Confusing battery replacement

I really need the help from experienced boaters about a new battery system.
My 30' Tolly has twin 120 HP diesels and each has an 8d battery. The electrical loads are split between the two batteries with most of the load on the starboard battery.

My current thinking is that the batteries were oversized so they could share the starting and house loads as according to sources it should take only 440 CCA to start the engines and I assume the 8d's to be much larger (sides are hidden from view). Both batteries need replacing so I'm looking at starting from scratch with a new setup, but also watching the cost.

What I'm thinking is to isolate one start battery and use the other one plus a house bank (200 A) to power everything else. I also have decided on AGM batteries because of their increased drawdown and lower maintenance. I would use one engine alternator (105A) to charge the isolated start battery and the other alternator to charge the the start and house bank.

Questions:
- Do I need an 8d battery to start a 220 cu.in. diesel engine? I'm an old guy and the thought of muscling 150 lb batteries in the bilge is depressing. A Trojan AGM 31 has 730 CCA and only weighs 67 lbs.
- Many sources I've read say there is little difference between start and deep cycle batteries and you can use a deep cycle for starting.
- Most AGM batteries I've looked at take a max charge of 60A, but I have 105A Leece-Neville alternators. How do I limit the charge to 60A?
- For the start/house side I assume I could use an automatic charging relay to manage the charge between the needs of the start and house batteries.

To those who have suffered through my confusing story, am I taking the right approach to this and making proper decisions?

My MS is a single eng but had a similar set up w 2 8Ds that served house & start. Also had a 3rd 8D for B&S thrusters. All AGM and I lije them for the reasons you stated.. I will not replace 8Ds for same reasons you cite. East Penn & Trojan confirmed to me that their AGM do start & deep cycle equally well and I see they list both AH and CCA/MCA for their AGMs.
A pair of GP31s are roughly equal to an 8D. A pair of GC2s also similar.
Why not use a GP31 for starting only and use 3-4 (depending on needs) GP 31s for a dedicated house. Use 1 alt for start & one for house. I'd add an emergency Sw to combine banks if/when necessary but if 1st eng started is the one w alt supplying start batty it will supplement the batty for 2nd eng start.
I believe alt output is determined by batty V rather than constant output and you shouldn't need to limit it... maybe others can confirm or correct me there.

8D is overkill to start a 220 cu in engine. I start a pair of 10 liter, 610 cu in, Cat 3208s with a single 8D. When the time comes to replace the 8D I will install a pair of group 31s.

I'm an old guy too. I don't move 8Ds or even 6 volt golf car batteries any more. That's what the local boat yard labor is for.

A reason they are 8Ds is because they do house and start.
Halvorsen and Island Gypsy are set up that way, as is their descendant Integrity. It seems to work.
At one stage I thought I would switch to drawing on one batt only while on the hook, preserving the other for start, but figured that risked drawing one too low while the other stayed 100%. I decided to draw on both. The genset with its separate battery becomes your savior, though in 12 years I only resorted to it once when the poor state of the batts on a newly acquired IG revealed itself.
Replacing each 8D with 2 AGMs of something else giving as much or more total amps is a good idea from the safety lifting angle.

NW
You’ve received some good advice. We’ve switched our start 8Ds to sealed FLA for about 1/2 the cost of AGM. I suggest you consider installing an ACR which will tie your two alternators together for charging the weakest link - usually the house bank.

Years ago I replaced my 8D batts with 6xGC lead acids and a single Group 31 start batt for my twin Perkins engines. I also recabled all the large cables and wired the alternators directly to their respective battery to avoid using the start cables for charging. I now have better control of all charge sources and loads separately. My house bank gained about 50% capacity and each battery weighs about 65 lbs instead of those 8D behemoths.

My stbd Balmar 120A alternator is derated to 100A to charge my 660AH GC house bank. My port stock 60A alternator charges the start and helps with the house charge with a selectable combiner. The single-bank 55A onboard charger charges the house bank and also the start batt when the combiner is switched on.

This system has worked as well as expected for about the past 10 years. I understand the advantage of AGMs but my batteries are easily accessed for servicing and my budget at the time didn't allow the battery upgrade. YMMV

If you search the forum for past threads on the subject, you'll see some great discussions.

