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Old 04-07-2016, 04:44   #1
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Alternator Belt issue 3YM30

I have a constant issue wearing out alternator belts on both Yanmar 3YM30 on my Fusion 40 Sailing Cat. this is due to the high charging current required for the house batteries. I see an answer is to either reduce the load on the alternator by increasing the pulley size or maintaining the belt tension with some sort of an automatic tensioner.

Hoping someone as done it all before?

Scrubby
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Old 04-07-2016, 06:01   #2
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Re: Alternator Belt issue 3YM30

Use Gates Red Stripe Belts, last longer than any belt I know of, also single belt really only good for about 80 amp alternator, then need two belts or flat serpentine belt
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Old 04-07-2016, 15:42   #3
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Re: Alternator Belt issue 3YM30

Alternattors are 80amp but rarely run more than 40 for any length of time. Belts need adjusting reguarly and replacement every 50 to 100hrs



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Old 04-07-2016, 19:30   #4
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Re: Alternator Belt issue 3YM30

I don't like the Gates, as much and prefer the Dayco TopClog, has twice the ply. If you have a smart regulator you can dial it back and more importantly you can ramp up the alternator's load which is close to 2hp. Pushing +100 amps is a bunch of work. I have my 120amp alternator dialed back to 90 on a single v-belt.
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Old 04-07-2016, 19:53   #5
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Re: Alternator Belt issue 3YM30

One other possibility is that the belts you are using are not the same angle as one or both of the pulleys. Possibly the alternator pulley is not a match for the flywheel pulley angle wise or is to small and puts undue load on the belt by bending sharply or the pulleys are not in exact alignment. Are the belts 1/2 in. or 3/8 in.?
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Old 05-07-2016, 10:24   #6
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Re: Alternator Belt issue 3YM30

you can look into converting to serpentine belt system Balmar offers one for that engine the serpentine belts are a way more efficient way to produce more power and will let you go to a higher amp alternator that wont have to work so hard
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Old 05-07-2016, 10:36   #7
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Re: Alternator Belt issue 3YM30

Make sure the pulleys are lined up by putting a straightedge on one of them.
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Old 05-07-2016, 10:50   #8
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Re: Alternator Belt issue 3YM30

Quote:
Originally Posted by jacktheflyer View Post
............. I see an answer is to either reduce the load on the alternator by increasing the pulley size or maintaining the belt tension with some sort of an automatic tensioner.
Those are not the answers. If you have an external regulator, try these:

Alternator heat, Regulator Controls, Small Engine Mode

Alternator heat, Regulator Controls, Small Engine Mode

Small Engine Mode - discussion with link to the picture of the toggle switch: Alternator heat, Regulator Controls, Small Engine Mode

Small Engine Mode - the picture of the toggle switch Alternator Output Management with External Regulators [Small Engine Mode]
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Old 05-07-2016, 10:59   #9
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Re: Alternator Belt issue 3YM30

I had the same problem with my Yanmar 2GM 20F. I installed an Electromax serpentine flat belt conversion kit and problem solved. It will also allow me to upsize my alternator in the future....if needed.
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Old 05-07-2016, 13:46   #10
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Re: Alternator Belt issue 3YM30

Quote:
Originally Posted by Stu Jackson View Post
Those are not the answers. If you have an external regulator, try these:
And what if one doesn't want to externally regulate?
I acknowledge your your experience and commitment to helping people out here Stu, but surely putting a bigger diameter drive pulley on will de-rate the alternator. ( Including cooling it less.)
There ARE people out there successfully outputting close to 100A with a single V belt and getting reasonable life out of their belts.

Also more bearing surface is known to prolong the life of belts.

From quick start:
Alternator pulley belt wrap, what does that mean? Belt wrap is the contact area the belt has with the pulley. but the greater the belt wrap the longer belt and pulley life can be expected. Alternators take quite a bit of power to run so good belt contact with the pulley is very important. If you have poor belt wrap or your pulley becomes "glazed" a glazed pulley looks very smooth it may be time to replace the pulley.
https://alternatorparts.com/alternator-pulley-size.html

Well it better work for the interim, 'cos that what I am doing on my diminished budget. I think alignment, pulley surface condition & correct tension play a decent part as well.

I may externally regulate as well, but not with a fancy $400
USB ---> PC unit, rather a ZM4, with a pot. $175US
alternator, smart alternator regulator

Probably put a couple of temp alarms in at $10 each. ( Eventually)
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Old 05-07-2016, 14:41   #11
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Re: Alternator Belt issue 3YM30

Quote:
Originally Posted by lateral View Post
And what if one doesn't want to externally regulate?
I acknowledge your your experience and commitment to helping people out here Stu, but surely putting a bigger diameter drive pulley on will de-rate the alternator. ( Including cooling it less.)
There ARE people out there successfully outputting close to 100A with a single V belt and getting reasonable life out of their belts.

Also more bearing surface is known to prolong the life of belts.

From quick start:
Alternator pulley belt wrap, what does that mean? Belt wrap is the contact area the belt has with the pulley. but the greater the belt wrap the longer belt and pulley life can be expected. Alternators take quite a bit of power to run so good belt contact with the pulley is very important. If you have
You don't have to externally regulate, I provided that information if you do.

The larger pulley on the alternator seems counter intuitive to me, because it means the alternator will spin more quickly at any given engine rpm, right?

If so, then it would seem to me that you'd need to find an alternator that had an output curve to match the expected rpms. Most alternators are based on the 2:1 or 2.5:1 pulley ratios common to our engines. If you enlarge the alternator pulley, you'd be putting more rpms on the alternator at low engine rpms that might be fine, but at cruising engine rpms that alternators gonna be turning over an awful lot. Would be it be possible to overload or overheat the alternator? Overload would occur, as discussed in one of my links, with a 50% SOC house bank. Without alternator temperature sensing, only available with an external regulator, you wouldn't know, would you?

I am deliberately asking these as questions, because it's one of the first times I've heard of this approach. Anything you can do to help me understand would be much appreciated.

Good luck, whatever you choose to do.

PS - I DO run a 100A alternator on a 3/8" belt.
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Old 05-07-2016, 15:24   #12
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Re: Alternator Belt issue 3YM30

Larger pulley on alternator -> lower alternator RPM
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Old 05-07-2016, 15:31   #13
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Re: Alternator Belt issue 3YM30

I have 140 amp alternators on my mains. When using all the amps only dual 1/2 belts will hold up. Current belts are 5 years old, about 2500 hours. If I could find a serpentine pulley to fit my Detroit mains I would switch.
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Old 05-07-2016, 15:35   #14
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Re: Alternator Belt issue 3YM30

Hi scrubby I have same boat same motors and same problem and have tried various remedies rust on the pulleys contributes to belt wear an old auto elec. told me,pretty hard to stop it .am looking into serpentine belts. Will let you know results
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Old 05-07-2016, 15:44   #15
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Re: Alternator Belt issue 3YM30

Quote:
Originally Posted by Jd1 View Post
Larger pulley on alternator -> lower alternator RPM
Uh Oh doh!

Thanks, I REALY REALLY shoulda known that.
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