alternator volts vs. amps - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 09-26-2011
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alternator volts vs. amps

Just got back from the boat this weekend. house batteries needed tobe charged with the Honda 2000. I've been running the engine and the volt meters show 13.5 to 14 volts output but when I put the amp meter to the alternator output wire it reads just 1.13 amps - not much and the batteries are down in amps. After using them all nite, tv, lites, fans they read 12.2 volts. I would think the 130 amp alternator would really be putting out its amps to bring them up. Voltage regulator, diodes, what could be wrong? Next step is to take it off and bring it to the battery guy.
chuck
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Old 09-26-2011
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Might be the regulator not calling for the alternator to charge, what kind of reg. do you have? Doesn't sound like an alternator problem as it's putting out the correct voltage, just not many amps (someone more knowledgable might be know if a diode problem could cause that).
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Old 09-26-2011
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thank you, Dancer
its an internal regulator . looks like its got tobe taken off an checked.
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Old 09-26-2011
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I'd check the voltage at the alternator output and compare it to the voltage across the battery terminals before you pull the alternator out. If there is a big drop, there is a poor connection, and it would produce your symptoms.
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Old 09-26-2011
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Amps are a measure of load (smaller resistance the more load)...

There isn't enough load (open circuit), meaning what Don said it true. Sounds like you have either A) a poor connection (open circuit, or poorly connected circuit) B) a huge resistance in line. C) Voltage reg is bad, and can't supply enough juice to send to the battery.
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Old 09-26-2011
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"but when I put the amp meter to the alternator output wire it reads just 1.13 amps"

Are you using a clamp-on DC ammeter? Or opening the circuit to properly put a normal ammeter IN SERIES in the output?

It just sounds like there may be some confusion about what or how you are measuring. If the connections are clean and the measuring is right, it is shop time. Even at idle, it would be a crude old regulator that put out 13.5-14v as opposed to 14.4 measured at the alternator output or the battery terminals. (Both locations will be the same IF the alternator sense lead is connected to the batteries properly, as it often isn't on a boat.)
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Old 09-26-2011
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I have the harbour freight clamp over the alternator wire and read on the 40amp setting.
which was 1.3 amps. its gotta come off and go to the shop.
thank you for the replies!
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Old 09-26-2011
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Chuck,

Before you pull off the alternator, it would really be wise to:

1. check that ALL connections and ALL connectors are clean and tight;
2. ensure that the belt to the alternator is properly tensioned;
and
3. measure the voltage at the battery while the engine is running.

What size wire do you have from the alternator positive terminal to the battery. Does it go to the starter solenoid? To the 1-2-OFF switch? To the battery directly? Which battery?

Be especially careful to check the ground connections. If the alternator doesn't have its own negative cable to the battery, it should have. Often, connection to the engine alone presents too much resistance in the circuit for proper charging.

Also, if you haven't used the Harbor Freight clamp-on ammeter before, try to find a DC circuit where you can verify its proper operation. It should be on the DC range, and clamped around ONLY ONE wire in a pair, not both.

I'd do these things before pulling off the alternator; it could be just fine.

Bill
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Old 09-27-2011
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Quote:
Originally Posted by chuckg5 View Post
Just got back from the boat this weekend. house batteries needed tobe charged with the Honda 2000. I've been running the engine and the volt meters show 13.5 to 14 volts output but when I put the amp meter to the alternator output wire it reads just 1.13 amps - not much and the batteries are down in amps. After using them all nite, tv, lites, fans they read 12.2 volts. I would think the 130 amp alternator would really be putting out its amps to bring them up. Voltage regulator, diodes, what could be wrong? Next step is to take it off and bring it to the battery guy.
chuck
The regulator's job is to regulate voltage (to the extent that it can regulate current it does so by lowering voltage) so if you're reading 13.5 to 14V then it sounds like the regulator is doing just fine. A busted regulator would show a low voltage. You can't present 13.5 to 14V to a discharged battery bank without the bank drawing current. It sounds to me like you have a problem elsewhere, or you have a problem with the amp meter. Did you do some verification? I.E. shut off the motor and make sure the meter reads 0, turn on some base loads (lights) and check for the expected current?
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Old 10-19-2011
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are you sure the amp meter is rated to measure DC current?
most clamp on don't measure DC..they measure AC current..

other wise..check the stuff others mentioned..poor connections to start with.
what happens if you put a 55W light across the terminals. think a spot light?
does the current go up? voltage change? if the regulator is working the voltage will not change much but the current will go up.

-dkenny
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