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Battery, Charge controller, switch wiring - clean slate

Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
Looking for some guidance as I replace the electrical system in my Bristol 29. I have a clean slate - my Yanmar 3GM30F is in place, along with my new engine box, cabin sole (lowered), sea berth (to port) galley to starboard - all wiring removed. I have battery boxes that will allow for the placement of 4 group 31 sized batteries. The battery boxes (sized for two batteries each) are in line with the front of the engine, one box to port, one to starboard (roughly 7 or 8 feet apart). I anticipate two 75-100 w solar panels and my Yanmar alternator to handle charging. I do not believe I need AC power integrated, but if that's straight forward and generally desirable for battery charging when docked then I will build in. Essentially looking for ideas as to the best battery switching and charge controller configuration. E.g., is it practical to create a house bank with 3 of the batteries (one would be relatively far from the other two - ie 7 or 8 feet)? Etc. Thank you, Matt
 
Jan 11, 2014
4,053
Sabre 362 113 Fair Haven, NY
Matt, Welcome to SBO.

My first answer to your questions is a suggestion to go to MarineHowTo.com and read everything. Lots of your questions will be answered and then you'll have more.

Next go over to Musings With MaineSail on SBO. Again lots of very good information and in particular a highly recommended main DC wiring system.

Consider using golf cart batteries instead of group 31s. GC batteries are true deep cycle batteries and will give you more power for your money and last longer. Again the MarineHowTo.com site has several articles on the topic.

If you have a stock internally regulated alternator, it may not be up to the job of keeping the batteries fully charged. Depends on use and how much motoring you will do. A better choice is an externally regulated higher output alternator. There are choices with this option. At the high end is a Balmar system at the low end is removing the internal regulator from the stock alternator and adding an external regulator. There's a website with lots of information on this, you should know it by now. :biggrin:

It sounds like you have done a lot of restoration work on your Bristol. Do you have plans for extended cruising? We all appreciate seeing photos of each other's hard work.
 
Sep 30, 2008
1,426
Catalina 310 Quincy, MA
Starting with a clean slate is good. You can build a system to suit your needs. To help you design it, you could refer to the tutorials in the archives of this forum, and at Maine Sail's site. Wiring charts to determine wire size and lengths of run will be helpful. Good luck!
 
Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
Dave, Tom, Thank you.
Being a newbie, please help me out with 'SBO' and Main Sail - sounds like he /they may be frequent posters here or have his/their own site - please clarify. Regarding my boat, the PO, David Browne, gets most of the credit. I never knew David, but here is his site that he built re the boat I now own: http://www.bristol29.com/ (lots of great photos). By all accounts David was a genuinely good fellow and sailor. He passed recently and I was fortunate to be able to buy his boat. To get a head start on finishing where David left off, James Baldwin did the interior work that I note - and now I will take it the rest of the way, being the beneficiary of the skills of two people who are far more knowledgeable than I am at this point. Thank you James and David. Here are some photos of the interior work. Long term plans are to trailer to the GA coast and go from there. In the meantime I will sail on Lake Lanier her in GA.
 

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Maine Sail

Moderator
Feb 6, 1998
11,014
Canadian Sailcraft 36T Casco Bay, ME
We'll really need to know a bit more about expected use, mooring or dock, coastal cruising, lake or offshore/long distance, how many successive nights at anchor etc., etc.. The system design can run the gamut from mild to wild depending upon desired usage.
 
Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
Thanks Maine Sail. Near term will be docked on Lake Lanier, sailing weekends, a night or two at anchor, then back to the dock (where I do have 120v). But, I want to build her so me and my wife (or one child at a time) can sail from East Coast to the Bahamas, at least - hopefully beyond. So, I am prepared to invest more now to have what I know I will not need for a few years, and I want to avoid failing to do now what I will wish I had done ahead of heading offshore. As it is now, I have, more or less, a clean slate. Thanks, Matt
 
Nov 3, 2018
16
Cape Dory, Albin 300ms Motorsailer, Vega Heart of Gold, Pagan Baby Baltimore
Hi Matt,
I was in the same position last spring- a new to me boat with an outdated electrical system and just enough knowledge to be dangerous. Doing some research I stumbled on MarineHowTo.com and MaineSails forum and read everything I could find. Then I hired a reputable marine electrician as a consultant. It was money well spent as we went over what I wanted to do with the boat and then came up with a bill of materials, wiring schematic, and options for positioning batteries, inverter, etc. and a priority list for the work. I spent most of the summer getting everything installed and will finish the last bit (alternator upgrade) this winter.

