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Old 17-10-2008, 03:08   #1
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Unhappy 1 alternator charging more than other ?

according to my B M 1 battery monitor, one engine /alternator puts out a max of 6 amps and the other set puts out a max of 20 amps , of course it takes hours for the lower output set to charge up low batteries so the other engine gets more use as it charges the batts up faster ! this cant be right ? is the 6 amp alternator faulty ? is it a wiring size /length problem any ideas ,please ?
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Old 17-10-2008, 03:39   #2
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need a lot more info. you need to get a multy meter and do some checks. 6 amps is very low into a "needy" battery. I would think that the alternators are probably rated at 35 amps (or more) . That is not to say that that is what they will put out. Your alternator regulators make that decision. As a starting point. check the voltage of your battery (s) after they have been sitting for a half hour or so. Do that and check back in here and I think that wiser people than me will be able to help.
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Old 22-10-2008, 01:21   #3
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The simple standard set up for an alternator is the sense wire is connected to the positive system. It "reads" system voltage. Low system voltage means higher alternator voltage. As the alternator charges the batteries the system voltage comes up until the alternator is "trickle" charging the system with just a slightly higher than system voltage.

The location where the sense wire picks up system voltage is important. There are a few theories on this. Some say put it near the battery. However if the battery is close to the alternator you may not be reading what the bus is seeing if the bus is "far" from the battery due to system losses. In a car this is important because we are generally consuming what we produce in this always on system. Sensing at the battery with deteriorated conenctions to the bus often can result in dim headlights.

In a boat, however, we are interested in topping up the batteries. So a sense wire onthe battery might make sense.

I hedge my bet and like the field pick on a lug between the battery and the bus - as equidistant as I can make it.

So - One alternator may be seeing a different system voltage than the other. Cause could be hookup location or clean vs. dirty connections, loose vs. tight connections etc.

If you have a charge controller, the internal function of the sense system is taken over by the controller to essentially charge at a higher rate for a longer period. So in this case your problem could be a lot more complex.
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Old 22-10-2008, 04:11   #4
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are you running your battery switch on all?
What is your battery configuration?
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Old 22-10-2008, 08:02   #5
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6 amps and 20 amps?? Neither of those numbers sound correct for an engine alternator. Even my puny little 6.5hp Yanmar 1GM alt can source 35 amps. Do you see this number change based on battery state? ie the lower the battery the higher the charge rate should be. I'm thing there must be a miss wire in your battery monitoring system that's preventing the alt from providing the necessary current. Could you by pass it and see what the charge rate is?
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Old 22-10-2008, 08:25   #6
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Is your battery monitor correct? The first thing I would do is check at the alternator with an amp meter to see what it is actually putting out.
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Old 27-10-2008, 11:35   #7
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Originally Posted by never monday View Post
are you running your battery switch on all?
What is your battery configuration?
hi, i have 2 banks of 2x75 amp batteries / 2 per engine, thru a switch on each ,which is always set on "all" . 2 motors /batteries/switches , i have always run the boat this way and never had a problem in 10 years !( ok i changed the batteries twice !)
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Old 27-10-2008, 11:37   #8
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Is your battery monitor correct? The first thing I would do is check at the alternator with an amp meter to see what it is actually putting out.
thanks chuck , i have a m/ meter can you explain how i can do this ,please ?
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