View Full Version : High Output Alternators

21-03-04, 08:27
Does anyone know of a current (!!) manufacturer of high output alternators? I remember seeing ad's for 'marine alternators' a while ago, but can't find a recent one. Its got to be continuous rating 90 Amps or more. Thanks, John.

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21-03-04, 09:15
Adverc supply a range of high output alternators from different manufacturers.

Have a look <A target="_blank" HREF=http://www.yachtretreat.com>http://www.yachtretreat.com (http://www.adverc.co.uk/products/products.asp?cat=2>here.</A>


21-03-04, 09:38
Merlin do the Balmar range of HOAs, as well as smart 3 or 4 stage regulators, galvanic isolators, battery monitors etc.

I've been dealing with Vicky Baker there and found her most helpful. She has advised on the best way to achieve "energy independence", rather than just selling me a bunch of stuff that I would probably never need.

<A target="_blank" HREF=http://homepage.eircom.net/~ajpower>http://homepage.eircom.net/~ajpower (http://www.merlinequipment.com/prod_area.cfm?area_id=38&ind_id=1>http://www.merlinequipment.com/prod_area.cfm?area_id=38&ind_id=1</A>


21-03-04, 09:39
"manufacturer" rather than supplier?

adverc (http://www.prestolite.co.uk/index.html>prestolite</A>

<A) supply them too.

and sterling power, and <A target="_blank" HREF=http://www.dg2k.co.uk/alternators.htm>driftgate 2000</A>

From the US electrodyne (http://www.zena.net/htdocs/alternators/alt_inf.shtml#Top>Zena</A>)

and <A target="_blank" HREF=http://www.balmar.net/Page13-alternators.htm>Balmar</A>

Bear in mind that a single belt might be marginal for this sort of output (esp. if running the waterpump too) & make sure you see an output curve before buying.Have just spent some time wondering why one of two lucas A127 (marelli inside) alternators, one 12V, one 24V; was causing the warning buzzer to sound at under 800 rpm. Not charging properly-obviously?- but turned out that it's always been like that, since some makers' 24V units have a very high cut-in speed; 1800rpm alternator speed in this case, compared to 1100 for the 12V one. Balmar's 24V ones look similar.

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21-03-04, 11:18
I have a 100 amp Magnetti Marelli which I bought through Adverc. You can obtain marginally cheaper auto alternators from any auto-electricians, but the Adverc-supplied ones come with the diode bridge field wire already fitted and to marine spec.

Costs for the auto ones around 140, marinised modded one 165 (from memory).

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21-03-04, 13:19
You may have to undertake a fair bit of machining to transfer your current pulley to your new alternator. I bought a 105 amp Prestolite from Adverc thinking it would be a simple matter to move the pulley on the Lucas alternator on my Lister Petter engine - but it wasn't. You may be luckier. But once fitted it gives me 100 amps on a single multi-V fan belt and I'm happy

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21-03-04, 13:35
Prestolite/Leece-Neville alternators are very good and "reasonably priced" (try Adverc, as others have said). The Prestolite units are substantially engineered and have a good output curve, with a fair output at low revs. I've been using a 90A Prestolite for several years, with good results.

If you can only drive the alternator with a single V-belt, it's doubtful whether it's worth going for anything bigger than 90A, because belt slippage could become a problem. Having said that, if (as you posted recently) your battery bank is around 400Ah, you'll find it virtually impossible to push more than 70 or 80A into it anyway, so there's no point in having a bigger alternator.

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21-03-04, 15:20
Most marine engines have 55 or 35 amp alternators - going up to 100 amps requires:-
1. Increase in drive-belt transmission - I fitted a machined-from-solid pulley on the alternator and a toothed heavy-duty belt.
2. A vast increase in X-sectional area of the charging circuit. I had 2 goes at the wiring (8mm2, 12mm2 & now 24mm2) before getting it right, at which point the splitting diodes melted their heat-sink.

The comment about the battery bank size lower down the thread is predicated on no other draws and a fallacious assumption about lack of circuit resistance.
I find 100 amps good to feed about 350ah in 3 banks.

The biggest problem is the lack of urge from the motor struggling with full demand.

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21-03-04, 18:27
Don't understand what you mean by "fallacious assumption about lack of circuit resistance" - could you enlighten us, please?

