House Battery System Configuration Brainstorming

[Gdavid]

I am thinking through my options on how I would like to configure the house battery set up on my new (to me) Mainship 34 MK1. In particular I'm trying to weight the cost an benefit of retaining the existing charger/inverter as it works and I already own it but it may limit the options I have for other components.

Currently the boat only has 2 - 27 group dual purpose, lead acid batteries that serve as a consolidated starting and house bank. It is charged by a 1500 W Promariner modified (Promariner call is a quasi sine) sine wave inverter/charger. It is incorrectly configured to feed the entire AC panel (which is clearly cannot support). The refrigerator onboard is a AC only unit, that was probably installed in conjunction with the inverter system. The boat has it's original 3kw onan generator which has it's own starting battery. The boat has an electric galley and no other battery systems onboard.

The intended use for the house battery system is pretty modest, I would like to be able run the refrigerator and small ac devices (charging laptops and tablets) for 12-18 hours between charging via shore power or running the generator. Because the boat has an electric galley, I don't anticipate any extended cruising that would not involve having shore power or running the generator at least once a day. I would also like to size, configure and position this battery bank to support future loads such as an upgraded windlass and bow thruster.

I have at least 2 locations I could easily place a dedicated house battery system with easy access to run all the wiring I need.

For purpose of discussion, I'm going to try to generalize my options into 4 approaches but certainly I could go about this in many ways. I'm open to other options.

Option 1 - Dedicated inverter bank, combined starter/house bank:
Leave the two group 27's in place as engine, electronics and house loads, install a new inverter specific bank of flooded lead acid or AGM type batteries to support the existing inverter. Rewire the inverter to limit loads to outlets and install a dedicated charger for the existing bank.

Option 2 - Inverter/house bank, dedicated starter bank:
Leave the two group 27's in place as engine battery only, install bank of flooded lead acid or AGM type batteries to support the existing inverter and house loads. Rewire the inverter to limit loads to outlets and install a dedicated charger for the existing bank.

Option 3 - Lithium Iron Phosphate House/Inverter Bank:
Upgrade inverter/charger to system with charging profile for LiFePO and install new house/inverter bank, properly wired and then install a simple, standalone charger for the starting battery or DC to DC charger to piggyback off of the LiFEPO.

Option 4 - Isolate starting to new bank shared by main engine and generator, replace the existing house/inverter bank with a larger capacity but reuse much of the wiring and battery box. Re-wire the inverter to outlets only.


Goals, constraints, considerations: I want to ensure I don't end up with a dead starting battery and no way to get home, the intended use is all local cruising so if I end up with a dead inverter bank and warm refrigerator, it isn't the end of the world, the boat isn't used far from civilization, I can throw out bad milk. I want a pretty fool proof system that my wife and kids can operate easily. Budget is not limitless, but I'd rather not have to replace components just down the road, I'm perfectly happy with the limited capacity and functionality of the existing inverter, we aren't running expensive components with it and the non-pure sine wave status doesn't seem to be a problem for now, the current (bad pun) issue is the miss-wiring and limited battery options at this point.

I'd appreciate any thoughts. Thanks

 

[sbman]

I like option 3 the best of the approaches you outlined no matter if you choose to go with LiFE batteries or stay with lead acid, it's the only option that puts in a new inverter that can support the house loads without using extension cords if you want to run something that isn't on the 'inverter outlet'. Modified sine is also likely to become a problem in time.

I would think there's going to be quite a bit of cost to rewire your AC panel for options 1, 2, and 4 to divide up the loads. Money would be better spent on a 3KW inverter that can be wired through it's automatic transfer switch and feed all the outlets the same as the genset. Easier to use, easier to configure and you don't have to rewire the AC panel. If you get an inverter/charger it can also charge the bank it's attached to. Put a DC-DC charger to charge the house bank and you'll have an isolated start battery that can be of any chemistry the DC-DC charger supports. You could carry one of the new lithium 'jump packs' as a backup if you are worried about the start bank becoming drained accidentally.

