2 Alternators - Single Engine???

[mvweebles]

Think you missed that the 70 amp was the original and the 150 amp may not fit there or may require substantial changes to the crankshaft pulley harmonic balancer to accommodate the required belt change.

Personally, I like the concept of redundant alternators for a single engine cruising boat.

Ted

Engine is sitting on a bench in a shop in Ensenada MX so this type of work is relatively inexpensive. I had the 70A alternator but wanted to upgrade. Might as well go dual at this point.

 

[Gordon J]

Yup, missed the point. I thought you had 150 and wanted to add 70. Still, Alternator’s are easy to change. I think I would keep it simple and simply have a spare on board. Maybe go to a 150 and keep spare.

 

[Gordon J]

I am confused. You said the 70 was donated and that the 150 is primary. If you have the 150 installed, I would stay with that and by a spare.

 

[mvweebles]

I am confused. You said the 70 was donated and that the 150 is primary. If you have the 150 installed, I would stay with that and by a spare.

Pic of the engine shows the Delco 70A standard alternator. I had purchased a 70A Balmar several years ago but never installed. I do want more charging so decided to purchase and install a 150A Balmar which required adding serpentine style belt. My thinking is that as long as I have the space and the cost is minimal, might as well just install the 70A Balmar as a second alternator vs carrying in a locker.

I like TTs application of daisy chaining them together. I see he liked it so much that he is doing same on his new boat, which tells me it worked pretty well.

 

[Steve DAntonio]

I had a very similar setup on my last boat, and ended up reworking it to be pretty much like what you are contemplating. I liked it so much, I'm doing it again on the new boat.


The setup was a 190A and and 85A alternator on the main engine. They were originally wired with the 190 to the house bank and the 85 to the start bank, each with it's own external regulator.


90% of the time the 85A alternator was doing nothing, so I rewired so both the 190 and 85 went to the house bank for a combined 275A output.



I also controlled both of them together from a single external charge regulator. This may seem counter intuitive, and lots of people will tell you you can't do it, but it actually works exceptionally well. Both alternators are driven by the save Field output from the regulator, and each drives to the same proportion of it's full output capacity. When the controller commands half field, or half output, each alternator puts out half of it's capacity. So the 190 puts out 80A, and the 85 puts out 42.5A. At full commanded output, they both put out full power. So it's always naturally balanced to each unit's capacity.


To charge the start bank, I used a DC to DC charger, Mastervolt in my case.


And my generator I left alone and it charged the generator start bank.


If you search my blog, there is an article on it.

I second all of this, however, I'd ideally use two identical HO alternators, unlike Tanglewood the stock alternator you show in the photo almost certainly isn't designed for continuous high output, so it will likely overheat, especially if charging LFP batteries, and as TW says use a single regulator, with both alt's sending output to the house bank, then share that charge from the house bank to start bank using one of several available devices such as Mastervolt DC-DC converter, Magnum SBC etc.

More on regulators here https://stevedmarineconsulting.com/alternator-charge-regulation/

And large battery banks https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Large-BatteryBank133_03-1.pdf

 

[mvweebles]

I second all of this, however, I'd ideally use two identical HO alternators, unlike Tanglewood the stock alternator you show in the photo almost certainly isn't designed for continuous high output, so it will likely overheat, especially if charging LFP batteries, and as TW says use a single regulator, with both alt's sending output to the house bank, then share that charge from the house bank to start bank using one of several available devices such as Mastervolt DC-DC converter, Magnum SBC etc.

More on regulators here https://stevedmarineconsulting.com/alternator-charge-regulation/

And large battery banks https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Large-BatteryBank133_03-1.pdf

Steve - as always, many thanks. The stock alternator goes away entirely. I have a spare 70A Balmar that I never installed, so will be 150A Balmar + 70A Balmar. Assume running two different amperage is okay?

BTW - for others, I just finished reading a recent Ken's Blog that features Steve's good work. He's really tops in the business.

https://www.kensblog.com/kensblog-inspection-at-the-factory/

Peter

 

[rsn48]

Stock alternators from the factory don't output their full AMP's. The internal regulator drops down the charging substantially so a 70 amp alternator will give you something like 35 amps.

The solution is Balmar or Electromaax regulator. With these regulator you turn your alternator into a smart one. Temperature is monitored and charging adjusted if the alternator gets too hot. For reasons I can not explain and I don't understand, the output is pretty much maximum when using these regulators and less stress on the engine and stuff than using two alternators. I would use the 150 amp alternator with regulator (note: you have to by pass the internal regulator, I'll link to a Jeff Cote talk).

