Help Me Understand The Basics Of Boat Battery Charging

[GeneraiT001]

Hi,
Trying to learn and would like to ask a few simple questions wrt eventually upgrading the batteries on my boat. Currently it has 3 x 100AmpHr FLA's. Eventually I guess I'd like to switch out the 2 x 100AmpHr house batteries for 2 x 200AmpHr LiFePo batteries. But first just trying to understand how things are supposedly working so far. I'm assuming all three batteries are in parallel as this seems to be the norm for a 12v system.

So, just with regard to those batteries (3 x 100AmpHr FLA's)...and assuming the only source of charging is the boat alternator:

While the engine is running, the alternator (Hitachi 55Amp) is producing somewhere between 20-50 Amps depending on engine RPM. Does this current go directly into the batteries or is it sent through some regulating device? I'm guessing the alternator is sending volts and not amps into the battery?What is the internal regulator of the alternator do....ensure the correct voltage is being sent into the batteries?

Is the alternator amperage (voltage) shared between all three batteries (max 50Amp / 3) at once?

If the batteries are fully charged (14volts?) what happens if the alternator is left running? What is the safety feature to prevent the FLA from overcharging?

I know this is painfully basic. Your patience with me is very much appreciated.

 

[Johann]

The stock alternator is controlled by an internal regulator that attempts to hold a voltage of around 14.4V. If the battery that the alternator is connected to is below this voltage, the regulator causes the alternator to produce current (amps) up to its maximum ability in order to raise the voltage. If you have a depleted battery it could take some time for the voltage to rise. Once the voltage reaches the regulators set point, the regulator will cause the alternator output current to decrease in order to maintain the set point voltage. BUT… the regulator also has a temperature control built in. As the alternator heats up, the regulator reduces the voltage set point, with the aim of reducing the output current and keeping the alternator from overheating.

The alternator could be connected to either the house or start battery bank, typically with some sort of relay that connects the two banks when the voltage rises above a certain point. In a stock setup there is no overcharging protection.

This article has some good info (really you should read everything on the MarineHowTo site)

Automotive Alternators vs. Deep Cycle Batteries - Marine How To

A Deep Cycle Battery Assassin The alternator pictured here helped to destroy a very expensive bank of TPPL AGM batteries in under two years. These batteries need an absorption voltage of 14.7V. The highest voltage I recorded on this vessel was 13.58V at the battery terminals. At this

marinehowto.com

 

[dLj]

Hi,
Trying to learn and would like to ask a few simple questions wrt eventually upgrading the batteries on my boat. Currently it has 3 x 100AmpHr FLA's. Eventually I guess I'd like to switch out the 2 x 100AmpHr house batteries for 2 x 200AmpHr LiFePo batteries. But first just trying to understand how things are supposedly working so far. I'm assuming all three batteries are in parallel as this seems to be the norm for a 12v system.

So, just with regard to those batteries (3 x 100AmpHr FLA's)...and assuming the only source of charging is the boat alternator:

While the engine is running, the alternator (Hitachi 55Amp) is producing somewhere between 20-50 Amps depending on engine RPM. Does this current go directly into the batteries or is it sent through some regulating device? I'm guessing the alternator is sending volts and not amps into the battery?What is the internal regulator of the alternator do....ensure the correct voltage is being sent into the batteries?

Is the alternator amperage (voltage) shared between all three batteries (max 50Amp / 3) at once?

If the batteries are fully charged (14volts?) what happens if the alternator is left running? What is the safety feature to prevent the FLA from overcharging?

I know this is painfully basic. Your patience with me is very much appreciated.

Let me see if I can take a stab at this.

Think of an analogy with water. You have water pressure (volts) and the quantity of water (amps). The pressure of water flowing, say through a hose, is similar to voltage. The quantity of water that is flowing is similar to amps. If you put too much water pressure into the hose, you will cause it to explode - it can't handle more that X amount of pressure. The diameter of your hose limits the amount of water that can flow. Increase the diameter of the hose and for the same pressure, you get more quantity of water flowing. So volts is similar to pressure, and amps is similar to quantity of water.

In the case of your alternator, it is regulated to produce a specific amount of pressure - volts. It is also limited to the quantity - amps, in your case 50 amps.

