Using 2 alternators to charge a house bank

[cutlass]

Ahoy geniuses

I've just doubled my house bank and as I have two engines Im having both alternators charge it

I got told that if I have two alternators charging at the same time I won't get the full amps combined of both. Why is this?

It was suggested that I get a battery switch to divide the house bank into two with an alternator going to each half so that when I have both engines running I get maximum input from the alternators. Is this true?

Thanks!

[CruisingFan]

If you have two alternators then you should be using two chargers/controllers or one charger/controller that has two inputs to charge the batteries. Not because you will not be getting the full amps, but because the alternators are (very slightly) different.

If you have two chargers/controllers then it may be simpler to wire the battery bank into halves, rather than having both chargers/controllers wired to every battery.

Using both alternators to charge the batteries will not result in an inexplicable loss of amps. As long as the system you have is working, I can see no logical reason to change it. If it ain't broke....

[goboatingnow]

Originally Posted by cutlass

Ahoy geniuses

I've just doubled my house bank and as I have two engines Im having both alternators charge it

I got told that if I have two alternators charging at the same time I won't get the full amps combined of both. Why is this?

It was suggested that I get a battery switch to divide the house bank into two with an alternator going to each half so that when I have both engines running I get maximum input from the alternators. Is this true?

Thanks!

what you will find is that during bulk mode, both alternators will work hard to charge, then during absorption, one will get lazy and other will do most of the work. Its fine, albeit annoying and causes one of the alternators to wear faster.

Dave

[CharlieJ]

If the alternators are externally controlled, they can be made to play nice together by using a Balmar Centerfielder. Link: centerfielder II (CFII-12/24)

Charlie

[Cheechako]

Ample Power sells a good dual alternator controller also. OTOH, having two separate systems might not be a bad thing... a little more manual attention needed though. Or install switches for the field on each alternator.. once the bulk charging is complete turn one off. Many regulators dont activate immediately. I was told once that the first to activate will keep the second from activating as it is reading high voltage already. ....?
In my cat I seldom ran both at once, usually motorsailed with the lee engine going to make water and/or amps...

[btrayfors]

Cutlass,

The problem is that the alternator on each of your engines has some sort of voltage regulator -- internal or external -- and when both engines are running and the alternator outputs are connected to a single house battery bank the two regulators will confuse one another.

The Balmar Centerfielder that Charlie J mentioned is a good solution, but ONLY if you have a Balmar MC-614 or MC-624 regulator on each engine. If you do not already have this configuration, then the Centerfielder will not work for you.

In that case, the best thing is probably.....nothing! One alternator will put out more amperage than the other once you get past the bulk charging phase, but so what?

Bill

[goboatingnow]

They don't confuse one another, its a matter of the way the regulation set points are mismatched and the output impedance is slightly mismatched. But they don't confuse each other. If the set points were identical and the impedances were identical, they'd share the absorption mode as well.

Dave

[Kettlewell]

The absorption rate of typical wet cell batteries is a maximum of around 25% of capacity, so that will be a limit too. In other words, if you have a total capacity of 400 amp hours you won't be able to push more than 100 amps in there max during the bulk phase of charging. Doubling your alternator output wouldn't improve charging time significantly.

[btrayfors]

Originally Posted by goboatingnow

They don't confuse one another, its a matter of the way the regulation set points are mismatched and the output impedance is slightly mismatched. But they don't confuse each other. If the set points were identical and the impedances were identical, they'd share the absorption mode as well.

Dave

Dave,

You can call it what you want, but the simple concept description is, indeed, "confuse one another".

Alternator regulators -- both internal and external -- work by sensing the battery voltage. Where they get the voltage reading varies according to design and installation; some internal regulators just sense the voltage at the output terminal. Other regulators sense battery voltage at the battery terminals...the best place.

Whatever the source of voltage info, if one alternator is charging and a second alternator is connected to the same bank, it will get an erroneous reading of battery voltage because the first alternator is already charging at an elevated voltage level. Unless there is some sort of traffic cop -- like the Centerfielder -- two charging sources will almost always "confuse" one another at absorption charging stage. And, this is true not only of alternators but also of wind generators, solar panels, battery chargers, or any other source of charging.

BTW, the chance that voltage set-points and impedences for two alternator/regulators will be the same is about one in ten million :-)

Kettlewell is right about maximum acceptance at absorption levels and above. The batteries will take what they're going to take, and no more, even if you have a 1,000 amp charging source. But, whether or not both alternators will contribute depends on their combined capacity vs. the acceptance level of the battery bank. AGMs, for example, can take just about all the amperage you can throw at them.

Bill

[Vyndance]

You can throw a ton of money at external regulators and combiners and controllers if you have the want. Without solar, wind and 150 amp alternators that ton of money in my opinion should just be thrown overboard.

If your motors don't start you won't ever charge your batteries. I would run both alternators to your start bank with a Blue Sea or BEP acr between the start and house.

[cutlass]

thanks guys!
really appreciate it

[RUSTYNAIL]

Paralleling alternators could cause some troubles. If one failed, you may not know it failed until the second one failed.

If you don't have an installed amp meter with an external shunt that shows the alternator current going into/out of the battery, you can get a portable clamp-on DC amp meter and monitor your alternator's current to know what's going on. I would install the next size up alternator before I would parallel two smaller one's. Some higher output alternators aren't physically much bigger, but have higher rated diodes and better cooling to allow more current output.

[JoeFish]

Originally Posted by CharlieJ

If the alternators are externally controlled, they can be made to play nice together by using a Balmar Centerfielder. Link: centerfielder II (CFII-12/24)

Charlie

Charlie,

Thanks this is just what I've been looking for.

J

[svfinnishline]

Balmar makes a dual input voltage regulator specifically for the one house battery bank two alternator problem. Its called the MC-612-Dual, so don't miss this solution for your problem when you search the Balmar website.

I have been using the 612-Dual for about the last 500+ hours of engine operation, it works well and is a simple solution.

[JoeFish]

I'm replacing older Rolls batteries with newer LiFeYPO4 batteries which can take a much higher charge rate which means I can double up on charging capacity and reduce engine run time when topping up the house bank.

Figuring out how to combine the output of two alternators on the same engine was a big question mark till I read this.

Thanks again.