Universal M25 Alternator mounting and drive

[jviss]

One of the worst aspects of the M25 installation in C36's is the inadequacy of the alternator mounting bracket and belt drive when a large alternator is fitted. I have the alternator bracket upgrade from Westerbeke/Universal that was issue in response to the breaking brackets years ago: it's impossible to properly align the pulleys with it. The larger alternator load is also stressing the other components. I had a circulating pump bearing fail two years ago (I carry a spare water circulating pump now).

My question is, has anyone ever developed an adequate, i.e., properly engineered bracket and pulley system for the M25 for large alternators? I'm thinking of wide pulleys and a belt like the serpentine belt on many cars now, more stable mounting for the alternator, and a way to take some of the load off the circulating pump.

Any information or insight is appreciated.

Also, is there interest in this? If I produced a kit that totally solved this, would it sell? Like, a replacement bracket system, wide pulleys for alternator and crank, an idler/tensioner, a separate belt drive for the circulating pump - for, say, $400? Or, what price?

Thanks,

jv

 

[Stu Jackson]

Nope, but don't know how big your new alternator is --

recommendations on our C34s (with M25s) have been to limit the new alternator to 90 to 100 Amps. Some have put larger 125s on. Pulley adjustment is best done with a belt tensioner. Alignment is another issue - some have added shims to get good alignment. I run a 100 A high output alternator with a Balmar M612 regulator with the "upgraded" new bracket on our C34 with a 3/8 belt and have no problems. I just (literally last night) heard of a new style bracket failure on a friend's M25XP (1988) boat, which dropped his alternator out of the loop by failing at the top of the bracket. As I get more info and pictures, I'll advise. Meantime, check the top of your alternator bracket, I know I will on our boat.

 

[jviss]

Stu

I have a 125A alternator. I guess the more important factor is the load - I'm charging up a 300 AH bank. So, at 1/3 C "bulk" charging I see 100A initially. The single belt doesn't squeal, but with the misalignment it makes a lot of black dust.

That bracket is a piece of junk, in my opinion. It doesn't fit properly, and tightening the pivot bolt bends it. Perhaps I should shim the alternator foot.

I would spend $400 on the kit I describe if it was available. I plan on making my own this winter.

 

[Stu Jackson]

Then I would submit that your alternator is too darn

big for both your engine and your house bank size. Yup, you'd see 100A initially, but I'll betcha it drops off pretty quickly after that on a shorepower charger in the same conditions if you were watching volts and amps, while the smart regulator will keep it in bulk for 23 minutes or so, based on the default time on the Balmar or Xantrex regulator you have. Your battery acceptance is going to outrace the alternator/regulator output every time, given the size of your house bank, which is relatively small compared to your alternator size.

If it was my boat, given your "issues" I'd either add another battery to the house bank to get to 400 ah, or use the "Amp Manager" feature of your regulator (if you have one) to reduce the regulator's call for amps to save your belt. Or both.

One of our guys did the amp manager with pretty much the rig you have now, and his belt problem disappeared.

 

[jviss]

Question

Not sure I understand your comments.

Regardless of the rated output of an alternator, it won't put out more current than the load can sink with maximum field current to the alternator. So, a bigger alternator on the same bank is simply over-rated and runs cooler, no?

Second, the bulk phase is not time based on most chargers, it is maximum current until the acceptance voltage is reached, which is usually adjustable, and nominally 14.4 Volts, no?

The shore power charger is a much lower current output device than the alternator; the Truecharge 20+ is actually 10A per channel, no? So, bulk to acceptance is something of a farce.

I think that since the alternator is rated near 1/3C for the house bank it is properly sized. I don't know what you mean by "battery acceptance is going to outrace the alternator/regulator output every time."

More questions on the rest, but let's start with this.

Thanks.

 

[Stu Jackson]

Good Questions

jviss,

Regardless of the rated output of an alternator, it won't put out more current than the load can sink with maximum field current to the alternator. So, a bigger alternator on the same bank is simply over-rated and runs cooler, no?

Yes, I agree. Over sizing, however, may be your belt alignment issue because of the extra stuff hanging there, perhaps unnecessarily.

Math time – sorry : general rule-of-thumb: alternator 25 – 40% of (house) bank, depending on battery types and rates of acceptance.

330 AH bank 125A alternator
330 x .25 = 82.5 A alternator
330 x .40 = 132 A
125 / .25 = 500 AH bank could be handled well
125 / .40 = 312.5 AH bank

So your alternator could be considered too large for your house bank or your house bank too small for the alternator.

Yes, may run cooler, but the acceptance of a 400 ah bank at 1/2C is usually around 50 amps, based on my readings and input from a few other folks who understand this stuff as well as you do. I also believe that there are acceptance rate charts somewhere that reflect this.

To that I’d simply add Tom Soko’s suggestion, just recently posted on the C36 Message Board (yet again, just like our website) that our engines be limited to around 90A because of the side loads on the engine appurtenances bearings.

A 90-100 A alternator would still not be more than half loaded. Yes, 125 A would be even cooler still, but the amp manager feature on the regulator could assist even more.

This limit applies to our M25 series engines. With a larger engine which could handle a larger laternator and not limit the alternator size, the bank/alternator sizing/matching would take precedence.
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Second, the bulk phase is not time based on most chargers, it is maximum current until the acceptance voltage is reached, which is usually adjustable, and nominally 14.4 Volts, no?

Yup, I agree, voltage varies with battery type employed and set for. Although some regulators, like my Balmar M612, have a 23 - 36 minute (adjustable on the M612) limit on bulk, regardless of the volts and amps, at least that’s the way I read the manual.
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The shore power charger is a much lower current output device than the alternator; the Truecharge 20+ is actually 10A per channel, no? So, bulk to acceptance is something of a farce.

