LiFePo4 batteries: Twin 24V Alternators on the main engine


Chris Paul
 

 

 

Hi All,

I have Lithium Batteries and I’m thinking about twin 24V Alternators on the main engine.

My thinking started about a year ago with "What 24V alternator to put on the main engine when changing to LFP batteries"
   Large frame, Small frame, What Output do I need??
   I decided to go with a small frame as the engine room is already rather full 
   The initial thought was to get a small frame 70A,24V BALMAR but that also required engineering - a new belt

   After much deliberation, I decided to go with what I had "MAHLE 55A" (small frame, running from a simple V-belt ) 
   I changed it from internal to an external regulaton ($150) & installed a BALMAR regulator.
   If my new Lithium batteries "cooked" the alternator then at least I did not destroy an expensive new alternator.
   The installer set the alternator output to about 40A continuously at 1800RPM. 

I then started thinking about getting a spare alternator incase the MAHLE cooked. 
Then I thought it would be smart to replace the existing 12V alternator and hence this email.
   

The basic idea:
Exchange the 12V alternator for a second 24V alternator

 

The 12V Alternator does not really do much -

It only works hard for 2 - 5 minutes after the engine starts. 

 

If the 12V alternator was replaced by a 24V-12V DC-DC charger then the battery would always fully charged – assuming 24V system is ok.

 

 

 


How should I set up?

 

1.     Most probably each alternator requires an external regulator (BALMAR or equivalent)

2.     I can see 2 set up options – and of course many intermediate options between these extremes

a.     Expensive, high output option - two large alternators ( maybe 2x150A = 300A total battery charging!!)

b.     Cheaper Lower output option (can be run by a simple single v-belt) maybe about 2x40A = 80A total battery charging

3.     The setup may benefit from an “alternator off” switch. (switch in the field current wire or use magnetic BALMAR probe). 
      For example, if you need to motor for a few days and the batteries are already full it may be wise to turn off one or maybe both alternators.
4.     Maybe install some type of alternator protection 
            a. "Sterling Alternator Protect"??
            b. put some lead batteries in parallel with lithium??

 

 

 

Advantages:

1.     Redundancy – Assuming you don’t burn out both alternators simultaneously, if one "cooks" you can continue with the other alternator.
2.     Even more redundancy - The 12V "Yanmar" Alternator now becomes a spare for the Generator

 

 

 

Right now I'm happy to go with the simpler, cheaper, lower power output ~50A alternators.
Here is what I see as the advantages of the lower power option:
   I am happy with 80A output, (faster charging comes from the 24V battery chargers and slow charging from solar)
   lower cost than high power option, (maybe $5K cheaper??)
   easy replacement (common truck type alternator - maybe not so simple if it is not insulated??). 
   Not waiting for overseas delivery.
   extra redundancy of 2 alternators, 
   same length V-belt for both alternators - hopefully

 

The high-power option also would have significant benefits, but it’s not for me as I really don't want more high tech & expensive systems.

 

 

 



So, is this a good idea?
Any ideas (good or bad) anyone has will be much appreciated as my knowledge & experience in these things is limited.



Regards, Chris Paul 




Chris Paul
SM#352, Glazig
Whangarei, NZ








Bill Kinney
 

Chris,

My perspective on this is a bit different.  

We cover a lot of miles in a year, yet the number of hours where we are running the engine in a year is truly inconsequential to our charging system.  400 or 500 hours.  In our world if the engine generated ZERO 24 Volt power we would hardly notice the difference in total generator operating hours. By my rough calculation, if we had ZERO 24V output from our main engine it would add about 20 hours a year to our generator operation.  Not exactly a crisis.

We have a single 50 amp 24 Volt alternator on the main drive engine.  When the engine is running, that is more than sufficient to supply all the power we use.  Our average power usage underway is about 13 Amps.  The only reason I can see for wanting more power than that from the main drive engine is to try to be a back up power supply in case of failure of the generator.  That is not something we feel we need, but others might disagree.