 

[Gdavid]

I like option 3 the best of the approaches you outlined no matter if you choose to go with LiFE batteries or stay with lead acid, it's the only option that puts in a new inverter that can support the house loads without using extension cords if you want to run something that isn't on the 'inverter outlet'. Modified sine is also likely to become a problem in time.

I would think there's going to be quite a bit of cost to rewire your AC panel for options 1, 2, and 4 to divide up the loads. Money would be better spent on a 3KW inverter that can be wired through it's automatic transfer switch and feed all the outlets the same as the genset. Easier to use, easier to configure and you don't have to rewire the AC panel. If you get an inverter/charger it can also charge the bank it's attached to. Put a DC-DC charger to charge the house bank and you'll have an isolated start battery that can be of any chemistry the DC-DC charger supports. You could carry one of the new lithium 'jump packs' as a backup if you are worried about the start bank becoming drained accidentally.

Thanks, I need to dig a little deeper and should probably diagram out exactly how the AC and DC is configured now in order to design the new setup and avoid hiccups.

 

[R. Bush]

Seems as if option 2 is your easiest way out if that is what you are looking for.

If you decide to up the ante and go for a system upgrade and a lot of new components you may also want to consider the option of converting your boat to a 24V system. It is something I have been looking into.

You can easily add a couple of switches to your system that will let you use the house bank for starting the engine if your main starter battery fails.

I'm sure you are going to get lots of good advice here on how to proceed. There a lots of places on the internet and uTube that talk about marine electrics. Have a look at some of the videos and advice from Jeff Cote of Pacific Yacht Systems e.g.:

 

[ranger58sb]

IIRC, from a long time ago... and if it helps...

Our 34 Mk III had a single 8D located to starboard, acting as a combined start/house battery. We didn't have an inverter; never got a round tuit on that. Never had any "dead battery" issues and we anchored out often; we just ran the genset 2x/day to charge.

The genset had it's own start battery, and it's alternator charged the genset start battery.

Were it me (without boatloads of more current specific analysis), I think I'd upsize the single start/house battery bank to the extent possible within space constraints, use it as a combined start/house (and inverter) bank... and call it good.

Upsizing would probably include some combination of physically-smaller batteries -- maybe four Group 31s, maybe six GC2s or maybe six of the taller L16s, etc. No 8Ds! Have to pay attention to overall weight, to avoid inducing an unsolvable list. I remember it was a pain to access that 8D to water it; I'd probably choose AGMs to solve that these days. Inverter to outlets,, and in your case, including the AC-only fridge.

In the years since then, we've noticed lots of boats are originally configured with combined start/house banks. Our two most recent boats, ditto, no issues.

That does of course mean paying attention to battery condition... but I've not ever found that very difficult.

-Chris

 

[Bacchus]

George

I think you should consider changes as separate decisions... how do you want banks configured and what batty chemistry you want.

My MS had a 2 8D combined house / start bank and a separate 8D thruster (B&S) bank. Gen had its own GP 24 start. MS had originally installed diode isolators for Alt & shore chargers to charge multi batty banks. I have switched from FLA to AGMs but how they are configured have little bearing on which chemistry to use IMO

Over time I have
1. Eliminated diode isolator and substituted a Sterling CVSR to charge house / start & thruster bank using Alt.

2. Eliminated gen batty charging from main eng alt & shore using gen alt to charge itself when run. I also replaced the gen on/off Sw with a 1-2-all-off Sw on same foot print & bolt pattern to allow adding a jumper from house to gen sw for use in an emergy to start gen or periodically to tie in gen batty to "top off" charge it I havent run gen in awhile

3. Recently moved main eng start to my thruster bank leaving a pure house bank. I have combined the 2 house 8Ds into one bank as I installed a Balmar smart gauge to better monitor house V & SOC and start V. The Balmar does not work with a switched configuration and was part of my decisions to combine. One plus I was looking was to separate high amp loads from the house bank. I had issues with V drop when starting affecting electronic nav equip when combined w eng start.