I would replace one 8d with group 31’s and do all my starting off of that bank. I would replace the rest of my 8D’s with golf cart batteries and run my house off of that. I would redirect alternator and battery charger to the GC bank and then use a smart combiner or echo charger to charge the start battery bank. This will give you the best of all worlds with out damaging dissimilar batteries during the charging phase.

tiltrider1 said:

I would replace one 8d with group 31’s and do all my starting off of that bank. I would replace the rest of my 8D’s with golf cart batteries and run my house off of that. I would redirect alternator and battery charger to the GC bank and then use a smart combiner or echo charger to charge the start battery bank. This will give you the best of all worlds with out damaging dissimilar batteries during the charging phase.

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Hi NWpilot. tiltrider has provided sound basic advice for a suitable twin engine powerboat electrical system design. However, be aware there are a LOT of subtleties involved in a proper system design. The devil is definitely in the details. It's very difficult to provide such a design via anecdotes and advice from a forum such as this.

To minimize cost, maximize utility, and verify system function and safety, I would highly suggest you employ an ABYC-certified marine electrician to survey your existing electrical installation, and design and specify a proper electrical system design for your particular vessel. Then, you can plan and budget accordingly for the installation, adjustment, and sea trial of the resulting installation.

There are as many ways to skin this cat as Carter has pills; not all are correct. Marine electrical systems engineering isn't learned from the WWW, nor overnight. And while the majority of experienced boat owners feel competent to do this sort of work, the emphasis is on experienced. And I thoroughly share your pain as a fellow "old guy". Smart money lets the youngsters hump batteries in and out of engine rooms. Smarter money for the inexperienced lets the young professionals tackle this whole enchilada. It's money well spent in many, many ways.

Regards,

Pete

OP I also think post #7 is the best solution. However would not use AGM for the house bank. Use gels if you want sealed. For starting, AGM are fine.

If you need to watch your budget then go with typical wet cells and then water them every few months.

NWpilot said:

What I'm thinking is to isolate one start battery and use the other one plus a house bank (200 A) to power everything else.

- Do I need an 8d battery to start a 220 cu.in. diesel engine? I'm an old guy and the thought of muscling 150 lb batteries in the bilge is depressing. A Trojan AGM 31 has 730 CCA and only weighs 67 lbs.
- Many sources I've read say there is little difference between start and deep cycle batteries and you can use a deep cycle for starting.

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What problem do you solve by changing architecture?

(You could maybe replace each 8D with a pair of G31s without changing basic architecture. Or maybe 3x G31s if you have a little additional horizontal space (more house capacity). Or maybe 4x GC2s if you have that additional horizontal space (even more house capacity). Or maybe 4x L16s if you have additional height as well (Lots more house capacity). None of that requires a change in basic architecture.)

Hire a guy to deal with the weight issues. 8Ds, multiple G31s, GC2s, whatever.

If reading is true, Trojan "deep cycle" batteries are more like dual purpose. (I don't know that for fact.) Could be appropriate for your situation, though.

-Chris

Changing architecture takes away all the decision making and manual switching to choose the start or house bank. It keeps the start bank isolated from house loads so there’s always power to start the engine. Battery monitors or state of charge instruments are usually designed to monitor one main “house bank” and one or two other banks for voltage only. This way you can see exactly where the batteries are, and when you need to replenish them. The start batteries are automatically charged when the engine starts and the charge voltage rises above a certain threshold.
His current system works, but it takes thought and manual switching to keep a battery isolated for starting, or choosing what battery to cycle for house loads. Some people like that as they get full control of the batteries, but automatic frees you from having to give it any thought.
I like agms for house batteries. In fact, I like them for both start and house duty. I hate filling batteries, and inevitably run them too low. Luckily, my wife has taken that duty from me, and she keeps them topped off. When I replace them though, agms will be my choice. That’s a big budget item on my boat. 16 gc2s cost a couple of bucks.

Brian
You hit on one of the major reasons I reconfigured my house / start to leave a pure house. I added a Balmar Smart Gauge for better house monitoring. It wouldn't work with switched batty bank.
Moving my start reduced the run by about 50% and I used an unused cable from the new house that increased the start cable size so reduced V drop starting.
Batty monitor wired directly to the new house bank working very well for monitoring SOC and V readout for start / thruster bank provides a reasonable indication of its SOC and I can monitor it returning to full charge easily while running.
I used a Sterling CVSR to share my measly 70A alt output to the bank(s) needing it.

