How Much Does Your Big Alternator Put Out?

[waterdog]

I have the happy little stock alternator that came bolted onto the M25XP.  What is that 50 or 55A?   It's a pleasant little alternator.   I've never noticed that it heats the cabin, chews through belts, or destroys bearings.  I haven't had to tension my belt in a year.   We live happily together. 

Of course, that doesn't stop me from having alternator envy.   I know some of the rest of you are leading enjoyable lives programming your external regulators, twisting exotic tensioning tools, and specifying nothing less than Gates green stripe.   But clearly you are getting a lot more out of your alternators than I am.  I suspect you all have a higher level of alternator satisfaction.  Your grass is greener than mine. 

But I'm wondering how much greener.

Here's my real question.  400 Ah bank.  50% discharge.  How long are you motoring for before you get to a 75% charge level?   No rated outputs and fancy theories about charge acceptance curves - just what are you getting real world?

I have a sneaking suspicion that all the alternator capacity in the world is not going to make my life better in full time cruising mode in the tropics and if I have to choose between a new alternator / regulator and another 120W solar panel, the additional solar panel is going to be a better investment.   


 

[Ron Hill]

Steve : WOW !! What a question!  It's apparent that you do not have a battery monitor on-board!!

I'm not too sure that there is anyone that can answer your question FROM Experience.  I'd have to calculate, but if you still had the fridge ON and the other minor electronics ON with the engine rumming (and your 55 amp Motorola alternator with it's internal Voltage regulator doing the charging) if you'd have enough fuel on-board to recharge 200 AmpHrs + usage !!  You'll probably only see about 14.5 - 15 amps steady charging from your stock alternator - because of the voltage regulator!!  It will put out 55 amps, but only for a nano second!
 
Does that give you an idea of why most of us have gone to a Hi output alternator with the ALL important smart 3 stage voltage regulator ?  A thought

[waterdog]

No. No. I do have a battery monitor on board.   But I have a 55A alternator and 180 Ah bank.  And I've never seen anything like 50A out of it.  Maybe 25 for a few minutes and then it quickly drops to 18 or something.   The batteries only accept so much.  I know how my system performs and it's inadequate.  I want to know how bigger systems perform and make a decision on what I would like to emulate.   I will upsize my bank to 400 Ah.  I'm trying to figure out where to sprinkle the dollars around the other charging resources. 

I want to know what kind of a dent a 100A alternator makes in a 200 Ah deficit.   ie. even with a large capacity alternator, does it make a meaningful dent any way?   Or am I not just better off spending my money on other charging resources?   Does an hour of motoring knock 40 or 50 Ah back into the bank?

Right now, I use 40 to 50A hours a day.  I'm anticipating this going to 100 Ah per day based on higher refridgeration load in a warmer climate.  SSB and computer use etc. 

Maybe a better question is if a 55A alternator limits out well below its rating because of the charge acceptance of the batteries, does having a 100A alternator influence the charge acceptance rate?   If so by how much?  Does the charging scale linearly with alternator size or is the real limitation the batteries anyway?

[Craig Illman]

Steve - It's the internal regulator of your stock alternator that's limiting your return to the bank. Stu found an inexpensive externally regulated alternator or you could get your stock alternator modified.

Craig

[Stu Jackson]

Careful here, guys.  Do NOT get an external regulator for your OEM 55A Motorola.  It'll fry up the alternator by making it output too much -- it's just an automobile alternator, not made for charging deep cycle discharged battery banks.  The internal regulators only provide an under voltaged tapering charge, takes forever.

400 ah bank, 100 A alternator, figure 50 -60 amp output from 50% to 75% charge at cruising RPM (engine & alternator) with an external regulator.  Down to 200 ah with 50 to 70ah to make up takes a bit over an hour.  As we know, the last 15-20% takes forever, discussed on recent threads about acceptance.  The alternator output and the acceptance are the controlling factors, and are [pretty much equal in this range of charging requirements, based on my last long thoughts on the matter. http://c34.org/bbs/index.php/topic,4454.15.html page 2 reply #20

BTW, these are also real world figures, since it's what I've been seeing for last year or more.  That's how I came to my conclusions.

The alternator comes from Jim Moe's Projects article (electrical upgrade V2 --  http://www.c34.org/projects/projects-electrical-system-upgrade-2.html).

Your choices:

1.  Stick with the OEM alternator and add solar

2.  Upgrade the alternator - use the engine for charging

3.  Upgrade and solar

4.  Either or and/or the above and generator

Just about the only choices out there, since you'll get only half the amps out of the OEM alternator with internal regulation.

Doing what you're planning, I'd add big solar.  Once you get away from wanting to have hot water showers in the morning (i.e., where it's hot outside but where a Honda 2000 generator would heat your water - but a 1000 wouldn't), you'll find cranking up a generator for the morning ablutions unnecessary.  Your boat, your choice.

[waterdog]

I think there's nothing wrong with 360W of solar panels on the bimini.   The more I think about it, the more I think that's the place to spend the generation $.  Stu, I'm a Canadian.   I once dove into a turquoise glacial fed lake at near 0C.   I don't need hot showers.  I need ice cubes - or at least cold beer...