I figure my gen is my back up for start if start battys have any issues and need a charge boost. Back up for gen batty should there be any issues is the gen sw that allows me to combine w house. My plan B back up is to make / carry a jumper to combine main eng starter to house bank.

I have decided to not replace 8Ds when needed but would instead use two GP31 AGM for start / thruster.
I considered and could use 4 GCs or GP31s for house bank. With AGMs East Penn confirmed that with AGMs GP31s work as well as GCs for deep cycle and the converse as well... GCs work as well for starting as GP31s. The reason it holds for AGM is that unlike FLA they do not/ or need to tailor plate design for each application. EP Duracell AGMs state both AH and CCA specs so easy to compare performance. I am pretty sure I will use all GP31s just to keep things consistent.

The decision around LiFePo is one I havent considered seriously as I wasn't interested in investing that much $$$, didn't think I'd be boating long enough to ever break even if the additional life is what is claimed. I do like and willing to pay the premium $ for AGM vs flooded but the changes I've made could easily handle or be satisfied by FLA battys if anyone wanted to (In that case I would certainly use GP31 for high amp start /thruster and 6V GCs for house.

What you decide re inverter & whether to separate loads or manage them manually is another separate decision IMO

Hope above thoughts help. Lots of different approaches and none always correct. Some are proponents of one large bank to service everything and that can work if managed correctly.

 

[Gdavid]

Thank you to all, a lot of food for thought to work through.

I really enjoy this kind of stuff and it is what brought me to this forum 5 years ago looking for and receiving some great advice on setting up my father's Mainship MK3, that boat already had a dedicated flooded lead acid 6 volt batteries in parallel & series but no generator. We added a generator and changed very little else. He has since upgraded to a newer boat and I am starting my own adventure with this old scow.

 

[Jeff F]

I had 4 group 31 AGMs in a combined start/house bank on my 34. I think that's the simplest solution. I kept an eye on voltage and never discharged them severely. No problems with supporting AC fridge and modest house loads for 36 hours.

My backup plan for engine start with a dead bank was to start the generator and charge from there. Genset had a dedicated battery. And I carry a lithium booster pack. Never had to do that.

Consider a monitoring system as well. If you are able to keep an eye on current and battery state of charge you'll learn a lot and hopefully avoid a dead bank.

 

[High Wire]

A few questions:
- Propane or electric stove?
- Electric water heater has an engine heating coil?
- What is the charger capacity of the I/C?
- Single or twins?
- What is the footprint available for a larger house bank? Can you fit at least 4 GC's?

Manual load shedding of the water heater is easy, especially if it can be engine heated. KIS, Just leave the breaker off. Our twenty gallon holds hot water 2-3 days after a few hour run. The other breakers can be left on. No need to go through a rewiring project for a small job.

We have 6 GC's as a single bank and use that to start the single Perkins engine. The gen has a separate M24 battery as the backup plan if we ran the house bank dead. Our cruise up the east coast to NY Erie Canal and back to FL was no problem even with 2 of the GCs accidentally left disconnected (my bad).
Run the gen an hour in the morning on cruising days or one more time for an hour at dinner if the microwave is needed or its a lay day at anchor.

 

[Mischief Managed]

I like option 2 and if you ever need more inverter capacity, you can just install a better inverter without doing anything else. I would use 4/0 wiring from the bank to the inverter so that it's future-proof, capacity-wise. If would include a 500 amp ACR/battery combiner in the mix so that the main engine alternator charges both banks and so you can easily use the house bank for emergency starting.

 

[Gdavid]

A few questions:
- Propane or electric stove?
- Electric water heater has an engine heating coil?
- What is the charger capacity of the I/C?
- Single or twins?
- What is the footprint available for a larger house bank? Can you fit at least 4 GC's?

Manual load shedding of the water heater is easy, especially if it can be engine heated. KIS, Just leave the breaker off. Our twenty gallon holds hot water 2-3 days after a few hour run. The other breakers can be left on. No need to go through a rewiring project for a small job.