First of all I want everyone to know that I'm not ignoring you. The responses gave me a wealth of information and I realize that there are several ways to approach this. I've pretty much decided to print this page and sketch each of the results so I can see what fits.

I spent part of yesterday searching for batteries and found that just as confusing. It's almost impossible to compare them, but the search goes on.
One of the problems is that Portland, Oregon is not a boat town. There are few outfits selling parts or providing services and those that do are very expensive. The Seattle area would be heaven and I could hire an electrician or laborer. My main help is my brother who is an electrical engineer, but his background is in electronics.

Once I've looked at all the systems proposed I'm going to try and find an ACR that will use both alternators to charge both battery banks and battery monitors for each bank.

The electrical architecture of the boat will be designed around the new battery system because the boat has suffered greatly over the years (before I bought it) from a lack of maintenance. There are feeds off both batteries running everywhere and loose wires everywhere. Items like the windlass have a bypassed switch and bailing wire fix in the chain locker. Several of the dash switches are dead.

But the boat is a solid Tollycraft and worth saving.

ps - I did a search on this sub and learned a lot but still had questions.

NWpilot said:

Once I've looked at all the systems proposed I'm going to try and find an ACR that will use both alternators to charge both battery banks and battery monitors for each bank.

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Do some research on DC-DC chargers as well. I have no experience with ACRs, but when I was re-architecting my system the ACR seemed like an outdated solution in comparison. The Victron Orion is a good example.

So for example you could have both alternators charging the house bank, with two dc-dc chargers maintaining two group 31 start batteries. All loads go to house bank. Lots of practical possibilities, and easy to build on in the future as you add solar, change battery types, etc.

If the alternators have a too high output, there are advantages to a modern external regulator setup. It's complex enough, and you want to get rid of all the jerry-rigged wiring... that I too would just hire an ABYC guy to lay it out.
These Pacific Yacht Systems guys have good tutorials, like the one below. Best of luck to you and please let the forum know how things work out, we'd love to see how it turns out.

Jeff F said:

Do some research on DC-DC chargers as well. I have no experience with ACRs, but when I was re-architecting my system the ACR seemed like an outdated solution in comparison. The Victron Orion is a good example.

So for example you could have both alternators charging the house bank, with two dc-dc chargers maintaining two group 31 start batteries. All loads go to house bank. Lots of practical possibilities, and easy to build on in the future as you add solar, change battery types, etc.

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ACRs are not outdated at all. Rod Collins (as good a pro as one could ask for) put out good read on ACRs. I recently had a Blue Seas ACR installed per Rod's writeup and all is well.

sunchaser said:

ACRs are not outdated at all. Rod Collins (as good a pro as one could ask for) put out good read on ACRs. I recently had a Blue Seas ACR installed per Rod's writeup and all is well.

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I shouldn't have used that term perhaps. Not suggesting they don't work, but that there are other solutions - dare I say more modern? - that should also be considered, especially when redesigning a system.

As was said above, many ways to solve for this. Sorry for any slight I may have caused.

1. Not sure which engines you have, my 120hp Ford Lehmans are 380 cu.in. The manual specifies 140 ah battery capacity pulling 1070 amps with a locked starter (the moment you push the switch) and 670 amps running draw. That indicates 2 grp 31s paralleled, 2 gcs in series, a 4d or an 8d, and adequate cables.
2. Main difference is lead plate thickness — used to be start batteries had thinner plates which allows a higher current flow but a shorter overall life. The lines seem to be blurring now.
3. The batteries are essentially sefl-limiting. At the correct charging voltages you won’t “over-amp” a battery, it won’t accept the charge.
4. A simple solution is to use one isolated bank to start both engines, charged by one alternator. Power the house with the other bank, charged by the other alternator. Replace the 1-Both-2-Off switch with an On-Off switch for a backup interconnect. Clean-up can be done by running start battery to one bus bar, both starters and one alternator connected to that bus. Use appropriate fuse on the alternator feed. Run house battery to a seccond bus bar and connect 2nd alternator and all the non-starter loads to that bus, again with adequate over-current protection.
The last 30’ Tolly I was on had 2 8ds on the bulkhead aft of the engines, very difficult to get to and maintain. Group 31 AGMs would make life a lot easier.
With winter coming on you have time to do some research and analysis, recommend Nigel Calder’s book.
Before you get too far along it’s also worth considering what style cruising you will be doing. If you want to spend 5+ days off the dock at a time, you want t big battery bank, external regulators controlling the alternators, and both alternators fed through a charge controller. On the other hand, if you only do one or 2 nights off the dock at a time, a 400ah bank will probably do just fine.
The boat name seems familiar. Did you or do you commute to OAK? I might have run into you several years back.

