Tachometer Reading from Alternator

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Tachometer Reading from Alternator

Postby Skip on Sat May 14, 2011 4:35 pm

I have an Ample Power alternator Model# APC-4023-S with A Smart Alternator Regulator V3. My engine is a Yanmar 4JH4AE. Recently I have had a couple of episodes with unusual revs on the tachometer. Once when I was running at 2500 rpm the tachomter pegged itself at the high end. I brought the engine down to idle and the revs then showed normal. I increased rpm gradually back up to 2500 and all was fine for awhile before the tachometer pegged itself again. The first time this happened I had been at a stady 2500 rpm for about an hour. Last weekend about 15 minutes after the engine was on when the engine was between 1200 and 1500 rpm the tach shot up to 2500 rpm. When I slowed the engine to enter the harbor the rpms then resumed reading normal. Can you explain what may be causing this and a remedy fot the situation?

Thank you.
Skip
 
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Re: Tachometer Reading from Alternator

Postby Coulomb on Sun May 15, 2011 2:39 pm

Are you sure the alternator is driving the tach? We thought Yanmar engines have a separate tach pickup.
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Re: Tachometer Reading from Alternator

Postby Skip on Sat May 28, 2011 7:44 pm

I was under the assumption that the tachometer was driven by the alternator so I will have to check this out more before I get back.

Skip
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Re: Tachometer Reading from Alternator

Postby Skip on Tue Jul 26, 2011 12:46 pm

The tachometer does receive it's input from the alternator. There is no flywheel reading for the tach. Any ideas on what might be causing this? Again the tach is fine up to between 1200 and 1500 rpms where the tach starts bouncing around alot. Beyond those rpms the tach will peg itself at 5000 rpms. Normal cruising rpm for my engine is 2800rpm.
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Re: Tachometer Reading from Alternator

Postby Coulomb on Wed Jul 27, 2011 4:05 pm

Read this first:
http://www.amplepower.com/primer/tach/index.html.

Applying an electrical load will make the alternator produce more and tach signal will thus be stronger.
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Re: Tachometer Reading from Alternator

Postby Skip on Tue Aug 09, 2011 6:02 pm

I spoke today with the Technical Support Services Manager at the Boatswain's Locker which represents Yanmar on the west coast. I described the tachometer symptoms to him as I did to you. He says that the Yanmar tachometers come from the factory set up to be driven by the alternators. He says that it is possible to take the reading from the flywheel instead of the alternator but that it usually is not a problem to have the tachometer driven by the alternator. Based on the present symptoms and that I had no probems for the first year and a half that I had my present Ample Power set up and the tachometer problems started six monthes ago the service manager thinks the problem is coming from the alternator. That possibly being the case would it be best for me to send my alternator back to Ample Power to see if there is a problem with the alternator?
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Re: Tachometer Reading from Alternator

Postby Coulomb on Wed Aug 10, 2011 4:51 pm

There's nothing in the alternator that would change. The tach signal is derived from one of the stators.

Have you tried to increase the load when the tach is dropping out?
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Re: Tachometer Reading from Alternator

Postby Skip on Wed Aug 24, 2011 9:54 am

I had a mechanic down to my boat yesterday and he took some readings from the alternator using a computer system made by Snap On tools. The reading was spiking all over the place above and below flat line. Bringing the rpm's up when the tachometer started to bounce around, the scope reading would flat line. He took the alternator off and we took it into a alternator shop. The shop said the diodes were bad.
My question now is may I possibly be overloading the alternator? I am using the alternator to charge a 675 amp hour battery bank of Lifeline AGM batterues. Again my alternator is a APC-4023-S. Is this alternator too small for my battery bank? If not, what might be another cause for the diodes failing with only about 120 hours on the alternator?
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Re: Tachometer Reading from Alternator

Postby Coulomb on Wed Aug 24, 2011 10:27 am

We're skeptical about the diodes being bad, especially if the alternator was otherwise charging normal. They can be tested easily with a simple digital meter. Get the old ones back and test them or send to us.

Did they replace the stator too? Commonly when a diode fails it short circuits and the stator gets too hot and melts the insulation.

Do you have a 1-2-both switch on the boat?
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Re: Tachometer Reading from Alternator

Postby Skip on Thu Aug 25, 2011 8:50 pm

At the time that the mechanic was on my boat 2 days ago testing the alternator, he pointed out to me that the alternator was not charging normally. The voltage was going up and down and the amps coming out of the alternator would sometimes completely cut out. So sometimes it was charging at a reduced level and sometimes not at all. I do have three battery switches on my boat. They are: 1. Engine 2. House Bank 3.Crossover to connect them together if my engine battery were to fail.
Later that day at the alternator shop the owner of the shop put my alternator on a machine that runs the alternator. I was a distance away from him but it looked like he touched some test eqipment to something on the alternator and he said the diodes were bad.
Yesterday when I picked up the alternator the shop owner told me he also replaced the stator because that was also not good. He showed me the old stator, which I took with me and have. I did not ask for the old diodes. He also said that when he opened the alternator case to replace the diodes he saw that one of the stator wire connections was contacting the case of the alternator. He believes that was probably what caused the problems with the alternator.
I then took the alternator back to the boat and had it reinstalled. The mechanic scoped it and showed me the difference from what it looked like before the alternator was repaired. The batteries were charging normally with volts and amps being correct. Also, the original problem that I wrote in to you about in May about the tachometer was now completely resolved.
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