 

[syjos]

It's convenient to have two alternators on a single FL 120. With two different battery banks; 2 group 31's for start and 6 golf carts for house the charging requirements are vastly different. With two alternators, there is no need for charge relays and other electronics to split a single alternator outputs to two battery banks. And it adds reduncy.

I have an 85 amp Leece Neville alternator with external Balmar Max Charge 614 regulator for the starting batteries. Which also powers the generator, thruster, windlass, 2 radars and autopilot. The 85 amp alternator is located in the stock location using stock mount, and belt. The output is dialed down to 50 amps.

An 150 amp Powerline alternator with another Max Charge 614 regulator for house powers everything else. The 150 amp alternator is located next to the other alternator mounted with a custom mount and add on double pulleys. The output on this alternator is set at 100 amps most of the year and cranked up to maximum output after being on the hook for several days and moving to another anchorage during the summer.

Both alternators have temp sensors on batteries and alternators

The start and house banks are totally isolated from each other. There is a selector that can parallel the two banks in an emergency.

This system was installed on Sandpiper 19 years ago. Had an identical system on a Mainship with single Perkins T6.3544 for 15 years with older Balmar external regulators.

 

[O C Diver]

It's convenient to have two alternators on a single FL 120. With two different battery banks; 2 group 31's for start and 6 golf carts for house the charging requirements are vastly different. With two alternators, there is no need for charge relays and other electronics to split a single alternator outputs to two battery banks. And it adds reduncy.

I have an 85 amp Leece Neville alternator with external Balmar Max Charge 614 regulator for the starting batteries. Which also powers the generator, thruster, windlass, 2 radars and autopilot. The 85 amp alternator is located in the stock location using stock mount, and belt. The output is dialed down to 50 amps.

An 150 amp Powerline alternator with another Max Charge 614 regulator for house powers everything else. The 150 amp alternator is located next to the other alternator mounted with a custom mount and add on double pulleys. The output on this alternator is set at 100 amps most of the year and cranked up to maximum output after being on the hook for several days and moving to another anchorage during the summer.

Both alternators have temp sensors on batteries and alternators

The start and house banks are totally isolated from each other. There is a selector that can parallel the two banks in an emergency.

This system was installed on Sandpiper 19 years ago. Had an identical system on a Mainship with single Perkins T6.3544 for 15 years with older Balmar external regulators.

That's how my system is set up. One of the guiding principles on mine is that I started with a new John Deere engine, and everything driven by the original serpentine belt was engineered to work together without any added load on that belt system. The alternator was designed to maintain the start battery with its standard internal regulator. There was nothing I could do to make it more reliable. There were a lot of things I could do, or add to make it less reliable. Driving a large frame alternator with an external regulator on its own belt gives me the additional power to the separate battery bank I need. Don't see how you can get more reliable than split systems without shared electronics or DC to DC battery chargers.

Ted

 

[FF]

"The start and house banks are totally isolated from each other. There is a selector that can parallel the two banks in an emergency."


Standard KISS (sail or motor) for many decades. Works great.

 

[Steve DAntonio]

Steve - as always, many thanks. The stock alternator goes away entirely. I have a spare 70A Balmar that I never installed, so will be 150A Balmar + 70A Balmar. Assume running two different amperage is okay?

BTW - for others, I just finished reading a recent Ken's Blog that features Steve's good work. He's really tops in the business.

https://www.kensblog.com/kensblog-inspection-at-the-factory/

Peter

Yes, as Tanglewood noted, you can use two different size alternators (provided they are HO rated) and they can be controlled by a single regulator. There's one caveat to this set up, Balmar regulators for instance include a temp sensor for the alternator case, that would throttle the field if the case became too hot. If you are operating two alternators from a single regulator, you could not monitor both. Beyond that, it's commonly done with Balmar MC 624s.

 

[rslifkin]

Personally I'd go with the small alternator for engine batteries, large for house setup. I'm not a big fan of connecting batteries for charging except when necessary. If you've got a way to parallel them for an emergency start, that could be used for charging in the event of an alternator failure.

