Alternator Won't Charge at Idle

Mar 9, 2015
33
Hunter 42 San Diego
I have a Powerline 120 amp alternator and an Incharge Heart regulator. In the past, I could run the engine at 1,000 RPM to charge the batteries while at anchor. On our last anchor out, at idle--800 RPM, the battery monitor shows about a 4 amp loss, and doesn't show neutral (no gain or loss) until about 1,150 RPM. Not until 1,350 RPM could I get 22 or 23 amps. I put on a new belt, checked the fuses, looked for any corrosion or bad connections, opened the regulator. I don't remember exactly how many amps I used to get at 1,000 RPM, but it was probably double what I'm getting at 1,350 now. I've read trouble shooting guides but nothing seems to address this. Any ideas would be greatly appreciated. Thanks
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
What SOC was the house bank with prior experience both before and now? If the house bank was down before but wan't now, you may not have any issues. Have you tried it since you did that work?
 
Mar 9, 2015
33
Hunter 42 San Diego
I have 2 Lifelines, 5 years old, 245 each. I try to not let them get much below 85% before recharging. The morning after checking everything, they were at 82%, down from 92% after charging the afternoon/evening before. That is about when I run the engine--85 +/- %. The odd thing that hasn't happened before is a loss of amps at idle when before the alternator would charge at that same percentage or state of charge. I'm an electrical idiot, but even to me, this makes absolutely no sense.
 

RoyS

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Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
I recently had that exact same problem with my stock Hitachi 35A alternator. That alternator was at least 18 years old and possibly 40 years old. Bought a cheap replacement alternator (55A) on line for $70 and that solved the problem. We will see how long the $70 alternator lasts. With only about 100 hours a year engine run time, it might outlast me.
 
Mar 9, 2015
33
Hunter 42 San Diego
I like the Powerline 120 alternator we have because it charges the battery quicker than the 80 amp Delco spare I have. So the Powerline has been recently serviced. I called Powerline tech support and they said to check the regulator, which I did and found nothing. I just can't understand why the battery monitor would show an amp loss at idle when in the past it's always shown a gain, and I've changed nothing.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
I'm an electrical idiot, but even to me, this makes absolutely no sense.
Not really. You're smart enough to notice the change. Good for you. None of us was born an electrician, we all learned.
I just can't understand why the battery monitor would show an amp loss at idle when in the past it's always shown a gain, and I've changed nothing.
Thanks for answering about the SOC, understood. Do you know what the voltages were when chasrging at idle, both earlier and now?
 
Mar 9, 2015
33
Hunter 42 San Diego
In addition to my lack of electrical knowledge, I'm old and have a poor memory. I think the battery monitor showed 13.5 or so volts as I was charging at 1,350 RPM, but I'm not positive. I was so concerned at the amp loss at idle I didn't pay attention to what the monitor showed for volts then, and I don't remember what voltage I was seeing in the past when the alternator was putting out significant amps at idle. But at 82% shouldn't that be bulk and closer to 14 something volts? Would a bad voltage adjustment on the regulator cause an amp loss that goes away at higher RPM?
 
Nov 1, 2009
19
Hunter 466 San Diego, CA
Had a similar problem with Balmar 60 series alternator. Turned out the positive battery lead had corroded near the connection at the alternator, adding enough resistance to not charge at idle. Cut it back 4-5" to good wire, reconnected and all good. Better than buying a new alternator....
 
Mar 9, 2015
33
Hunter 42 San Diego
Thank you. I'll check that lead. My regulator is mounted to the engine room door, so that wire harness gets movement every time the door is opened, which made me think it might be something there.
 
Sep 24, 2018
2,549
O'Day 25 Chicago
I've had a couple of automotive alternators on their way out only give a charge above a certain RPM. I've also seen poor connections cause similar issues. Voltage slowly dropped until the truck stopped running. We thought the alternator was shot at first. You can also bring your alternator to a shop to have them verify it's functioning correctly
 

LloydB

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Jan 15, 2006
806
Macgregor 22 Silverton
I=E/R I have found record keeping is superior to memory and experience has proven it's never too late to start. Intuitive solutions are most often found by those who have slogged through the details of previous problems. Even though these days I sometimes trick myself I still reach for my VOM before my hammer.
 
Jan 22, 2008
309
Hunter 34 Herrington South, MD
I've had a couple of automotive alternators on their way out only give a charge above a certain RPM. I've also seen poor connections cause similar issues. Voltage slowly dropped until the truck stopped running. We thought the alternator was shot at first. You can also bring your alternator to a shop to have them verify it's functioning correctly
 
Jan 22, 2008
309
Hunter 34 Herrington South, MD
I agree many alternators won't charge at low rpm. You can try to put in a smaller pulley so it would spin faster. Not sure what impact that would have on the alternator but it might ensure more output at lower engine rpm.
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Not really. You're smart enough to notice the change. Good for you. None of us was born an electrician, we all learned.

Thanks for answering about the SOC, understood. Do you know what the voltages were when chasrging at idle, both earlier and now?

Hi folks
One thing to check is the diode pack. There are several (varies by model of alternator) diodes that turn the alternating current produced in the stator windings (not the rotor windings) into direct current. These windings are all out of phase with each other (typical is three windings (phase) and 6 diodes). If one of these diodes goes south you loose that winding for half a cycle. The output would be off for all RPMs if that happens but especially for lower RPMs. You would probably not notice it at the higher RPMs as the regulator will just up the rotor current to "make more alternating current in the stator" but at lower RPMs with the rotor current at max it does show up.
 

RoyS

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Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
When my alternator started showing this problem (at idle speed only) there were two other symptoms. The alarm at the helm engine panel started making a soft alarm sound (I could not hear it) and there was a slight burning odor near the engine. Replacing the alternator solved the problem.