Charging Sytem Problem?

[johnmurray]

In a previous post I asked for advice on replacement batteries and I thank those who gave me some answers. In the end I was able to find 4Ds, similar to the original batteries that came with my new 2005 A-FC and I had them installed a couple of days ago. 10 years was a good run for the original batteries!
After the new battery installation my mechanic noticed that my alternator was running hot and the voltage displayed was less than the expected 13-14 volts. He then changed out the aternator on the assumption that it was defective, but the new alternator displayed the same symptoms as the old one.
Does anyone have any insights as to what the problem might be or can some diagnostic steps be suggested?

[mike66]

Do you have a separate regulator from the alternator? My first inclination would be to check all your wiring for good connections and corrosion around the terminal lugs. Sometimes the ground connection can be overlooked. Are your battery banks connected by a switch? Isolate just the engine start battery while testing the voltage to take the others out of the equation.

[mike66]

Another couple thoughts..measure voltage at the alternator terminals and at the battery terminals...should be close to the same. Excessive voltage drop would be a bad wire. Also jumper cables could be used between the alternator and the battery to see if your voltage at the battery while charging increases. My voltage regulator has a feature where the alternator output is reduced for a few minutes on startup....make sure you give the system time to come up to voltage while testing.

[johnmurray]

I think I found the answer to my problem after researching the archives on this site.
It appears clear that, as described in the Albin archives, there ia an electric heating feature that is part of the Yanma 6LPE warmup process that causes a voltage drop during that warm up, and then the voltage goes to normal once that heater cuts out, usually five or ten minutes after start-up. If one is not aware of that feature, then a voltage check on a cold engine as soon as the engine was started would show an abnormally low voltage and lead to the conclusion of a faulty alternator. After installing my new batteries, my mechanic checked the engine and noticed a low voltage reading so he assummed a faulty alternator and did a replacement. With the new alternator, the start-up voltage was still low, but as we know now he did not wait long enough for the engine to warm up a bit.
I went down to the club yesterday and checked the engine again but this time I gave it some warm-up time. After 10 minutes at a fast idle, the volt meter registered 14. When I dropped the engine speed to a slow idle the volts dropped to about 12.5 -13. When I goosed the engine the volts went back up to 14.
I think that is the way it is supposed to be and the way it has been since day one, although I can't say I had ever checked the volts before the engine was warmed up a bit. My boat now has an unecessary new alternator, I am $500. poorer, but may be a little wiser!

[mike66]

Unless you want to stay on good terms with your mechanic at all costs, why are you paying for the new alternator? Glad you found the reason for the low voltage.

[Dudley]

where can you get a new alternator for $500. I got a quote yesterday, 1-2-15 for a Yanmar Alternator, $1,800. a chineese after market is $180.00.

[johnmurray]

My mechanic purchased the alternator from a local auto-electric supplier here in Ottawa and I think it was the same kind that came with the boat when it was new, but not a Yanmar part.
By the way, I have dealt with the same mechanic for about twenty years and we have given each other breaks over the years so I did not make an issue over the unnecessary replacement. As a matter of interest, before purchasing the replacement my mechanic called the local Yanmar dealer (who has the same Yanmar engine in his own boat) and the dealer apparently did not know about the start-up voltage drop issue either.
Alls well that ends well...Happy New Year!

[Dudley]

after starting the engine I have always noticed that it takes 3 minutes for the alternator to start charging. I can only check the voltage with the GPS. Somewhere I read that this is a feature of the 6LPA-STP.

[ScubaPete]

after starting the engine I have always noticed that it takes 3 minutes for the alternator to start charging. I can only check the voltage with the GPS. Somewhere I read that this is a feature of the 6LPA-STP.

I don't know much about Yanmars other than my generator engine, but on Cummins, there is a heating coil that preheats the intake air for better starting and less smoking on cold days. That heater draws a lot of current and the voltmeter will drop down to around 12v or less when it's activated. Once it cycles off, the voltage at the helm will read 14v again. The alternators are working and charging the whole time, but apparently the heaters draw more amps than they can keep up with, so the system runs at a deficit (below 12v) for a short while.

[Dudley]

the problem with my 6LPA-STP was indeed the preheaters for the intake air. There is a relay on the top of the engine that engaged and never disengaged. In the past it worked perfectly. I would start out and the voltage would stay at 11 volts and then after 2 minutes the voltage would suddenly jump to 13.5 volts. I thought it was caused by the alternator not being turned on until the engine heated up. I thought that the alternator would cause so much drag on the engine when it was cold that the relay kept it from activating until the engine was running at full efficiency. What an ordeal it put me through. The mechanic simply unplugged the connector to the relay on top of the engine and my voltage jumped up to 13.4 volts. I can live with the engine smoking until it warms up by itself without draining my batteries. Has anyone set up a push button to activate the heaters so we do not have to rely on a timer that can malfunction?

[Halcyon]

My 6Lps do the same voltage thing. I had the heaters replaced because I was told when they get old the elements break and the little buts enter the intake air. The motors have 2 each and I paid $50 each for the part. Replacing them seems like cheap insurance. I did not notice a reduction in start up smoke so I guess my old ones were OK.