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Old 30-08-2018, 14:24   #1
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Dual alternator and oversize alternator success (or failure) stories

It appears to me that the 3 and 4 cylinder Yanmar engines, so widely used as sailboat auxiliaries, cannot accept large-frame alternators. Part of the problem is that the large-frame alternators all use the J-180 engine mount. The other part of the problem is that there isn't enough clearance in the stock location -- I'm going from photos, but it looks like there's a heat exchanger or something in the way.


The dual mount and custom mount alternators, most set up so that the pulley faces (and rotates) in the opposite of the usual direction, really look like science projects to me. I don't like to rely on science projects. Has anyone had good luck with these setups? Are they durable and reliable over a period of years? Will they fit in the engine space provided in most cruising boats?
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Old 30-08-2018, 16:31   #2
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Re: Dual alternator and oversize alternator success (or failure) stories

I have a 3ym30 and it accepts just a small frame (like a Balmar 60 Series or MG small frame) in the standard position, and there is a manifold pretty darn close to the back so deeper alternators are not a solution, so the Balmar High output red ones are unlikely to fit. I am sure there are some good alternative mounts that would work with enough engine room space around the engine.
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Old 30-08-2018, 16:54   #3
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Re: Dual alternator and oversize alternator success (or failure) stories

Most engine compartments are as small as they can get away with, because most sailors want cabin space instead. So regardless of Yanmar, you may be stuck with a small frame alternator, unless you want to modify (cut through) the side of the engine bay.

There are a number of alternators from a number of companies where "the same" small frame alternator is made in varying depths, so they may offer 45-55-65-70-80-90A versions that are all the same except for extending that much further behind the pulley and mounting foot/feet.

And if you've got an older engine with a V-belt...somewhere around 90-100A is going to be the limit you can put on a v-belt anyway.

Sometimes, if you pick a slow time (weekday midmorning?) and take your old alternator to an auto chain (or bring a cardboard mockup of it, and the model number) you can find someone who knows what they've got, and they'll pick things off the shelf so you can take a look to see what options might do the job for you. "I need one of these but three inches longer". Sometimes you can luck out. Or, checking the alternator shelves at a junkyard. Often there's a light truck model that is a higher capacity small frame.
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Old 30-08-2018, 18:59   #4
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Dual alternator and oversize alternator success (or failure) stories

My 165 amp Mark Grasser gives me about 100 amps or a little less continuously. I have the temp limit set conservatively to 90c.
My 660 AH AGM bank will usually only accept that kind of power output for about 20 min. Then the batteries acceptance rate is less than 100 amps, so if I doubled the output to 200 amps, it would accept that for I would guess less than 10 min, and at 15min or so I’d be less than 100 amps.
So all that extra alternator and money wouldn’t have bought me much at all.
LFP is of course the exception, do you have an LFP bank, or other real high amp load your trying to run off of an alternator?
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Old 30-08-2018, 19:17   #5
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Re: Dual alternator and oversize alternator success (or failure) stories

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LFP is of course the exception, do you have an LFP bank, or other real high amp load your trying to run off of an alternator?

I'm trying to think through alternatives based around a bank of 8 L16s, roughly 1200 Ah at 24 volts; C/5 would put me at 240 amps.
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Old 30-08-2018, 19:52   #6
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Dual alternator and oversize alternator success (or failure) stories

Good God, 1200 AH at 24V?
In a boat with a three or four cylinder engine? May I ask why? Just curious is all.
That kind of sized bank would I think be best charged with a generator and large chargers.
240 amps at 24 V is 5700 Watts or so, with inefficiencies calculated in , it would take a 7.5 KW genset to make that?
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Old 30-08-2018, 20:16   #7
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Re: Dual alternator and oversize alternator success (or failure) stories

I've had a large frame Balmar 95 Series (210 amp) attached to my Yanmar for four years using a kit sold by Balmar. I figured Balmar would have to stand behind it.

The thing is very beefy and has been trouble free.

AltMount Pulley Kit: 48-YDA-4JH-B
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Old 30-08-2018, 20:30   #8
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Re: Dual alternator and oversize alternator success (or failure) stories

Thinking outside the box.