Your battery is where the energy is stored, it has a total quantity it can store - in your case 300 amp hours, 3 - 100 amp hour batteries.

Your battery has a requirement of how much pressure it should see for things to "work right"... If you don't give it enough volts - it won't charge correctly - if you give it too many volts other bad things happen as in you can destroy your batteries ability to store energy.

When you are charging the 3 batteries hooked up in parallel - that's similar to having a hose filling three buckets of water - you are filling all three at the same time.

The analogy begins to break down much beyond that and more details of batteries and electrical systems needs to come into play. Generally speaking, for flooded lead acid batteries it' really hard over charge them due to the increased internal resistance of the battery to accept more power as they begin to reach a fully charged state. It fact, one of the difficulties with lead based batteries in sailboat is that they rarely get fully charged.

Let me know if this is not useful - or about as clear as mud and I can try to take another stab at it...

dj

 

[dlochner]

Let's get more basic and talk about charging and batteries.

All batteries, LA and LFP share a similar characteristic, the closer to fully charged (100% State of Charge (SOC)) the higher the battey's internal resistance. The big difference between LA and LFP batteries is the shape of the charge curve, LA batteries have a hockey stick curve, fairly flat at low SOCs with a sharp up turn as the battery approaches 100% SOC. LFP batteries have a flatter curve, the internal resistance does not sharply increase until the battery is very close to 100% SOC. There are plenty of graphs on line showing these two charge curves.

There are 3 charging stages with various and sometimes confusing names, the easiest way to understand them is to think of them as the Constant Current (amps), Constant Voltage, and Float. In the CC stage the charger (alternator, charger or solar) will supply as much current as it possibly can to the battery. Initially, because the battery's internal resistance is low the voltage will be low, as the battery becomes more fully charged the internal resistance increases, to maintain this constant current the voltage ramps up until it reaches a specific voltage, the absorption voltage which is determined by the particular battery. When the absorption voltage is reached the charger holds the voltage constant while the current decreases because it takes more voltage (force) to push current (amps) through the battery. At some point the amount of current the battery can accept drops to around 1 or 2 amps and the charger goes into the float stage where a very small current is provided at a low voltage, usually in the low 13v range. All of this is based on Ohm's Law and the relationship between resistance, current, and voltage. The specific values for current acceptance (max amps), absorption voltage, and float voltage depend on the particular battery chemistry and how the battery was manufactured.

Alternators come in 2 basic flavors, internally regulated and externally regulated. Internally regulated alternators have pretty simple regulators mostly designed to keep the alternator from burning up while providing a charge current to the start battery. When an alternator is producing electricity it is also producing heat. The more electricity it is producing, the more heat it is producing. The internal regulator tries to balance the electrical demand (how much charge is needed and/or the amount of electricity being consumed) with the alternator's temperature and favors keeping the alternator cooler over providing electricity. This works OK for cars and powerboats, not so well with sailboats. The parameters for the internal regulator are set at the factory and can't be altered.

Externally regulated alternators have the same issues as internally regulated alternators with regard to heat and power production. The big advantage is the amount of control available to alter the parameters to maximize power production and to match the battery's need while keeping the alternator at a safe temperature.

In general any charging source will equally divide its power across all the batteries (and loads). A 50a alternator charging 3 batteries will provide about 16a to each battery at its maximum output. The actual power distribution is more nuanced than this, however for now, this explanation will do.

Power coming from a charging source does not necessarily go to the batteries first. The electrical system (the devices that are powered on) simply see it as another source of electricity. If the charger is capable of producing more power than the electrical demands at anyone time, the excess power will then charge the batteries as they become not a source of power, but a load on the power system.

If the batteries are fully charged and the alternator is running, the regulator will drop the field voltage which will decrease the amount of power being produced to match the total load on the electrical system.

All this is very confusing until you get it, then you wonder why you struggled so long with it.

 

[GeneraiT001]

Thank you all for the info and time to write it up. As a followup:

i know there is a switch in the boat (mine is pictured below) that allows you to separately select just the starter battery or just the batteries used for all the other boat electronics or both to use all 3 batteries for the house/boat electronics. I'm pretty sure the positive lead from the starter battery is wired directly to the #1 terminal on that switch and then one of the positive wires from the other 2 batteries are wired to terminal #2.