 

[catalinajack]

Balmar regulators have the ABILITY to monitor alternator temps. It is done with a temp sensor from the alternator to the regulator. It is not required but is recommended. I can tell you from experience that these sensors sometimes fail which, in my case, shut down the alternators. I removed them. I should have, but have not, been monitoring the case temps with an infra-red thermometer. I will do so next time out. No expert here but I hazard a guess that, if an alternator is within the manufacturer's published temp parameters while operating in a hot engine room and at maximum output, then onging monitoring, while nice to have, is not necessary. On the other hand, if a sensor fails, one only needs to disconnect it. I may, indeed purchase new sensors, about $40 times two.

Yes, as Tanglewood noted, you can use two different size alternators (provided they are HO rated) and they can be controlled by a single regulator. There's one caveat to this set up, Balmar regulators for instance include a temp sensor for the alternator case, that would throttle the field if the case became too hot. If you are operating two alternators from a single regulator, you could not monitor both. Beyond that, it's commonly done with Balmar MC 624s.

 

[twistedtree]

Balmar regulators have the ABILITY to monitor alternator temps. It is done with a temp sensor from the alternator to the regulator. It is not required but is recommended. I can tell you from experience that these sensors sometimes fail which, in my case, shut down the alternators. I removed them. I should have, but have not, been monitoring the case temps with an infra-red thermometer. I will do so next time out. No expert here but I hazard a guess that, if an alternator is within the manufacturer's published temp parameters while operating in a hot engine room and at maximum output, then onging monitoring, while nice to have, is not necessary. On the other hand, if a sensor fails, one only needs to disconnect it. I may, indeed purchase new sensors, about $40 times two.

I think Steve's point is that you can't monitor the temp on BOTH alternators since the Balmar regulator only has one temp sensor. So you would need to pick which of the two alternators to monitor. If you can establish that one is consistently hotter than the other, then that would be the one to monitor.


This is the same fundamental reason why I think this dual alternator/one regulator trick should only be used when the alternators are both on the same engine. Someone asked about this earlier.


You COULD put them on different engines, but that could result in them operating at different RPMs with different output capabilities, and different cooling capacity. High output demand at low RPMs creates the most heat, and that's the alternator you would want to put the temp probe on. But which one is it? You have no way of knowing. At least if they are on the same engine, they will be turning at the same speed, or proportionally so depending on pulley sizes.

 

[catalinajack]

Twistedtree, I did get Steve D's point. I would never question anything he says or advises. Last year I got rid of the Drivesaver shaft couplers on our boat based on his observations. I was merely pointing out that the temp sensors are optional, not integral to the regulator.

I think Steve's point is that you can't monitor the temp on BOTH alternators since the Balmar regulator only has one temp sensor. So you would need to pick which of the two alternators to monitor. If you can establish that one is consistently hotter than the other, then that would be the one to monitor.


This is the same fundamental reason why I think this dual alternator/one regulator trick should only be used when the alternators are both on the same engine. Someone asked about this earlier.


You COULD put them on different engines, but that could result in them operating at different RPMs with different output capabilities, and different cooling capacity. High output demand at low RPMs creates the most heat, and that's the alternator you would want to put the temp probe on. But which one is it? You have no way of knowing. At least if they are on the same engine, they will be turning at the same speed, or proportionally so depending on pulley sizes.

 

[Steve DAntonio]

Twistedtree, I did get Steve D's point. I would never question anything he says or advises. Last year I got rid of the Drivesaver shaft couplers on our boat based on his observations. I was merely pointing out that the temp sensors are optional, not integral to the regulator.

Please do feel free to question anything I say, especially if it doesn't make sense;-)

 

[rolomart3]

I had a very similar setup on my last boat, and ended up reworking it to be pretty much like what you are contemplating. I liked it so much, I'm doing it again on the new boat.


The setup was a 190A and and 85A alternator on the main engine. They were originally wired with the 190 to the house bank and the 85 to the start bank, each with it's own external regulator.


90% of the time the 85A alternator was doing nothing, so I rewired so both the 190 and 85 went to the house bank for a combined 275A output.



I also controlled both of them together from a single external charge regulator. This may seem counter intuitive, and lots of people will tell you you can't do it, but it actually works exceptionally well. Both alternators are driven by the save Field output from the regulator, and each drives to the same proportion of it's full output capacity. When the controller commands half field, or half output, each alternator puts out half of it's capacity. So the 190 puts out 80A, and the 85 puts out 42.5A. At full commanded output, they both put out full power. So it's always naturally balanced to each unit's capacity.


To charge the start bank, I used a DC to DC charger, Mastervolt in my case.


And my generator I left alone and it charged the generator start bank.


If you search my blog, there is an article on it.

