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Old 03-03-2015, 03:40 PM   #1
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Alternator question

Are both alternators on twin Diesel engines used to charge the batteries? The reason I'm asking is that the boat we are buying is 1000 miles north and I have no way to check. I would like to have two sets of batteries charged by different alternators if that is possible.
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Old 03-03-2015, 03:46 PM   #2
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It's possible but whether or not that is the case you will have to find out.
Often one alternator is set up to charge the engine starting batteries, the other alternator is used to charge the house batteries but no one can tell you from here.
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Old 03-03-2015, 04:16 PM   #3
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Alternators trying to charge the same batteries would fight each other so the common and most natural setup is independent port to port and starboard to starboard. It gets more complex when the port and starboard are combined into any number of possible configurations. At this point the alternator outputs are usually wired to a battery combiner device. As previous posters have said there is no way of knowing what is what on any particular boat without a thorough survey. There are simply dozens of battery themes and schemes out there.
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Old 03-03-2015, 04:27 PM   #4
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Yes hard to say without actually looking at the boat's wiring.
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Old 03-03-2015, 06:04 PM   #5
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GreenSailor-As already stated, there's no common practice. There's almost as many variations in DC power systems aboard boats as there are boats! So...you've got to either put your own eyeballs on the installation, or pay someone knowledgeable (and local) to do it for you.

FYI, here's a pretty good reference for a "preferred" method of DC wiring aboard boats.

https://amplepower.com/primer/prefer/index.html

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Old 03-03-2015, 07:43 PM   #6
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If you have a large house battery, this is an idea.

Balmar Centerfielder II Charge Controller



I helped set up a twin to use the Belmar smart Voltage regulators on both alternators then through the center-fielder II charge controller.

Balmar Digital Duo Charge

The starting battery's were charged by a duo-charge from the house batt. one each to the starts, giving 30 Amp to charge what was pulled out to start. Both alts. (100amp) charged the house bank.

Works great all current goes to the house and when the Duo-charges sense charge voltage they act as 30 amp battery chargers to charge the starting battery using the house battery's.

No isolators, battery switches or even thinking about it and even works with a solar panel charging the house, when voltage is input the Duo-charges charge the starting batts. as needed then stop when full.


I have a Duo-charge and a smart regulator with a high output alt. large house bank and small start batt. but only one engine so simpler setup.
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Old 03-03-2015, 11:07 PM   #7
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My boat came wired so whichever battery was selected at the batt switch, that battery or batteries got the charge from the alternators and that was the source of power for all loads. If I wanted to charge both the house and start batts from the alternators, I had to select ALL on the switch. If I forgot to select 2 for the house at anchor, all loads used came from both batts. It was a miserable setup that required continuous attention.

I recabled so each alternator feeds its batt directly with no switch...stbd to house batt and port to start batt. The loads are run through a set of switches that allow me to choose the offside battery for power if needed or both batts for start if needed. The charges can be shared through a switchable combiner.

Now I never have to mess with the switches except for the small combiner ON/OFF switch on the helm overhead panel. It also allows me to use a single bank charger to provide recharging to both banks. That and a battery SOC meter has made my electrical life very simple now.

Some of the values need to be updated in the schematic below, but the connections are still current (no pun intended) on my boat.

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Old 03-04-2015, 12:05 AM   #8
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No idea what you have, but easy to do it right. Use a Balmar Dual Charge, some Blue Seas RBS and ACR and its set and forget. Both engine alternators (Leece Neville 200A) go to the house bank, then linked to each engine bat via the ACR's.
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Old 03-04-2015, 12:30 AM   #9
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Life is simpler with a single engine and alternator (and no genset).
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Old 03-04-2015, 10:48 AM   #10
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Also running 2 alternators off one engine with one only charging the house bank is a good option.

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Old 03-04-2015, 09:57 PM   #11
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The 2 alternators will not "fight" each other. Voltage regulators in the alternators adjust the field to provide a certain set voltage. If two alternators are connected to a common battery bank both will provide current until the set voltage is reached then both will keep the voltage at the set point.

