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Old 09-10-2016, 10:58   #1
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Larger crank pulley for more amps

I have been looking for a previous thread on this but failed to find one. It appears that alternators that are based on auto applications but installed on a marine diesel - as most seem to be of this type - suffer from the low RPMs that diesels typically operate at. The result is poor output and poor cooling of the alt. When my Universal M35B Kubota engine cruises at about 2,000 RPM, the alt is still only running at about 2,750 RPM. Auto alts often rotate at around 8,000 or higher.

I can't really expect to reduce the size of the alt. pulley or greater slippage will occur due to less contact area of the belt and reduced belt life, so the logical next step is to increase the size of the crank pulley. I have not seen any reference to someone doing this. My crank pulley is only about 4" and the alt. pulley is about 2.5". I cannot find any reference at Universal or Kubota to a larger pulley - though it seems an oversight to me. I see that Balmar or Ample Power have a conversion kit to change both pulleys to a serpentine belt and this might increase the ratio. The new crank pulley is one that slips over the existing crank pulley - a smart move it seems to me.

So my question is - has anyone managed to find and install a larger v-belt crank pulley? I could just machine another generic one to simply replace the existing crank. But for some time I have had in mind a similar idea to Balmar in which I would take a cast-iron dual-belt pulley of about 6 or 7 inches diameter and machine it out inside to fit over the existing crank. The dual belts will allow me to use a larger alt as well. I wonder which method would be preferred. Any machining work is fun for me.

Any advice would be welcome. Thanks, RR.
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Old 09-10-2016, 11:26   #2
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Re: Larger crank pulley for more amps

It's kind of a moot point. What effects your ability to put in amps the most is the battery itself. Typically a high output 100 amp alternator starts out at maybe 85-100 amps but reduces quickly due to the battery's ability to absorb the input within 15-20 minutes.
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Old 09-10-2016, 11:56   #3
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Re: Larger crank pulley for more amps

It isn't quite a mute point as some of the alternators are rather anemic (to be kind). They are meant to recharge a cranking battery and not a house battery. I replaced my M35 alternator with a Balmar 200A alternator and a serpentine kit.
In retrospect, I think I went too far the other side .... 120 or so amps would probably have sufficed.
I don't recall if the serpentine pulley for the crank was bigger than the original - if it was it was a marginal increase at best.
The change over required machining an upper tensioning bracket for the alternator and, after a short while, a replacement of the lower alternator bracket as the original aluminum casting is not strong enough (cracked all over the place).
The issue I am having now is alternator cooling at high output - sustained output into lithium batteries tops out at about 100 - 120 or so amps because then the alternator cuts back due to overheating.
You might try an external regulator to increase output of your internally regulated alternator (don't omit alt temp sensing!!)
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Old 09-10-2016, 13:32   #4
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Re: Larger crank pulley for more amps

I did so on my old Yanmar engine. My generator hade a 50 mm pulley and the engines pulley was 65 mm. The generator was very small, 35 A. I took a 35 mm plastic disk and machined it out inside so it fitted over the old pulley. The new was 150 mm in diameter. There wasn’t space for any larger. With that large pulley I did get so much larger surface that I did not have any problem with slipper.

A wet cell battery can take corresponding 25% in current what it has in capacity. If you mount a larger generator that could be a limit. When you have come up to 14.4 V its time to reduced the current, but then the battery will be charged to 75%.

I believe that the risk of overheating the generator is bigger. With an external regulator you can handle that problem.
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Old 09-10-2016, 14:09   #5
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Re: Larger crank pulley for more amps

Quote:
Originally Posted by Jd1 View Post
It isn't quite a mute point as some of the alternators are rather anemic (to be kind). They are meant to recharge a cranking battery and not a house battery. I replaced my M35 alternator with a Balmar 200A alternator and a serpentine kit.
In retrospect, I think I went too far the other side .... 120 or so amps would probably have sufficed.
I don't recall if the serpentine pulley for the crank was bigger than the original - if it was it was a marginal increase at best.
The change over required machining an upper tensioning bracket for the alternator and, after a short while, a replacement of the lower alternator bracket as the original aluminum casting is not strong enough (cracked all over the place).
The issue I am having now is alternator cooling at high output - sustained output into lithium batteries tops out at about 100 - 120 or so amps because then the alternator cuts back due to overheating.
You might try an external regulator to increase output of your internally regulated alternator (don't omit alt temp sensing!!)
Lots of good info here. Definitely go with external regulation with temp sensing if you are going high output. Otherwise you will eventually burn up what you have.

Going with the serpentine kit on high output is almost a must. That way you could reduce the size of the alternator pulley. You could also add an idler pulley to the belt set up allowing you to increase the wrap on the alternator. If you do do this make sure you do not get to crazy with the belt tension or you will end up with cracked fittings all over.

I also had a cooling issue on my alternator as JD1 did. Installing an inline blower motor pointing at the bottom of the alternator resolved this issue for me. Just ended up having poor air circulation in that area.

