Two Diesels: Double the Charging ?

[Cheechako]

Originally Posted by DotDun

An alternator may put out 14.4v, but you won't read that until the battery is (almost) charged.

Watch the voltmeter on your 12v panel during the charging process, that's the same voltage the regulator is seeing.

Hmmm, my voltmeter on the panel would read what the alternator is charging.... about 14.3+ volts....

[DotDun]

Originally Posted by Cheechako

Hmmm, my voltmeter on the panel would read what the alternator is charging.... about 14.3+ volts....

Then your batteries are not down very much, probably less than 20% down.

Run your batteries to 12.0v measured with all loads shut off. Depending on the size of the bank and alternator, you'll probably see mid-high 12s when starting the charging process. As the batteries are charging you'll see the voltage rise, probably going over 14v at ~70-80% charged. The regulator held a target of 14.4v the whole process, but the alternator couldn't produce that at the higher current draw (when the batteries were low).

[Jerry Woodward]

Originally Posted by DotDun

Then your batteries are not down very much, probably less than 20% down.

Run your batteries to 12.0v measured with all loads shut off. Depending on the size of the bank and alternator, you'll probably see mid-high 12s when starting the charging process. As the batteries are charging you'll see the voltage rise, probably going over 14v at ~70-80% charged. The regulator held a target of 14.4v the whole process, but the alternator couldn't produce that at the higher current draw (when the batteries were low).

So, back to my original question (I thought this would be a simple answer). If a single alternator can't produce the peak voltage due to a higher current draw when the batteries are low, doesn't this suggest that two alternators would be better?

[DotDun]

Originally Posted by Jerry Woodward

So, back to my original question (I thought this would be a simple answer). If a single alternator can't produce the peak voltage due to a higher current draw when the batteries are low, doesn't this suggest that two alternators would be better?

Your original question was about chartering a Lagoon 380 and charging the house batteries by running both engines.

Now you are asking a theoretical question which I understand as, "will 2 alternators charge batteries faster than one". In general, the answer is yes, but obviously, a single answer won't cover all cases. What is the acceptance rate that is best for the particular batteries? Can they be damaged if you charge them too quickly? If the 2 alternators are on 2 different engines, it's probably not more efficient to run both just for battery charging.

As to your original question, my experience has been that most production cats coming out of the factory and going into charter have the default configuration of a house bank starting one engine with a start battery servicing the other. Each engine charges it's own bank and until the owner adds an aftermarket gadget, the two banks will act as standalone. You might find an emergency start switch that allows connecting the 2 banks, hence combining the output of the 2 alternators, but there is a reason for the big warning sign next to the switch that says "Emergency use only".

YMMV

[Sunspot Baby]

Previous posts run contrary to my experience. The first engine you start will begin charging the bank (assuming proper switch position). When you start the 2nd, the regulator will see the output voltage of the first and assume that it is not needed.

Balmar sells a unit called a center fielder that can fix the problem. It reads the field of the first engine and energizes the second alternator to the same level.

George

[DotDun]

Originally Posted by Sunspot Baby

Previous posts run contrary to my experience. The first engine you start will begin charging the bank (assuming proper switch position). When you start the 2nd, the regulator will see the output voltage of the first and assume that it is not needed.

I'm curious how you know this is happening?

[btrayfors]

Originally Posted by spiritcat

The issue with two regulators fighting each other is the reason I only use one engine to top the batteries up, unless motoring when both may be running.
It is far better to have one engine and alternator working at optimum levels rather than two working at 50% capacity.

Peter

Correct. And, they almost NEVER work together at 50% capacity, for reasons earlier mentioned.

Some alternators with internal regulators sense the "battery voltage" from the main positive outpost lug.

Having two charging sources fighting with one another for supremacy is almost never a good idea. And, thus far, there are few alternatives to efficiently use two charging sources. The Centerfielder is an attempt to do that on multi-engine vessels, but users and installers have reported several problems with it.

