Alternators - leave them alone and forget about them

[DDW]

It matters hugely. It's part of my core argument. If you have multiple sources you can be opportunistic. If you get a boost from 30% to 50% take it and move on.

Exactly the same regardless of chemistry. Obviously if you have a source of charge, use it.

You have a genset but really you'd rather not have it. And you haven't acknowledged solar in the mix. For sure you should charge with that $800 setup. Make sure the BMS communicates.

I have as much solar as will fit on the available deck space. It contributes a modest amount, but nowhere near the daily consumption. In Alaska last year, with rain nearly every day, not that much at all. The alternator regulator will communicate to the BMS, but that is a very small addition to function in my view. Primarily it serves to kill the alternator output when the BMS disconnects, saving the alternator diodes and preventing the voltage spike. The same function is served by a FET isolator to an LA bank, very likely more reliably. And the latter (but not the former) also solves the backup power problem.

 

[Jeff F]

I am very pleased with the set up (AGM batteries by the way). Just my experience

My experience was exactly the same. And then I switched over to Lithium.

 

[Simi 60]

My experience was exactly the same. And then I switched over to Lithium.

Same here
AGM were great ..,..........until they weren't.

Lifepo4 has been a game changer out here for us

 

[Jeff F]

Exactly the same regardless of chemistry. Obviously if you have a source of charge, use it.





I have as much solar as will fit on the available deck space. It contributes a modest amount, but nowhere near the daily consumption. In Alaska last year, with rain nearly every day, not that much at all. The alternator regulator will communicate to the BMS, but that is a very small addition to function in my view. Primarily it serves to kill the alternator output when the BMS disconnects, saving the alternator diodes and preventing the voltage spike. The same function is served by a FET isolator to an LA bank, very likely more reliably. And the latter (but not the former) also solves the backup power problem.

Great. You've got a well thought out solution to your individual needs.

We'll agree to disagree on the difference chemistry makes.

 

[Jeff F]

But if you want to talk more about your particular needs, what's your daily house load? Avg/reasonable max. And how much installed solar capacity do you have? Also how big is your lithium bank?

 

[Insequent]

Interesting. As i mentioned earlier, going to li for me really made me reconsider the need for high charging.

Would you be willing to limit house charging from your alternators to 30a per side?

I can think of no imposition and lots of benefits. Maybe I misunderstand your use case.

No, I would not be willing to do that! Sure, with my current 2740W of solar I could do it, but there is no point in changing.

In summer I can likely stay anchored in one place indefinitely with solar covering house loads and water heating. In winter, maybe not. I spend around 100 nights per year at anchor. At times I move every day, but mostly I'll stay in one place for several days.

My overnight draw is +/- 350 Ah. If I have one or two additional fridge/freezers plus ice maker running then I can use 450Ah overnight. I don't measure day use, but guess its similar.

Having two large alternators provides options in cases where an extended period of poor weather occurs. The alternators cost $580 each, and have been a great investment.

TT covered the BMS shutdown etc. Its not an issue for me. I have 3 x 300Ah LFP in parallel. Never had a failure, the chance of 3 dying at the same time is very, very small.

One thing that's useful to do with LFP is to set max voltage around 0.2V below battery max spec. That means you never reach 100% charge, but given the flat SOC curve etc you lose only a minor amount of Ah capacity.

Getting back to the first post, choose 2 of 3 charge sources for periods away from shore power. A genny only has to be one of them if you want A/C. I only ditched the genny in the boat back in 2012 because it was near end of life and I did not want death by a thousand cuts in keeping it going. A genny on board that gets little use is not a big deal, it just further increases options. As TT indicated, setting voltages differently can prioritise one source.

 

[Jeff F]

TT covered the BMS shutdown etc. Its not an issue for me. I have 3 x 300Ah LFP in parallel. Never had a failure, the chance of 3 dying at the same time is very, very small.

Yes, I have 2x300 with the same rationale. I may add a third shortly. You have to have a way to know if (when) one shuts down, but that's pretty easy. But I have a nagging feeling that I should try to stay within ABYC guidelines. That's just me. I can imagine selling Escapade in a few years, and don't want to have that hanging over my head.

