Alternator going Bad?

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TBOT422
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Alternator going Bad?

Post by TBOT422 »

I think our alternator is going bad. On a recent cruise one morning, I noticed the volt meter at the helm only showed about 13 V after starting the engine and it normally showed close to 14. I then checked out battery monitor and the charging rate was only about 15 amps at idle and 22 amps at 2000 RPM. Voltage never showed above 13 on the helm meter or the battery monitor with the engine running. After reading some threads on this site, I see a relationship to a second problem I have been having. The tach has been flaky for awhile. It generally shows the correct RPM and would suddenly jump up about 500 RPM. I had suspected a poor connection at the tach gauge because I was able to lightly tap the gauge itself and the reading would correct. Since I now know that the tach gets its reading from the regulator in the alternator, combined with the voltage and charging rates shown by the battery monitor, I suspect my alternator is going bad. First question is that most likely the case or could it simply be poor connections at the alternator?

Second question since we are presently cruising, If it is going bad, what problems would I encounter if it failed completely? Would the engine continue running? I assume all the electronics would continue to work until the batteries went dead, but I have a portable generator to recharge the batteries as needed.

Third question, if we decide to repair or replace, has anyone installed the optional 72 amp alternator from Universal ($615) or its equivalent? I'm really not into a major upgrade that would require replacing pulleys or changing wiring, but if the 72 amp alternator was completely plug compatible with the standard 51 amp alternator, it might be worth a few extra bucks. My thinking is that I would then have the old alternator rebuilt and carry as a spare.

Thanks
Gary & Janet
The Best of Times (Hull #422)
KenKrawford
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Re: Alternator going Bad?

Post by KenKrawford »

I think you should be able to operate without a functioning alternator until the fuel pump quits from lack of power. Since the stock alternator is nothing special, you could take it off and have it tested at an auto alternator shop. I have no experience with a 72 amp alternator but $615 sure seem like a lot of money for an alternator of any size.
Ken Krawford
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TBOT422
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Re: Alternator going Bad?

Post by TBOT422 »

I'm assuming as long as the batteries have voltage, the fuel lift pump would continue to operate. Correct? I will have no problem keeping the batteries charged up with the portable generator (and occasional stops at a marina).

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Gary & Janet
The Best of Times (Hull #422)
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TBOT422
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Re: Alternator going Bad?

Post by TBOT422 »

I may have fixed my alternator issue. I won't know for sure until the batteries are run down again and there is a load put on the alternator. We have been staying at a marina for a couple of days, and got the batteries fully charged from shore power. I decided to do my usual engine check before departing tomorrow and noticed the belt seemed a little looser than normal. I was able to grab the alternator pulley with my hands and make it turn underneath the belt. After tightening a little the pulley did not slip and I was able to turn the crank shaft with my hands on the alternator pulley. Started the engine up and had over 45 amps for a few seconds on my battery monitor. It dropped off quickly to around 25 amps or less since the batteries were fully charged, but I am hopeful that was the only problem. Battery voltage was showing 13.8 V. We'll see how it performs under load after I run the batteries down a little. I noticed the other day that if I disconnected the house bank that was run down to 75 percent of capacity and left the engine start battery that was fully charged as the only battery in the system, the alternator output did increase, so it still may not work perfectly under load. But I am encouraged.

I feel stupid for not thinking about that earlier.
Gary & Janet
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Re: Alternator going Bad?

Post by TBOT422 »

I don't think tightening the belt has solved all my alternator problems. It will put out 45 amps or so at start up, but then begins dropping down current output. The voltage at the helm meter basically just shows whatever the battery voltage is, as they get charged up, the voltmeter will show over 13 volts, but if they are discharged, the voltage is under 13 V with the engine running. Still cruising, but when I get home, I will clean all wiring contacts, and see if the problem goes away. If not, then I will evaluate repair or replacement of the alternator.
Gary & Janet
The Best of Times (Hull #422)
JeffnCristol

Re: Alternator going Bad?

Post by JeffnCristol »

Can I ask what was the solution here?? We're experiencing similar issues... Start the engine - the battery monitor shows it's charging. Within a few minutes - the monitor shows negative input to batteries, & the tach drops to zero. We have a Balmar alternator & external regulator. We also have solar, & we've turned that off to confirm it's not interfering.

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wolfe10
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Re: Alternator going Bad?

Post by wolfe10 »

Jeff,

Assuming you have checked for CLEAN and TIGHT connections on alternator, regulator and battery: If you are "in port", remove the alternator and take to an alternator shop. Most have a nominal charge for checking alternators.
Brett Wolfe
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Re: Alternator going Bad?

Post by TBOT422 »

In our situation, after pulling the alternator and having it tested at a shop (no charge), I learned that is just how the stock alternator works. The stock 50-amp alternator with its internal regulator does put out close to 50-amps for a few minutes right after starting, then drops down to about 15-20 amps regardless of how low the batteries are. Sure they're charging, but not nearly as fast as one would desire when cruising. We opted to install solar panels to generate additional charging capacity. You have a different situation with a Balmar alternator and external regulator. It is good that you have isolated your solar panels, because I have also learned that the stock internal regulator will shut down the alternator when the battery voltage exceeds about 14.1 V, and our solar charger will take the batteries up to 14.2 V. So if the batteries are near full and the sun is shining and we're motoring along, sometimes the tachometer will drop to 0. I just turn off the solar panels and all is fine. I just have to remember to turn them back on when we drop the hook.

You might want to check the specific gravity of all the cells in your battery bank before pulling the alternator to have it tested. You might have a battery problem where the batteries simply will not accept a charge.
Gary & Janet
The Best of Times (Hull #422)
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