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Old 04-03-2012, 06:01 PM   #1
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Alternator Power

I have had trouble with my twin engine diesel not keeping my house batterys charged. I bought a larger alternator and a three level smart voltage regulator. All were installed by the instructions but I am still having trouble keeping the house batterys charged. My radar, chart plotter,VHF and depth sounder start acting week after about two hours off the shore power/charger.

My stb engine and alternator charge the house batterys and my port engine and alternator charge the starting batterys.

House batterys are 6 volt golf cart batterys (4 ea) connected in series and then in parallel to provide 12 volts on the house side.

The start batterys are two goupe 27 battery conneted in parallel.

Any ideas?

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Old 04-03-2012, 06:14 PM   #2
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I would suspect the batteries. You have 500 ah capacity and your nav equipment should not pull more than 20 amps. Have you checked the batteries to rule them out? Have you checked voltage at the batteries when you are running the motors?

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Old 04-03-2012, 06:40 PM   #3
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Sounds like batteries are not able to hold full charge. If wet batteries - be sure distilled water is above plates. How old are the batteries, too old? Have they been run too low on charge too often? Hate to say it, but you may simply need new batteries. If they're not wet then other boaters will need to chime in... I only use wet.

Also, if they are new wets... Have you ever brought them up to full charge and held them there with charger on for a couple hours? That is important to do to get them best accustomed to holding full charge.

First of all I caution you that it is up to you how aggressive you may get with overcharging any battery as it could cause explosive or other problems; so make sure to have plenty of distilled water already in cores and be very careful in general. But the following has at times worked for me on wet batteries, as this tends to "shake down" the metal plates and drops oxidation off their sides to enable better charging and charge retention. So... you may try a “tall charge”... wherein the batteries are brought above their top-charge needs with a separate high amp charger and held there for a couple hours by keeping charger on. Again, I recommend caution to only do this if you feel you know what is occurring, have all safety precautions at hand, and are comfortable to handle any problem that may occur.

Best luck!
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Old 04-03-2012, 07:03 PM   #4
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Are you sure the alternator is actually charging? Put a VOM across the output of the alternator while underway. If you're not getting 13.5+ volts then its not charging.
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Old 04-04-2012, 12:43 AM   #5
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Agreed, Check that the alternator is working. Be sure that the wiring is correct, that an error wasn't made. The regulator may have several fuses, have you checked them?

When the boat is running there are more loads than just the electronics which means a much larger draw than you may realize. lights, fridge, even the engine, depending on mfgr. may require some power and the alternator/regulator themselves.

So maybe without the alternator those batteries fall off faster than you think they should.

The alternator should be able to carry the entire load plus recharge the batteries so even if the batteries are suspect it shouldn't matter at least while the engines are running. Engines off is another matter.

If the alternator is working, then is it working fully. Was the rotational speed of the alternator considered. All of them need to be spun at a certain minimum rpm to make full power. Is it? Not the engine revs, but the alternator revs. Maybe, depending upon your cruising rpm, the alternator is simply running too slowly to keep up. A clip on dc ammeter would be usefull here. Do you have the spec sheet or access to it to see what the alternator output curve is to see what revs it needs vs the engine revs for full power.
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Old 04-04-2012, 12:52 AM   #6
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Thanks for the response

I need to check the alt output when I next get out. Something seems wrong here. The batterys are new.
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Old 04-04-2012, 05:12 AM   #7
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The batterys are new.

And have NEVER been discharged below 50%?

New or old its the depth of discharge , and how long they sit empty , that kills batts.

My suggestion as always a SOC meter so you can watch what is happening.

A V meter doesn't show much of anything besides an instant reading.

Best under $200 you will ever spend.

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Old 04-04-2012, 10:10 AM   #8
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I don't mean to come on strong, but I'm kinda shaking my head here. Apologies in advance if this is tough talk...

Did you do the alternator installation yourself? Do you have experience in doing this or did you get help and advice from someone who does? Do you have a voltmeter on the boat? Ammeter? Battery monitor? Surely after installing the alternator you confirmed it was charging, right?

If you don't have the essential equipment for the job, turn it over to a professional who knows what he's doing. If you're running your house batts dead b/c of an inoperative alternator, you're costing yourself more money than it would cost to have a pro do the job in the first place.
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Old 04-04-2012, 11:11 AM   #9
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A pro? In Valdez Alaska? Show me where I could find one with out having to fly them in from Anchorage and I will jump on it. You can hardly get your car fixed here.

Yeah, I did the installation myself. I agree that I need to improve my monitoring instruments to find the source of this problem.

I will look at the batteries again. I don't know for sure that they havn't been discharged beyond 50% or are low on water.

Thanks for ideas. I am not offended.
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Old 04-09-2012, 01:03 PM   #10
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you might check if perhaps you have any sort of automatic switch installed between the alt and batts. a bluesea switch could possible cause all charging going into the start batts and not the house batts.
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Old 04-10-2012, 11:23 AM   #11
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Some alternators need to be brought up to a certain rpm to initiate charging.

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