Using 2 alternators to charge a house bank

[goboatingnow]

We all know what might be happening. We all know what could be happening. It would just be nice to have some numbers and to know what actually IS happening in any given case. And there's no simple way to predict that, given the current lack of integrated charge controllers.

well a couple of shunts and a cheap ammeter will let you know all that.

You can of course do some maths etc, and predict what will happen, or you can measure the real life performance.

As to you example, when a battery is on absorption mode, i.e. when the regulating action is happening, currents are very low, so it doesn't really matter.

BUT , yes everyone has said without a current steering control, you cannot tell which (well you can) source may finish the charging. Note its not as simple as the setting of the regulation voltage. its more to do with the ratio of the source output impedance's. when the source is regulating its output, that doesn't mean its stopped charging. its still contributing current. ( just not the same).

Dave

[cutlass]

Thanks everyone for all this great information

Forgive my ignorance but could I get full charge off both alternators by having a switch splitting my house bank in two, with each alternator supplying a half. When not charging I combine the house bank. When charging I split the house bank so essentially each alternator operates individually

[goboatingnow]

Originally Posted by cutlass

Thanks everyone for all this great information

Forgive my ignorance but could I get full charge off both alternators by having a switch splitting my house bank in two, with each alternator supplying a half. When not charging I combine the house bank. When charging I split the house bank so essentially each alternator operates individually

Doesn't really give you Any advantage. In bulk with a single bank , both alternators will work hard , in absorption the battery typically needs a small amount of current easily supplied by one alternator.

Dave

[David M]

I have a twin engine boat that charges a common house bank. I installed a digital ammeter for each alternator. I can easily see that there are no problems. Nothing more is required for this to work. The engines have identical alternators and share the load within a few amps, even when turning at two different speeds.

A bigger deal than necessary is being made out of doing this.

[Capn Morgan]

Originally Posted by 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...

Hi Cheechako

I like the option of switching off the field but I haven't had the guts to try it. Would this be best done remotely with relay for control at some distance or would a simple switch in line suffice?

[travler37]

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

So they are mismatched and allways going to be....slightly off.....
How do you fix this?A external charge controller or run seperate banks/engines.
Thank you for clarifying something that can not be done long term.Matching exactly.............
Mark

[mitiempo]

Originally Posted by travler37

So they are mismatched and allways going to be....slightly off.....
How do you fix this?A external charge controller or run seperate banks/engines.
Thank you for clarifying something that can not be done long term.Matching exactly.............
Mark

I don't think it needs fixing. They will both be at max output (depending on temperature) until the lower of the 2 set points is reached. At that point the lower will defer to to the higher set point alt and from then on the output will be lower anyway. As the resistance rises in the batteries they will accept less and less. The batteries are always the determining factor for a given voltage set point.

It is not the issue that many think it is - it works.

[travler37]

Originally Posted by mitiempo

I don't think it needs fixing. They will both be at max output (depending on temperature) until the lower of the 2 set points is reached. At that point the lower will defer to to the higher set point alt and from then on the output will be lower anyway. As the resistance rises in the batteries they will accept less and less. The batteries are always the determining factor for a given voltage set point.

It is not the issue that many think it is - it works.

I agree,
As long as you are running BOTH engines for another reason.Besides charging bats.If not is a waste of dollars/fuel after a certain point.At $4 a gallon me thinks a charge controller with a bats are almost full alarm would be more cost efficent.Asuming cost is a factor.
Mark

[mitiempo]

In the op's case yes you are right. If anchored it doesn't necessarily make sense to run both. But if moving the advantage of 2 alts/1 bank is there.

In a sailboat the 2 alts can be on the same engine.