We have 6 GC's as a single bank and use that to start the single Perkins engine. The gen has a separate M24 battery as the backup plan if we ran the house bank dead. Our cruise up the east coast to NY Erie Canal and back to FL was no problem even with 2 of the GCs accidentally left disconnected (my bad).
Run the gen an hour in the morning on cruising days or one more time for an hour at dinner if the microwave is needed or its a lay day at anchor.

- The stove is electric, a simple two burner, 120V Kenyon (not an induction)
- The water heater is connected to the engine
- The charger side is 30 amps
- Single 160 perkins, I don't have the specs on the alternator, there is a receipt from it's replacement but looks stock.
- Plenty of footprint for additional batteries. The current location, which is on starboard, just forward of the starboard fuel tank has access above to service flooded battery types and the battery box is bulky, a thinner battery box would allow more batteries, there is room on the port side but no access above so maintaining flooded batteries would be difficult here.

 

[Iggy]

I would consider solar panels. They will extend the life of your batteries between recharging.

 

[High Wire]

- The stove is electric, a simple two burner, 120V Kenyon (not an induction)
- The water heater is connected to the engine
- The charger side is 30 amps
- Single 160 perkins, I don't have the specs on the alternator, there is a receipt from it's replacement but looks stock.
- Plenty of footprint for additional batteries. The current location, which is on starboard, just forward of the starboard fuel tank has access above to service flooded battery types and the battery box is bulky, a thinner battery box would allow more batteries, there is room on the port side but no access above so maintaining flooded batteries would be difficult here.

Your charger is small for a 4 or 6 golf carts batts. The stock alternator is about 60 amps which is ok for starting batts but small for a GC house bank. You will want to be able to recharge relatively fast for minimum gen run time. FWIW we have a 2000 watt Magnum I/C which has 100A charger and upgraded the alternator to 100A. Refrigerator is a small current draw but for a long time. So it is the biggest AH draw on the hook.

You won't be able to run your electric stove or microwave more than 2-3 minutes off the inverter so need to run the genny for that.

 

[Gordon J]

Not one of your options, but you might consider firefly batteries for the house bank. Two group 31 batteries will give you 240 AH. You get lithium -like performance without the science/engineering project.

Gordon

 

[Gdavid]

Thanks again to all for the thoughtful input.

I will have to take another look at the firefly batteries, last time I looked into them they were similar in price to the current pricing of Lithium Iron Phoshate, I've heard there are some quality control issues with them as well but i need to research some more.

Because the stove is electric, I plan to run the generator for every cooked meal, I'm not looking to support the stove off an inverter but I will run the microwave off of it. The majority of our cruising is during the summer and I don't hesitate to crank up the genny to run Air conditioning as well, it is humid on the Chesapeake and my family has become pretty spoiled boaters, I grew up jumping in jellyfish invested water to cool off (in the snow, uphill, both ways, etc).

My wife and I have 3 kids so water and waste holding is a pretty limiting factor, generally only anchor out for 2 days in a row maximum. The Chesapeake is too silty for water makers and limited areas to treat and pump overboard, so tankage will be a limiting factor to days on the hook. The kids really enjoy a marina with a pool so we make it to a dock at least every 3 days, if I end up oversizing the battery and it only gets a full charge at the dock, it would be fine for now. Solar is a possibility, but between running the generator for meals and frequent docking, I don't see it as a priority this year.

Aside from correcting the AC system to limit the inverter to supporting the outlet outlet circuits, it will eventually need some other upgrades, I only have one 30 amp input so I have to manage loads even at the dock. I also have a good used 8kw genset sitting in my garage that will go into the boat as an upgrade to the single cylinder 3kw. When that goes in, I will probably upgrade the AC panel and add a second 30 amp shore connection. I was honestly surprised at the little MJDA, I had heard they were really load and obnoxious machines, but this one is set up well and I don't mind listening to it at all. The previous owner did a pretty thorough sound insulating effort and that must be helping.

 

[Gdavid]

Thanks again to all, I think I'm going with option 4 but will incorporate as much feedback along the way.

