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Old 22-04-2015, 06:30   #1
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Alternator idles at zero

I have a Yanmar 3jh4e witha a Balmar alternator that reads zero when idleing but come back up when running. Belt is tight and connections seem good. Any ideas?
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Old 22-04-2015, 06:35   #2
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Re: Alternator idles at zero

What exactly does "zero" and "come back up" refer to? If current, then yes, this is normal. There is minimum alternator speed necessary for output at any given voltage. Idle speeds rarely are enough for this - and if it was, the alternator load would probably stall it or cause governing issues. You could decrease the engine rpm necessary for full output by changing to a smaller alternator pulley.

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Old 22-04-2015, 07:09   #3
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Re: Alternator idles at zero

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Originally Posted by pisail View Post
I have a Yanmar 3jh4e witha a Balmar alternator that reads zero when idleing but come back up when running. Belt is tight and connections seem good. Any ideas?

Fairly normal for high output alternators. You are simply below the cut-in speed.
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Old 22-04-2015, 10:19   #4
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Re: Alternator idles at zero

Sorry I wasn't very clear, the tach reads zero until I rev it up and it is alternator driven
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Old 22-04-2015, 10:51   #5
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Re: Alternator idles at zero

When your alt is turning slow it will not put out any power, this includes the power (or signal) used by the tach. I have a similar problem, except that my alt rarely puts out enough signal for the tach to work at all. I am working on a photo sensor to get the tach working.
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Old 22-04-2015, 10:56   #6
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Re: Alternator idles at zero

Also happens if your battery bank is full. Were you plugged into shorepower?
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Old 22-04-2015, 11:17   #7
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Re: Alternator idles at zero

Normal for balmar regulators.

Turn on some loads (lights etc) to cause the regulator to kick on. You should see the tach read at that point.
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Old 22-04-2015, 11:17   #8
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Re: Alternator idles at zero

What regulator do you have? Most the time this issue is the regulator doesn't kick in. It's normal on many.
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Old 23-04-2015, 09:33   #9
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Re: Alternator idles at zero

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Originally Posted by pisail View Post
I have a Yanmar 3jh4e witha a Balmar alternator that reads zero when idleing but come back up when running. Belt is tight and connections seem good. Any ideas?
If you have a programmable alternator regulator you may be able to change the programming to activate your alternator driven tach at lower RPMs/alternator output.

As an example, we have a similar condition with our tachs (two tachs driven off the same alternator...)

e.g., We programmed our Balmar regulator to delay 45 seconds after engine start before initiating a slow [60 second] ramp-up of alternator output. During the 45 second delay period, the tachs read zero, but the trade-off is worth it to us. [i.e., We don't want a 120amp alternator to start putting out maximum current to a depleted battery bank immediately upon engine start...]

The tachs always provide readouts once the start-up delay period is over no matter how small the output is from the alternator.

Good luck working this out.

Cheers!
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Old 23-04-2015, 16:12   #10
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Re: Alternator idles at zero

I have an old boat with old lehmans and had similar issue on one engine. I suspected the regulator, but it was no longer in production, so swapped the alternator and now have current out at low RPM. Under $200. (my tachs are hall effect running off a sender, so that wasn't my issue.)
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