[Hawk]

I take it you mean a cold "Canadian" beer, Steve.
Tom

[waterdog]

Well that's the next big problem isn't it.   How much beer can I get aboard?  Will it last until I make it to Mexico?

[Rick Johnson]

Steve,  Texas summers are hot and humid.  The PO of my C34 installed a Technautics refrigerator and Seimens solar panels.  The solar panels will just keep up with the drain on the frig, so I always have cold beer.  A great trio (solar, frig, beer)...

Rick

[sailaway]

Alternator output. The big problem is the m25 engine is a little underpowered for the 34. If you put a larger  output  alternator it will rob hp from the engine. You don't  get anything for free. Solar cells sound like a good choice. Charlie

[Ron Hill]

Charlie : There's no doubt about it - a Hi output alternator does take about a 2 HP side load to operate.  However, when you really want to put a bunch of amps back in to the battery in a short period of time - it's the only way to go!!
Solar is great, but has it's limitations, which I'm sure that you're aware of.  Wind is also great, but has it's limitations.  The little Honda is nice when there is less than 12kt of wind and it's cloudy. 
If you move every day, the Hi output alternator gets the amps back fast and when you get into WX (head wind/waves) and need all of the engines HP, chances are that the alternator is "loafing" by that time (with practically NO side load).  A few thoughts. 

[Tom Soko]

Stu,
I have to take issue with your statement "Do NOT get an external regulator for your OEM 55A Motorola."  I did that for about 10 years, and had no problems.  I used an Ample Power regulator on the OEM Motorola, and I'm still using that same regulator on my LeeceNeville 90A alternator.  I've had the LeeceNeville for about 3 years, also without a problem.  In fact, I might go as far as to say that the regulator upgrade was the biggest bang for my buck for increased charging.  You effectively double the output of the stock alternator.  With a 40-50% discharged battery bank, I would see 35-40A coming out of the alternator for extended time periods.  Hope this helps.

[Stu Jackson]

Tom, could you please post a link to your regulator writeup in your website.  I think it would be helpful for folks to see what you've done and how it worked for you, in the great detail I remember that you provided.  Thanks.

[Tom Soko]

Stu,
Actually I did not write up anything for the C36 website concerning an alternator upgrade.  I followed the lead of Rodd Collins, a former C36 owner, and now an active participant on the CatalinaOwners.com bulletin board (Maine Sailor).  His LeeceNeville writeup is at:
http://www.c36ia.com/node/502
Another alternator upgrade article by Fred Jackson is at:
http://www.c36ia.com/node/474
Both of these are on the C36IA website, under the Articles tab, then under the Upgrades tab.
I really liked the idea that the LeeceNeville alternator was a direct swap, with no modification of brackets, arms, etc., and is rated at 90A.  I know  that other owners have gotten away with much larger alternators, but in talking with Joe Joyce at Westerbeke/Universal, the max we should be putting on our engines is 90A.  I bought the alternator locally, and they put on the external regulation plate.  The cost was about $225, and it only took me about 15 minutes to install.  Hope this helps.

[Stu Jackson]

Thanks, Tom, yes, Rod's was the one I was thinking about, sorry about any confusion.

In that recent thread on alternator heat, I mentioned a discussion over on co.com with another C36 owner, who proposed that the largest alternator would provide a better solution because it would only operate at the acceptance level of the house bank which seems to be about 50 to 60 amps for a 50% discharged bank of around 400 AH, and thus place a smaller percentage load on the larger alternator.

So, like so many other things in boating, there are choices:

1.  OEM alternator with internal regulation:  smallest output (starts at 25 A and rapidly tapers off - why they're called "tapering" chargers) based on alternator size (55A) with internal automotive regulation of only 13.8 V, not smart or fast charging, delivers chronically undercharged conditions if dependence is on alternator for charging when cruising with little access to complete charges from shorepower.

2.  Tom and Rodd's external regulation of an OEM or larger alternator - don't know about the "smarts" of the regulator, so read their references

3.  External regulation - smart charging, fastest amperage into the bank
   3a.  Up to max 90 to 100A alternator based on engine load and consideration of bearings
   3b.  A big 110 to 125 A alternator - the argument "for" is that the alternator won't heat up so much because it is being used at a smaller % of its designed total capacity
   3c.  Either or all of these using amp management or small engine mode for regulator signal control for alternator output (and heat); can provide equalization mode that internal regulators cannot

The cost of the alternator varies widely from manufacturer to manufacturer.  Balmar is nearing $400 and the Leece Neville and the Blue Circle are considerably less expensive.  Both of these are straight swaps with no alignment or bracket issues.

So far, we've seen them all here.  And many of us have been happy with each of these varieties.  Each one has advantages and disadvantages, and in all cases should be based on how you use your boat.

One other thing previously noted:  sooner or later your alternator is going to get OLD (ours was 20 when we replaced it).  Even those of you with early 1990s boats have units that are nearing well over ten years old.  100 hours at 5 knots = 500 miles times 10 years is 5,000 miles.  Doesn't sound like much compared to a car, does it?

The wiring differences between the old and new alternators and regulators can be found here: http://c34.org/bbs/index.php/topic,4548.0.html.  These supplement Fred Jackson's excellent article posted by Tom (nope, we're no relation to Fred).