We never expect the engine alternator to charge the batteries from a low state of charge.  All we really ask of it is to keep the batteries full when the engine is running.  I don't see a rational for more than that for the way we use our boat.  It is hard for me to imagine a Super Maramu using more than 50 amps from the 24 Volt system for more than a few minutes while underway.

The drive engine makes a very inefficient battery charger. Instead of spending time, money and resources working on the tiny fraction of a year you are under engine power, it seems (to me!) you would be better spending those resources reducing power usage, and optimizing power generation that is useful at anchor--where you will spend the vast majority of your time.

Bill Kinney
SM160, Harmonie
Port Louis, Grenada
http://www.cruisingconsulting.com


Dean Gillies
 

I concur generally with Bill K's comments, except I would personally prefer to go with a little more alternator output. I think 40A is too low. I get about 80A but would like a little more.

Maybe this preference is coloured by the fact I am running an LFP battery system which will almost always accept as much energy as you can throw at it. If I'm running the engine for an hour or so it's nice to get that energy boost. 

Bill runs Firefly batteries, better than standard AGM, but he is still more likely to keep his batteries at a higher state of charge (it's better for the batteries) than I do. So the incremental benefit from a bigger engine alternator is much less important.

When motoring for very long periods my alternator will often be off completely since my battery management system disables it when the SOC goes over 95% and doesn't re-enable it until it drops below 90%.  So a big alternator has no benefit when motoring a lot.

The concept of changing the 12V alternator for an equivalent 24V model and using a DCDC/B2B to maintain the engine battery is interesting. 

You get redundancy in the 24V alternator, and the 12V charge system still has a single point of failure (The DCDC).  Of course if, like me, you already run a DCDC as a second redundant 12V charge source then you are moving back to a single point of failure again by removing the12V alternator.

At the end of the day, for me, I think the better solution is to upsize the 24V alternator and install a small DC-DC converter as a redundant 12v charge source. The 24V bus already has redundancy in charging via the generator and solar/wind if that's installed.

It will be interesting to hear what others think.

--
Dean Gillies
SV Stella *****,  Amel 54-154


Chris Paul
 

Hi Bill,
Thanks for your prompt and considered reply.
Very interesting. 
I think twin alternators would benefit LFP batteries more than lead as they will happily accept another 80A any time.
Here is my point of view.
Electricity is the heart of our boat. So for me it is very important that I have many levels of redundancy.
I hope to be able to cope with whatever situation I am thrown into.
I have 800W of solar and am planning to increase to 1400W soon. 
Even with 1400W of solar on a cloudy day it may only produce 100W.
My generator is 20 years old and I expect it to break down anytime, without much notice. 
If it breaks down in conjunction with another problem (reasonably common in my experience) 
then it may turn into a drama that I would rather avoid.
When I run my engine I also want it to also give a significant reduction in Generator time. 
I figure I might as well gain two benefits at the one time if I can.




Now Bill, consider this scenario (this really sums up why I want more redundancy):
It is late October, almost cyclone season.
You are in a remote Pacific island location, 10 days sail to get to the nearest port out of the cyclone belt.
Your Whisper Power generator breaks down.
The parts you need have a 1 month delivery time (actually takes 2 months for you to receive, then maybe a few weeks to fix).
What would you do?
Wait - probably not. 
I guess you would buy extra fuel gerry cans, strap them to your rails amidships fill up your fuel tank & motor/sail out of there.
Maybe on route, you would turn off your freezer, maybe you would even hand steer sometimes.
- On my last boat I turned off my freezer so I had enough power for the course master electrical steering

This is the reason I want alternative charging methods. 
I want redundancy (first alternator with a high output 40A regulator) and then even more redundancy (a second alternator also with 40A regulator).
My LFP batteries can easily accept every amp I can give them. 
My ONAN generator is 20 years old, still ok, but far more likely to break down than your WhisperPower.  
If I was caught in the above scenario & my generator broke down I could get out of the cyclone zone without much stress. 
Maybe I would have to run my engine with 2 alternators (80A) for 4 hours a day.
Maybe I would have to keep changing tack so the 800W (hopefully 1400W by then) solar panels point towards the sun, 
but I would arrive in port with fuel in the tank & my wife would still be happy - freezer still going!