Here's the vision.


  1. On a mono, it is not possible to install enough solar panels to meet electrical needs, at least not in northern latitudes, not with a below-deck autopilot, not without hippie-like conservation measures. Not without compromising windage, storm readiness, and appearance. Therefore, some sort of generator onboard is a necessary evil.
  2. All sizes of DC alternator driven by the propulsion engine are smaller, lighter, and cheaper than gensets of equivalent capacity.
  3. With today's hybrid inverter-charger technology, there are no serious tradeoffs in converting between DC and AC power.
  4. Ditching the propane system entirely provides savings of cost, space, and weight that are greater than the incremental cost, space, and weight penalty of the necessary compensatory upsizing of the electrical system.
  5. With an electric galley I arrive at a daily power budget of 4-5 kwh. With reasonable reserves this leads me to a FLA bank of 24 kwh (12 L16s), which at C/5 will accept a charge of 4.8 kw or, at 24 volts, 200 amps. This will conveniently allow sufficient charging with an hour of engine time assuming no solar; a modest amount of solar (600 watts in 4 panels of 150w each on the aft lifelines x 5 hour average = 3kwh per day) does reduce this to a twice-a-week thing.
  6. Sizing is also driven by occasional needs to run the air conditioning on the hook or a dive compressor. Either of this is around 2kw or a little more (I have a nice 2cfm compressor I plan to move to a future boat)
  7. Wind and water generators, despite many years of serious engineering effort by talented people, remain fiddly technologies of last resort
So, I'm exploring, on paper, the idea that ditching a genset (and the propane gear) in favor of the best available DC generators driven by the propulsion engine puts me ahead in cost, space, weight, convenience, reliability, etc. I'm challenging the received wisdom. I may back off and accept the received wisdom at some point, but I'm not there yet.
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Old 30-08-2018, 22:29   #9
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Re: Dual alternator and oversize alternator success (or failure) stories

Many years ago, Steve Dashew had exactly the same thinking. He developed some very sophisticated dc systems where multiple dc alternators were driven off the main engine. He eliminated the separate genset reducing the associated weight and the complexity. He also used L16 batteries set deep in the bilge. This was before cost efficient solar panels and inverters. Today, such a setup would be easier, better, less costly, and more efficient. I think his Offshore Cruising Encyclopedia discusses these ideas. Steve has made this book available free on line. It's excellent reading. I have no affiliation with Steve, just read his books and was impressed.
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Old 31-08-2018, 02:24   #10
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Re: Dual alternator and oversize alternator success (or failure) stories

A long time ago (20 years or so) when alternators were mostly crap I fitted one of the Electrodyne (Electrodyne | Brushless Automotive Alternators) models that Dashew mentions in that book. I dealt directly with the 'old man' there who, semi retired, enjoyed himself with the marine projects as opposed to the main business of battle tanks and rescue vehicles that their gear was mainly fitted to.

It was more expensive, it was more difficult (not off the shelf), it needed a custom bracket, etc, and we even needed to convince the old man to approve the sale in the first place because they only sold 'stuff that works'!

But, in the same space (couldn't fit a bigger frame size in the engine box) it tripled the previous output, and continued to exceed it's own rated output even when running for hours and hours getting very hot (external regulator and diodes, massive heatsink and fan).

I'm not sure if these Electrodyne models are still available but I certainly count it as a success story.

It was an 'over the top' solution but it ended up being cheap, and a godsend in the long run when other cruisers were either having constant problems and replacing alternators or simply not being able to produce enough amps in the first place.

We also installed a small Yanmar DC genset, and although it wasnt a propulsion engine it might still be interesting concept wise, see my post here: http://www.cruisersforum.com/forums/...ml#post2703590

This ran a big shaft driven DC alternator at the back, and it gave me an idea in relation to a propulsion engine.

Instead of where that genset mounted a watermaker pump, in a propulsion setup maybe you could run a big alternator there instead?

So, I'm saying, above the propshaft where there might be more room compared to a side mount at the front? This would very much depend on the individual boat of course, in terms of space available. In a cat there is often more vertical height there than width. On a mono, maybe not, it depends.

