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Old 06-12-2019, 08:10 PM   #1
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Battery Configuration

My 36í Grand Banks currently has 2 8D AGM and 1 4D AGM batteries. The 4D is dedicated to the Genset with the 8 Dís as Batt 1&2 on selector. Port engine starts with Batt 1 and starboard engine starts with Batt 2. This configuration doesnít make sense to me as it doesnít give me a dedicated starter or house battery and seems like serious overkill for a generator starter battery.

Would really appreciate any suggestions you might have for configuring this better. One thought I have had (just a thought without a good base understanding of these things so welcome input on why it doesnít make sense)

Use the 4D as dedicated starter battery for generator and both engines leaving me with the 2 8Dís as house battery (right now the 4D is charged via the generator only, not connected to my Freedom 20 charger and has no voltage monitor). Not sure I can do this and still have the alternators charge Batt 1&2.

I will have an electrician do what needs to be done but just not sure the best way to proceed, just know that the current configuration doesnít make sense to me and it seems to me that I have plenty of battery power with the genset.

Thank you for any feedback.
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Old 06-12-2019, 09:14 PM   #2
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Are the batteries deep cycle? Starting? Dual use? Flooded? How old are they and in what condition?
Are you looking to keep them or replace them?

What type of engines are they starting?
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Old 06-12-2019, 09:38 PM   #3
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Your natural instincts are correct. A small dedicated group 27 starter battery is all you need for the generator. All you need to start both engines is one group 31 starter battery. Two G31’s in parallel if you are the paranoid type. Fill all he remaining area with deep cycle batteries for your house bank. Our alternator and battery chargers should be wired to the house bank. A DC to DC charger or a smart combiner goes between the house bank and the starter batteries. Generator alternator is wired to the gen battery. Your 1,2,all switch stays the same. Your engines are wired to the start batteries.
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Old 06-12-2019, 09:50 PM   #4
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Lots of different ways to configure batteries. I would have a small sealed lead acid battery to start the generator and another to start the main engine. Would have a house bank appropriate for your needs of the chemistry you prefer, but definitely deep cycle. Charging the house and main engine batteries is where it gets tricky.

On my single engine boat, I added a second alternator. So 1 for each bank.

You could charge the house bank with the engine alternator and use one of several devices to charge the engine battery off the house bank.

You could reverse the charging order.

You could tie the house and engine batteries together with a switch or electric relay / solenoid while the engine is running and have them separated when it's shut off.

You could have the house bank also start the engine. If you let the house bank get to low, you may have to run the generator to charge the house bank (several hours) before leaving.

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Old 06-12-2019, 10:04 PM   #5
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Your natural instincts are correct. A small dedicated group 27 starter battery is all you need for the generator. All you need to start both engines is one group 31 starter battery. Two G31ís in parallel if you are the paranoid type. Fill all he remaining area with deep cycle batteries for your house bank. Our alternator and battery chargers should be wired to the house bank. A DC to DC charger or a smart combiner goes between the house bank and the starter batteries. Generator alternator is wired to the gen battery. Your 1,2,all switch stays the same. Your engines are wired to the start batteries.

Since the OP already has a 4D and the 2 8Ds, I would consider adding a GRP 27 for the genset, and then repurposing the 4D to start both engines. Then combine the two 8Ds into a single house bank. Down the road, he could change out the 8Ds when they needed replacing or he wanted to upgrade his capacity. The 4D could be replaced with 1 or 2 GRP 31s when it gets tired.

Iím not smart enough to know what to do with Twin alternators, but generally I like the idea of sending all charging sources to the house bank and then some type of DC-DC charging to keep the starting batteries charged.

I would say that the 1, 2, Both switch would change. Depending on how things were configured, you could add an On/Off switch between the House bank and House panel, then put the House bank on #2 and the starter battery on #1. You would leave the switch on #1 unless for some reason the start batter was drained. Then you switch to #2 and start the engines from the House bank.

Iím sure there are other and maybe better ways to do it.
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Old 06-13-2019, 05:17 AM   #6
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[QUOTE=darrelltate;773808]My 36í Grand Banks currently has 2 8D AGM and 1 4D AGM batteries. The 4D is dedicated to the Genset with the 8 Dís as Batt 1&2 on selector. Port engine starts with Batt 1 and starboard engine starts with Batt 2. This configuration doesnít make sense to me as it doesnít give me a dedicated starter or house battery and seems like serious overkill for a generator starter battery.

I think what you describe was a pretty standard GB36 set up - except that the 8d's were wired through a Bat1/Bat2/Both switch by the lower helm. (distinct from the battery switches under the forward cabin steps). Most of these boats were rarely swinging on the hook more than 1-2 nights - 110v cooking, no inverters in the original configuration.

The 4d gen start battery was deliberately separate so it couldn't be drawn down by house loads. The 8ds easily handled light house loads,(fridge, lights, pumps) for 1-2 nights, select either Bat 1 or Bat 2 when anchored so the other is always available for starting. If you forgot forgot and drained both 8d's -either start the gen and wait for charger or jumper cables from the 4d for a quick start.

