What volatage should I expect from my alternator?

Tim Good

Tim Good

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A decent bulk charge should be kicking out in excess of 14v right? So unless my batteries are full shouldn't my alternator be doing the same?

I tried disconnecting the solar panels in case it was confusing things but it still only reaches about 13.7v under engine.

Thoughts?
 
northcave said:
A decent bulk charge should be kicking out in excess of 14v right? So unless my batteries are full shouldn't my alternator be doing the same?

I tried disconnecting the solar panels in case it was confusing things but it still only reaches about 13.7v under engine.

Thoughts?
Click to expand...

I would say that 14.4 is ideally the minimum you should hope for but whether your alternator/regulator can achieve that depends will depend upon it's design.

Richard
 
Where are you measuring that voltage? On the alternator and to engine block for -ve, or at the battery posts?
 
northcave said:
A decent bulk charge should be kicking out in excess of 14v right? So unless my batteries are full shouldn't my alternator be doing the same?
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I think there is possibly some misconception here.
Bulk is by definition what the alternator does before the voltage set point has been reached, that is the current is limited by what the alternator can put out or by RPM or possibly by what the batteries can absorb.
Once the set point has been reached the current is limited by the voltage regulator, which means you move into absorption charging.
So 13,7v could well mean that a decent bulk charge is taking place, provided that the batteries had been well discharged before it started. But if the voltage does not continue to climb as the charging proceeds, it could mean that the set point is too low, resulting in a very long charging time. As mentioned, 14,4v is often recommended as set point.
All in my humble opinion.
 
Older alternators charge at about 13.8v so if you have an older alternator it's doing what it was designed to do. It isn't doing as good a job as a modern alternator so you my want to look into fitting an advanced alternator regulator.
 
Make and model of alternator would be helpful. I had one on my seagoing boat that maxed out at 13.7 volts - I ruined a lot of batteries very quickly with it :(
 
northcave said:
... it still only reaches about 13.7v under engine.

Thoughts?
Click to expand...

How have you measured the voltage? If the batteries are still receiving a charge, the system voltage will be reduced. Once the batteries are fully charged, and are receiving almost no current, the voltage will rise to the alternator's set voltage. If this is less than 14v, you will probably achieve some benefit by fitting a "smart" regulator.
 
PaulRainbow said:
Older alternators charge at about 13.8v so if you have an older alternator it's doing what it was designed to do. It isn't doing as good a job as a modern alternator so you my want to look into fitting an advanced alternator regulator.
Click to expand...

Do you meant a regulator in conjunction worth my old alternator or just a new alternator with a regulator?
 
Silly question here - the alternator puts out more charge the higher the revs go right? But is it a linear, I mean do you get 80% of its charge power at 900 revs or only 33% assuming max revs are 2700?

I ask because when we run the engine to charge and heat the water, how fast do we need to run it?
 
Colvic Watson said:
Silly question here - the alternator puts out more charge the higher the revs go right? But is it a linear, I mean do you get 80% of its charge power at 900 revs or only 33% assuming max revs are 2700?

I ask because when we run the engine to charge and heat the water, how fast do we need to run it?
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In the Olde days of dynamo's you had to rev the engine to get more charge. Alternators don't work in the same way. You'll typically get 75-80% of the output at around 2000 RPM. A fast idle is a good engine speed for battery charging. Not too much noise, not too much fuel and most of the charge output.
 
Colvic Watson said:
Silly question here - the alternator puts out more charge the higher the revs go right? But is it a linear, I mean do you get 80% of its charge power at 900 revs or only 33% assuming max revs are 2700?

I ask because when we run the engine to charge and heat the water, how fast do we need to run it?
Click to expand...

Alternator manufacturers publish output curves which show how much current the alternator can deliver at different revs. Typically, the output current rises fairly quickly and then levels off with increasing revs. You might reasonably expect 50% of max current at perhaps 30% of max revs. The attached graph shows output curves for some Prestolite alternators. Note that the speed refers to alternator revs, not engine revs (most alternator pulleys allow the alternator to spin at 2-3 times the engine revs).

Of course, the fact that the alternator is capable of generating a certain current doesn't mean that the batteries can accept that current - they may, or may not, depending on the battery bank's size and its state of charge.

View attachment 58149
 
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1st off i'd clean all the battery and alternator connections, connect your meter direct to the battery posts with engine running at about 1200 rpm. Note the voltage.

Now move one lead at a time to the battery connector looking for any drop in voltage.

Measure at each side of the battery isolator switch, looking for a ssignifi ant voltage drop.

Before you buy anything, I'd suggest you try a known good car battery, disconnecting what you have for this test.

That way you can discount a faulty battery cell pulling down the charging voltage.

Alan
 
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