The house bank will be four group 31 sized AGM batteries split between the existing battery bank location and across the engine room on the port side using equal length cables, being maintenance free, I can use tie down straps and just cover the battery terminals for protection. The two existing 27 lead acids and the box they are in, will move back next to the generator and support the generator, main engine and navigation electronics. The windlass and eventual thruster will feed off of the house/inverter bank to avoid voltage drops messing with my electronics. The alternator will feed the engine bank and a charging relay will go to the house bank. For now the inverter/charger will be retained but rewired correctly. The house bank will primarily be charge when docked or off of the generator when run for meals or Air conditioning.

I'll have a combiner between the two banks as well as a booster pack to start the generator. I suspect the health of the two 27 lead acid batteries, the were reportedly too week to start the engine earlier this spring when the charger was left on and a float switch was stuck on. They would be relatively cheap to replace if needed.

I think this approach will limit the need for a massive rewiring effort and allow for future upgrades later without too much rework. Eventually, I'd like to pursue LiFePO4 technology but the market for marine chargers to really benefit them is limited at this point, to my knowledge.

 

[rgano]

I like option 4 with anything but lead acid batteries. I don't see much advantage in a house bank configured with lead acid batteries. Add a parallel switch between house and start bank for that time when your start bank has a dead batt and your house bank is healthy enough to start the genny. Been there.

 

[catalinajack]

And I like Option 4 with flooded batteries. No shortage of opinions here.

I like option 4 with anything but lead acid batteries. I don't see much advantage in a house bank configured with lead acid batteries. Add a parallel switch between house and start bank for that time when your start bank has a dead batt and your house bank is healthy enough to start the genny. Been there.

 

[Gdavid]

And I like Option 4 with flooded batteries. No shortage of opinions here.

I've had good luck with flooded golf cart batteries in the past, my only hesitation in this case is that I would have trouble accessing half of the bank to check fluid levels. In my experience they are very good as long as you have your charger set up properly to avoid over charging them, but you need a proper setup charger for any battery type so that should really be held against them.

Catalinajack, you have probably seen my boat around your area before, the PO kept it in the boat shed at West River Yacht Harbor, named Graceland. It is now down at HHS.

 

[ranger58sb]

We kept our Mk III at West River Yacht Harbor... back in the '90s.

-Chris

 

[Xlantic]

I've had good luck with flooded golf cart batteries in the past, my only hesitation in this case is that I would have trouble accessing half of the bank to check fluid levels.

A battery-watering system will solve that problem. Flow-Rite is a good brand.

 

[Gdavid]

Thank you again for the solid input. I have re-configured the inverter wiring so that it no longer feeds the entire AC panel, from now on it will only feed select outlets including the refrigerator but it will continue to default to powering them through the shore power or generator source when available.

I read through the inverter/charger manual installation manual carefully as I did not want to create any new problems for myself and was surprised to see that feeding entire panel was one of 3 recommended configuration options. It certainly isn't an ideal configuration for me and I feel much better about the current setup. We were on the boat the other evening, showing my sister around when the dock power went out due to a storm and the inverter kicked in attempted to power the air conditioning, which had been running at the time, clearly a problem and I can't see how the installer of this system thought it was a good idea.

The two group 27's which are undersized for my needs are also definitely deteriorated and need to be replaced, I left the refrigerator running for about 1.5 hours the other day and they were too weak to start the engine.

I think I'm going with a combined house/starter bank of 3 - 200 AH AGM batteries. I'm doing one bank for now because my inverter is the only charger on the boat now and if I add another AC powered charger, it will likely exceed the capacity of my single 30 amp shore power inlet. Re-wiring for a second 30 amp shore power input will be a good project left for the off-season.

 

[Jeff F]

Sounds good. I meant to suggest earlier that you can run a lot of the small electronics on 12v through built in USB ports or car adapters in a lighter plug. On my 34 I had the inverter wired to the fridge and two plugs, but a couple of 12v USB bars as well to handle devices.