How do you wire this so that you can charge all 3 batteries at the same time and yet isolate the 2 batteries you want to use just for house power?

 

[jssailem]

@Johann has provided an excellent summary answer to your question. The link is further a solid resource.

The issue with your question is that it is based on the provided assumptions. Your boat may have been altered by any number of owners or boat workers before you acquired it. You mention three batteries. Johann assumes that two are house batteries and one is a starter battery. That is because, after years of experimentation, it has been proven to be an effective configuration for a sailboat.

With the Lithium opportunity comes a variety of internal redesigns of electrical systems.

Perhaps while you are learning and enjoying the sailing capabilities of your boat, you can expand your knowledge of DC and AC electrical systems for boats. Exploring the information on the "Marine How To" site is excellent. Reading about boat electrical systems, "Boatowners Mechanical and Electrical Manual" by Nigel Calder, or his new adventure into online instruction. About BoatHowTo - BoatHowTo

Knowledge is a powerful thing.

 

[jssailem]

I'm pretty sure the positive lead from the starter battery is wired directly to the #1 terminal on that switch and then one of the positive wires from the other 2 batteries are wired to terminal #2.

With electricity, it is black or white. The wires are going from the positive battery lead, or they are not. "Pretty sure" is a phrase that can get you into a lot of trouble.

If not absolutely (bet your life) sure, I would encourage you to inspect and become sure visually.

The switch image you provide has been used by many sailors to manually control the charge current from an alternator to a chosen battery. What has been learned over the years is the unreliability of sailor' memory to ensure that all the batteries are charged and ready for their intended use.

Jump on the boat, turn the switch to charge the house batteries. Anchor out for the night. Wake and go to start the boat motor, only to discover the start battery is dead.

Johann posted

The alternator could be connected to either the house or start battery bank, typically with some sort of relay that connects the two banks

You can find a detailed discussion of this "relay" setup on Marine How To. BlueSea Electrics provides an ACR unit (https://www.bluesea.com/products/category/35/Automatic_Charging_Relays) that has saved many a sailor from the embarrassment of a dead starter battery.

 

[Don S/V ILLusion]

How do you wire this so that you can charge all 3 batteries at the same time and yet isolate the 2 batteries you want to use just for house power?

there is no single correct answer. Depends how your boat charging system is configured. Generally, charging of all batteries is done irrespective of the switch by an ACR relay or isolator such that all batteries are interconnected only during charging.

 

[Davidasailor26]

Thank you all for the info and time to write it up. As a followup:

i know there is a switch in the boat (mine is pictured below) that allows you to separately select just the starter battery or just the batteries used for all the other boat electronics or both to use all 3 batteries for the house/boat electronics. I'm pretty sure the positive lead from the starter battery is wired directly to the #1 terminal on that switch and then one of the positive wires from the other 2 batteries are wired to terminal #2.

How do you wire this so that you can charge all 3 batteries at the same time and yet isolate the 2 batteries you want to use just for house power?

That’s a pretty typical 1/2/Both switch used for selecting which batteries get all the loads and charging sources. MarineHowTo has a good article on those at 1/2/BOTH Switch Considerations

Those types of switches were used very often on older boats and they can be effective for managing multiple banks. Their main drawback is that the management is all manual, and at least somewhat error prone. Forget to switch to “both” periodically and one bank might not stay charged. Forget to switch out of “both” overnight and you might find you don’t have a charged battery to start the engine. Accidentally switch to “off” when the engine is running and you might fry your alternator.

One alternative is to rearrange the charging system to use FET based battery isolators or automatic charging relays (ACR’s) to automatically combine the banks when they’re charging but separatr them when they’re not. If you move to lithium it’s common to use a DC/DC charger to charge one bank from the other.

 

[dlochner]

Thank you all for the info and time to write it up. As a followup:

i know there is a switch in the boat (mine is pictured below) that allows you to separately select just the starter battery or just the batteries used for all the other boat electronics or both to use all 3 batteries for the house/boat electronics. I'm pretty sure the positive lead from the starter battery is wired directly to the #1 terminal on that switch and then one of the positive wires from the other 2 batteries are wired to terminal #2.

