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Battery, Charge controller, switch wiring - clean slate

Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
In reviewing MaineSail's Musings, it looks like using GC2s (6v) and/or GC12s (12v) would provide greater battery cycle life than using Group 31s or similar, if you have the space (the GCs being roughly 1.5" taller that the 31s) . I have measured areas that will accommodate battery boxes on my boat and I have an area that is 33" x 7.5" to starboard of the engine box and area that is 13.3" x 14.3" to port of my engine box - both with enough height to accommodate the GCs. So I have room for two GC12s or three GC2s to starboard and I have room for two GC12s or GC2s to port (or combo of the two). Wire distance from the two 'battery box areas' is roughly seven feet. My initial plan (before reviewing MainSail's notes re the GCs) was to proceed with four Group 31s (as I wanted bank(s) with at least 500Ah capacity); now I am inclined to go with three GC2s to starboard, one GC2 to port and one GC12 to port and wire the four GC2s for 'House' and the GC 12 as 'Reserve', using the diagram that MainSail posted in this thread, modified to accommodate fact that four of the batteries I am now considering are 6v and one would be 12v. Any thoughts as to the wisdom of this approach, or better combination of the GCs is appreciated. Thank you.
 
Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
It won't do this. See the combine / un-combine parameters below.



Not this either. The batteries are simply charged in parallel providing the parameters shown below are met.

Charging a start battery first does not ensure it is fully charged before paralleling occurs it only means it is charged for 30 seconds or 90 seconds before the parallel conditions are met.. One common misconception of the ACR is that a start battery is first charged until full, then separated, and then the house bank is charged. This is not the case, they are simply charged in parallel together, so long as the bus voltage, measured at the "A" or "B" terminal (bi-sensing) remains above 12.75V for 30 seconds or 12.35V for 10 seconds.



To address the question of the house bank taking a long time to combine with the start battery, we first need to consider a few things:

Start battery energy use?
The start battery is using very little stored energy to start the engine. Usually considerably less than .5Ah. This is due to the cranking duration, loaded to unloaded, averaging 0.75 seconds to about 1.5 seconds. This means your previously full start battery will still be at about 99%+ SOC. A 99% SOC battery does not really require immediate charging and has many, many, many more starts in it before any charging would even become necessary. In this image we have a 44HP diesel cranking diagnostics. Average cranking voltage = 12.04V, Average cranking Amps = 286A and the loaded to unloaded starter duration is 0.765 seconds.

Even if we round up the cranking duration to 2 full seconds we are using just 0.17Ah
If we correct for Peukert we are looking at a max of about 0.29Ah's.

How long to attain combine/parallel?
From 50% DOD/SOC, the max depth of discharge recommended by most lead acid battery makers, it takes about 2 minutes at a .2C charge rate for even a high acceptance AGM battery to attain 13.0V. Blue Sea knows this and this is why they have two differing combine points, one at 13.0V & 90 seconds and one at 13.6V & 30 seconds.

This battery began charging at 50% SOC when the clock read 12:00. The charge rate was .2C or the bare minimum recommended charge current for this Lifeline AGM battery. As can be seen it is already at 13.1V.

Think about this snap shot if you are concerned about an ACR for charge management.

The rumor goes something like this: By using a battery combiner, on "high acceptance" AGM batteries, and feeding the alternator or battery chargers charging current directly to the house battery bank first, “it will leave your start battery under charged“ because it will never get to the combine voltage or will take too long to get there.

If you are practicing good battery management, and have even the minimum suggested charge current for an AGM or flooded battery, this is really a non-issue. In 2 minutes of charging, at .2C or 20% of Ah capacity from 50% SOC, the AGM battery voltage is already at the parallel/combine level for the Blue Sea ACR. Even at .1C or 10% of Ah capacity the time to attain 13.0V is not very long, just a few minutes more.. To get from 13.0V to 14.4V+ does take more time but the relay has already combined at 13.0V and both banks are now being charged.

Battery voltage will rise pretty slowly from the low 13's on but, to get to an ACR's combine level, is relatively quick and easy, especially if you have your system set up properly. Echo Chargers, Duo Chargers and a number of other DC to DC chargers also turn on at similar voltages and those devices require all charge sources to be fed to the house bank. On cruising boats with disparate sized banks Blue Sea recommends feeding charge current to house first, not start, to avoid relay cycling.



What about relay cycling?
In a system with similarly sized banks, for both house and start, the charging sources can be fed to the start battery first. This is often easiest because it is how the factory wiring often exists from the builder. On cruising boats, with disparate size banks, it is recommended to feed the alternator to the house bank to minimize the risk of relay cycling and voltage drop.