Not the elegant solutions in modern boats, but actually pretty simple and we kept the stock set-up on our GB36. No issues doing the Canadian part of the loop for a couple of summers with infrequent plug ins, never did anything to the batteries. Would run the gen for 1-2 hrs at full load, cool boat, cook dinner etc. each evening.
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Old 06-13-2019, 05:54 AM   #7
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I have a somewhat similar set up on my Mainship 34HT.
I have taken the first step to eliminate the diode isolators that MS installed. Details in project section of Bacchus website under projects.
I'm considering changes similar to what others recommend in your case.
One step I have already taken is a suggestion from another here on TF.
If your gen has an on/off SW (mine did) you can likely find a similar SW 1-2-off-all.
I swapped my gen SW (same footprint & mounting bolts) and 1 is my normal gen batty charged only by the gen and my normal operation position. 2 is my house/start bank.
This allows me to add in addnl batty power in an emergency should my gen batty fail and it allows me to combine the two to "top off" charging gen batty by shore charger or alt while running if I haven't ran the gen in awhile.
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Old 06-13-2019, 08:22 AM   #8
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My 36’ Grand Banks currently has 2 8D AGM and 1 4D AGM batteries. The 4D is dedicated to the Genset with the 8 D’s as Batt 1&2 on selector. Port engine starts with Batt 1 and starboard engine starts with Batt 2. This configuration doesn’t make sense to me as it doesn’t give me a dedicated starter or house battery and seems like serious overkill for a generator starter battery.

Use the 4D as dedicated starter battery for generator and both engines leaving me with the 2 8D’s as house battery (right now the 4D is charged via the generator only, not connected to my Freedom 20 charger and has no voltage monitor). Not sure I can do this and still have the alternators charge Batt 1&2.

I think you're saying the 8Ds are dedicated to start each respective engine... without regard to the battery switch? And so maybe the battery switch is for selecting which of those two 8Ds runs the house load for a while?

If so... I don't know that I'd do much of anything different... except for changing to more easily manageable sizes... but that's also depending on your anchoring intentions.

If you'll anchor out occasionally... is different than if you'll anchor out every day for the rest of your life.

If the former, your electrical set-up is easily workable as is. (See Flatswing's post.) I'd just switch each 8D -- as they age off -- to 3x G31s if you have room for that, just for ease of schlepping batteries when necessary. In many cases, this would also be upsizing each "battery" (bank, for house purposes) from approx 245 Ah to approx 300 Ah, which might also be useful. Or there are other choices if you don't have room for 3x G31s, including staying with 8Ds and paying somebody to schlepp when necessary.

And I'd switch your 4D genset battery to smaller a G24, G34, or maybe G27 depending on whatever the cranking amps are that your genset engine needs. (Consult manual for that.) This is a good application for a decent AGM battery, too, given charging only by genset alternator, given that you don't need to match types with other batteries on the same charger, and given AGM's low self-discharge rate.

Useful -- and cheap -- to add a set of jumper cables, but you'd likely never need them.

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Old 06-13-2019, 10:04 AM   #9
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Batteries are brand new deep cycle.
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Old 06-13-2019, 10:17 AM   #10
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I can’t thank everyone enough for your input!!

I am new to the forum and have found it, and all of you, to be an invaluable resource!!

I can see the logic of the existing configuration now but can also see some benefit to changing. Going to see what my electrician says and look at costs (he is rebuilding my alternators). All three batteries are less than 6 months old so will use them and replace per suggestions over time.

Going to also make sure I have jumper cables!!

THANK YOU VERY MUCH.
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Old 06-13-2019, 10:23 AM   #11
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Quote:
Originally Posted by darrelltate View Post
My 36’ Grand Banks currently has 2 8D AGM and 1 4D AGM batteries. The 4D is dedicated to the Genset with the 8 D’s as Batt 1&2 on selector.
I have the exact same setup. My plan is pretty much what dhays says above.

I plan to do it in steps:

Step 1: Make the 4D the start battery for both engines and generator. Make the 2-8D the house bank. Wire all chargers to the house bank and connect the start battery to the house bank with an ACR.

Step 2: Install a dedicated generator start battery that charges from the generator alternator (probably group 27).

Step 3: When the 8Ds die, replace them with 6xTrojan T-105.
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Old 06-13-2019, 11:08 AM   #12
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I have two group 31 batteries in parallel that starts my engine and generator and powers my windlass and bow thruster. These batteries are charged by the engine alternator or generator alternator.

There is no battery charger for the start batteries. I can never understand why a charger is needed for start batteries. We don't need to charge our car batteries with a charger while parked. The alternator recharges the batteries after starting engine or generator. The engine is running when the bow thruster or windlass is utilized. Nothing else is powered by the start battery. Unless the battery is failing or there are electrical leaks, the batteries should maintain their charge.

For house, I have 6 golf cart batteries, charged by a second alternator on the single Lehman or the inverter/charger.

There is a battery switch that can combine house and start batteries. If the start batteries need topping up, which rarely occurs, the battery switch is turned to "Both" and the house charger will top up the start battery. If the start battery dies, which has never happened, the house battery can start generator.