How do you wire this so that you can charge all 3 batteries at the same time and yet isolate the 2 batteries you want to use just for house power?

This article will answer your questions and cause you to ask some more.

1/2/BOTH Switch Considerations

1/2/BOTH Battery Switch Considerations - Ever wonder how to make the 1/2/BOTH switch easier to use, let this article explain how to do that.

marinehowto.com

 

[Scott T-Bird]

With that switch, you really don't have a dedicated start battery and a dedicated house bank. When you look on the back of the switch, there are just 3 studs. There are 2 studs for input (current from the batteries) and 1 stud for output (current flowing to the "loads"). With that in mind, you select the input (Position 1 or 2) to serve both the starting load and house bank loads together. You don't have starting isolation. Select "Position All" and you may as well have all 3 batteries wired in parallel.

If you want to use one battery just for starting, you will need to select the position that is connected to the "start battery" when you are starting the engine. Perhaps it is Position 2 (you will have to confirm). Then, when you want to use the house bank while anchoring, you would manually switch to Position 1(assuming that it is connected to 2 batteries in parallel that you call "house bank". What you haven't made clear to us is how your batteries are connected to the switch. We are all assuming that you have one battery connected to one position and you call that "start" and that you have 2 batteries connected to each other in parallel that you call "house bank" connected to the other position. But your first post seemed to indicate that you have 3 batteries wired in parallel. This would not be normal, and you should confirm with all of us exactly how they are connected to the switch. It is more accurate to call the "start battery" an "auxiliary battery".

If you want to truly isolate the starting load from the house bank loads, you will need a different switch configuration. You could install a switch with 4 posts (2 inputs and 2 outputs) or 2 separate "On / Off" switches if you really want isolation between the start battery and the house bank. This has additional complications that you will need to learn about.

Another consideration that you must investigate is how the alternator is connected to the batteries for charging. With your switch, the boat builder's typical installation makes a very short cable run from the alternator to the starter. That's because they want to avoid installing a long cable run from the alternator to a battery directly. Instead, they let the current back-feed the batteries from the starter. The purpose is to select which battery to charge with the switch or to charge all batteries simultaneously on "Position All".

You can avoid making these manual selections with an ACR. But then you will need to connect the alternator output directly to a battery and not back-feed the current thru the starter.

 

[Stu Jackson]

Some further reading for you in addition to the fine links already provided:

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations (New 2020 - Rod finally got around to diagramming what I had done in the above link in 2009 )
1/2/BOTH Switch Considerations

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowners.com/showthread.php?t=137615

This is a newer primer for boat system wiring design with a thorough diagram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation

 

[GeneraiT001]

With that switch, you really don't have a dedicated start battery and a dedicated house bank. When you look on the back of the switch, there are just 3 studs. There are 2 studs for input (current from the batteries) and 1 stud for output (current flowing to the "loads"). With that in mind, you select the input (Position 1 or 2) to serve both the starting load and house bank loads together. You don't have starting isolation. Select "Position All" and you may as well have all 3 batteries wired in parallel.

If you want to use one battery just for starting, you will need to select the position that is connected to the "start battery" when you are starting the engine. Perhaps it is Position 2 (you will have to confirm). Then, when you want to use the house bank while anchoring, you would manually switch to Position 1(assuming that it is connected to 2 batteries in parallel that you call "house bank". What you haven't made clear to us is how your batteries are connected to the switch. We are all assuming that you have one battery connected to one position and you call that "start" and that you have 2 batteries connected to each other in parallel that you call "house bank" connected to the other position. But your first post seemed to indicate that you have 3 batteries wired in parallel. This would not be normal, and you should confirm with all of us exactly how they are connected to the switch. It is more accurate to call the "start battery" an "auxiliary battery".

If you want to truly isolate the starting load from the house bank loads, you will need a different switch configuration. You could install a switch with 4 posts (2 inputs and 2 outputs) or 2 separate "On / Off" switches if you really want isolation between the start battery and the house bank. This has additional complications that you will need to learn about.

Another consideration that you must investigate is how the alternator is connected to the batteries for charging. With your switch, the boat builder's typical installation makes a very short cable run from the alternator to the starter. That's because they want to avoid installing a long cable run from the alternator to a battery directly. Instead, they let the current back-feed the batteries from the starter. The purpose is to select which battery to charge with the switch or to charge all batteries simultaneously on "Position All".

