How to determine maximum size of alternator

[HKTim]

I have a Yanmar 4JH57 engine. The primary alternator is the original Valeo 120 amp. I am planning to add a secondary alternator. My first choice is a mastervolt 130 amp unit. I have one already and it will suit my purpose well which is to charge a mastervolt lithium house bank. But it is a big beast. It weights 10 kg and its physical dimensions are approximately 2-3 times larger then the Valeo. I have a choice to downsize to a mastervolt 90 amp alternator which comes in around 5 kg. Does anyone have any guidance when designing a two alternator set up? Specifically, is it a bad idea to have a much heavier alternator on one side of the engine then the other side.

Thanks






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[offpist]

You have to messure if you can fit the lage alternator.
We have one Balmar 200A and one Balmar 150A fited on an 4JH4AE.

Dont have any experience with the mastervolt alternators but they seem very good and Mastervolt also claim they are rated for continius power, Balmar is not.

You can use the Mastervolt regulator on most alternators but you have to convert it to negative controll.

(We have 1000AH winston Lifepo4 and the Mastervolt mass combo ultra 3000-150.)

[HKTim]

Thanks. I have plenty of space so that is not a concern. My concern is if there will be a problem hanging a 10 kg alternator off one side of engine shaft against a 3-4 kg alternator on the other side. I need to have a custom mounting bracket built but when discussing this with my mechanic he said his preference is to use similar weight alternators in this kind of set up. So am trying to verify if he has raised a valid concern.

Thanks


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[boatbod]

The 4JH57 should be fitted with a serpentine belt from the factory so side load should be reasonable. High output alternator are large because they need to dissipate lots of heat, especially if charging batteries that can accept huge current (like lithium). Make sure the mounting brackets are robust and you should be ok.

[crabcake]

Originally Posted by offpist

Dont have any experience with the mastervolt alternators but they seem very good and Mastervolt also claim they are rated for continius power, Balmar is not.

Not doubting your word, but are you sure Mastervolt clearly claims they are rated for "continuous power." I looked at both the 130/12's and the specs allude to low RPM output - but nothing ironclad and no figures given in the spec sheets I read. Just have never seen an alternator that could do full rated output across the board at all RPM's. FWIW, that doesn't mean one doesn't exist!

I always get a little concerned when the marketing and advertising people get creative

[S/V Alchemy]

I don't know the output of that Yanmar, but I gather it's up there. Be aware that altenator loads, particularly from big ones, are parasitic loads on the drivetrain. You may create problems not only from obvious sources, such as wear on the internals, but in terms of lost output at the prop end; effectively you are changing your 'real" as opposed to rated power/torque curve. You may find 2,100 RPM (or whatever) does not move you as fast in flat water as it did before the big alt's "friction".

Solutions may include a prop repitching or simply monitoring your usage or having an alternator disconnect method.

That said, maybe you will end up working your engine right to spec. Most people do not. A good way to tell is to install an exhaust gas temperature (EGT) monitor. It's cheap insurance against overworking your engine.

[S/V Alchemy]

Originally Posted by crabcake

Not doubting your word, but are you sure Mastervolt clearly claims they are rated for "continuous power." I looked at both the 130/12's and the specs allude to low RPM output - but nothing ironclad and no figures given in the spec sheets I read. Just have never seen an alternator that could do full rated output across the board at all RPM's. FWIW, that doesn't mean one doesn't exist!

I always get a little concerned when the marketing and advertising people get creative

Yes, so do I. External regulation gives you fewer amps at the chosen voltage with less heat and chance of damage. I would prefer that to a blazing hot alternator. I've tried to plan my energy requirements so it is essentially supplemental to solar and wind, meaning "intermittent power for years and years" is far preferable. Besides, you size this stuff to the acceptance rate of the bank, otherwise it's a case of "fat guy in a sitz bath".

[scubano]

The physical size of the alternator should make no difference as long as it is correctly installed and the belt tension is right. Depending on the state of charge of the battery bank the alternator will use up to 2.5 horsepower under a full load (discharged battery bank)

[Cheechako]

I don't think the weight of the alternator is an issue... assuming you can design a proper bracket anyway. The side load is caused more by the amperage of the alternator on the belts right?

[smac999]

Originally Posted by crabcake

Not doubting your word, but are you sure Mastervolt clearly claims they are rated for "continuous power." I looked at both the 130/12's and the specs allude to low RPM output - but nothing ironclad and no figures given in the spec sheets I read. Just have never seen an alternator that could do full rated output across the board at all RPM's. FWIW, that doesn't mean one doesn't exist!

