battery charger and engine alternators....

[CliffA]

recently I was thinking about how the batteries on my boat are charged and a question came up in my mind.....when the engines are running does the charge from the alternators take priority over the onboard battery charger regardless if the charger is being powered by shore power or the genny?....

in other words if i am on shore power or genny power without the engines running the onboard charger is charging the batteries....when i start the engines does the onboard charger get bypassed and the charge form the engine alternators begin charging the batteries?....

thanks...
cliff

 

[Bt Doctur]

Typically engine starting batteries are charged by the engines alternators and are dedicated to the engines if they are fuel injected. Meaning each engine has its own battery .

House batteries are charged by a batterycharger/converter on shore power or generator power.

 

[trit21]

The above is not how I have seen boat wired but certain boat may be that way. What I typically see is ALL batteries are charge by the on board charger. They may be on a different bank such as mine 3house batteries on one bank, 2 engine start batteries on another bank. Typically the alternator will put out more voltage and more current than your charger is capable of supplying so when the engines are started the alternators will supply power to charge the batts regardless if you are connected to shore power or not. For example again, my charger will supply 14 volts but is limited to 60 amp max while my alternators supply (limited by my alternator regulator which is external to the alternators) 14 volts but will supply 100 amps each at max output.

 

[Bt Doctur]

TO: SERVICE MANAGER TECHNICIANS No. 97-5
PARTS MANAGER
Revised June 1999. Information underlined is new.
Multiple EFI Engine Battery Precautions
Models
MCM, MIE Engines with Electronic Fuel Injection.
Situation
Alternators: They are designed to charge the battery that supplies electrical power to the engine
that the alternator is mounted on. When batteries for two different engines are connected, one
alternator will supply all the charging current for both batteries. Normally, the other engine’s alternator
will not be required to supply any charging current.
EFI Electronic Control Module (ECM): The ECM requires a stable voltage source. During multiple
engine boat operation, an electrical onboard device may cause a sudden drain of voltage at the
engine’s battery. The voltage may go below the ECM’s minimum required voltage. Also, the idle
alternator on the other engine may now start charging and this could cause a voltage ‘spike’ in
the engine’s electrical system. In either case, the ECM could shut off. When the voltage returns
to the range that the ECM requires, the ECM resets itself. The engine will now run normally. This
ECM shut down usually happens so fast that the engine just appears to have an ‘ignition miss’.
Recommendations
Batteries: Boats with multi-engine EFI power packages require each engine to be connected to
its own battery. This ensures that the engine’s Electronic Control Module (ECM) has a stable voltage
source.
Battery Switches: While engines are running, battery switches should be positioned so each
engine is running off its own individual battery. DO NOT run engines with battery switches in
“BOTH” or “ALL” position. In an emergency, another engine’s battery can be used to start an
engine with a dead battery.

 

[Bt Doctur]

I guess I will never understand why you would have twin engines and combine everything into a single engine electrical system .I do understand the manufactures being that cheap though.
If each system is independent , they can never both stop working .combine then and a glitch in one engine takes out both engines.
Keep you house batteries and your genny batteries but get you motor batteries out of the equasion.

 

[paulswagelock]

Short answer to the question asked, at any rpm above idle, the alternator will put a voltage on the battery that your charger will sense as fully charged, and hence will not supply a charge.

 

[FootballFan]

I have had the same question in the past - what is the correct operation - should the switch for the charger be on or off during operation of the engines.

Feedback I got was it depends on the year and model of the boat. There was a time in the past where it mattered, in later models the chargers were "smart" enough for it not to be a problem.

Mark

 

[Bt Doctur]

But again, why do you feel the need to charge the engine batteries when the engine batteries are charged by the engines alternators and should be dedicated to ONLY the engines.
charge your house batteries and your genny batteries . Even if you manage to kill those you still have 2 strong engine batteries to start your engines.

 

[CliffA]

But again, why do you feel the need to charge the engine batteries when the engine batteries are charged by the engines alternators and should be dedicated to ONLY the engines.
charge your house batteries and your genny batteries . Even if you manage to kill those you still have 2 strong engine batteries to start your engines.

Bt Doctur i undertand your question and it is a good one that makes logical sense....the only reason i can think of to include the engine starting batteries as part of the charger circuit is if the boat is not used for a long time the starter batteries could run down.....also if the boat is only used for a slow 'cocktail cruise' for a couple hours every couple weeks that may not be enough time for the alternators to keep the starting batteries fully charged...

cliff

 

[CliffA]

Short answer to the question asked, at any rpm above idle, the alternator will put a voltage on the battery that your charger will sense as fully charged, and hence will not supply a charge.

thanks....that is kind of what i suspected but wasn't sure...

cliff

 

[trflgrl]

But again, why do you feel the need to charge the engine batteries when the engine batteries are charged by the engines alternators and should be dedicated to ONLY the engines.
charge your house batteries and your genny batteries. Even if you manage to kill those you still have 2 strong engine batteries to start your engines.