Also Bill I wanted to say this:
I re-read your article about replacing your ONAN generator with 
WhisperPower M-GV 2 variable speed DC generator.
I love it, so many advantages over the ONAN AC generator: 
it's new, 
quieter, 
Permanent magnet simplicity (maintenance free!)
15% more fuel efficient, 
simple DC straight into the batteries
more space in engine room.
less heat
(not sure if the exhaust elbow problem has been solved with the DC generator - but interested to know) 
Thank you for writing up your articles.

Regards, Chris Paul 
SM #352
SV Glazig, 
Whangarei, NZ


On Saturday, 13 August 2022 at 04:07:07 pm NZST, Bill Kinney <cruisingconsulting@...> wrote:


Chris,

My perspective on this is a bit different.  

We cover a lot of miles in a year, yet the number of hours where we are running the engine in a year is truly inconsequential to our charging system.  400 or 500 hours.  In our world if the engine generated ZERO 24 Volt power we would hardly notice the difference in total generator operating hours. By my rough calculation, if we had ZERO 24V output from our main engine it would add about 20 hours a year to our generator operation.  Not exactly a crisis.

We have a single 50 amp 24 Volt alternator on the main drive engine.  When the engine is running, that is more than sufficient to supply all the power we use.  Our average power usage underway is about 13 Amps.  The only reason I can see for wanting more power than that from the main drive engine is to try to be a back up power supply in case of failure of the generator.  That is not something we feel we need, but others might disagree.

We never expect the engine alternator to charge the batteries from a low state of charge.  All we really ask of it is to keep the batteries full when the engine is running.  I don't see a rational for more than that for the way we use our boat.  It is hard for me to imagine a Super Maramu using more than 50 amps from the 24 Volt system for more than a few minutes while underway.

The drive engine makes a very inefficient battery charger. Instead of spending time, money and resources working on the tiny fraction of a year you are under engine power, it seems (to me!) you would be better spending those resources reducing power usage, and optimizing power generation that is useful at anchor--where you will spend the vast majority of your time.

Bill Kinney
SM160, Harmonie
Port Louis, Grenada
http://www.cruisingconsulting.com


Paul Harries
 

I like the KISS philosophy, address key concern as directly and simply as possible.
As your main worry is generator failure in a remote location, have you considered buying a compact gas powered Honda generator as a backup?

--
Paul Harries
Prospective Amel Buyer


Bill Kinney
 

I think we might have a better generator backup alternative than you credit.

When we are underway, we normally cycle our batteries from something  between 93% and 100% (depending on solar input that day) down to 60-70%. Without running the main engine, the generator runs for 70 to 90 minutes to come back to 93%, and we are good for another 24 hours or so. That cycle from 70% to 93% is about 110 Amp hours. Our total battery discharge might come close to double that if we assume zero solar input.

Our little small case alternator outputs about 48 amps continuously, and with a conservative average consumption of 13 Amps, that leaves us with a net charging capability of 35 amps.  In other words, without counting any solar input at all, our little alternator can keep up with our entire routine underway usage running only 6 hours a day.  Even if we ran the engine at normal cruising speed (1 gal/hr) for those 6 hours, that would give us almost 2 weeks of fuel starting at a half tank. Cut back to the minimum 1500 RPM needed to get full output from the alternator, and you are looking at nearly double that. And we still arrive with BOTH freezers running... and no empty jerry jugs. :)

I am pretty comfortable with our emergency backup generation capability. It's not pretty, or efficient, but it's backup...

---------
After almost 350 hours of operation, we continue to be very happy with our WhisperPower generator.  The whole system is well designed and has worked exactly as we hoped.

