one of the joys of a big pilothouse boat.

First I thought I'd carry the dinghy up top, then a Laser. There are two in my household. Now I'm thinking I could quite happily plaster it with panels.

Edit to add: more capacity also goes a long way. If you know that typical production > typical usage capacity makes you a winner, ultimately.

Given the price of cheap batteries that's probably a cheaper and more effective alternative to more solar. I can double my house bank from 3x daily use to 6x daily use with $2100 in batteries and a bit of cabling.
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Old 01-25-2023, 08:47 AM   #99
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Yeah, I could probably get up to 3+ kw without really giving anything up. It's one of the joys of a big pilothouse boat.

First I thought I'd carry the dinghy up top, then a Laser. There are two in my household. Now I'm thinking I could quite happily plaster it with panels.

Edit to add: more capacity also goes a long way. If you know that typical production > typical usage capacity makes you a winner, ultimately.

Given the price of cheap batteries that's probably a cheaper and more effective alternative to more solar. I can double my house bank from 3x daily use to 6x daily use with $2100 in batteries and a bit of cabling.

Even without going LFP I can easily double my house bank in the available space and without worrying much about weight. And eventually I'll install a hardtop which would give room for me to probably double our solar capacity.



At this point, my biggest sticking point for the eventual next battery replacement is whether it's time to go LFP or not. The costs are starting to look better, but I've still got a few sticking points to worry about (cold weather during winter storage, making sure my insurance doesn't have issues with LFP, etc.). And realistically, given enough solar, our usage patterns aren't particularly abusive to a lead bank, so I haven't had a pressing need to jump to LFP.
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Old 01-25-2023, 09:23 AM   #100
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The costs are starting to look better, but I've still got a few sticking points to worry about (cold weather during winter storage, making sure my insurance doesn't have issues with LFP, etc.). And realistically, given enough solar, our usage patterns aren't particularly abusive to a lead bank, so I haven't had a pressing need to jump to LFP.
My 300 ah drop ins are easy to heft around. If I ever store ashore in the frozen north I'll take them home and do some balancing and capacity testing.

They're a little over $1,000 each. If you want to go there it might be easier than you think...
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