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21-03-04, 22:16
Thanks for all the ideas. I didn't mean just manufacturers, I meant suppliers as well; sorry if I didn't make that plain.

The boat has 405Ah of domestics and I was thinking of running an additional alternator to the existing one with the existing one charging the engine start battery only. The cabling will be all renewed so no problem with cabling - I will use the appropriate sizes! As I understand it the biggest problem is mounting the additional alternator with an extra pully on the crank to drive it, together with using appropriate pulley and belt sizes for the speed and power transfer requirements of a high capacity alternator.

If I find a suitable alternator, I can't quite see how I'm going to achieve this yet...

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21-03-04, 22:45
Going back to basic's, do you have a problem charging the batteries at present?.
Why not leave the existing one charging the domestic, and fit a small one to charge the engine battery. As it's only putting back starter amps it will be lightly loaded, and most engines allow right and left hand mounting, and us the existing common belt.
Alternativel, if you have a second alternator and a voltage sensative relay, when the engine battery is up, you can link to service bank and have thus two smaller alternators running in tandem.


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22-03-04, 08:40
Volvo Penta sell a second alternator kit which contains all the special brackets, pulleys, etc, you'll need. For your 2040, it mounts on the starboard side of the engine, and should be part number 3581044-9 (although my VP accessories brochure may be out of date!). The VP kit comes with a 60A alternator, although you may be able (as I did) to persuade the VP dealer to keep the alternator and just sell you the rest of the kit.

I have a 90A Prestolite charging my domestic bank with Adverc control, and the original engine alternator just charging the start battery. No diodes, no relays, and built-in redundancy should one alternator fail.

A word of warning: the VP kit is only designed to take a regular-size, small case alternator. If you try to hang a large case unit on it, there'll be lots of problems. I installed a VP second alternator bracket on my 2003T engine, and initially mounted a large-case 130A alternator on it. Unfortunately, the weight of this unit caused excessive vibration problems, as well as belt slippage problems, and I took it off.

Incidentally, whilst I had the 130A alternator, I never saw much more than 90A charge into my 660Ah domestic battery bank, even when they were fairly low. And that's a real current figure, as measured by my Link 10 meter, rather than a "fallacious assumption"! Hence my remark that there isn't much point in using an alternator bigger than around 90A unless you have a huge battery bank to take the charge.

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24-03-04, 12:25
Yes but a 120 Amp alternator is only rated as 120 amps when it is relatively cool, and is driving a battery bank that will take that amount of current. The physics of batteries means that a battery will only accept a given charging current at any one time. The actual current depends on the state of charge, the plate size and construction, age etc etc. I think you did pretty well to get 90 Amps out of a 120 Amp alternator.

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24-03-04, 17:18
Your comment about the physics of batteries was exactly the point I was making - that with a 400Ah battery bank you'll be lucky ever to push much more than 70-80A in.

As far as temperature effects are concerned, most decent alternators for marine use are output-rated at 50degC, which I don't think of as particularly cool. If you're thinking of running an alternator fairly hard, an easy and cheap precaution is to re-route the combustion air intake to the engine compartment, so that the cool incoming air is directed at the alternator.

The 90A Prestolite alternator I'm using can easily pump out 80A+ if the batteries are low.

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24-03-04, 17:55
It's been covered in so many words several times in this thread - but it's not just battery capacity that reduces an alternator output below it's rated one.
The cross-section of the wire, the presence of splitting diodes, heating up of the circuit all contribute to this back EMF.

Industrial/traction lead-acid batteries will take a much faster charge than gel or Ca/Pb batteries.

I can quite easily get 88 amps out of my 100 amp alternator for the first few minutes of charging 300 ah from 12.2 volts, by the time battery voltage is up to 13.8 that's back down to 75 amps.

Rather than limiting alternator size because of battery capacity there are good reasons for a larger output alternator to speed charging - the smart regulator takes care of any risk of overcharging.

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24-03-04, 20:35
Anyone who is interested in charging their batteries efficiently is going to have a battery-sensed regulator, so your comment that "The cross-section of the wire, the presence of splitting diodes, heating up of the circuit all contribute to this back EMF" is irrelevant - the regulator will be working according to the voltage at the battery, and all the losses you mention are automatically factored out.

Given that most of us acknowledge that batteries are only capable of accepting a certain rate of charge (based on lots of factors), what do you think are the "good reasons for a larger output alternator to speed charging", and how do you think that works?

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