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Old 11-05-2021, 07:23   #1
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Alternator output fluctuates

Hey all,

I recently installed a balmar mc 614 and a balmar 120 amp alternator. I've got a yanmar 4JH2-ute. Engine has the serpentine kit on it as well.

We decided that the since most projects are close enough to being done we will start going out. Well here we are, cruising around and during a 3hour motor, I noticed that our alternator puts out 20-50amps depending on the battery SOC, then all of a sudden it drops down to 2-8amps and then pumps back up.

Any ideas?

I've got two sets of batteries located in different locations for the house bank, both with temp sensors, and the alternator has temp sensor. Not seeing anything on balmars site about why this would be so hoping someone here can shed light

Thanks!
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Old 11-05-2021, 07:36   #2
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Re: Alternator output fluctuates

How long does it stay at the 2-8 amp level?
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Old 11-05-2021, 08:05   #3
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Re: Alternator output fluctuates

Sounds like a faulty connection to me. I assume to old alternator was charging OK? It's amazing how just a bit of insulation or crud under a connection can affect output. I would disconnect and check everything, including grounds, to be sure that you have good metal to metal contact at all points. Make sure all insulated crimp connections do not have plastic extending under the nuts. Make sure all connections to the engine are free of corrosion and paint.

I suspect this will solve your problem, but you can check that the regulator is working by measuring field voltage at the alternator. Should be 6-11 volts depending on how you have set your belt load. Also, you can check the magnetic field of your alternator with a screwdriver or wrench at the armature with the ignition on. Should be a nice strong pull.
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Old 11-05-2021, 10:07   #4
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Re: Alternator output fluctuates

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Originally Posted by mikereed100 View Post
Sounds like a faulty connection to me. I assume to old alternator was charging OK? It's amazing how just a bit of insulation or crud under a connection can affect output. I would disconnect and check everything, including grounds, to be sure that you have good metal to metal contact at all points. Make sure all insulated crimp connections do not have plastic extending under the nuts. Make sure all connections to the engine are free of corrosion and paint.

I suspect this will solve your problem, but you can check that the regulator is working by measuring field voltage at the alternator. Should be 6-11 volts depending on how you have set your belt load. Also, you can check the magnetic field of your alternator with a screwdriver or wrench at the armature with the ignition on. Should be a nice strong pull.
Thanks! I've just done a whole new wiring job moving everything over to properly sized wires and bus bars. I'll go over everything again and double check make sure connections are tight and non insulation is overlapping. I'll run through some of these checks and go from there. Much appreciated!

Old stock alternator was dead but the 180amp large case was driven off the crank pulley worked fine, but major refit has been done, and all systems are completely new. Also the old 180amp alt was on a 10awg wire to the starter...god knows how that survived. Everything was just layer over engine(belts rubbing wires) nothing secured.
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How long does it stay at the 2-8 amp level?
Only a short bit - 10 seconds or so?
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Old 12-05-2021, 01:34   #5
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Re: Alternator output fluctuates

Are you measuring Actual alternator current or net house current from a battery monitor?

Which bank is alt connected too? Where is sense wire? What are the bank voltages when it’s doing this? What Soc and how big a bank?

Is there an acr to other banks?

The pumping as you call it could be from an acr cycling on and off. Or likely many other causes.
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Old 12-05-2021, 14:36   #6
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Re: Alternator output fluctuates

When they say "check every connection," that means EVERY SINGLE ONE. I helped install a Balmar 200A alternator. It shipped with a little adapter to install between the harness and the alternator because of the difference in the plugs. We had a similar problem with the output varying. Checked all our wiring. Several times. Then accidentally bumped into the little adapter cable and the field wire slid out of the terminal. We temporarily fixed the problem by removing the terminal from the housing, sliding the wire into the badly crimped terminal, and putting a tiny spot of solder on the terminal. No, I don’t like soldering wires. The adapter was replaced by Balmar, but we pull-tested all the terminals before we put in the new one.
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Old 12-05-2021, 14:39   #7
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Re: Alternator output fluctuates

Loose connection or a temp sensor is kicking in.
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Old 12-05-2021, 18:51   #8
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Re: Alternator output fluctuates

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Loose connection or a temp sensor is kicking in.

And Balmar DOES tell you what their sensors do. If they don't Maine Sail already has: the old MC-612s would drop to 50%, the newer sensors step down.


Please let us know what you've found. All the best.
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