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Old 15-03-2014, 13:18   #1
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Alternator/Exciter Question/Problem

Hi everyone,

I have a 80 Amp, Hitachi-type, internally-regulated alternator on my Yanmar 4JH4AE. Starting last fall, I noticed that the alternator didn't charge at idle (as in no output whatsoever), but since we view the alternator as a tertiary means of charging our batteries I didn't troubleshoot it. Now that I've finally got around to it, I'm stuck. Here's my observations:

No charge from alternator until approximately 1500-ish RPM. Then it jumps up to a reasonable charge rate (in my tests 60-ish amps, but I had fairly full batteries). Bringing the throttle back down, the alternator keeps charging a few amps at idle. Voltages are as expected- no odd voltage readings.

So, my initial thought was there was an issue with the exciter wiring. however, the "battery" light stays lit on the engine panel until the alternator starts putting out amps. I unplugged the back end, "T" type connection for the S and L terminals, and the L (lamp) terminal puts out the battery bank voltage (with very minimal voltage drop) when I turn the key to the "on" position. In other words, I feel good about the wiring for the exciter input to the alternator.

This leads me to believe that there is an internal issue with the alternator, and that the exciter wiring inside the alternator is faulty. When I get to 1500-ish RPM, the alternator self-excites, so that is why the output appears to be okay from that point onward.

Of course, I want to double-check with the gurus here to get other opinions. Like I said, I can always juke the engine up to 1500 RPM, but at the same time I like things to work properly. Can this be fixed, or is this a time-for-a-new-alternator type situation? Keep in mind this alternator set me back all of 80 bucks, so any repairs approaching that amount wouldn't be worth it.

Thanks for the inputs!

Frank
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Old 15-03-2014, 13:46   #2
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Re: Alternator/Exciter Question/Problem

Be sure those terminals are clean both on the receptor and the alternator. Once you take it to 1500 rpm and it starts charging... can you back down the rpm and it still charges? Also.... are your batteries already pretty charged? maybe it's sensing too high voltage to kick in...? Run your batteries down overnight or fo r a day and try it.
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Old 15-03-2014, 14:13   #3
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Re: Alternator/Exciter Question/Problem

Frank,
Your tests and analysis covers about everything I could suggest. The only source of the problem that I can think of is, as Cheechako posted, corrosion on the terminals or internal to the alternator.
I believe the excitation circuit internal to most alternators is common with the rectified output of the diode trio. Since you get normal output from the alternator that circuit must be intact. Corrosion could reduce the excitation coming from the key switch to less than that needed by the field circuit (< 1 amp, normally).
I have never taken an alternator apart so I don't have any advice on what to do if you decide to pop the casing open.

Good luck,

John
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Old 15-03-2014, 14:58   #4
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Re: Alternator/Exciter Question/Problem

It may well be the solenoid.
Sorry about the crappy photo below, but i had the hold the ipad and the torch and try and push the button.
These solenoids last about 2 years, max, for me and then die in the butt.
The Cole Hearse ones are bloody expensive but I got some excellent cheap ones from a sports fishing boat shop in Key West. I think less than $20?? The sport fishing guys use them a lot.

You need the 200 amp continuous duty rated one. NOT the 85 amp, or the Intermittent ones.

Change it over and if that fixes it buy a spare

I don't understand what they do or how they work but its something to do with the switching between the starter battery and the house bank. When you start the engine if the solenoid isnt working properly it does what you say.
Oh, there is a way you can sometimes check if its the problem... Start the engine at idle, then go down and bang it with a wooden spoon from the galley (dont tell the wife) they will often come on then.

I charge at 1,200 rpm, not at idle.

Hope this helps.

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Old 15-03-2014, 15:25   #5
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Re: Alternator/Exciter Question/Problem

Thanks for the input, guys! the terminals looked good and clean, but I hit them with a wire brush just to make sure. Mark, where is that solenoid?? Do you have the 4JH4? Do you think it might be an ex-charter thing?

Frank
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Old 15-03-2014, 15:44   #6
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Re: Alternator/Exciter Question/Problem

Quote:
Originally Posted by GeoPowers View Post
Thanks for the input, guys! the terminals looked good and clean, but I hit them with a wire brush just to make sure. Mark, where is that solenoid?? Do you have the 4JH4? Do you think it might be an ex-charter thing?

Frank
Hi Frank,

I thought it was a Beneteau thing, but I'm not sure. Mine is a 4jh3e and the boat is a French built 2001 model.