You can avoid making these manual selections with an ACR. But then you will need to connect the alternator output directly to a battery and not back-feed the current thru the starter.

Thanks. Its true, I'm not sure how the batteries are connected at the moment. They are just 3 LFA's right next to each other and enclosed in plastic cases, so I cant see how they are wired. Will have a look at that (in the spring) and get more detail on whats going on Thank you for the write up.

 

[Ralph Johnstone]

While the engine is running, the alternator (Hitachi 55Amp) is producing somewhere between 20-50 Amps depending on engine RPM.

Let me offer some reality as to what is REALLY going on in your existing charging system. You're not even in the right ballpark and that's why your results in charging are so poor. Same as mine used to be.

Like you, I also have a Hitachi model LR155-20B 12V 55 amp alternator. This is an internally regulated alt. which puts out a maximum of ~12A bulk charge to any number of batteries all at 50% state of charge (SOC) and the alt. was still cool. Once it gets up to an operating temperature of ~170° F and the batteries with an inceased SOC, you sit at ~ 8 - 9A. This rarely gets you much over an SOC of 80% after running on engine all day.

I installed a Balmar ARS-5 external alternator regulator after the boat was about 10 YO and went from ~ 10A charging again at 50% SOC to :

That was >250% increase in bulk charging and a minuscule fraction of the cost of an LiFePo upgrade. I've never had a glitch out of the Balmar ARS-5 and the little Hitachi 55A supplies all of my electrical needs including a refrigerator when on the hook for a few days.

Maybe a few too many new electrical terms and concepts thrown in there for you all at once so don't hold back with any questions.

 

[dLj]

Let me offer some reality as to what is REALLY going on in your existing charging system. You're not even in the right ballpark and that's why your results in charging are so poor. Same as mine used to be.

Like you, I also have a Hitachi model LR155-20B 12V 55 amp alternator. This is an internally regulated alt. which puts out a maximum of ~12A bulk charge to any number of batteries all at 50% state of charge (SOC) and the alt. was still cool. Once it gets up to an operating temperature of ~170° F and the batteries with an inceased SOC, you sit at ~ 8 - 9A. This rarely gets you much over an SOC of 80% after running on engine all day.

I installed a Balmar ARS-5 external alternator regulator after the boat was about 10 YO and went from ~ 10A charging again at 50% SOC to :

That was >250% increase in bulk charging and a minuscule fraction of the cost of an LiFePo upgrade. I've never had a glitch out of the Balmar ARS-5 and the little Hitachi 55A supplies all of my electrical needs including a refrigerator when on the hook for a few days.

Maybe a few too many new electrical terms and concepts thrown in there for you all at once so don't hold back with any questions.

The sailing plans of @GeneraiT001 are stated as: "My plan is too take a year to get familiar with the boat then sail it down to the Caribbean, stay awhile, then through the Panama Canal and up the west coast to Nanaimo, BC."

For this kind of trip, I would highly recommend going to LiFePo house batteries. Traveling that far, if it comes to pass, will mean a lot of time on his boat. So, your posting - @Ralph Johnstone - you made above is not the best system for that kind of sailing. It will be very difficult to keep LA batteries fully charged and in good shape for the kind of time away from shore and the LiFePo batteries will be much better, will be less expensive over the long run, and more reliable than any LA based system. Just my 2 cents worth...

dj

 

[shemandr]

There are simple questions. But not simple answers. If the OP looks back on past threads discussions about batteries are abundant and lengthy. They are worth reading. But many get well into the weeds and may cause confusion. Nevertheless, it is not a simple process.

 

[BigEasy]

Like you, I also have a Hitachi model LR155-20B 12V 55 amp alternator.
I installed a Balmar ARS-5 external alternator regulator after the boat was about 10 YO. I've never had a glitch out of the Balmar ARS-5 and the little Hitachi 55A supplies all of my electrical needs

Ralph, so you are using the ARS-5 external regulator with a Hitachi alternator? How did you disable the internal regulator and install the ARS-5. I thought that you had to replace the internally regulated alternator to one that was compatible with external regulation equipment. (Balmar alt / Balmar reg)