On exhaust elbows, I think they really need to be considered a routine maintenance item both for generators and drive engines.  Some last longer than others, but realistically, none of them have design and metallurgy to last for the life of the engine. The catch is that it is hard to predict failure ahead of time since the lifespan can vary a lot depending on the usage cycle even on identical engines.  WhisperPower doesn't list a replacement schedule for theirs.  On my list for next year is to pull it off and have a look. The engine runs pretty heavily loaded all the time, so I don't expect a lot of soot buildup... but you never know until you look!

Bill Kinney
SM160, Harmonie
Port Louis, Grenada
http://cruisingconsulting.com


 

Chris,

One thing some people forget about is the Isolation of both the 12v system and the 24v system. be sure that you have considered that, including the 24-12 converter. Victron makes an Isolated converter. 

Bill

CW Bill Rouse Amel Owners Yacht School
720 Winnie, Galveston Island, Texas 77550 
   

On Fri, Aug 12, 2022 at 10:26 PM Chris Paul via groups.io <chris__paul=yahoo.com@groups.io> wrote:

 

 

Hi All,

I have Lithium Batteries and I’m thinking about twin 24V Alternators on the main engine.

My thinking started about a year ago with "What 24V alternator to put on the main engine when changing to LFP batteries"
   Large frame, Small frame, What Output do I need??
   I decided to go with a small frame as the engine room is already rather full 
   The initial thought was to get a small frame 70A,24V BALMAR but that also required engineering - a new belt

   After much deliberation, I decided to go with what I had "MAHLE 55A" (small frame, running from a simple V-belt ) 
   I changed it from internal to an external regulaton ($150) & installed a BALMAR regulator.
   If my new Lithium batteries "cooked" the alternator then at least I did not destroy an expensive new alternator.
   The installer set the alternator output to about 40A continuously at 1800RPM. 

I then started thinking about getting a spare alternator incase the MAHLE cooked. 
Then I thought it would be smart to replace the existing 12V alternator and hence this email.
   

The basic idea:
Exchange the 12V alternator for a second 24V alternator

 

The 12V Alternator does not really do much -

It only works hard for 2 - 5 minutes after the engine starts. 

 

If the 12V alternator was replaced by a 24V-12V DC-DC charger then the battery would always fully charged – assuming 24V system is ok.

 

 

 


How should I set up?

 

1.     Most probably each alternator requires an external regulator (BALMAR or equivalent)

2.     I can see 2 set up options – and of course many intermediate options between these extremes

a.     Expensive, high output option - two large alternators ( maybe 2x150A = 300A total battery charging!!)

b.     Cheaper Lower output option (can be run by a simple single v-belt) maybe about 2x40A = 80A total battery charging

3.     The setup may benefit from an “alternator off” switch. (switch in the field current wire or use magnetic BALMAR probe). 
      For example, if you need to motor for a few days and the batteries are already full it may be wise to turn off one or maybe both alternators.
4.     Maybe install some type of alternator protection 
            a. "Sterling Alternator Protect"??
            b. put some lead batteries in parallel with lithium??

 

 

 

Advantages:

1.     Redundancy – Assuming you don’t burn out both alternators simultaneously, if one "cooks" you can continue with the other alternator.
2.     Even more redundancy - The 12V "Yanmar" Alternator now becomes a spare for the Generator

 

 

 

Right now I'm happy to go with the simpler, cheaper, lower power output ~50A alternators.
Here is what I see as the advantages of the lower power option:
   I am happy with 80A output, (faster charging comes from the 24V battery chargers and slow charging from solar)
   lower cost than high power option, (maybe $5K cheaper??)
   easy replacement (common truck type alternator - maybe not so simple if it is not insulated??). 
   Not waiting for overseas delivery.
   extra redundancy of 2 alternators, 
   same length V-belt for both alternators - hopefully

 

The high-power option also would have significant benefits, but it’s not for me as I really don't want more high tech & expensive systems.