I would sell the 85 amp and buy a Balmar 12 volt 310 Amp high capacity alternator. I would install it where you planned to place the 85 amp one.
Then I would get an inverter, i would sell the Northern Lights geny because with a 12volt-400 Amp alternator capacity and a 4000 watt inverter the geny is no longer needed.The space cleared from removing the geny maybe used for additional Lithium Io batteries.


I would also get rid of all led acid batteries. If the thruster batteries are in series to form 24-volts, replace each with a Lithium Ion battery. Otherwise, create one central bus powered by all Lithium Ion batteries.


In the outside case of total loss of electric power to start the engine, buy two Viking 12,000 mAh starter packs and use them in parallel to restart the main engine.


Make it a one-battery-bank boat and save yourself a lot of grief and expense.


My 3 ceents
.

 

[mvweebles]

I would sell the 85 amp and buy a Balmar 12 volt 310 Amp high capacity alternator. I would install it where you planned to place the 85 amp one.
Then I would get an inverter, i would sell the Northern Lights geny because with a 12volt-400 Amp alternator capacity and a 4000 watt inverter the geny is no longer needed.The space cleared from removing the geny maybe used for additional Lithium Io batteries.


I would also get rid of all led acid batteries. If the thruster batteries are in series to form 24-volts, replace each with a Lithium Ion battery. Otherwise, create one central bus powered by all Lithium Ion batteries.


In the outside case of total loss of electric power to start the engine, buy two Viking 12,000 mAh starter packs and use them in parallel to restart the main engine.


Make it a one-battery-bank boat and save yourself a lot of grief and expense.


My 3 ceents
.

A lot to digest in this post. I thought of much of it and decided against.

First, for long term off grid, I'm matching system to amount of solar I can install, which is 800w. Marginal extra battery capacity is fine for cloudy days, but realistically, more than 1000ah is a waste for this use case (I will have 700ah of house battery).

Second, getting rid of genny. Thought of that, but I plan to cruise the tropics where there is rain, heat, and bugs. Even at anchor. I just don't see running off an inverter and batteries. Best I can tell, it's damn hard on them long term vs genny. The numbers work, but in reality, feedback I got from actual users was they were burning up inverters..

Third, getting rid of lead acid or AGM batteries. That was my original plan. Maybe I need a fancy BMS or something, but best I could tell is LFP do not have the pure CCA that AGM have. And frankly, they are 4x the cost and will not get much use. So it just didn't make sense to me. Again, the raw numbers look impressive until I dug a little further and discovered some limitations of LFP.

Finally, a massive single Balmar vs a pair. Point taken. But I had the smaller one, and mounting a 150A one was feasible without too much work. Now that I have twisted trees good thinking about daisy chaining them, I really like the setup for redundancy. By far, biggest draw will be recharging the house bank. Having the extra ooomph makes sense, and having ability to dial back is also good. Plus, there is built in redundancy. No switching required.

I really appreciate all the feedback. Much to think about. I thank you all for taking the time to respond.

Peter ,

 

[syjos]

A single giant alternator doesn't provide the redundancy of two alternators. If I was redoing my 85/150 amp alternator system, I'd get two identical alternators and two Balmar regulators. Wire it so they charge two banks or one.

We anchor for 5 to 7 days in one anchorage and we don't let the batteries get that low. We run mostly off the inverter but we run the generator several hours a day for battery charging, hot water, holding plate freezer and electric heaters to take the chill off or dry towels.

With excellent sound enclosures, dual stage warlock mufflers, exhaust gas / water separaters and current generator technology, a running generator is totally unobtrusive to those on board and nearby. The generator on Sandpiper has been mistaken for a pump while running.

I believe a generator is essential enough that I've replaced generators on Sandpiper 3 times in 19 years. A generator may not be as green as solar or wind but I have a fricken Power Boat!

As for batteries, everyone has an opinion. I buy lead acid Group 31 and golf cart batteries from Costco because I get the most bang for $ and Costco's generous return/exchange policies and their two cash back programs. And I can replace these batteries 2 to 3 times for the cost of AGM and other high tech batteries.

 

[FF]

If a boat is going to attempt to charge batts with a massive alt , a Balmar would never be my choice.

A DN 50 from a rebuilder is built for 24/7 opertation.

Alternators by Model Family | Delco Remy

Folks with larger engines (detroit) can bolt them to an engine PTO no belt hassles , and the engines oil system will keep it cool.

Unless the boat is commercial, in use 24/7 a stand alone engine to drive the alt would make more sense.