I always get a little concerned when the marketing and advertising people get creative

continuous power means you can run it full output for hours or days. most alts will get hot and lower output over time.

no alt will put out max power at idle. that is not what they are stating.


I don't see how the weight has any effect, other them making brackets strong enough. this has nothing to due with the shaft at all. the belts will see a 120a load on one side and a 130a load on the other. almost the exact same. the weight is only for heat disapation

[UNCIVILIZED]

What your mechanic may be referring to, in perhaps poorly chosen words, is that theoretically, if you mount 2 alternators of the same size on an engine 180 deg. apart from each other, then the pull on the seals & bearings in the engine from them is negated. Whereas if you have 2 alternators on an engine that are different sizes, & mounted obtusely in relation to each other, then they could cause some components in the engine to die prematurely. But as to how fast this "death" may happen I can't even begin to guess at.

I can't say that I know how factual the above statement, & theory is. But I've seen it in more than a couple of places. And it might be worth researching. Including on different forums oriented specifically towards engines & such.

Though I do wonder about it's veracity a bit, given that in millions upon millions of cars, there are multiple belts on the engine for power take off, led at odd angles to various sized loads. Such as the AC compressor, alternator, & water pump, etc. Most of which exert a not insubstantial sideways loading on the power take off pulley. Yet these engines run for tens & hundreds of thousands of miles without issues from this. So then, are marine diesels so much more fragile than these automobile engines?

I'm curious, is your mechanic one who works on boats a lot? So that he has enough depth of knowledge from which to form conclusions like the above. If in fact that's what he's trying to tell you.
Also, I can't help but to wonder how some other diesels have their power take offs for other systems setup. Such as those on an 18-wheeler, whose engine has to power a multiplicity of heavy sub-loads.

If you find out much could you please post it here on the forums. It would likely benefit many of us. And a bibliography of relevant informational links would be great.

Edit: One thing which would definitely make sense, is to have two alternators that are parts compatible with one another. That way if both of them go down in the middle of nowhere, then you may be able to cannibalize components from them in order to get one up & running.


offpist, that engine of yours is so clean that it looks like a computer generated image, or a pic that's been "tuned" via photo editing software. Dang!

[offpist]

Originally Posted by UNCIVILIZED

offpist, that engine of yours is so clean that it looks like a computer generated image, or a pic that's been "tuned" via photo editing software. Dang!

Thanks. That engine has been arround the world and has 5200 hours on it. Still going strong.

[Inhancer]

S/V Alchemy, I am not as knowledgable as you but wonder why 2100 rpm with heavy generation would be slower than 2100 with small generation. Wouldn't psame prop rpm give same speed?

[John Holbrook]

Originally Posted by Inhancer

S/V Alchemy, I am not as knowledgable as you but wonder why 2100 rpm with heavy generation would be slower than 2100 with small generation. Wouldn't psame prop rpm give same speed?

Yes speed will be the same.

With regards to load on the engine as a rule of thumb absorb twice as much with a 30% increment in speed. So if your engine can produce 50hp at max Rpm of 3000rpm and the prop is correctly match the prop will absorb 50hp at 3000rpm. At 2300rpm the prop will absorb 25hp and at 1800rpm 13hp. At 2300rpm your engine may have the ability to produce say 35hp at the crank, 10hp more than the prop can absorb so an additional alternator will present no issues at this rpm but you will use slightly more fuel.

At close to max rpm the additional alternator could overload the engine. Crankshaft vs prop hp charts at various rpm are normally on the manufacturers websites.


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[botanybay]

Originally Posted by John Holbrook

Yes speed will be the same.

With regards to load on the engine as a rule of thumb absorb twice as much with a 30% increment in speed. So if your engine can produce 50hp at max Rpm of 3000rpm and the prop is correctly match the prop will absorb 50hp at 3000rpm. At 2300rpm the prop will absorb 25hp and at 1800rpm 13hp. At 2300rpm your engine may have the ability to produce say 35hp at the crank, 10hp more than the prop can absorb so an additional alternator will present no issues at this rpm but you will use slightly more fuel.

At close to max rpm the additional alternator could overload the engine. Crankshaft vs prop hp charts at various rpm are normally on the manufacturers websites.


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Well put

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