It was really helpful to have a pro holding my hand while I did the work and now I have a system that I know intimately and better yet, understand. Best of all, so far everything has worked flawlessly.

Tom
 
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Maine Sail

Moderator
Feb 6, 1998
11,014
Canadian Sailcraft 36T Casco Bay, ME
You always want to start with a good foundation, your heavy gauge battery cabling, switching & charging. It can grow from there...

With this diagram you have two switches to flip ON & OFF, HOUSE and START. There is also an emergency cross connect switch and a hidden ON/OFF in the battery compartment before the charge/always on bus so the house bank can be fully isolated if need be and all charging can move to the START/RESERVE battery. This same diagram can also be used with two hidden battery switches one for START and one for HOUSE and then use the Blue Sea Dual Circuit Plus battery switch.

 
May 23, 2018
10
Allied Princess Southwest Harbor
As Maine Sail said, we really need to know more about your usage. For example what systems will you have? In particular will/does the boat have refrigeration. Do you have an autopilot that you will use a lot when sailing? Those are likely your two biggest power users and will determine both the required size of your battery bank and your charging requirements. If you don't have refrigeration and use the boat primarily on weekends, 150-200 watts of solar will keep your batteries charged supplemented by your alternator when motoring. Maine Sail's diagram is good, but I would wire the start battery differently. Essentially, I would connect the alternator output directly to the start battery and then connect the house bank to the start battery with the ACR (automatic combiner relay labelled "voltage sensing relay" in Maine Sail's drawing). The reason for that is the start battery will be used only to start the engine. Unless you have starting issues, the draw down on the start battery will be small (less than 1 amp-hr for your engine). Consequently, when the engine starts the alternator will very quickly recharge the start battery and bring its voltage above the ACR connect voltage to allow charging of the house bank. In Maine Sail's diagram the alternator is connected to the house bank which after a day on the hook may be significantly drawn down. Thus, it will take a LONG time to bring the house bank voltage up enough to turn the ACR on and start charging the start battery. The result is that over time, you may not adequately charge the start battery and put it in a position of not having enough charge to start the engine and even cause damage to the battery.
 
Jan 11, 2014
4,053
Sabre 362 113 Fair Haven, NY
Essentially, I would connect the alternator output directly to the start battery and then connect the house bank to the start battery with the ACR (automatic combiner relay labelled "voltage sensing relay" in Maine Sail's drawing).
It is much better to connect the alternator to the house bank or larger bank, this will help to ensure the house bank is fully charged. The alternator will sense the voltage at the battery it is connected to and will base its charge voltage on that battery. The house bank will almost always be at a lower SOC than the start battery and will accept a higher charging voltage for a longer period of time.

Although the starter draws a lot of current (~200 amps) it does so for a very short period of time. If you do the math, starting the engine only consumes 1 or 2 amp hours of battery capacity, an amount that is quickly replaced by the alternator. Once the start battery comes back up to 100% SOC the alternator will reduce its output, leaving the house bank at a less than ideal charging voltage.

With the alternator connected to the house bank, the start battery will still be quickly charged at an appropriate voltage. When the start battery is fully charged the ACR will open and isolate it. Meanwhile the house bank continues to be supplied with an appropriate charging voltage.

If I recall correctly, there is also a problem with the ACR cycling on and off when the charge source is connected to the start battery. However, I don't recall the explanation well enough to explain it to someone. @Maine Sail has explained on his website or forum
 
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Maine Sail

Moderator
Feb 6, 1998
11,014
Canadian Sailcraft 36T Casco Bay, ME
When the start battery is fully charged the ACR will open and isolate it.
It won't do this. See the combine / un-combine parameters below.

Meanwhile the house bank continues to be supplied with an appropriate charging voltage.
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.

In Maine Sail's diagram the alternator is connected to the house bank which after a day on the hook may be significantly drawn down. Thus, it will take a LONG time to bring the house bank voltage up enough to turn the ACR on and start charging the start battery
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.

I would wire the start battery differently. Essentially, I would connect the alternator output directly to the start battery
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.
 
Jan 11, 2014
4,053
Sabre 362 113 Fair Haven, NY
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.

@Maine Sail Ah, the devil is always in the details. Thank you.