 

[ghost]

I have my inverter powering the entire panel and there are some significant benefits in doing so. The inverter can fix low or dirty voltage being input from shore and supplement the amperage when the boat peak loads exceed the shore power capability. However the biggest downside is the inverter trying to run the whole panel if the shore power drops out. To solve that I have a relay that connects the three main circuits in my panel. If the relay does not see shore power voltage, two of the three circuits drop out immediately reducing the load to the “away from shore” circuits. I also have a small ten amp circuit breaker that I can throw manually to add the load shedding circuits back in (after one has turned off all but maybe one breaker on the load shed panels). If you forget about that breaker and try to run too much current, it simply trips and you are back to load shedding mode.

There are pros and cons to every setup. That’s about the best you can say.

 

[ghost]

Thank you again for the solid input. I have re-configured the inverter wiring so that it no longer feeds the entire AC panel, from now on it will only feed select outlets including the refrigerator but it will continue to default to powering them through the shore power or generator source when available.

I read through the inverter/charger manual installation manual carefully as I did not want to create any new problems for myself and was surprised to see that feeding entire panel was one of 3 recommended configuration options. It certainly isn't an ideal configuration for me and I feel much better about the current setup. We were on the boat the other evening, showing my sister around when the dock power went out due to a storm and the inverter kicked in attempted to power the air conditioning, which had been running at the time, clearly a problem and I can't see how the installer of this system thought it was a good idea.

The two group 27's which are undersized for my needs are also definitely deteriorated and need to be replaced, I left the refrigerator running for about 1.5 hours the other day and they were too weak to start the engine.

I think I'm going with a combined house/starter bank of 3 - 200 AH AGM batteries. I'm doing one bank for now because my inverter is the only charger on the boat now and if I add another AC powered charger, it will likely exceed the capacity of my single 30 amp shore power inlet. Re-wiring for a second 30 amp shore power input will be a good project left for the off-season.

I never liked relying on having to remember to do something to keep from winding up with the inability to start the boat. While separate charging might be nice, an inexpensive automatic charge relay will isolate your starting battery whenever it is not being charged for around $50.

Many small fridges will easily consume 50 amp hours a day, which is a lot to ask of a single group 27 battery, let alone an older one. We cruised on a small boat for years with nothing but a small ice box. Not as convenient as a running frig, but I never woke up stranded because I couldn’t start the boat either! Packing the frig with block ice still works and can easily get you days.

BTW, I have a 1400 amp hour house bank. I can easily charge it with a single 120amp charger off my 30amp shore power. No need to put in a second service just to charge multiple small banks.

 

[Gdavid]

Not one of your options, but you might consider firefly batteries for the house bank. Two group 31 batteries will give you 240 AH. You get lithium -like performance without the science/engineering project.

Gordon

I just realized that you own the Ocean Alexander a few slips away from me at HHS, I've been walking past it for a few days now scratching my head trying to figure out if it was the one that used to carry a helicopter on the aft deck, the radar arch really far forward looked familiar to me. I found myself searching through the archives to confirm it. That is a fascinating and beautiful boat.

edit: I guess you just sold it

 

[boomerang]

On our 34 ,we ended up and are happy with a house bank of 3 ,with the option of adding another. group 27 flooded deep cycle batteries for a total of 270AH. 270 is the bare minimum ,for us, that will give 2-3 days at anchor without recharging. The big draw is the 12v refrigerator that uses around 4 amps pretty much continuously in warm weather followed by the fresh water pump that gets used minimally. When anchored we also leave the AIS on and maybe 1 vhf. All lights are LED which helps ,especially the anchor light that stays on all night. We cook with propane but the occasional microwave use via the inverter is a power hog. The engine start is a group 31 dual-purpose that can be paralleled by the ACR combiner if needed. I do have the anchor windlass connected to the engine battery (hence the dual-purpose and not a starting) since we only use it after the engine has been started.
I'm hard-pressed to upgrade the stock 65A alternator on the Perkins because of the cost of a complete serpentine belt system, high-output alternator and programmable regulator would be in the $2000 range. The stock alternator struggles...and by struggles I mean it gets hot as hell, to bring the current system up to a full charge so I'm really hesitant to add the 4th group 27 to the house. Also, the alternator field is energized from the engine ignition key via a relay but senses the house bank first and only after it's brought them up to almost full (4-6 hours from 50% discharge @ 1650 RPM), does the ACR kick in to start charging the start battery, unless I manually engage it via the on/off/auto switch. At the dock everything is charged by a ProMariner Pronautic 50A charger which seems to be fine for the system.
It sounds complicated but it's really not. The spares we keep are an alternator, a belt & a relay for the field connection to the ignition.