I agree with you it's ideal to have dedicated engine batteries, but to me it's about how what I have works so that I know what's going on when I'm on shore power only vs. alternator only vs. generator only vs. alternator+generator. Until/unless I change my wiring to the ideal setup, I have to understand how to manage existing to minimize my risk of being dead in the water.

I can't find the thread/quote right now, but another member linked something helpful when I had a similar question about my 3 battery setup, and IIRC it goes like this:

On shore power only, charger is charging all three of my batteries based on their individual needs.
On generator power only, charger is charging all three of my batteries, again based on their individual needs.
With engines running and generator off, alternators are charging the batteries that are selected--for me that means port engine starting battery is being charged by port engine, because it's isolated on its own switch; and of the two remaining batteries, only one is being charged by the starboard engine, depending on whether that selector switch is in position 1 or position 2.
(I'm open to corrections here)

Cliff's question takes the third scenario a step farther; rarely do I run the generator while under way, so it hadn't occurred to me to wonder. In that case, based on the logic I've read above and the assumption the generator may self-regulate when alternator current is present....

The port alternator is charging the battery tied to that engine.
The starboard alternator is charging the battery that's selected on the switch.
The charger MAY be charging the third battery since it's not getting an alternator charge?

Again, open to corrections/new info--every time I see a thread about batteries/generators I learn, learn, learn!

 

[CliffA]

The port alternator is charging the battery tied to that engine.
The starboard alternator is charging the battery that's selected on the switch.
The charger MAY be charging the third battery since it's not getting an alternator charge?

i think i agree....

while connected to shore power and both engines running above idle speed i think my starboard engine alternator is charging the dedicated starting battery for this engine....the port engine alternator is charging my 'house bank' of batteries which includes the starting battery for the port engine....the genny dedicated battery is being charged by the onboard charger.....although i don't see that running the engines above idle speed when connected to shore power would be a frequent event...

while running the genny with both engines running above idle speed i think the starboard engine alternator is charging the dedicated starting battery for this engine...the port engine alternator is charging the 'house bank' of batteries which includes the starter battery for the port engine....the genny decicated battery is being charged by the genny....

phew!!!....:smt119....

if this is not correct please feel free to correct me...

cliff

 

[paulswagelock]

One caveat, if you have an ACR or any type of combining relay, then it will be even more complicated. Not sure if SR used those regularly, but Chaparall does.
It will take the alternator output of a battery and distribute it to multiple batteries as long as the line voltage is above a certain limit. It does not allow voltage to come the other direction, so you could not kill multiple batteries leaving a load on too long.

 

[trflgrl]

i think i agree....

while connected to shore power and both engines running above idle speed i think my starboard engine alternator is charging the dedicated starting battery for this engine....the port engine alternator is charging my 'house bank' of batteries which includes the starting battery for the port engine....the genny dedicated battery is being charged by the onboard charger.....although i don't see that running the engines above idle speed when connected to shore power would be a frequent event...

while running the genny with both engines running above idle speed i think the starboard engine alternator is charging the dedicated starting battery for this engine...the port engine alternator is charging the 'house bank' of batteries which includes the starter battery for the port engine....the genny decicated battery is being charged by the genny....

phew!!!....:smt119....

if this is not correct please feel free to correct me...

cliff

Not correcting, just highlighting where our statements differ so the rest of the gang can keep adding to the education. The input I got from the other thread I mentioned makes me think in multi-battery setups including a selector switch, the alternator charges only the selected battery. If you put the switch on "both" or "all," your statement would jive that in theory the alternator is charging anything connected to that switch, but Bt Doctur posted something that included the following, and I remember reading/hearing similar guidance before; we don't use the "both" option while under way.

Battery Switches: While engines are running, battery switches should be positioned so each
engine is running off its own individual battery. DO NOT run engines with battery switches in
“BOTH” or “ALL” position. In an emergency, another engine’s battery can be used to start an
engine with a dead battery.