The ACR relays are smart enough to detect a voltage trend upwards between 12.35V and 12.75V. If voltage is trending UP, and 12.35V is attained before 10 seconds, it will remain closed unless 30 seconds expires before it attains 12.75V. If wired incorrectly, for the application, the relay can still suffer from relay cycling, especially with low current charge sources, despite the in-built logic to help minimize it.

I would urge anyone reading this to take a few minutes to read the Blue Sea technical document on relay cycling. Most installers and DIY's miss this:

Blue Sea - Preventing Relay Cycling (LINK)

Think of an ACR/COMBINER/VSR as nothing more than an electronically voltage-change triggered BOTH/COMBINE switch and it will become much easier to understand.

ACR Closed:


ACR Open:


This part of the ACR installation instructions is also very often missed on cruising boats.
This is all great information! Is there a way to dumb it down a bit? I’m doing an overhaul of my battery system. I mainly daysail or long weekend trip (maybe 4 or so days). I can plug into shore power when back at the docks. I’ve read a bunch on your website. I plan on installing an ACR with dedicated start and house batteries (2 series 6v batteries). Something along the picture above without the solar (well mostly). Also, I am not sure I can completely separate my house from the start without massive rewiring. Any advice that you can put in, let’s say apprenticeship electrican level, would be nice.

Also, why the disconnect switch next to the house batteries? So 4 total switches?
 
Last edited:
Jan 11, 2014
4,269
Sabre 362 113 Fair Haven, NY
Also, why the disconnect switch next to the house batteries? So 4 total switches?
Each electrical source has its own switch, start battery, house battery, alternator. This allows any one source to be isolated from the others. (although the alternator disconnect switch serves another purpose, see the thread on that).

Why isolate each bank independently instead of using a 1-2-both switch? In case on battery bank completely fails it can be isolated from the other banks quickly and easily. This also allows the reserve/start battery bank to be used to run basic DC systems, VHF, electronics, nav lights or the house battery to start the engine. The switch is a Blue Sea Dual Circuit Plus.
 
Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
Oh that makes sense about the switch. Any by isolating, I mean in the sense that maine sail has them isolated with his picture. House wiring coming off the house, and start wiring off the start battery. Then an emergency switch between the two.
 
Jan 11, 2014
4,269
Sabre 362 113 Fair Haven, NY
Oh that makes sense about the switch. Any by isolating, I mean in the sense that maine sail has them isolated with his picture. House wiring coming off the house, and start wiring off the start battery. Then an emergency switch between the two.
Yes, the emergency switch is actually the main DC switch. The Dual circuit turns 2 circuits on or off and has an emergency position in which both banks are connected to both out puts. This is why you need the extra switches. If one bank is dead and it is connected to a good bank, the dead bank will kill the good bank. So, isolate the bad bank and put the switch in the emergency position and everything works again.
 
Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
The way my beneteau is wired now already has two independent switches with a jumper between the two. So instead of a Off/1/both/2 switch it has 3 switches. They are common ground, batt1, and batt2. I bought it last fall and have never liked the way it was wired.
It won’t take much to get it wired correctly, just time and a bunch of explitives. It need new batteries and a charger. So I figured now is the perfect time for a little rewiring fun.
 
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Nov 7, 2011
2,550
Catalina 30 Mk II Barnegat, NJ
This is all great information! Is there a way to dumb it down a bit?
Sure. Install a positive bus bar connected to your house bank. Connect all charging sources to the positive bus bar. Install the recommended Blue Sea ACR between the positive bus bar and the start battery. The ACR will take care of connecting the start battery to the charge sources when appropriate.
 

TomY

Alden Forum Moderator
Jun 22, 2004
1,878
Alden 38' Challenger yawl Rockport Harbor
This is all great information! Is there a way to dumb it down a bit? I’m doing an overhaul of my battery system. I mainly daysail or long weekend trip (maybe 4 or so days). I can plug into shore power when back at the docks. I’ve read a bunch on your website. I plan on installing an ACR with dedicated start and house batteries (2 series 6v batteries). Something along the picture above without the solar (well mostly). Also, I am not sure I can completely separate my house from the start without massive rewiring. Any advice that you can put in, let’s say apprenticeship electrican level, would be nice.

Also, why the disconnect switch next to the house batteries? So 4 total switches?
You can simplify things. We're coastal sailors and live well with a small house bank (2 grp 27) and starting battery. The starting battery is isolated with only an On-Off switch. The only other battery switch is a 1-2-Both switch for the house bank, and that stays on BOTH anytime we're on the boat.

I've never run the starting battery down, there really is no way to do so except by running the starter long term but you can carry a set of jumper cables if you're worried (or a separate jump battery).

We charge off an obsolete dual post 70 amp. Balmar alternator that keeps both banks charged (sense wire on House bank). No added switches, isolators, combiners, or gizmos.

We do have all wiring correctly fused, right from the batteries. It's a simple DC system with no AC onboard(we're very rarely on a dock).