However, it may be good practice to separate the battery banks and charging so each alternator charges a separate bank. With separate banks and separate charging, you would have a charged bank if your house load draws down one bank or if a battery or alternator fails.
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Old 03-05-2015, 07:47 AM   #12
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Originally Posted by neworleansrich View Post
The 2 alternators will not "fight" each other. Voltage regulators in the alternators adjust the field to provide a certain set voltage. If two alternators are connected to a common battery bank both will provide current until the set voltage is reached then both will keep the voltage at the set point.

However, it may be good practice to separate the battery banks and charging so each alternator charges a separate bank. With separate banks and separate charging, you would have a charged bank if your house load draws down one bank or if a battery or alternator fails.

Actually they wont "fight" you are correct.

However only one will do any work, here's why.

The alternators voltage regulators (VR) are not very smart and only works like a gas peddle, go faster or slower they will both sense voltage of the same battery then one will charge at one rate and the other will charge at another rate, close but slightly different.

The voltage regulator that puts out the higher voltage will take over all the charging as the other will sense the higher voltage and think the battery is charged (it will be reading oh say 14.2 volts put out by it's brother and think hey the battery is full.

The two dumb VR built in to the alts will not allow the regulation needed with duel alts. charging a common bank.

One alt will wear out faster as it will always be doing the work and the other will be doing nothing. But they won't fight, just a bit of bitching from the worker.

To make it work you need two smart VR's and one common voltage sense in between giving the smart VR a single reference voltage and control input that they will use to control winding voltage to their individual alt. thus providing maximum output by both that is adjusted as the battery voltage changes.

Read up on the many different setups used in a duel to one bank situation, they would not exist if there was no need.


https://amplepower.com/primer/twoeng/index.html

Using 2 alternators to charge a house bank - Cruisers & Sailing Forums

http://www.google.com/url?sa=t&rct=j...87519884,d.eXY
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Old 03-05-2015, 10:09 AM   #13
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Actually they wont "fight" you are correct.

However only one will do any work, here's why. ......

The voltage regulator that puts out the higher voltage will take over all the charging
as the other will sense the higher voltage and think the battery is charged (it will be reading oh say 14.2 volts put out by it's brother and think, "hey the battery is full!" .......

One alt will wear out faster as it will always be doing the work and the other will be doing nothing. ........

To make it work you need two smart VR's and one common voltage sense in between ......

Read up on the many different setups used in a duel to one bank situation, they would not exist if there was no need.
With the (new to me) boat, I now find myself in this situation.

Thanks for this post.
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Old 03-05-2015, 10:29 AM   #14
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With the (new to me) boat, I now find myself in this situation.

Thanks for this post.

My pleasure,


Love your OA.
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Old 03-05-2015, 11:09 AM   #15
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The 2 alternators will not "fight" each other. Voltage regulators in the alternators adjust the field to provide a certain set voltage. If two alternators are connected to a common battery bank both will provide current until the set voltage is reached then both will keep the voltage at the set point.
Sorry, I used the word "fight" to mean that they would fight over who does the charging.
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Old 03-05-2015, 11:23 AM   #16
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Actually they wont "fight" you are correct.

However only one will do any work, here's why.


The voltage regulator that puts out the higher voltage will take over all the charging as the other will sense the higher voltage and think the battery is charged
But if the bank is either very large or very deeply discharged, then the amperage out of the "winning" charger may be (actually, will be, if the bank is large enough or the discharge deep enough) less than the acceptace rate of the bank, the voltage will not exceed the other regulator's set point and that regulator will put out additional amperage as well.
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Old 03-05-2015, 11:38 AM   #17
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Also running 2 alternators off one engine with one only charging the house bank is a good option.

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And I like the tensioner on the second alternator.
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Old 03-05-2015, 01:09 PM   #18
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But if the bank is either very large or very deeply discharged, then the amperage out of the "winning" charger may be (actually, will be, if the bank is large enough or the discharge deep enough) less than the acceptace rate of the bank, the voltage will not exceed the other regulator's set point and that regulator will put out additional amperage as well.

