Choice of alternator

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Choice of alternator

Postby MollyBlossom on Sat Nov 14, 2009 6:26 am

I am considering purchasing one of your alternators. I can only use a single belt and would be happy with 96 amps when the unit is hot. Which would be a better choice #4023 with a 2.6 inch pulley or #4024 with a 3 inch pulley. The 2.6 inch pulley would be at 4500 rpm at cruising speed and the 3 inch pulley at 4000 rpm. My thought was the extra belt rap might help prevent belt slippage.

Martin Basch
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Re: Choice of alternator

Postby Coulomb on Mon Nov 16, 2009 11:06 am

The more belt wrap the better, but width is also important. What is the present width?

The other consideration is when do you want to charge most? When you're running at cruising speed you're probably going to be at it for a while, so losing a few Amps at the top end is OK. If you're just running the engine to charge, then you want maximum Amps at a lower RPM - in which case the #4023 is suggested.
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Re: Choice of alternator

Postby MollyBlossom on Mon Nov 16, 2009 12:52 pm

The present belt width is 1/2 inch. We use the alternator while at cruising speed to replace about 300 amp hours used overnight. We have been using an 80 amp output alternator which wasn't quite enough current. The pulley diameter on the engine is 7 inches and we cruise at 1700 rpm.
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Re: Choice of alternator

Postby Coulomb on Mon Nov 16, 2009 3:29 pm

With a 1/2 belt, you can use either alternator with the 2.6 inch sheave. Using a 3 inch sheave would give you more belt life, however, if you use a Dayco TopCog belt life isn't so much as issue.

You'll get a few more Amps with the #4024 at cruising RPM, with either sheave.
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Re: Choice of alternator

Postby MollyBlossom on Sun Dec 06, 2009 9:30 am

How would you compare the Gates Super HC belt with the Gates Fleetrunner a new green stripe belt or do you prefer the Dayco Top Cog V belt?
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Re: Choice of alternator

Postby Coulomb on Mon Dec 07, 2009 11:33 am

Many years ago the Gates greenstripe was one we suggested, but then they got hard to find and we switched to the Dayco TopCog. It works very well so we haven't tried others since.
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Re: Choice of alternator

Postby MollyBlossom on Tue Feb 16, 2010 9:04 am

I just bought your #4023 alternator with a 3 inch pulley. It doesn't seem to get the power out that you advertise in your specifications. These are the measurements I have taken.
Alternator RPM 4667 measured with digital tach
engine room temp 74 deg F
Alternator Case Temp 145 deg F
Current out 91 amps Measured two ways, with clip on ammeter and with link 2000

Shouldn't it be between 96 and 114 amps as shown on your web site? The battery bank was discharged before the test and measured about 13.3 volts, not near the absorption voltage of 14.1 volts. What should the field voltage be in order to get the specified current out? I will check that next.
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Re: Choice of alternator

Postby Coulomb on Wed Feb 17, 2010 12:21 pm

Hot and cold alternator ratings come from specifications developed for emergency vehicles, and field voltage is 14V.

The regulator and the wires carrying field current from the battery to the regulator, and from the regulator to the alternator all impose a voltage drop. It would be interesting to know what that is in your case.
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Re: Choice of alternator

Postby MollyBlossom on Thu Feb 18, 2010 2:22 pm

How can the field voltage be 14 volts when charging a discharged battery bank? The battery voltage had only gotten up to 13.3 volts when I made measurements.
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Re: Choice of alternator

Postby Coulomb on Thu Feb 18, 2010 6:22 pm

14 Volts is the "standard" for specifying alternator output. It wouldn't be practical to specify output across every value of field voltage and alternator RPM.
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