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Old 01-25-2020, 04:44 PM   #1
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Alternator Mainship

HI, I have a 2006 Mainship Trawler 34 with single Yanmar 315.
I find upon starting that the alternator gets very hot and does not start charging batteries for about 8 - 10 minutes.

Does this engine have a block heater that draws all current from the alternator til engine is warmed before charge goes to the batteries or is there some other issue?
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Old 01-25-2020, 04:53 PM   #2
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Slipping belt or shorted diode causes this.
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Old 01-25-2020, 05:31 PM   #3
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Are you sure it is a 315 hp Yanmar. AFAIK, the Mainship 34T was built with the Yanmar 6LY 370, an occasional Cummins 370 or twin Yanmar 240s.

If it does have a Yanmar 370 then it has an intake air heater that draws about 60 amps for a few minutes until the engine warms up. During that period it will put a severe load on the alternator. You will usually notice low voltages of 12 or so until the heater kicks off, then the voltage jumps to 13 or more.

If it really is 315 hp there are two possibilities. One is a detuned version of the 370 with a DTE suffux or maybe a UTE suffix such as 6LY-DTE. This one also has an air preheater. The other possibility is a Yanmar 6LP of 315 hp. I don't think that one has an air preheater.

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Old 01-25-2020, 07:19 PM   #4
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yes, definitely Yanmar 315 6LPA engine number M57495
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Old 01-25-2020, 07:21 PM   #5
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Belt not slipping. Diode has been replaced with a VSR.
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Old 01-25-2020, 07:42 PM   #6
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Ok, it is a Yanmar 6LP. Not sure if it has an air heater. Does your voltage stay low after starting and then jumps up after a few minutes. If so, it probably does have an air heater.

What you are experiencing is entirely normal. If it is like the 6LY you can get blanks to replace the heating coils from Yanmar. Or just cut off the coil with side cutters. It isn't necessary for starting, just to limit initial smoke.

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Old 01-25-2020, 09:04 PM   #7
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Quote:
Originally Posted by DavidM View Post
Are you sure it is a 315 hp Yanmar. AFAIK, the Mainship 34T was built with the Yanmar 6LY 370, an occasional Cummins 370 or twin Yanmar 240s.

If it does have a Yanmar 370 then it has an intake air heater that draws about 60 amps for a few minutes until the engine warms up. During that period it will put a severe load on the alternator. You will usually notice low voltages of 12 or so until the heater kicks off, then the voltage jumps to 13 or more.

If it really is 315 hp there are two possibilities. One is a detuned version of the 370 with a DTE suffux or maybe a UTE suffix such as 6LY-DTE. This one also has an air preheater. The other possibility is a Yanmar 6LP of 315 hp. I don't think that one has an air preheater.

David
My 6LPA-STP has two air heater coils.

For the purposes of troubleshooting, try temporarily pulling the wires from them and tape them. Start the engine to see if the problem persists. If it does, the timers associated with the coils are NOT the problem. If the issue goes away with this troubleshooting method, the heater timers are the problem.

Since the heaters are simply there to avoid heavy smoking at the first moments after startup, some have simple removed the coils which by the way can corrode and get sucked into the cylinders causing catastrophic damage. I check mine twice a year for integrity.
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Old 01-25-2020, 11:19 PM   #8
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Belt not slipping. Diode has been replaced with a VSR.


I think you are confusing a diode isolator with the "diode" David Marchand mentioned.

The diode D.M. mentioned is internal to the alternator with 5 others which turns, rectifies, the AC into DC.

The diode isolator literally isolates the battery sets so the alternator can charge them but they are isolated from discharge when the alt. is off.
But that isolator has nothing to do with the actual alternator itself.
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Old 01-26-2020, 12:45 AM   #9
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Thanks for all the info guys.

Yes, immediately after starting the engine the battery drops tp 11.9v to 12.0 v and stays there for several minutes and the alternator gets very hot to the touch.
A few minutes later the batteries start showing normal charging voltage, 13.9 or more.
So is the heating within the engine controlled by a set time or is it by temperature?

Where do I find the heating coils, and if I disable them does the battery then receive charging immediately the engine is started?
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Old 01-26-2020, 06:58 AM   #10
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I can speak about the Yanmar 6LY, but apparently the 6LP is the same. The coils are in the intake after cooler and sit on top of it. You can unhook the wires to them and see if it makes any difference in smoke. With them unhooked the voltages and alternator will act normally and the voltage should immediately rise to 13+.

They unscrew from the top of the after cooler and it sounds like they are the same as the 6LY so you can replace them with a blank plug you can buy from Yanmar. Or you can just clip the coil so it won't be in danger of corroding and breaking loose someday.

I believe that the coil is controlled by engine temperature. Mine takes about 5 minutes to turn off in warmish ambient temps.

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Old 01-26-2020, 09:48 AM   #11
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The original comment of ďvery hotĒ drove my response. Metal at 70deg and above could be viewed as very hot to the touch, but without a shot with an IR thermometer, it is just a guess. I suppose over 90 deg C would flag an issue to me. Before, during and after current Amperage readings would be most useful.
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