I'm always moving, so that's the big difference between us.

Thanks much for the detailed feedback. Your arrangement sounds great.

 

[slowgoesit]

I don't want to use fuel consumption as an argument against running the genset. Maybe it costs $.40/kwh from the alternator vs $.50/kwh from the genset. I don't care. It's not really relevant to the debate. And I can certainly argue that those who have gensets and use them 10 hrs a year should be looking for reasonable opportunities to flash them up.

For our boat (I can't speak for other people's setups), the cost/kwh is significantly different from what you quote above.

Our generator uses a hydraulic motor, with hydraulic pressure provided by PTO off of the main engine, or off of the standalone diesel engine, which also doubles as a get home engine.

Real world numbers: If we are generating power with only the main engine running, our cost is about $0.083/kwh.

If we are running the generator off the standalone diesel engine, which uses a little over 1 gph, at today's prices of diesel, the cost is about $0.94/kwh, a little over an 11 fold increase!

So, for us, on our boat, with our setup, there is little if any reason to run the generator using the standalone diesel engine while underway.
I AM considering upgrading our main engine driven alternator however, if for no other reason than to have further redundancy. You can't have too much redundancy IMHO

 

[Jeff F]

You can't have too much redundancy IMHO

I'm poking a bit at redundancy. Some have a need for maximum redundancy. I'm too minimalist and cheap for that. So I have to be smarter about needs, risks and failure models.

I'm never more than 50 miles from shore or a day or two from civilization.

Your cost via hydraulically driven alt are way off. How do you measure that? See ensuing discussion on that.

 

[twistedtree]

For our boat (I can't speak for other people's setups), the cost/kwh is significantly different from what you quote above.

Our generator uses a hydraulic motor, with hydraulic pressure provided by PTO off of the main engine, or off of the standalone diesel engine, which also doubles as a get home engine.

Real world numbers: If we are generating power with only the main engine running, our cost is about $0.083/kwh.

If we are running the generator off the standalone diesel engine, which uses a little over 1 gph, at today's prices of diesel, the cost is about $0.94/kwh, a little over an 11 fold increase!

So, for us, on our boat, with our setup, there is little if any reason to run the generator using the standalone diesel engine while underway.
I AM considering upgrading our main engine driven alternator however, if for no other reason than to have further redundancy. You can't have too much redundancy IMHO

I agree that those numbers don't make sense, and it's probably in how things are measured. Ballpark fuel consumption will be 1gph while producing 10kw of power. To really compare you would need to accurately and simultaneously measure the load on the generator, and fuel burn of the engine. With your main engine, you would need to measure fuel burn with the loads turned on and off, and take the difference. With older diesels this is nearly impossible to do accurately.

 

[rslifkin]

By my best estimate, for my boat with gas engines, I'd burn about 0.13 - 0.14 gal/hr additional per KW of power extracted from my engines via the alternators. That's accounting for some inefficiency (assuming 1.5 - 1.6hp required to produce 1kw).

That's solidly better than my generator can do (at full load, 6.5kw, it'll burn a little over 0.15 gal/hr per KW, at 4kw load it's up to almost 0.19 gal/hr per KW and it gets worse as load gets lighter). Just keeping the generator running with no load burns about 0.3 gal/hr.

 

[twistedtree]

By my best estimate, for my boat with gas engines, I'd burn about 0.13 - 0.14 gal/hr additional per KW of power extracted from my engines via the alternators. That's accounting for some inefficiency (assuming 1.5 - 1.6hp required to produce 1kw).

That's solidly better than my generator can do (at full load, 6.5kw, it'll burn a little over 0.15 gal/hr per KW, at 4kw load it's up to almost 0.19 gal/hr per KW and it gets worse as load gets lighter). Just keeping the generator running with no load burns about 0.3 gal/hr.

Gas generator too, I presume? Fuel consumption relative to load is pretty linear with diesels within reasonable load ranges - say 20-90% load. It goes to hell outside that, especially at the low loads. Gas engines a much less linear, consuming a lot of fuel even when lightly or moderately loaded - just as you are seeing, assuming the gen is gas too.