 

 

 



So, is this a good idea?
Any ideas (good or bad) anyone has will be much appreciated as my knowledge & experience in these things is limited.



Regards, Chris Paul 




Chris Paul
SM#352, Glazig
Whangarei, NZ








Scott SV Tengah
 

Chris,

My first priority would be to increase your solar output. We are at 960 and have figured out a way to add 380*2=760w of hard panels over the Bimini. Assuming they're installed correctly, they just work. Take a look at half cut cells as they tolerate shading far better. 

Regarding alternators, I will preface by saying that I stuck with the standard Mastervolt 110amp 24v alternator that is spec'd on most 54s. I changed the external regulator to the Alpha pro II, which has a lithium profile. It outputs anywhere from 80-90 amps at my miserly 1300rpm (per Amel, the most efficient speed, maximizing range). I disagree with Bill that it has no meaningful impact on generator usage, at least in my case.

We have 450AH of Victron lithium batteries. My 11kw Onan has 200amps of 24v charging capacity. As you know, the lithium batteries will take full current until almost full, so my generator usage is very optimized.

I don't know how much you motor, but let's assume 400-500 hours. 400 hours X 80 amps from alternator = 3200 amp hours into my batteries. Even at my 200 amps of charging via Onan/230v chargers, that's 3200/200 = 160 hours of generator usage saved per year. Don't know about you, but as a result of that, we rarely run our generator and we're cooking with electric and running the dishwasher daily and water maker every third day or so.

For me, nearly eliminating my generator usage (we do run it now and then to make sure it doesn't become a rust ball) is not about saving diesel costs. It's about maintenance and the associated time to source diesel, replace parts, change oil, etc. And listening to that damn Onan. And of course, environmental considerations.

Another side effect is that while my batteries will happily accept 200amps until nearly full, they actually are happier taking 80amps. This gives them more time to top balance as they get full.

I know this doesn't help you decide between keeping your current setup or adding more alternators, but just want to state that our 24v engine alternator contributes a meaningful amount without adding additional operating hours.

How long will you be in Whangarei? We are in Fiji now, but intend to head there for cyclone season.

--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Chris Paul
 

Hi Scott, 
Thanks for your reply.

Yes - more solar - Agree 100% 
A priority for me is to reduce generator time and the twin alternator idea had this in mind. 
Currently I have 780W on arch
I am considering about 400W on the railings as many other boats have.
I'm not happy with soft panels on the bimini.
   The bimini is expensive & time consuming to replace (maybe 3 months during cyclone season). 
   When I see older bimini's with flexible solar I also see stretched seams & sharp edges & places where water drips probably will come.

Please let me know how you can get 760W of hard panels above the Bimini. 
Maybe not possible on my SM as the boom is very close to bimini
(My crazy idea was to recut the main sail clew maybe 6-8" higher - thus lifting the boom enough for hard panels??)
(maybe your boom on the 54 is a bit higher??)

Also my boat came with a wind generator on the mizzen below the radar.
It is currently not connected & I am not sure I even want it because:
 1. The mizzen staysail cannot be used (I love ghosting in flat seas)
 2. An electrician told me it will not work well in conjunction with existing MPPT solar regulators and lithium batteries. 
     Probably needs a new regulator - hopefully someone can explain more about this.
     It will however work on a windy night! 
 3. It is noisy & a bit anti-social.
 4. Old technology, Expensive & time consuming to replace or fix (Solar now has more bang for the buck!)



So my redundancy plan is something like this:

Large battery bank 900Ah lithium + 100Ah of Lead as back up

Electrical cooking - (not using gas unless it is an emergency)
   still have gas connected but have not used since lithium was installed
   no filling of gas bottles - 
   no compliance problems

1KW Electric Outboard -  
   Adds about 25% extra electrical requirements to the existing Amel electrical use - 
   WIFE HAPPY 
      no flooding or starting issues, 
      she can talk on mobile phone while motoring, (we can easily talk to each other)
      light weight comes in 2 parts so no crane required - she sets it up by herself
 
We still have 15HP Yamaha 2 stroke OB 
   main engine back up - my redundancy plan if my Yanmar is out of action.
   speed, if required 
   After buying the electric outboard we hardly use the Yamaha.