Obviously there will still be side loading (vertical) issues to consider, but since this would be a custom install that could be accounted for.

Food for thought maybe?

Another approach mentioned in some other threads is to just have a Honda generator instead, and apart from the fuel, not really have any complicated 'science project' as you put it. Just plug it in.

But for normal use, I would still like this Honda to be 'installed' in some way, able to be used at any time, underway or at anchor, in it's own vented deck locker or something. Etc.
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Old 31-08-2018, 05:27   #11
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Re: Dual alternator and oversize alternator success (or failure) stories

http://www.cruisersforum.com/forums/...d.php?t=193270
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Old 31-08-2018, 05:28   #12
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Re: Dual alternator and oversize alternator success (or failure) stories

Check out Eco-Tech and Zena
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Old 31-08-2018, 05:34   #13
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Re: Dual alternator and oversize alternator success (or failure) stories

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Originally Posted by jmh2002 View Post
We also installed a small Yanmar DC genset, and although it wasnt a propulsion engine it might still be interesting concept wise, see my post here: http://www.cruisersforum.com/forums/...ml#post2703590

This ran a big shaft driven DC alternator at the back, and it gave me an idea in relation to a propulsion engine.

Instead of where that genset mounted a watermaker pump, in a propulsion setup maybe you could run a big alternator there instead?

So, I'm saying, above the propshaft where there might be more room compared to a side mount at the front? This would very much depend on the individual boat of course, in terms of space available. In a cat there is often more vertical height there than width. On a mono, maybe not, it depends.

If I follow what you're saying, the alternator would be driven from a jackshaft (either directly or by a belt). The jackshaft would, in turn, be driven off a crankshaft pulley. That would work, and as you point out, might be a useful way to take advantage of the available space on some boats. There would be some custom pieces, and even if it's a fairly straight shot I would want to put in hanger bearings and U joints.



Quote:
Another approach mentioned in some other threads is to just have a Honda generator instead, and apart from the fuel, not really have any complicated 'science project' as you put it. Just plug it in.

But for normal use, I would still like this Honda to be 'installed' in some way, able to be used at any time, underway or at anchor, in it's own vented deck locker or something. Etc.

I think that the little suitcase generators are great products in many situations. Quiet, well thought out, reliable. Honda did a great job. The Yamaha equivalents are also very good.



I would not want to use one daily on a boat because of the carbon monoxide risk, because of the fuel handling problem, and because of the impossibility of mounting them permanently anywhere (because they air air cooled and do not have a wet exhaust).
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Old 31-08-2018, 07:12   #14
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Re: Dual alternator and oversize alternator success (or failure) stories

Mounted a second generator 40Amp belt driven by the idle prop shaft on a steel Reinke twin keel, 36ft, 9to full weight.
Advantages:
second generator identical to generator in the Nanni 3100HE diesel. Serves as backup when the main one is failing.
At >3kn output is enough to drive the Autohelm 4000
At 5kn (average speed) it produces about 4kW
Just barely enough to also service the fridge (not freezer)
It ran for 25'000 nm before I sold the boat.
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Old 31-08-2018, 10:31   #15
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Re: Dual alternator and oversize alternator success (or failure) stories

From the wound of your project I suspect that a genset is the solution. Taking that much power of alternators may well exceed the allowed power and side thrust loading of the engine. Trucks and busses do fit very large alternators but they are normally driven from a power take off not the front pully I believe.
There is however an even more problenmatic issue. Unless you are prepared to accept very short life from you bank you need to ensure that it is chared to 100%. Getting a 1200a/h bank bank from 50% to 95% takes no more time (3-4hr) provided you can reach C5 but that is 240a @ 24v. The power required to drive it is around 7.5hp. You are looking at a 7-10kw generator. To get to 100% you then need about 50a fora further 3hr or so.

I have seen a very successful example on a large cat with lithum banks and about 5kw of solar on the aft deck but you would not fit it on a mono of less than 50-60ft and would still have issues with shading.
Going all electric is great but if you also want A.C. and are using the sort of power that a small house does youare not going to do it without a power station!
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