AV8R,

The boat (1979) has twin Volvo TMD40 engines at 220 cu.in. producing 130 hp each according to the sea trial.
It was originally sold to a couple in Seward, AK by Alaska Marine Engine. I more recently bought it in Portland, OR. It had been sitting idle in a marina since the current owner passed away. The owners lived in Calif. and he came up to Oregon only to fish, thus the lack of maintenance. I have no idea about the owners in between, but have an ad showing it for sale by Classic Yachts and located at Chinook.

Jeff F said:

I shouldn't have used that term perhaps. Not suggesting they don't work, but that there are other solutions - dare I say more modern? - that should also be considered, especially when redesigning a system.

As was said above, many ways to solve for this. Sorry for any slight I may have caused.

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There are ACR’s and then there are Smart ACR’s, Echo Chargers and DC to DC chargers.

Using an ACR to combine a start bank with a house bank is going to shorten the life of the start bank. Not the end of the world unless you have a combination of lead acid and gel type batteries.

You can improve the situation by upgrading to a Smart ACR, Echo Charger or DC to DC charger. These devices do not combine the banks but allow only the appropriate amount of voltage and amps to pass from one bank to the next. This way each bank gets what it needs with out being over charged.

ACR’s are outdated technology for most marine applications but they still work, sort of and do it very inexpensively. Unfortunately people tend to use ACR’s unaware that better technology exists.

tiltrider1 said:

There are ACR’s and then there are Smart ACR’s, Echo Chargers and DC to DC chargers.

Using an ACR to combine a start bank with a house bank is going to shorten the life of the start bank. Not the end of the world unless you have a combination of lead acid and gel type batteries. .

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I'm not keen on combining draw downs while at rest of a house bank with a start bank via any means. Charging is a different story, especially when cruising.

"Marine How To", the Rod Collins website, covers proper ACR installation in some detail citing the associated myths. On vessels with two alternators, i.e. twin engine vessels, the objective is to properly wire and use a a Smart ACR to take the output from the start battery engine alternator and use/combine it to charge the lower voltage house bank.

At rest the start battery bank is isolated from house bank draw down via the Smart ACR. Obviously whether accomplishing this task with a DC to DC or an ACR, battery bank monitoring for both start and house bank is a plus if not a necessity.

BTW, for starting as mentioned by other posters, there are good sealed FLA 8 Ds out there costing much less than AGMs. They've been around the heavy equipment and marine business for quite some time. As oft mentioned, young strong backs are helpful.

av8r said:

Before you get too far along it’s also worth considering what style cruising you will be doing. If you want to spend 5+ days off the dock at a time, you want t big battery bank, external regulators controlling the alternators, and both alternators fed through a charge controller.

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Once again OP, if you are planning long durations at anchor living off your house bank, then consider gel batteries for the house instead of AGM. AGM are fine for starting though.

Mako said:

Once again OP, if you are planning long durations at anchor living off your house bank, then consider gel batteries for the house instead of AGM. AGM are fine for starting though.

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I think that’s the second time you recommend against agm for house loads. I’ve had really good experiences with agm house banks. Why do you dislike them?

With twin alternators you might also consider a balmar centerfielder. It combines the output of two alternators so you can aim all the output to your large house bank. Then use a smart combiner to handle the start bank charging.
Lots of ways to skin this cat for sure, pluses and minuses for each scenario.

AGM need full charging between draining and don't hold their charge as well (think winter storage). If you live off the hook then you likely rely on your solar and are not reaching full charge each day. AGM work better for shorter bursts of high energy, versus long slower draining. Hence, great for starting batteries!

