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Charging at idle ?


Fusion

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I have an issue at idle (500rpm) my alternator seems to suck the power? After a good hour of motoring and the voltage has been up to 14.4V then sustained @ 13.6V. As soon as I throttle back to idle and drop the pick (5 min) the voltage pulls down to 12.4V. If I switch off the ignition as soon as I throttle back the batteries sit at 13.1 for ages. Is my alternator faulty? Low revving Perkins 5 it's at 1000 RPM, 6.5 & 1300 and 7.5 @1600 . 1850rpm max and gigs a hole.

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Fusion, I don't think the problem will be the Alt exactly. Hmmm, in fact I am at a bit of a loss with this one, because if we are talking about good batteries being pulled down that much in a few minutes, that is an enormous load. So.....First question is, no second wuestion. First Q is as asked before.

Has this got a multistep Alt charge controller?

What size battery bank are we talking?

Have you found the batteries not peforming as they once used to?

 

At first thoughts, I don't think the problem will be the Alt. They either charge properly or poorly or go Open circuit. I can't think of anything that could allow the Alt to charge and then end up sucking up the juice again.

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before this problem if you dropped pick with engine idle, then turned off, after say 20 mins minimum load what would the batteries sit at?

 

my batteries quickly move to 12.85-90 they are two huge gels , only about two years old. if they where going to 12.4 in 5 mins I would be concerned, it would take a massive load to cause that, do you have an in line amp meter to show what the drain is during this 5 min period?

 

do you use a windlass in reverse to drop anchor? dumb question but got to ask.....

 

is it just house batteries or house and starter (do you run them parrallel or isolated?

 

cheers

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If you have a charging relay that links the house & starting banks with engine running you may have an issue with a crook battery. Which bank is the voltmeter monitoring? Does the charge light come on at idle? What is your battery configuration?

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I think the fourteen.2 and 13.6 are two stages of the charging voltage. Normally the third stage will be at about 13.2. That is the charge going in.

The 13.2 will show when the motor is stopped. But some of it represents a surface charge that will dissipate over a day or so with no use and more quickly if you are using some power. You also get lower charge level apparent if while charging you are using some power.

Normally the issue is the resulting voltage after the surface charge has gone. Since the final float charging the third phase is very slow taking about ten hours one generally only gets about 80% of full around 12.65.

It depends on what the initial voltage is how much an hour of motoring will bring up the batteries to an enduring voltage.

What you are describing seems to be that the v shows 12.four (my four key has quit) if you anchor and continue idling. That suggests the battery is at that and the alternator is not charging at idle (I don't know that it should be but you can check what happens when you increase the speed) and that there was no surface charge because either you used the battery to lower anchor or more likely had some things running like vhf gps. This should be the higher of the battery or the alternator. That v is not very highly charged and suggest it was originally well down.

The second scenario is switching everything off and it drops from 13.6 to 13 .2 where it stays for some time. That initial drop is normal and then it will go more slowly. What level is it at after a day?

I suspect you may not be comparing two equivalent scenarios apart from whether the motor is idling.

I suppose it is possible you have a current draw while the motor is idling and you could maybe check for that.

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how about at marine or mooring run engine for a while idle back and disconnect battery, turn engine off and monitor the battery, if you can then put a known and external load onto the battery say a 3amp light or such like and just verify that its not the actual battery thats crapped out....

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Hi ya,

is the voltage the same with engine on and Idle and engine off but ignition on ?

 

With engine off and ignition on you can drop the positive off the battery and measure with a multi metre the current draw.

Make sure you have the leads in the right slots on the metre to measure high amps...

If everything is off except engine electrics, and the draw is high, then look to see what may be connected straight to the ignition key. You may even have a minor short.

I get point one of a volt drop in this case. It is about what I would expect because you are powering up the guages and a very small draw to the alternator.

Note * dont disconect the alternator (or a bat connection) while the engine is running, you may kill the field windings of the alternator.

Your alternator is obviously putting out some current and the top end charged voltages are fine.

Do you have an electronic connector between your engine and house battery (combiner/isolator) or similar?

One possibility is one of the windings on the alternator is shorting. To check this, loosen the alternator belt, turn ig on, and then slowly turn the alternator pulley by hand. If it has a short the volt meter will "bounce".

cheers

Martin

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