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Dual alternator setup to charge one battery bank

PostPosted: Tue Sep 28, 2010 3:10 pm
by tbeetle
Technical question for the forum regarding how to set up two alternators, on a single engine, to charge a single battery bay:

how should this be wired / configured?

I have a new Yanmar 4JH5E arriving at the boat (a repower from Perkins 4-108); I will be mounting the Ample Power 4023-S 105AH alternator onto the motor in lieu of the Hitachi 80AH alternator. The Emon-II will be monitoring the batteries and managing the SAR V3 regulator.

It is possible to mount a second 4023 alternator onto the Yanmar 4JH, and I'm keen to do this. My expectation is that each alternator will work less hard to charge the battery, and running two alternators provides redundancy should one alternator fail.

What I do not know is how to manage the control and charging output of two alternators charging the same battery bank. I have done some digging around on the web and have not come across documentation on how to manage two alternators, etc.

- rob macfarlane

Re: Dual alternator setup to charge one battery bank

PostPosted: Wed Sep 29, 2010 11:19 am
by Coulomb
As long as the two alternators are alway spinning at the same time, just hook them in parallel and they'll operate as one.

Re: Dual alternator setup to charge one battery bank

PostPosted: Wed Sep 29, 2010 11:44 am
by tbeetle
Coulomb wrote:As long as the two alternators are alway spinning at the same time, just hook them in parallel and they'll operate as one.


Thanks, that sounds incredibly easy! and raises two additional questions:

1. Is there a problem if one alternator stops spinning (e.g., alternator belt breaks)?

2. By being in parallel, does this mean that the field coil wire from the SAR V3 should go to each alternator's field coil, and the SAR V3 supplies the same voltage to each alternator's field coil? e.g., attach SAR V3 field coild wire to the no. 1 alternator and simply run a wire from there to the no. 2 alternator's field coil input.

I guess there's a third question now:

3. Allowing that both alternators are the same (Ample Power 4023), does it matter if one spins clockwise and the other spins counterclockwise? (assume that both have a bi-directional fan installed) It looks like adding a second alternator to the Yanmar will require mounting the second alternator in reverse position such that it faces back towards the motor, and this will cause that alternator to spin in the opposite direction to the alternator mounted 'normally' on the motor.

- rob macfarlane

Re: Dual alternator setup to charge one battery bank

PostPosted: Wed Sep 29, 2010 7:47 pm
by Coulomb
1. A non-spinning alternator with field current applied will get warm, and it's a waste of energy, but not a major problem in the short run.

2. Yes, but the field junction would be best close to the regulator.

3. Direction of rotation makes no difference.

Re: Dual alternator setup to charge one battery bank

PostPosted: Thu Sep 30, 2010 10:52 am
by tbeetle
Thank you very much, I'm going to quite enjoy the setup. Now to go put it together!

- rob