A large engine at low load is the recipe for a slobbering engine.

 

[O C Diver]

A single giant alternator doesn't provide the redundancy of two alternators. If I was redoing my 85/150 amp alternator system, I'd get two identical alternators and two Balmar regulators. Wire it so they charge two banks or one.

We anchor for 5 to 7 days in one anchorage and we don't let the batteries get that low. We run mostly off the inverter but we run the generator several hours a day for battery charging, hot water, holding plate freezer and electric heaters to take the chill off or dry towels.

With excellent sound enclosures, dual stage warlock mufflers, exhaust gas / water separaters and current generator technology, a running generator is totally unobtrusive to those on board and nearby. The generator on Sandpiper has been mistaken for a pump while running.

I believe a generator is essential enough that I've replaced generators on Sandpiper 3 times in 19 years. A generator may not be as green as solar or wind but I have a fricken Power Boat!

As for batteries, everyone has an opinion. I buy lead acid Group 31 and golf cart batteries from Costco because I get the most bang for $ and Costco's generous return/exchange policies and their two cash back programs. And I can replace these batteries 2 to 3 times for the cost of AGM and other high tech batteries.

As previously mentioned, I prefer to maintain the original system for the start battery and prefer the large frame commercial duty 220 amp Leece Neville alternator with its own serpentine belt. The commercial series alternators have over size bearings and are designed to run continuously at rated output. If I felt I needed a backup to that system, for less than $1K, I could have a spare alternator, Balmar regulator, and a serpentine belt (have the belt already). They wouldn't take up much space and are fairly easy to change out.

Ted

 

[sbman]

A lot to digest in this post. I thought of much of it and decided against.

First, for long term off grid, I'm matching system to amount of solar I can install, which is 800w. Marginal extra battery capacity is fine for cloudy days, but realistically, more than 1000ah is a waste for this use case (I will have 700ah of house battery).

Second, getting rid of genny. Thought of that, but I plan to cruise the tropics where there is rain, heat, and bugs. Even at anchor. I just don't see running off an inverter and batteries. Best I can tell, it's damn hard on them long term vs genny. The numbers work, but in reality, feedback I got from actual users was they were burning up inverters..

Third, getting rid of lead acid or AGM batteries. That was my original plan. Maybe I need a fancy BMS or something, but best I could tell is LFP do not have the pure CCA that AGM have. And frankly, they are 4x the cost and will not get much use. So it just didn't make sense to me. Again, the raw numbers look impressive until I dug a little further and discovered some limitations of LFP.

Finally, a massive single Balmar vs a pair. Point taken. But I had the smaller one, and mounting a 150A one was feasible without too much work. Now that I have twisted trees good thinking about daisy chaining them, I really like the setup for redundancy. By far, biggest draw will be recharging the house bank. Having the extra ooomph makes sense, and having ability to dial back is also good. Plus, there is built in redundancy. No switching required.

I really appreciate all the feedback. Much to think about. I thank you all for taking the time to respond.

Peter ,

Inverters have improved significantly over the past 5 years. Not all of the marine inverter manufacturers have kept up with technology advances. Victron makes some solid units, but even smaller companies are making reliable, durable units that will provide good service in full time daily use even with heavy loads. I helped rewire a GB 42 in a from the ground up restoration and we used a 2500W commercially rated inverter unit, with no AC going into the boat from the shore power, all onboard AC is provided by inverter and Carbon Lead Acid batteries. The owner uses power saws, electric tea kettles, hair dryers, etc... in a full time live aboard scenario. It has been very reliable.

Often overlooked when considering lithium is charge acceptance rate. The lithium batteries can accept significantly higher charge rates than lead based batteries.

A completely dead lead acid battery requires 8-10 hours to achieve a full charge and go through the bulk and absorption cycles and reach float and get to 100% full. You need 100% full on a regular basis to get good life out of lead acid. Running your genset in the morning for 2-4 hours, getting the bulk phase done and letting solar finish it off is a good strategy. A larger alternator or genset won't really help with charging lead acids any faster. They typically accept about 0.1C maximum. For example a 600AH bank will accept 60 amps initially and it tapers down from that during the charge cycle.

Lithium batteries can accept a far higher charge rate up to 80% full, and it then begins to taper off. Lithium batteries can accept 0.5-1C so a 600AH bank will accept up to 300-600 amps charging current and it maintains that longer with less taper. So your genset run (with one or more large capacity chargers) can be significantly shorter, charge to 80%, and you really don't have to worry about getting them to 100%, they will actually last longer if you regularly charge to only 80%.