In 19 years of cruising and anchoring 5 to 8 days in one spot, we've never had a starting issues. With less batteries on board, I can afford to replace the starting batteries every 5 years and the house batteries every 6 to 7.

For backup, if all batteries are dead, the battery in the dinghy can be used to jump start the generator.

For the belt and suspender crowd, carry a small lithium jump starter. I don't have one, but I was able to start my Lehman with a friends jump start battery.
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Old 06-13-2019, 11:22 AM   #13
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Your plan to use your 4D for starting engines and generator only and the 8D's for house is what I would do.

Rewire the battery selector switch to be able the to select battery or parallel the battery banks.

Wire one alternator to charge start battery and the other alternator for house. Connect the charger to house battery.

With the money saved not buying a generator battery, buy a battery monitor that measures amp hours in and out of your batteries. Buy one that measures two banks or install a switch to let you select which battery to monitor.

You will want to upgrade the battery charger and alternator to higher output eventually.
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Old 06-13-2019, 11:31 AM   #14
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Unless I am missing something I am going to follow raindog and take dhays suggestions. While am am sure there are a lot of other, equally, good configurations I can really make sense of this configuration which is important to me.

Thanks again to everyone that replied and all of the good advice.

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Old 06-13-2019, 12:36 PM   #15
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Unless I am missing something I am going to follow raindog and take dhays suggestions. While am am sure there are a lot of other, equally, good configurations I can really make sense of this configuration which is important to me.

Thanks again to everyone that replied and all of the good advice.

Never take any suggestions from me when it comes to electrical. Check my ideas with your electrician. In particular, I have no experience with twins.
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Old 06-13-2019, 12:51 PM   #16
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There is no battery charger for the start batteries. I can never understand why a charger is needed for start batteries. We don't need to charge our car batteries with a charger while parked. The alternator recharges the batteries after starting engine or generator. The engine is running when the bow thruster or windlass is utilized. Nothing else is powered by the start battery. Unless the battery is failing or there are electrical leaks, the batteries should maintain their charge.

For house, I have 6 golf cart batteries, charged by a second alternator on the single Lehman or the inverter/charger.

I would submit that you do have a charger for your start batteries, it is that alternator. You then added a second alternator to charge your house bank.


I only have one alternator. That alternator feeds the house bank. Instead of a second alternator, I have a Xantrex Echo-Charger that charges my start battery from the house. Alternators are pretty reliable and not very expensive. OTOH, so is an Echo-charger. I think it cost about $108, has no moving parts, no belts, and very little that can wear out.


Your setup has the advantage of being able to supply the full output from the one alternator to the thrusters while they are running. Once your start batteries are topped up however, that alternator isn't doing much.
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Old 06-13-2019, 03:26 PM   #17
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I would submit that you do have a charger for your start batteries, it is that alternator. You then added a second alternator to charge your house bank.

Your setup has the advantage of being able to supply the full output from the one alternator to the thrusters while they are running. Once your start batteries are topped up however, that alternator isn't doing much.
I'm aware that the alternator charges the start battery under way.

I'm referring to a 110 volt battery charger or inverter/charger that charges the start battery while on shore power that a lot of boats are equipped with. It's not necessary to keep the start battery charged up if the start battery does not power anything when the engine is not running.

My start batteries powers the radar and autopilot while under way. I have a solenoid at the start battery that shuts the battery off when at rest.

The first alternator is a Balmar 100 amp with a Balmar MaxCharge set to deliver 60 amps. The second alternator is a Balmar 120 amp also with a Max Charge set to deliver 100 amps. Both are small frame alternators on the single Lehman.
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Old 06-13-2019, 04:07 PM   #18
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There are more than one way to configure a system and none are best for everyone. I agree with your leaning but whether it is best for you only you can factor in how you use your boat.
Not many 8Ds are really deep cycle... if they are rated w CCA it's a dual purpose compromise at best. Not saying using them as house won't work - I have 2 8D AGM as house / start and pondering whether I want to go thru changing the wiring when it's time to replace.
Read this re deep cycle... it's a well done analysis.
https://marinehowto.com/wp-content/u...le-Battery.jpg
Also Nigel Calders Marine Electrical Handbook outlines different battery bank options as is worth reviewing.
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Old 06-13-2019, 04:46 PM   #19
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My start batteries powers the radar and autopilot while under way. I have a solenoid at the start battery that shuts the battery off when at rest.

The first alternator is a Balmar 100 amp with a Balmar MaxCharge set to deliver 60 amps. The second alternator is a Balmar 120 amp also with a Max Charge set to deliver 100 amps. Both are small frame alternators on the single Lehman.

Nice setup!
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Old 06-16-2019, 06:00 AM   #20
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"Nothing else is powered by the start battery. Unless the battery is failing or there are electrical leaks, the batteries should maintain their charge."

Depending on age and abuse start batts will loose 1/2% to 3% per day , just existing.

If the engine is not run often enough , a no start can occur.
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