​

 

[ttmott]

Unless you have EFI engines that are sensitive to undervoltage then the following is standard across industry:
First - alternators vs charger vs whatever; as long as they are relatively new technology they can all charge a common battery or battery bank at the same time. The battery demand will set the charge level and the alternator(s) / Charger(s) will automatically adjust to the demand. No harm, No foul.
The typical alternator / battery bank arrangement is set up for redundancy in getting the engines started and not necessarily for charging. If, for example, an alternator diode shorts and drains a bank down the boat has a healthy bank that can first start it's engine then the other.
In the past, most boats with multiple battery banks were connected with Isolators which enabled one charging source to charge multiple independent banks. So, for example, bad alternator and generator is shut down or don't have a generator so you have one engine with a down battery bank. By starting the other engine that engine's alternator's voltage will cross the Isolator's threshold and allow charging current to cross from one battery bank to the other. The down side to the old isolators is there is a voltage drop due to the electronics that will not allow the full 14+ volts to transfer over. Now there are ACR's which are actually high current relays and sense charge voltage delta to a connected bank and close allowing the full charging voltage to cross to another connected bank.

My boat doesn't have the capability to select "both" or "all" in the battery switches but regardless, if it did I would never set to those positions unless I was dealing with a problem.

 

[trflgrl]

Laugh WITH me, not AT me, ok? It was in one of my own threads!

http://clubsearay.com/showthread.php/72680-Battery-switch-positions-and-charging

 

[Bt Doctur]

When you charge your batteries during layup and leave them be until the following spring, do they still start the motors Yes= good batteries No= bad batteries
When you car is parked for a month .does the battery go dead. Bet it dosent .
Anything above 1200-1500 rpm is in charge range. so even a slow cruise should be showing 14.6V or they need servicing.
You would not believe how many tows are made for dead batteries that were boiled dry . were kept on a charger and not serviced.

 

[Bt Doctur]

just finished working on a Fountain that had both motors die at the same time.
Luckily in open water.
2 batteries 1 battery switch. both electrical systems combined.
What I found was the alt feed wire chafed the way it was routed and grounded itself to the alt housing because it was slightly melted. owner had battery switch on both (the only way to start the motors) and both 90A fuse link blocks were blown.
The system power and alt feed were both crimped together / stupid idea. Repair was to direct feed the system power because it has its own 50A breaker and to wire the alt feed thru the 90A block.
The "combiner jumper" was found under the dash on the main buss. each buss had its own feed but there was a jumper across both buss bars combining both electrical systems.
Once this was removed and power re-routed . the single feed to the ign circuit breakers was removed and individual feeds from both the port and stbd systems was wired in.

Now each motor is independant of each other. A plus was finding a therm stuck open because the temp gauge could now read its own gauge and not be affected the the other motors sender.
A second battery switch was installed . a jumper cable installed between the #2 posts of each switch allows motor batteries to be combined by the "all" "all" setting on both switches.
And where the switches are installed a third backup battery can be added just by adding jumpers to the #2 position of either switch.

 

[ttmott]

Laugh WITH me, not AT me, ok? It was in one of my own threads!

http://clubsearay.com/showthread.php/72680-Battery-switch-positions-and-charging

WITH always...
So, yes, the charger should always be on the battery side of the master battery switches; in other words not "switched". Also, on the boats that are designed to be kept in the water the critical safety devices like bilge pumps and things like stereo memories are not switched.
you might want to consider changing out that charger and getting rid of those isolators; they do go bad and will cause battery and reliability issues.

BTW - are you folks in the Loretto area of Tenn?

 

[trflgrl]

WITH always...
So, yes, the charger should always be on the battery side of the master battery switches; in other words not "switched". Also, on the boats that are designed to be kept in the water the critical safety devices like bilge pumps and things like stereo memories are not switched.
you might want to consider changing out that charger and getting rid of those isolators; they do go bad and will cause battery and reliability issues.

BTW - are you folks in the Loretto area of Tenn?

I'm following some of what you're saying.
The charger, bilge pumps, and stereo aren't switched.
As for an isolator, I found this mention in my owner's manual:

"The crossover charging system utilizes a battery isolator unit with an electronic sensor to determine a low battery bank and send power to it from the engine alternators. It is an automatic system with no switches...."

So if nobody has messed with the setup in 26 years (one can hope, right?), and it hasn't failed anywhere, then using battery selector switches DOESN'T affect which are charging when alternators kick in--battery need does? My mechanic did mention upgrading the charger as a "nice to do" so it's on our list. Focus remains on getting the generator back in business (a reason we've been much more diligent in using the selector while on the hook and not routinely choosing "both") and budgeting for fall/winter haul out for outdrive service, anything he finds while doing that, and possible bottom paint, so I'm hoping the charging setup can hold out a little longer!

Someday I'll get all this straight....probably about the time I'll want a different boat!

We're east of Nashville--Percy Priest is our pond.