Electricity generation - 
   Generator 200A , 
   Twin alternators hopefully 80A when set up, 
   Solar hopefully 60A, 20- 30A now 
   Wind 15A?? more likely 5A (even more likely ZERO AMPS)

So I have numerous options: 
   Once my twin alternators are set up if I run the engine for 2.5 hours it puts out 200AH = 1 hour of generator time
   Once my solar panels are increased I should save generator time.
   The mizzen staysail should also save some engine time.

So it is all a work in progress but I'm slowly getting there.

 
Scott,
I will probably be in Whangarei, or near by, for cyclone season. 
I hope to do some cruising around NZ this summer.
There are 3 other Amels in Whangarei and it is a very friendly marina.
We don't have a car - just cycle or walk as most things are close by.

Regards, Chris Paul 
SV Glazig
SM #352 (2002)
Whangarei, NZ


On Monday, 15 August 2022 at 10:25:40 am NZST, Scott SV Tengah <scott.nguyen@...> wrote:


Chris,

My first priority would be to increase your solar output. We are at 960 and have figured out a way to add 380*2=760w of hard panels over the Bimini. Assuming they're installed correctly, they just work. Take a look at half cut cells as they tolerate shading far better. 

Regarding alternators, I will preface by saying that I stuck with the standard Mastervolt 110amp 24v alternator that is spec'd on most 54s. I changed the external regulator to the Alpha pro II, which has a lithium profile. It outputs anywhere from 80-90 amps at my miserly 1300rpm (per Amel, the most efficient speed, maximizing range). I disagree with Bill that it has no meaningful impact on generator usage, at least in my case.

We have 450AH of Victron lithium batteries. My 11kw Onan has 200amps of 24v charging capacity. As you know, the lithium batteries will take full current until almost full, so my generator usage is very optimized.

I don't know how much you motor, but let's assume 400-500 hours. 400 hours X 80 amps from alternator = 3200 amp hours into my batteries. Even at my 200 amps of charging via Onan/230v chargers, that's 3200/200 = 160 hours of generator usage saved per year. Don't know about you, but as a result of that, we rarely run our generator and we're cooking with electric and running the dishwasher daily and water maker every third day or so.

For me, nearly eliminating my generator usage (we do run it now and then to make sure it doesn't become a rust ball) is not about saving diesel costs. It's about maintenance and the associated time to source diesel, replace parts, change oil, etc. And listening to that damn Onan. And of course, environmental considerations.

Another side effect is that while my batteries will happily accept 200amps until nearly full, they actually are happier taking 80amps. This gives them more time to top balance as they get full.

I know this doesn't help you decide between keeping your current setup or adding more alternators, but just want to state that our 24v engine alternator contributes a meaningful amount without adding additional operating hours.

How long will you be in Whangarei? We are in Fiji now, but intend to head there for cyclone season.

--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com


Daniel Alexander Thompson
 

Very interesting thread.

I have 4x175 watt solar falling about on the aft cabin top because i can't find a calm day to install them on the railings. And I have five really rubbish lead acid batteries. My genset needs repaired.

I turned off the hugely inefficient upright Mango fridge (constant 16 amps) that i have no idea how the original Mango owner managed to power. I plan to replace it with a bigger upright fridge freezer combo.

But i still manage to power a 150 litre freezer that sits - rather insanely - in the wet locker next to the nav table and also a 60 litre vitrifrigo freezer. We turn the big freezer off while we sleep.

I also turn on an "under salon" freezer to chill water on really sunny days.

I refuse to buy a water maker.

So all of you. Feel blessed that you are discussing back up electricity for your electric hobs!!

Daniel
Oronia Mango #14