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Old 29-11-2017, 04:47   #16
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Re: Puzzled by new alternator low output

Greetings and welcome aboard the CF, jreyn.
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Old 29-11-2017, 08:44   #17
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Re: Puzzled by new alternator low output

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Originally Posted by LifePart2 View Post
Wow, three answers already! Thanks!

I am pretty sure the single belt is not slipping. It is not getting particularly hot. Nor is the pulley. It is a brand new belt - do they take a little time to settle in? i know I had to retighten it alreay.

The batteries are at about 50% - sitting at about 13v. When full, they sit at 13.2v

Yes it is the 39 hp yanmar. It should be able to handle the hp drawn by the alternator easily. I get that the belt might slip, so I was watching for that. But I don't think it is the case. Also, I had the previous alternator running at 70 amps without any belt problems, also on a single belt. As I said, I am only looking for 100 amps from this one. Even 70 would be good. Being rated much higher than that, it should be able to handle the lower output for long periods.

I know the built-in regulators are not as good but still I am surprised that it is only putting out 40amps. The current is unlikely to be dropping as a result of the internal resistance of the battery, as the LiFePO4 can take high current right up to full charge, unlike the lead acid that gets slower and slower. So I guess it must be the regulator dropping the charge? Yet it is still well below the 14 v set point of the regulator.


Noel
If I remember correctly, Balmar recommends a double belt or serpentine above 90 amps. Your 180A is way too big for a single belt setup. From the Balmar web site:

“Balmar 6-Series Alternators from 70A-100A can perform with a ˝” Single Vee pulley. If you need to charge above 100A, then you will need a Dual Vee or K6 Serpentine pulley system to be present on your engine to avoid a pulley upgrade. If a Dual Vee or Serpentine is not present, then an AltMount® Conversion Kit is required.”
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Old 29-11-2017, 09:07   #18
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Re: Puzzled by new alternator low output

How big is the alt cable, pos and neg, from the alt to house bank? And what is the voltage at the back of the alt, (pos and neg at alt) and at the batteries while running. Measure both.

With a 180a alt. You should probably be 2/0 straight from alt to battery.
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Old 29-11-2017, 09:34   #19
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Re: Puzzled by new alternator low output

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Originally Posted by smac999 View Post
How big is the alt cable, pos and neg, from the alt to house bank? And what is the voltage at the back of the alt, (pos and neg at alt) and at the batteries while running. Measure both.

With a 180a alt. You should probably be 2/0 straight from alt to battery.
smac speaks my mind. Also check for losses at the alternator terminal. This is a sticky wicket because the stock terminals are really too small for the size cable that is needed, so they often work loose. Grease helps prevent corrosion but worsens the "working loose" problem. Some high-amp rebuilders use a nonstock oversize terminal, which helps.

The best thing to do is run welding cable or some other highly flexible stranded cable to minimize the stress on the terminal. Then you can run 2/0. You should also be running 2/0 from the alternator case to the battery -- don't rely on a ground connection through the engine block at these amperages.

All the terminations matter a great deal in this situation, be sure everything is clean and properly crimped and torqued. An IR thermometer will show up bad connections. Check both the + and ground.
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Old 29-11-2017, 12:04   #20
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Re: Puzzled by new alternator low output

Valuable stuff here to be sure, but you guys realize this is a resurrected zombie thread right?

The OP posted ten months ago, problem probably been solved by now!
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