True to an extent, if the bank is large enough and the standard alt is being used (55-70 Amp). Remember acceptance rate tapers fairly fast and will drop with battery heat as well, a smart charger will compensate to 1/10 of a volt and control not only the voltage produced by the alt but the amperage as well, this is important as the stages of proper battery charging require a change in the voltage as will as amperage during the four stages of charging. A standard built in VR will only adjust the alt. voltage and then to (if you are lucky) within .5 volts or so. Note the difference between bulk and acceptance phase is .2 volts (12 volt lead acid) This is no way to treat an expensive large battery bank.


"The BULK stage involves about 80% of the recharge, wherein the charger current is held constant (in a constant current charger), and voltage increases. The properly sized charger will give the battery as much current as it will accept up to charger capacity (25% of battery capacity in amp hours), and not raise a wet battery over 125 F, or an AGM or GEL (valve regulated) battery over 100 F.


The ABSORPTION stage (the remaining 20%, approximately) has the charger holding the voltage at the charger's absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger set points) and decreasing the current until the battery is fully charged. Some charger manufacturers call this absorption stage an equalization stage. We don't agree with this use of the term. If the battery won't hold a charge, or the current does not drop after the expected recharge time, the battery may have some permanent sulphation.


The FLOAT stage is where the charge voltage is reduced to between 13.0 VDC and 13.8 VDC and held constant, while the current is reduced to less than 1% of battery capacity. This mode can be used to maintain a fully charged battery indefinitely."



http://www.chargingchargers.com/tutorials/charging.html



Usually if one has a large (>700ah) bank then they have a larger then standard alt. at least over 100amp then for a while when the bank is low both will put in some charge given the limitations of the VR's and battery temp which will not be compensated for. This is almost a required situation for external smart VR's

Built in VR's barely keep the voltage under-control, remember auto based VR's only need to top off the energy used to start an engine and then not to blow light bulbs with too high a voltage and keep up with the usual loads in a car. The last thing in the world they were designed was to do is carefully go through the four stages of proper battery charging.

A smart regulator will do all 4 stages and with temperature compensation both at the alternator case as well as the battery temperature.

With standard automotive based alternators the limiting factor is heat internal to the alt. as the charge rate will drop 40-60% as the alt heats up. Hitachi Alts (Yanmar diesels) are very bad in charging large banks as they regulate to around 13.4 volts when heated up, this will never charge a battery over about 80%.


Unless you are a weekend cruiser with a small battery bank, or run your gen-set all the time you will benefit from smart external regulation with temperature compensation and large capacity alternators.


This is a great read and he makes it simple, however it is a sailing forum.

Musings Regarding External Regulation - SailboatOwners.com
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Old 03-05-2015, 08:27 PM   #19
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I personally have had very good results with "automotive" Delco alts. I use two 105 amp units on one engine and a 70 amp on the other. The twins charge the 1100 AH house bank. The voltage climbs from the 13s to the 14s when the second is brought on line. They have internal dumb VRs. I monitor the two setups using digital LED volt meters at the helm. I've been running this for three years and all seems well.
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Old 03-05-2015, 09:01 PM   #20
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True to an extent, if the bank is large enough and the standard alt is being used (55-70 Amp).
And, conversely, if the bank isn't large enough, the additional capacity of a second alternator isn't necessary, even with an external VR.

But don't get me wrong -- I completely agree that a smart VR is best. I am really just responding to the idea that the second alternator is useless because the two alternators will fight each other (I think that myth was dispelled above), or because the VR won't allow one of the alternators to put out any current -- I believe it will, even with a dumb VR, so long as the batteries can absorb more current than the one alternator, alone, is putting out. So, in practical terms, put on two alternators if you think you may need that much current (and in that regard the focus should be on net output, ie, after subtracting current consumed by blowers, etc.), and use a smart VR if possible.
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