Gels are a bit more sensitive and need proper charge-management also, but perform better on deep discharging and partial charging back. Hold up well to colder temps than AGM and keep their charge better when you're away from the boat for months.

My experience with both. However, my favorite batteries are still 2V industrial cells. Hunting lodge was off-grid and those big batteries were real workhorses. Amazingly heavy but that was a concrete slab floor, not a wood or fiberglass hull.

But it is the 21st century, so maybe it's time to start considering lithium. I can see how for those who live on the hook and charge via solar, that Li would have great advantages.

Mako said:

But it is the 21st century, so maybe it's time to start considering lithium. I can see how for those who live on the hook and charge via solar, that Li would have great advantages.

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For the OP who is considering redesign I'd say build in a way that allows you to change battery types, as much as possible. Maybe you don't want Li now, but you should anticipate that need. Solar as well

I had a big GC house bank when I rewired. 18 months later I replaced it with Li with no changes other than software configurations.

Also wrt starting batteries, a basic SLA group 31starting battery is cheap, easy to handle, and will give years of service if properly maintained. If you give it a dedicated 15a charger it'll be happy and reliable. That's largely what led me down the DC charger path. Save the fancy battery selection for the house bank.

Some clarifications to the puzzle.

- The boat is normally at anchor in the marina and the batteries are kept charged by a Sterling 60A charger which will handle 3 banks.
- I plan on taking extended trips when ready, then to Astoria (180 mi. R/T) and eventually up the Columbia River to Idaho (600 mi. R/T). I will travel at a leisurely pace of about 50 mi. per day.

- I have estimated my electrical usage when at anchor for overnights at about 130 AH and based the battery draw down at 50% max. so 260 AH for a 16 hour period at anchor. I'm thinking that if I design for a 300 AH expandable house bank then I wont have to combine it with a start battery.

- If I end up with some 8D no maintenance batteries I can enlist relatives to help place them and not have to crawl into the bilge afterward to add water. I can't sit upright in my bilge. Everything is done laying on my side.

- At this point in time I'm looking at going on the less expensive route since I still have many repairs to make and all new electronics.

What I'm currently looking at is sealed FLA group 31 batteries with about 1000 CCA each for starting and a sealed FLA house bank. I would like to consider AGM for house but my Sterling charger only accepts one type of battery. I'm still working on sketches on the proposed system.

NWpilot said:

What I'm currently looking at is sealed FLA group 31 batteries with about 1000 CCA each for starting and a sealed FLA house bank. I would like to consider AGM for house but my Sterling charger only accepts one type of battery. I'm still working on sketches on the proposed system.

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How about this:
- each alternator charges its own start battery. Sterling charges each start battery.
- each start battery supplies a 30 amp dc-dc charger to house.

That should allow you to use existing charger and alternator regulation, and give you high quality 60a charge to your house bank. And you can use whatever type of battery you want for the house bank.

Mako said:

AGM need full charging between draining and don't hold their charge as well (think winter storage). If you live off the hook then you likely rely on your solar and are not reaching full charge each day. AGM work better for shorter bursts of high energy, versus long slower draining. Hence, great for starting batteries!

Gels are a bit more sensitive and need proper charge-management also, but perform better on deep discharging and partial charging back. Hold up well to colder temps than AGM and keep their charge better when you're away from the boat for months.

My experience with both. However, my favorite batteries are still 2V industrial cells. Hunting lodge was off-grid and those big batteries were real workhorses. Amazingly heavy but that was a concrete slab floor, not a wood or fiberglass hull.

But it is the 21st century, so maybe it's time to start considering lithium. I can see how for those who live on the hook and charge via solar, that Li would have great advantages.

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Interesting. My experience with agms is much different than yours.
I find the self discharge of my previous agms to be much less than the fla I’m running now. Also, the resting voltage on my agms has always been a little higher, as well as operational voltage.
It always took a cycle or two to sort of wake them up for the season, but they always performed well for me.
I’m getting ready to change all my batteries, a pretty big investment, so battery talk is on my radar right now. Thanks for sharing your thoughts.
Anyone else have a bad experience with agms?

I think that if budget is the most important consideration then nothing beats Costco 6V golf cart batteries. They seem to be very popular here on TF also, for house banks.