Because we don't have refrigeration, we stay well charged without any solar and can anchor for a few days without worry.

It all depends on how much power you want. Conservation can eliminate much complexity in your DC system, if you want to.

I also wonder if you are going to run out of space on your boat for the wiring, switching, batteries and cables, etc. Space onboard - anywhere, especially around wiring, is a luxury.
 
Jan 11, 2014
4,269
Sabre 362 113 Fair Haven, NY
If you would like to see a simple yet effective design check out the current edition of Good Old Boat magazine where Tom Young, (yes our TomY) leads us through a rehab of his ~1960s electrical panel.
 
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TomY

Alden Forum Moderator
Jun 22, 2004
1,878
Alden 38' Challenger yawl Rockport Harbor
If you would like to see a simple yet effective design check out the current edition of Good Old Boat magazine where Tom Young, (yes our TomY) leads us through a rehab of his ~1960s electrical panel.
Thank you, Dave! And your piece on a DIY Wrench Wrap really has me thinking. With the basic wrenches I have onboard, metric and SAE, plus duplicates of several sizes as we all know, I bet I have wasted more time finding the wrenches I need than it would take to make several of these sleeves.

 
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Mar 16, 2010
5,943
Beneteau 411 Oceanis Annapolis
I would not be connecting half of my 12vdc battery system between two vaults and two separate 6 vdc batteries with a long connector. I think you are off on a tangent with this 500 Ah battery system for a 29 ft boat, especially with the desire to keep it provisioned with solar panels. That is a bunch of panels crowding your small boat. Consider a blended approach that includes a smaller, robust house battery, a high-output aftermarket alternator, a new smart shore power charger, a digital battery monitor and high-charge capacity batteries. In other words, get your DC power requirements started with generation, not storage. A mistake here gets battery and re-work labor intensive.

You could begin with some inexpensive flooded batteries as your ‘trainers’ and have everything in place to drop in some AGM/Gel/whatever in the future if you get to your dream voyaging.
 
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Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
I think you are right. I had begun coming to the same conclusion as I decided to look at going with one or two Trojan T1275s (flooded) for house and a one T1275 for start. Thank you.
 
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Likes: TomY
Jan 11, 2014
4,269
Sabre 362 113 Fair Haven, NY
I would not be connecting half of my 12vdc battery system between two vaults and two separate 6 vdc batteries with a long connector. I think you are off on a tangent with this 500 Ah battery system for a 29 ft boat, especially with the desire to keep it provisioned with solar panels. That is a bunch of panels crowding your small boat. Consider a blended approach that includes a smaller, robust house battery, a high-output aftermarket alternator, a new smart shore power charger, a digital battery monitor and high-charge capacity batteries. In other words, get your DC power requirements started with generation, not storage. A mistake here gets battery and re-work labor intensive.

You could begin with some inexpensive flooded batteries as your ‘trainers’ and have everything in place to drop in some AGM/Gel/whatever in the future if you get to your dream voyaging.
@Gunni makes a good point. Unless the boat has refrigeration 2 GC batteries will meet most of your electrical needs for the near term. Coupled with a couple of solar panels and an externally regulated alternator you should be fine. https://marinehowto.com/marine-alternator-installation-tips-tricks/
 
Jan 22, 2008
7,116
Beneteau 323 Annapolis MD
I think you are right. I had begun coming to the same conclusion as I decided to look at going with one or two Trojan T1275s (flooded) for house and a one T1275 for start. Thank you.
I have a B 32 3, 3 x 31 batteries. I only have two online overnight, the third shut off in case the others fail by morning. Usually with fridge and lights I use 40 ah overnight, 50 in the summer with all the fans running. I could get by with one battery I suppose.
 
Oct 22, 2014
10,404
CAL 35 Cruiser Portland OR, moored EVERETT WA
You know Ron... One is good, Two is better, and Three is best... Unless you are talking about wives or girlfriends at the same time. Then all bets are off.
 
Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
Hey all, so I’m at the boat tonight and plan on overhauling my electrical system over the next day or so. I’ve read most here and think I have a decent plan. Please comment if you have any suggestions or advice.

Basically I have a system that is ground/house/start pic 1. I plan on connecting the ACR and battery roughly as on pic 2. The plans may change when I actually start wiring and planning. But hopefully you will get the gist.
 
Apr 7, 2016
184
Beneteau First 305 Seward, Alaska
Hey all, so I’m at the boat tonight and plan on overhauling my electrical system over the next day or so. I’ve read most here and think I have a decent plan. Please comment if you have any suggestions or advice.

Basically I have a system that is ground/house/start pic 1. I plan on connecting the ACR and battery roughly as on pic 2. The plans may change when I actually start wiring and planning. But hopefully you will get the gist.
Ugh apparently I’m not smart enough to post a pic...