 

[rslifkin]

Gas generator too, I presume? Fuel consumption relative to load is pretty linear with diesels within reasonable load ranges - say 20-90% load. It goes to hell outside that, especially at the low loads. Gas engines a much less linear, consuming a lot of fuel even when lightly or moderately loaded - just as you are seeing, assuming the gen is gas too.

Yup, gas generator. One of the old flathead Onans. A diesel will be more linear, but still somewhat inefficient under light loads. And a smaller engine for a generator may be a somewhat more primitive engine than the main, so there may be a general efficiency difference there.

 

[cafesport]

We have a pair of externally regulated 175 amp 24v alternators. Way more capacity than our batteries or hotel loads ever need or use. I’ve 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.

 

[Gdavid]

We have a pair of externally regulated 175 amp 24v alternators. Way more capacity than our batteries or hotel loads ever need or use. I’ve 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.

That is very interesting, is the generator located in the same engine room or in a separate mechanical space?

 

[O C Diver]

That is very interesting, is the generator located in the same engine room or in a separate mechanical space?

One of the differences between a generator and an alternator is heating the engine room. An alternator generates heat that isn't expelled through an engine exhaust pipe (any more than that the engine is doing while cruising). A generator running draws more fresh air into the engine room and expels some amount out the exhaust pipe. If the generator is in a sound shield, there may be a perception of the engine room being cooler as much of the generator heat is trapped inside the sound shield.

This is a good reason to have big vents feeding the engine room and an exhaust blower removing engine room heat whenever the engine or generator is running.

Ted

 

[Delfin]

I've been following the challenges that come with adopting lithium for a long time. By far the most intractable challenge has been hooking them up to the alternator.

I have a solution. Don't. Leave the OEM alternator charging the start battery and look elsewhere for charging sources for the house bank.

Let's assume you have a lithium house bank sized to accomodate 24 hours typical use.

I can think of three viable ways to charge the house bank away from the dock. Alternator, genset through AC charger, and solar.

None of these are any better or worse for the battery. The charge cycle doesn't have to match the discharge cycle. There is no necessity in achieving or maintaining full charge, and no practical constraint on charge rate. Lithium is liberating that way.

It seems to me you can pick any two out of three charging sources and get on with life. If you're optimizing for liveaboard at anchor you've learned to do without alternator input. Why not give it up completely?

Go ahead. Shoot me down. But honestly I'm tired of the alternator angst when maybe we can just not go there. Not going there might be easy.

Tell me again why charging from the engine is a good idea. We needed it way back when, but now? Why do we treat it as a necessity? My Prius had a 12v start battery but no alternator. Let's be a little creative.

What angst? De-rate the alternator to 75% output and be done. If you don't have a programmable regulator, start there, not LFP.

 

[Jeff F]

What angst? De-rate the alternator to 75% output and be done. If you don't have a programmable regulator, start there, not LFP.

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.

 

[rslifkin]

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.

In some ways, yes. It eliminates concern for whether the batteries ever actually make it to 100% or not. But it doesn't change the basic mechanics of needing to be able to put as much power back into the batteries as you use from them. Of course, what it takes to meet that requirement will vary depending on the boat, the location, and usage patterns.

 

[Jeff F]

In some ways, yes. It eliminates concern for whether the batteries ever actually make it to 100% or not. But it doesn't change the basic mechanics of needing to be able to put as much power back into the batteries as you use from them. Of course, what it takes to meet that requirement will vary depending on the boat, the location, and usage patterns.

Right. In practice my experience is that LFP gives much more flexibility in when you charge and how fast you can charge. That opens up new possibilities in how you choose your charging sources

 

[Delfin]

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.

 

[Jeff F]

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.

 

[Delfin]

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.

 

[Jeff F]

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.

 

[Jeff F]

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?

 

[Jeff F]

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.

 

[rslifkin]

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.

 

[Jeff F]

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?

 

[Jeff F]

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.

 

[rslifkin]

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.