VO5
Well-Known Member
Alternators...why would someone fit two alternators on an engine ? Any good reason ?
Why ?
- Thread starter VO5
- Start date
Welshgirl
Well-Known Member
balance, redundancy, extra power, because they had a spare in the shed, it looks good,
give up,
why?
give up,
why?
Robin
Well-Known Member
WE inherited 2 alternators on our last UK owned sailboat, a Jeanneau Sun Legende that was fitted out for extended cruising. It had a Yanmar 4JHE 44hp engine with one alernator feeding the engine and windlass battery bank and another bigger one feeding the main service battery bank as well as the secondary services bank with high power usagestuff like the fridge/freezer, SSB etc on it. one alternator was the original Yanmar supplied one about 90A output IIRC and the other was a 150A Bamar, high out put one. Both were controlled by adverc 'smart regulators.
Our current boat a Beneteau oceanis 36 has a single upgraded 150A Bamar alternator and smart regulator on a Yanmar 3GM30, 30hp and the original Yanmar 90A (!think)alternator is also kept on board as a spare if needed. There is a switch in the charge circuitry that cuts the Bamar 150A output if needs be to supply the full engine hp to driving the boat rather than giving up lots of extra hp to charging,
Alpha22
Well-Known Member
All the above or to charge two banks of batteries. Domestic and engine start.
Perhaps one is a much higher rating than the other.
Perhaps one is a 240v AC generator. There are a few about.
Perhaps one is a much higher rating than the other.
Perhaps one is a 240v AC generator. There are a few about.
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prv
Well-Known Member
Not uncommon on boats with serious battery systems. Leave the engine's basic low-power alternator to recharge the engine start battery, and add a fancy expensive high-power alternator dedicated to the main deep-cycle bank. Keeping the two systems separate means you don't need to worry about any kind of split-charge system, or boiling an already-full engine battery while you charge up a massive depleted service bank.
Pete
Pete
pvb
Well-Known Member
My last boat had the original 50A alternator simply charging the start battery, and a second 90A alternator with Adverc control charging the domestic bank. A very simple system. No need for splitter diodes or VSRs. No chance of overcharging the start battery. Redundancy if one alternator failed.
Avocet
Well-Known Member
To the above reasons, I'd also add the possibility of less black belt dust round the engine bay, and longer belt life (given that each belt is driving less load than one huge alternator).
Roberto
Well-Known Member
I have two alternators, charging two totally separated battery banks (engine vs domestic)
FWIW very happy with the setup and will surely choose the same solution on the next boat
FWIW very happy with the setup and will surely choose the same solution on the next boat
LadyInBed
Well-Known Member
I've also got two alternators, one is 12v t'other is 24v
fisherman
Well-Known Member
I would like to fit the second one, not quite organised yet, one for engine batteries one for service, no voltage drop through a diode, possible better sensing, twin belts, both run the water pump so fail safe, what's not to like?
nigelmercier
RIP
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Ditto, but with a southern accent.
sailorman
Well-Known Member
as long as one has a jump lead or 1-2-both
VO5
Well-Known Member
Humm....I think I will fit a second one, now that I understand the benefits.
Thank you all for your contributions.
Best.
Thank you all for your contributions.
Best.
pvb
Well-Known Member
A jump lead or a dedicated bridging switch - never a 1-2-Both!
sailorman
Well-Known Member
Why ????
pvb
Well-Known Member
Because if you have two alternators charging 2 battery banks, you don't need a 1-2-Both switch, it will only confuse. Two simple on/off switches are all that's needed.
Marsupial
Well-Known Member
In the event that one alternator fails you must take it out of circuit (I would take it off the engine IF POSSIBLE) THEN connect the two battery banks together with a set of jump leads - so you now have one bank. A 1 - 2 both switch is asking for expensive problems if its used incorrectly - so don't fit it.
Dual output alternators used to be quite common used for all the reasons mentioned above, they are still around but not that common now?
Dual output alternators used to be quite common used for all the reasons mentioned above, they are still around but not that common now?
William_H
Well-Known Member
Dual alternators are fitted to fix a particular problem. I certainly would not fit another unless there was a specific problem. Like having 24v and 12v sytems or if you need a lot of alternator power for charging. Assuming your concern is the latter then either fit or monitor the existing amp meter to see just what your existing alternator is doing. Is it often operating near its limitof current. If not another alternator will do nothing except add redundancy in case of failure.
You might consider fitting a 240v AC alternator. This will only work at one specific drive speed to get correct frequency but will give a lot of power for all sorts of things plus could drive a shore charger if needed.
Good luck olewill
temptress
Well-Known Member
I have 2 alternators on my engine. One is 60amps and feeds the starter battery, the other is a 160amp Balmar on dual belts feeding the domestic batteries. Works very we for us.
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fisherman
Well-Known Member
Problem with an alternator is it doesn't do the job under about 3000 revs. With my pulley sizes that's 950 on the engine, which ticks over at 450-500. No difference with a bigger output, so although mine is 40 amp and I run a lot of equipment my biggest demand is 28 amps which is achieved at engine revs 1100, so bigger output is not the answer. Smaller pulley, yes but cripple the belts, the only answer is Adverc.