 

[rgano]

On our 34 ,we ended up and are happy with a house bank of 3 ,with the option of adding another. group 27 flooded deep cycle batteries for a total of 270AH. 270 is the bare minimum ,for us, that will give 2-3 days at anchor without recharging. The big draw is the 12v refrigerator that uses around 4 amps pretty much continuously in warm weather followed by the fresh water pump that gets used minimally. When anchored we also leave the AIS on and maybe 1 vhf. All lights are LED which helps ,especially the anchor light that stays on all night. We cook with propane but the occasional microwave use via the inverter is a power hog. The engine start is a group 31 dual-purpose that can be paralleled by the ACR combiner if needed. I do have the anchor windlass connected to the engine battery (hence the dual-purpose and not a starting) since we only use it after the engine has been started.
I'm hard-pressed to upgrade the stock 65A alternator on the Perkins because of the cost of a complete serpentine belt system, high-output alternator and programmable regulator would be in the $2000 range. The stock alternator struggles...and by struggles I mean it gets hot as hell, to bring the current system up to a full charge so I'm really hesitant to add the 4th group 27 to the house. Also, the alternator field is energized from the engine ignition key via a relay but senses the house bank first and only after it's brought them up to almost full (4-6 hours from 50% discharge @ 1650 RPM), does the ACR kick in to start charging the start battery, unless I manually engage it via the on/off/auto switch. At the dock everything is charged by a ProMariner Pronautic 50A charger which seems to be fine for the system.
It sounds complicated but it's really not. The spares we keep are an alternator, a belt & a relay for the field connection to the ignition.

I am worried that your 65-Amp OEM alternator might give up the ghost with all that stress. Are you pulling it for maintenance by a shop every so often? I understand the hesitancy to go the expense of a bigger alternator system, but I replaced a 65-Amp one a Ford Lehman 120 single belt system with a 100-Amp internally regulated alternator without a big issue. Besides, the 100-Amp alt will rarely if ever hit 100 Amps, but it will certainly outperform the one you have with far less stress. If you are concerned about the charger working your current alt a bit too hard you can knock the power setting of that PN50 down in 25% increments.

 

[boomerang]

Oh I'm worried about the stock alternator quitting while trying to bring the batteries up from a depleted state too! That's why we carry a relatively inexpensive spare with us. It's not too bad to change but not something one enjoys doing, especially while cruising.
I looked into a better quality Balmar 70A, one where I could use the same belt & get by, but they are rather adamant about it's rotation for cooling. I was one on the "lucky" Mainship Perkins owners who got a contra-rotating 6.354. It runs like a top but in this case, I would rather have had the standard-rotation one.

 

[catalinajack]

Balmar 100-amp alternators can be used safely with a single belt, external regulation of course. Use with an alternator temp sensor as recommended by Balmar. Take a look at Rod Collins' marinehowto.com website. Everything you need to learn about systems is right there.

Oh I'm worried about the stock alternator quitting while trying to bring the batteries up from a depleted state too! That's why we carry a relatively inexpensive spare with us. It's not too bad to change but not something one enjoys doing, especially while cruising.
I looked into a better quality Balmar 70A, one where I could use the same belt & get by, but they are rather adamant about it's rotation for cooling. I was one on the "lucky" Mainship Perkins owners who got a contra-rotating 6.354. It runs like a top but in this case, I would rather have had the standard-rotation one.