Bill

[Dave]

Originally Posted by btrayfors

Having two charging sources fighting with one another for supremacy is almost never a good idea.
Bill

Maybe not - but with solar, wind, and multiple alternators it's pretty common to have several charging sources all "monitering" each other's contribution potential. My alternators will shut down my solar, which in turn shuts down my wind turbine.

FWIW R & C Leopard cats have always had 2 starter batteries and a separate larger house bank. The older Leopard cats used large diodes to separate banks and direct the charging first to the motor's own starter battery and then to the house bank. The newer Leopards simply use a relay on each side to join respective starter battery to the house bank when an ignition switch is activated. With both motors running both starter batteries and the house bank are all in parallel and the alternators both contribute until one senses a cutout voltage.

Dave L38 #38

[Sunspot Baby]

Originally Posted by DotDun

I'm curious how you know this is happening?

How I know what is happening. That a regulator will see voltage from another source and not kick in, or that the Balmar unit causes them both to work?

If you have a charging source, one engine say, running at 14+ volts, you will see that voltage at the battery. A new regulator coming on line sees that voltage and has no way to know where it comes from. It will not kick in until it sees a lower voltage indicating a low battery.

The Balmar unit, I accept the manufacturers explanation of how it works.

There are several threads on this forum discussing the Center Fielder, and members seem to agree it works. My charging time is certainly less since I installed one.

Hope that helps.

George

[Wotname]

Originally Posted by btrayfors

Correct. And, they almost NEVER work together at 50% capacity, for reasons earlier mentioned.

Some alternators with internal regulators sense the "battery voltage" from the main positive outpost lug.

Having two charging sources fighting with one another for supremacy is almost never a good idea. And, thus far, there are few alternatives to efficiently use two charging sources. The Centerfielder is an attempt to do that on multi-engine vessels, but users and installers have reported several problems with it.

Bill

Just another viewpoint, all twin engine general aviation aircraft operate with two alternators, two regulators, one battery and a balancing / load sharing device. I don't have the details to hand of exactly they achieve this but it isn't high tech (and it can be hard to set up according to my electrical mates)!

[DotDun]

Originally Posted by Sunspot Baby

If you have a charging source, one engine say, running at 14+ volts, you will see that voltage at the battery. A new regulator coming on line sees that voltage and has no way to know where it comes from. It will not kick in until it sees a lower voltage indicating a low battery.

The Balmar unit, I accept the manufacturers explanation of how it works

This discussion has probably run its course, but there is some misconception about regulators and how smart they are.

A car regulator (non-smart) will "hold" it's pre-set voltage regardless of other charging devices. The variable is whether the batteries will take any charge current at that voltage level, which is an action of the batteries, not the regulator. Obviously, if there is another charging source that is holding a higher voltage than the pre-set mentioned here, there will be no charging current from this unit, but that's due to ohm's law, not the regulator.

A smart regulator, like the Balmar MC-614, works by using a timed/calculated process to change the target voltage in the various steps to reach/maintain full charge. Reading the manual, the 614 starts in a bulk charge mode of 14.6v, in the flooded deep cycle setting, for a period of 18 minutes (time is admin controlled). This happens even if another regulator is already holding the batteries at 14.6v. Again, whether the batteries accept any charge current from this unit is action of the batteries, not the 614. After 18 minutes, the 614 then does it's various calculations to decide what stage to goto next. Granted, if a second source already has the batteries charged, the 614 will use very little current to excite the field to achieve the voltage set point, hence the 614 will then use this information in it's decision whether to go to the next step.

http://www.balmar.net/PDF/mc-614-manual.pdf

I certainly agree that running 2 charging sources can/does mess with a smart regulator. And it is certainly not efficient from a diesel pov. But, the OP's question was whether he'll be able to charge batteries faster by running both engines during an upcoming charter. The answer depends on how the alternators are wired, the size of each alternator, the rate of acceptance by the batteries, etc.