Its high up in the engine compartment on the small facing firewall above the engine. So when you open the engine bay look up as high as you can. If its not there, i guess you dont have one, or uses another device.

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Old 15-03-2014, 15:54   #7
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Re: Alternator/Exciter Question/Problem

All alternators do not start charging when you first start the engine. Most will not start charging until the engine reaches 1100-1200 rpm. Then it is best if you are not underway with the engine to keep a load on it by keeping the rpm's between 1000-1500 until the charging is done. The worst thing to do is to let a diesel engine idle for any length of time without a load on it. Diesels engines require internal heat, meaning water temp to be at least 120 deg before putting them under a heavy load. This is why we are seeing many diesel engines at the end of their lives with only 1200-2500 hrs on them instead of the 10k-16k hrs that they should run. This is a problem found mostly on sailboats and will continue to happen until everyone understands what they are doing.
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Old 15-03-2014, 16:48   #8
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Re: Alternator/Exciter Question/Problem

If the indicator lamp (alternator light) is changed out to a globe of higher wattage it will act as a bigger resistor and also cause these symptoms.
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Old 15-03-2014, 17:43   #9
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Re: Alternator/Exciter Question/Problem

Well...nothing lasts forever, especially in the salt-water environment. Could be the brushes sticking. Bad connection. one bad diode. The list goes on. They are cheap to rebuild if you use an automotive rebuilder. Less than $100. With that you get new bearings.
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Old 15-03-2014, 18:06   #10
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Re: Alternator/Exciter Question/Problem

I don't think there is anything wrong. Lots of alternators need a few revs to "kick" in.
Some regs have a delay to disallow charging during starting.
If you start, and then give it a rev, the charge starts, then if you idle, it trickles a few amps...Now stop it and start it again, slowly increase the revs, does it charge more and more as revs increase? then it is fine...
Alternators are not rocket science. There is an electromagnet inside on a thing arranged like knitted fingers. This is called a claw pole. One line of fingers is + the other -, that flies past the stator coils and makes AC electricity. The regulator determines how much electricity it makes by varying the amperage (voltage) to the claw poles. You might have dirty brushes or slip rings, so it needs a bump to get the volts high enough to pass the resistance of the dirt.
Get a hold of a multimeter and measure across the field contacts, or the F terminal to ground, you should get zero ohms, if its high, it needs a clean up and service.
Good luck
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Old 15-03-2014, 18:10   #11
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Re: Alternator/Exciter Question/Problem

I'm assuming that this behavior is different than it was before, because most alternators do not put out much, if any, amperage at idle speeds unless the pulley ratio is very high.

If it did use to give good output at idle, have you checked for belt slippage? A glazed or loose belt might slip at idle but seat well at higher rpm's and stay seated when the rpm's are lowered.

Mark
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Old 15-03-2014, 18:10   #12
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Re: Alternator/Exciter Question/Problem

IMO, the rectifier is blown. As with most alternators of this type, no parts available. Replace it for ~$200.

This alternator should put out at least 20a at engine idle.
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Old 15-03-2014, 18:32   #13
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Smile Re: Alternator/Exciter Question/Problem

Alternators will start charging about 2000-3000 rpm
Different makes & models at different rpm
Is your rpm enough below 1500rpm on engine ????
I suspect you have a 2-1 pulley ratio ?
Most alts have a redline of 10,000 plus.
You could change your pulley ratio ?

I don't know if this is the answer but is
Definitely worth checking !!!!
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Old 15-03-2014, 20:03   #14
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Re: Alternator/Exciter Question/Problem

Quote:
Originally Posted by MarkJ View Post
Hi Frank,

I thought it was a Beneteau thing, but I'm not sure. Mine is a 4jh3e and the boat is a French built 2001 model.

Its high up in the engine compartment on the small facing firewall above the engine. So when you open the engine bay look up as high as you can. If its not there, i guess you dont have one, or uses another device.
Nope, I don't have what you've got. But thanks for the assist!

Frank
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Old 15-03-2014, 20:12   #15
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Re: Alternator/Exciter Question/Problem

Thanks for all the other comments. I did check belt slippage when the problem first appeared, but no luck there. Since nothing else changed, and it did have a small output at idle RPM before, I'm thinking it must be the internal bits of the alternator. As it is now, my battery monitor is reading -3-ish amps when the engine is at idle, which is probably from the blower running and incidental loads.

Frank
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