Good luck
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Old 09-10-2016, 16:43   #6
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Re: Larger crank pulley for more amps

Mark Grasser makes serpentine kits that over drive the alternator.
Basically your premise is correct, in a normal marine application we are under driving the alternators which gets less power and causes them to overheat, to optimize operation and I suspect their life, they do need to be driven at higher RPM than we do.


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Old 09-10-2016, 16:51   #7
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Re: Larger crank pulley for more amps

I don't necessarily believe that speeding up an alternator will increase your charging amps. An alternator produces alternating current which is fed to a voltage regulator to produce direct current. If the alternator is designed to produce 120v @60 hz, then once it reaches that speed, it is producing the required voltage. Speeding it up is just going to clip anything above the hz. Voltage will remain constant with fluctuations being felt as current increases. Your alternator has an optimum rpm/speed. Once you reach that, and figure out what IT is, adjust the pulley sizes to accomodate the rpm at your operating rpm.

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Old 09-10-2016, 16:59   #8
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Re: Larger crank pulley for more amps

Well I have added reduced diameter on the alt, and added a second belt at the same time.

Every alternator has a rpm/power curve on a graph, best is to find the most efficient alt speed, then your engine best speed, and that ratio determines pulley size.

Attached photo refers: This Volvo Penta had a 35A standard alternator, I was asked to upgrade it so I fitted a 110A Alt, but to transfer that horsepower I needed to fit another belt, and one that would not pass over the water pump pulley and ruin the bearings on it. It was a cheaper and easier option than a toothed belt.
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Old 09-10-2016, 17:08   #9
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Re: Larger crank pulley for more amps

Thanks to all who responded.


I tend to be one who does not want a part failing due to being at the extreme limit of performance but wants reasonable costs. My plan was to get a well-regarded Delco CS130D or CS144 (the latter being a larger-bodied alt., more heavy-duty, and often rated for well over 100 amps) and install a dual V-belt system. Certainly I would consider a serpentine system if the Wise Gurus on this forum feel that would be better.


I already made up a more robust tension adjustment that uses a ready-rod for that purpose and it works great, including the fact that I need no tools for adjustment. The new alt. location is further away from the heat of the engine for better cooling, being more on its own - fortunately I have lots of room in the area. I will probably use an external regulator of either bought or my own design. As a rule of thumb, larger pulleys increase the contact area and the life of the belt and reduce slippage so I prefer larger pulleys.


For sure, limitations of a given charging system can reduce effectiveness, but right now I am lucky to get 25 amps into about 2 gel cell banks of 350 AH at start of charging even when the banks are well-depleted. If I can get charging of 75 amps it will be a huge improvement. I don't want to reduce the lifespan of batteries by cooking or superfast charging any more than needed but still want reasonable charge times - whatever that is.


Thanks again, RR.
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Old 09-10-2016, 17:15   #10
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Re: Larger crank pulley for more amps

Quote:
Originally Posted by dridas View Post
I don't necessarily believe that speeding up an alternator will increase your charging amps. An alternator produces alternating current which is fed to a voltage regulator to produce direct current. If the alternator is designed to produce 120v @60 hz, then once it reaches that speed, it is producing the required voltage. Speeding it up is just going to clip anything above the hz. Voltage will remain constant with fluctuations being felt as current increases. Your alternator has an optimum rpm/speed. Once you reach that, and figure out what IT is, adjust the pulley sizes to accomodate the rpm at your operating rpm.

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I think that you need to rethink your understanding of how these systems work. There are a lot of errors in your description.

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Old 09-10-2016, 17:35   #11
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Re: Larger crank pulley for more amps

Read the description of the belt kit
http://www.markgrasser.com


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Old 09-10-2016, 17:46   #12
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Re: Larger crank pulley for more amps

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Old 09-10-2016, 17:52   #13
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Re: Larger crank pulley for more amps

My Westerbeke W46 has 4 x 5/16" threded holes for the crankshaft pulley puller. I machined a spacer and a larger pulley from a junkyard auto, indexed for the 4 holes, to drive my second house alternator. 20 yrs, no problem
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Old 10-10-2016, 06:56   #14
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Re: Larger crank pulley for more amps

As has been stated Mark Grasser DC Power Solutions is building serpentine kits with larger crank pulleys. Not as simple as it seems because the water pump pulley also needs to increase in size, if that belt also drives the water pump..

Speeding up the alt yields improved cooling and higher output at low RPM. Mark is also doing external rectification which allows both small case alts and large frame alts to perform significantly better before over heating.

This is one of Marks Yanmar kits during the development stage.



External Rectification:


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Old 10-10-2016, 14:46   #15
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Re: Larger crank pulley for more amps

dridas is right. More RPMs on an alternator do not = more amps.
The old generators were like that ,,,the faster they turned the more amps.
But alternators these days put out the same amps at almost all speeds ( RPMs )
If you want more amps get a higher rated alternator ,,, dont speed up the one you have.
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