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Alternator problem

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brian_mcwhirter

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"Hi all,
I'm running an &

"Hi all,
I'm running an '87 alpha one 260. I replaced the alternator last spring, and the battery about a month ago. I ran the boat today, and at idle I'm reading between 13.4-13.7 volts, on both an analog and digital gauges. At higher RPM's (25-3500), it drops as low as 13, but typically it's right around 13.2. This seems a little low to me. The test specs on the alternator show the regulator set-point at 14.62V. Is this normal or what?
Thanks."
 
Slipping belt? Where did you

Slipping belt? Where did you take your voltage readings? Battery or alternator output lug?
 
"I measured with a multi-meter

"I measured with a multi-meter across the battery terminals, and that jives with what the gauges say. I have had problems with belt slippage resulting in squealing, but currently the belt is pretty tight. No slippage that I can tell."
 
"If the charging system is wor

"If the charging system is working as it appears, then there could be a component drawing down the voltage/current at higher RPMs or the belt is slipping at higher RPMs.

Try turning off the bilge blower and see what happens. Have you observed the drive belt at higher RPMs? How old is the belt? A new belt may solve the issue of slippage at higher RPMs. If you change the belt, you'll have to retighten it after a few hours unless you have a belt tensioner."
 
"All measurements were taken w

"All measurements were taken with no accessories running. The alternator belt is somewhat wimpy, I believe 3/8" across the wide part. It's not old but I've read that size does matter in regard to spinning the alternator. I'll try one with a little more heft."
 
"Check the pulley on the alte

"Check the pulley on the alternator for width. The belt must ride down in the pulley but not enough to bottom out. The belt gets it`s grip on the sides so unless the whole belt is within the pulley , it isn`t getting it`s maximum turning power.Putting a wide belt on a narrow pulley defeats the purpose, so to speak !!"
 
"Has the alternator been bench

"Has the alternator been bench tested for output? Is there any way you can measure the amps going to the battery? Just because it's fairly new doesn't mean it can't be faulty. There might be an open diode. Sometimes they blow open and you'll get reduced output, sometimes they'll blow closed and create a short and blow a fuse. There are inexpensive ammeters that you can put against the cable to get a measurement. Have you got a friend with a DC clamp meter? These are expensive to buy...$400 plus in some cases, so try to borrow one."
 
"The set point for the regulat

"The set point for the regulator is OK, but it won't achieve that voltage unless the output of the alternator is sufficient enough to increase the battery voltage to that set point in order to drop it to the trickle charge rate.

Could be the regulator's not tripping to allow a charge to flow.

So when the engine's running, what happens to the voltage if you turn on a pump or a light?

How much of a drop in voltage is there when you first crank the engine over?
And how fast and to what voltage does it recover?"
 
What is the voltage at the alt

What is the voltage at the alternator? Poor connections between the alternator and the battery could cause the low voltage at the battery as well.
 
"I appreciate all the suggesti

"I appreciate all the suggestions and comments. I removed the alternator and took it to the local Napa to see if they could bench test it. Apparently if the alternator isn't in their data base, they can't do it. Purchased a larger profile belt while I was there to see if it would make a difference. In the driveway with muffs, it was showing as high as 13.9V at the battery. When the weather clears up, I'll take the boat for another spin, see how it does with normal loading.
Thanks again."
 
I believe most 12 volt batteri

I believe most 12 volt batteries actually produce about 13.2 volts.(2.2 volts per cell x 6 cells). Charging voltage should certainly be higher if the alternator is functioning.
 
"Brian McWhirter
13.9v is in

"Brian McWhirter
13.9v is in the ball park for a properly charging alternator. Take into consideration your meter may be off a bit.
In a charging system, when the voltage is low it can mean the amperage draw is high and if the voltage is high it can mean the amperage draw is low. Which relates to a fully charged battery.
Bert"
 
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