Here's where I think I was getting confused. Let's say we have a house bank at 60% SOC and a start bank at 99%SOC. The charging source kicks in (alt, solar, or charger) and goes into a bulk stage at 14.8v. The
ACR then combines the batteries, the Start battery quickly goes to 100% SOC and after a while the charge source drops to absorption at 14.2 v. If the ACR keeps the batteries combined then both batteries will be at 14.2 v which is more or less fine for the house bank, but it is over charging the start battery.

To my way of thinking this is bad for the start battery and the ACR should stop combining them, until the start battery is low enough to require charging. I must be missing something here.
 
Oct 22, 2014
9,926
CAL 35 Cruiser Portland OR, moored EVERETT WA
Dave. Does this help...
BlueSea - An ACR does not direct the charge to the battery that “needs it the most” or has the lowest terminal voltage. If there is a charge present on either battery, indicated by a high enough voltage, the ACR will combine the batteries.
 
Jan 11, 2014
4,053
Sabre 362 113 Fair Haven, NY
Dave. Does this help...
BlueSea - An ACR does not direct the charge to the battery that “needs it the most” or has the lowest terminal voltage. If there is a charge present on either battery, indicated by a high enough voltage, the ACR will combine the batteries.
Yes, I realize that, however, what happens when you have one battery that is at 100% SOC and the other isn't. When the one battery is being charged at a high rate, say 14.8 v the other battery will also receive that 14.8v but it will not be able to accept the charge because it is at 100%. Wouldn't that be over charging the battery? Wouldn't that be bad for the battery?
 

Maine Sail

Moderator
Feb 6, 1998
11,014
Canadian Sailcraft 36T Casco Bay, ME
@Maine Sail Ah, the devil is always in the details. Thank you.

Here's where I think I was getting confused. Let's say we have a house bank at 60% SOC and a start bank at 99%SOC. The charging source kicks in (alt, solar, or charger) and goes into a bulk stage at 14.8v.
Here lies the confusion.. Bulk charge is maximum current attempting to increase the battery terminal voltage. With depleted batteries you don't achieve 14.8V for a long while.

Take for example a Trojan SCS-225 G-31 flooded battery being charged from 50% SOC at .15C. With a charge current equal to 15% of Ah capacity the battery will rise to about 13V in just a few minutes but will then take close to two hours before it attains 14.8V. Why? Because it takes current to increase battery terminal voltage. If we fed that same battery a 1C charge current, or 130A, it would come up to 14.8V within a matter of seconds. Conversely if we charged it at 0.05C it would take about 6 hours to get to 14.8V.

The ACR then combines the batteries, the Start battery quickly goes to 100% SOC and after a while the charge source drops to absorption at 14.2 v. If the ACR keeps the batteries combined then both batteries will be at 14.2 v which is more or less fine for the house bank, but it is over charging the start battery.
Remember both batteries are in parallel which means voltage is at parity. You can't overcharge one bank without over charging the other.

To my way of thinking this is bad for the start battery and the ACR should stop combining them, until the start battery is low enough to require charging. I must be missing something here.
What is being missed is that the last 4% of charge takes a long, long time to put back into a battery. So even just a tiny bit out of a start battery does not mean it will be "full" very quickly because charge efficiency is not linear and is very,very low in the high 90's as a % SOC. The start battery will also not attain an absorption voltage until the house bank does. Chronic undercharging is the number one killer of batteries on sailboats and this is why start batteries, even charged by an ACR usually well outlast the house bank.

The ACR and other VSR/combiners are by far and away the number one selling charge management devices in use today. Are they the "best", no but they are far from the worst. They are reasonably priced and easy to install.

They are not just used in marine applications but in trucking, service, mining, fire / rescue applications and others too. If these devices were "over-charging" start banks on a routine basis we'd be hearing about it. I routinely see start/reserve banks out last deep cycled house banks even though folks often assume they are being over-charged.

So long as both banks can be charged using the same or very similar voltages, within about 0.1V to 0.2V for absorption, there is really nothing wrong with an ACR.

If you want to mix banks or chemistries, the best device for this is a true DC to DC charger such as the Sterling Power BB1230 or Sterling Power BB1260 . They even make a BB122470 that can charge a 24V thruster or windlass bank from a 12V house bank..
 
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Jan 11, 2014
4,053
Sabre 362 113 Fair Haven, NY
Here lies the confusion.. Bulk charge is maximum current attempting to increase the battery terminal voltage. With depleted batteries you don't achieve 14.8V for a long while.
Now it makes sense, that was the part I was missing. Thank you.
 
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Dec 19, 2018
28
Bristol 29 Kate Lake Lanier
All, thank you very much for the information and your dialogue. All of this helps begin lifting the fog.