The comparison there was a bit of a mis-match, which you picked up on right away, although I was considering the amperage max out of either device (alt. or charger) as percent of its total output, then liked to the bank’s acceptance.

Bulk to acceptance applies regardless of the charging source (assuming a three stage regulator on the alternator). Those stages are based on the definition of each of the stages of charging, not on the size (amperage output) of the charging source.

I have a 75 A charger on our Freedom 15 I/C, so my two sources are pretty close, and I get similar readings on the Link 2000 from both with 1/3 C and ½ C starting points.
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I think that since the alternator is rated near 1/3C for the house bank it is properly sized. I don't know what you mean by "battery acceptance is going to outrace the alternator/regulator output every time."

That means the acceptance will control rather than the (oversized) max. Amperage output of the alternator, noted above. Sorry for the obtuse analogy.


Stu

 

[jviss]

Clarification

You wrote:

"So your alternator could be considered too large for your house bank or your house bank too small for the alternator. "

Neither of these make sense to me. For a given house bank size, the alternator should be selected for most efficient and fastest charging (without damaging batteries); so the alternator should be sized for at least the maximum current during the bulk charging phase, which is typically 1/3C, or larger - and the larger alternator rating won't put a bigger load on the engine, it will simply have more thermal margin. So, a 100 Amp alternator at 100A output or a 125A alternator at 100A output achieves the same result, with the same load on the engine (and mounting). So, the alternator can't be too big. The house bank can be too big, the limit being the alternator's thermal and electrical rating, and the alternator mont and drive system limits. It is most efficient, and fastest and best for longevity for flooded cells to charge them initially at the bulk rate. If you increase the house bank size, which is based on your electrical needs, you should make sure the alternator, and mounting and drive system, are sufficient to charge the house, or that portion of it you charge at one time, at the 1/3 bulk rate. So, the house bank can't really be too small for the alternator, only too small for your electrical requirements.

My analysis - comments?

 

[Stu Jackson]

Th point, jviss, is this

That the acceptance of the house bank is usually only 50A in our "range" of house bank sizes at 1/2 C, so even my 100A alternator is only needing to put out 50A with a half depleted, in my case, 360 AH house bank. That's why I did the math exercise. Tom Soko's been through this on the C36 Message Board just this with with Eric.

I hope you relaize that I'm not trying to argue with you, just presenting some facts on battery acceptance of house banks compared to alternator sizing criteria from many sources, including Ample, West Marine, Calder, Jack Rabbit and others, and what has worked for us.

Remember, please, also, that the 90A limit was based on Universal M25 engines, like we both have on our boats.

 

[jviss]

I don't agree with all that,

... but I don't think we'll ever totally agree. One point of confusion, when I was saying "1/3C" or such, I was referring to the charging current as a fraction of the house capacity.

The alternator won't create too big a load if there isn't a load to pt on it - hence, a huge alternator is not too big if hte house bank can't absorb its capacity.

Alternators should be sized for the Bulk phase, no Acceptance.

You CAN have too large a house bank; batteries don't have as long a useful life if they aren't fully charged, and 600AH with a 90A alternator would mean you'd have ot be very careful to not discharge them much beyond 70% or so, or you will have to charge for HOURS AND HOURS to fully charge them.

 

[Stu Jackson]

I kept adding to it for the past few minutes, so try again

and, yes, the larger the house bank, the longer it will take to replenish.

However, the larger the house bank for any given daily load, the longer the batteries themselves will last because the total % of drawdown will be less.

Plus, I keep coming back to the size of your engine and its bearings. Sorry about that reality.

 

[jviss]

I know!

Stu,

I'm puzzled. You say: "Plus, I keep coming back to the size of your engine and its bearings. Sorry about that reality." But that's why I started this thread! That original bracket was good for a 35A alt. for charging the starting battery. The new bracket is a piece of junk. What I want is a proper bracket and pulley/drive system for taking 125A at 12 Volts - 2H - off this engine. Clearly, the existing bracket and pulley belt are inadequate, and the water pump bearings are not up to the load imposed either.

Sure, please post the links to the C34 discussion.

 

[Stu Jackson]

I agree

however, the "flimsy" bracket is NOT what I keep referring to, it's the size of yoru alternator against the engine bearings that's the limit.

Try these links for starters:

Engine charging: http://c34.org/bbs/index.php/topic,4338.0.html

Overall system: http://www.c34.org/projects/projects-electrical-system-upgrade-2.html

 

[Stu Jackson]

If you're a member of the C36 Website MB

try this link

 

[jviss]

Links

Thanks for the links.

A caution, though, in the first, the article by Jim Moe, there is some misinformation; for example, his description of three stage charging is incorrect; and his description of why one shouldn't connect old and new batteries together to form a bank is a bit odd, too. His explanation of "no current limiting" is incorrect, since the field current is typically limited on external regulators; his explanation of the use of diode isolators is incorrect, since most, if not all external regulators allow for remote sense, which should be implemented in any case, and not regulate to alternator output voltage (my Heart Interface/Xantrex smart regulator is set up for external sense, an installation option).

I looked at the wiring diagram: no remote sense line for the alternator. I'm also not a big fan of fuses in the power lines: there can be a significant voltage drop across a fuse, like when you are charging your batteries(!); and, if the batteries are close enough to the panel, they are not necessary according to ABYC. No remote sense and fuse in line is nearly the same problem as the isolation diode problem.

Remember, at 100A you drop .1V per miliOhm, and .1V is significant in battery charging circuits.