You can discharge lithiums to 20% regularly and it will not degrade them. Yes they are 4X the cost, but they should last 4X as long and give you many options for how often you charge, how deep you discharge and the built in BMS takes care of all the management for you. The good ones come with long warranties, and given the deeper discharge available, you don't need as many of them. They aren't for everyone, but if you plan to live aboard for 10+ years they can make sense.

Personally I would not start my diesel with LiPO4 (LiFE) batteries, I'd use a separate starting battery for that and dedicate lithiums to a house bank.

 

[Transaxial]

Folks - could use some good thinking on whether I should add a second alternator or not; and if I do, how it should be run.

BACKGROUND (see DC diagram attached):

• Weebles: Willard 36 with single Perkins 4.236 (80hp).120VAC and 12VDC (no 240VAC, no 24VDC)
• Battery Banks:
  • 600AH Lithium house
  • 2x group 31 AGM for gen start, thruster, and windlass. Note, gen does not have dedicated battery. Frankly, I am out of room.
  • 1x group 31 AGM for engine start

NOTE - there is a Renogy DC-DC converter between the Lithium batteries and the AGM/G31s
​

• Charging Sources (all new):
  • 150A Balmar regulated alternator (primary)
  • 70A Balmar regulated alternator (secondary - sort of a freebie - question is should I install this, and if so, where/how?)
  • 15A alternator on the generator (useless?)
  • 800kw solar panels
  • 3.2 kw Magnum hybrid charger (shore power or gen set)

EXAM QUESTIONS:

• See hand-written notes on attached diagram. I already have the two Balmar alternators. Q: Should I install the second one? Engine is out of the boat and sitting on a bench, so welding a bracket is pretty easy at this point.
• Q: If I add the second Balmar, where should I run the 70A hot?
  • Same bus-bar feeding the House bank as the 150A making 220A
  • Different bus bar feeding the G31s AGMs?
  • Don't bother with the second Balmar?
  • Something else?
  Q: What to do with the weeny output of the 15A alternator on the NL 6kw generator? Anything?
• Other comments/observations are welcomed. Attached wiring diagram has been changed a bit, but for purposes of this post, is correct for the DC wiring.

Thanks in advance!

Peter
View attachment 100087

View attachment 100088

Wish I had read this thread before I reworked the front of my 6D14 Mitsubishi, 6.5 liter NA inline 6 diesel 115 hp. I wanted to add a 9 gpm clutch pump for the new thruster so had a 4 B groove pulley machined to fit on the front of the oem 2 B pulley that drives the water pump and a large frame 24 V alternator that was original equipment on the engine. Start batteries are 2- 31 series batteries in a dedicated system with a 24 V 10 amp automatic charger to keep charge up on shore power. On the port side is a 160 A 12 V truck alternator driven by 2 B belts and charges the house bank which is 4 or 6 golf cart batteries. A spare of both 12 and 24 alternators is on board. A Xantrex 2000 watt inverter charger draws from house bank and recharges it when on shore power. My boat sits for several months at times so the chargers keep the LA batteries at optimum voltage. The small pulley on the far port drives a Detroit centrifugal water pump for the keel cooled transmission, hydraulic cooler, and engine exhaust manifold cooler and could be used for other coolers like the water cooled alternators mentioned in this thread and for refrigeration condensers. The double belt configuration seems to balance side load on the crank and since the belts don’t have to be super tight, there is no excessive load on any component. To keep this system simple, I keep spares of all the alternators , belts and starter and a couple sets of good booster cables to be able to get 12 or 24 volts from a variety of battery combinations.

I have a good space available and am pretty far along in designing a 6-8 kw 1800 rpm D1105 Kubota genset to supply extra power when refrigeration and water maker is needed on long trips. This genset is close to both other battery banks and I wonder about the pros and cons of running off the house bank (12 v) or just hooking to one 12 volt of the 2 31,s in the 24 volt bank. The Kubota has its own little alternator. A separate 12 v battery would also be possible. The existing system seems to work very well and I don’t want to throw it out of balance or over complicate what is working. Lots of good ideas in this thread but at this stage I don’t want to reinvent the wheel!!

My boat is currently designed to run on minimum 12 v power and the addition of a genset would allow going to the next level of appliances and offer battery charging when the main engine is not being run. Sounds similar to to OP’s boat.