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alternator low voltage

Old 07-13-2019, 07:56 PM
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Default alternator low voltage

I have a cummins engine with 150 hours .my alternator has 2 cables the thin cable battery sensing wire? and the big positive cable that travels to my starter then to my batteries.when I check the voltage its the same at the battery and alternator. It is charging at 13.8v is this too low I am having a few starting issues but im not sure if I need a new starter battery anyway.
the belt seems fine.
thanks in advance
daniel
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Old 07-14-2019, 05:40 AM
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The voltage is fine, 13.8 is normal charging voltage. Cummins is pretty strict in their recommendations for starting current. You should probably have an 8D battery and it should be in good condition.
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Old 07-14-2019, 05:49 AM
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The regulator in the alternator should adjust the voltage from just over 12v to a little over 14.5 v as needed
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Old 07-14-2019, 06:04 AM
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thanks very much mr hudson
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Old 07-14-2019, 06:06 AM
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I have cummins 6bt and I think the battery is way to small its a bit bigger than a car battery.thankyou for the info mikie.i need to stop being so cheap
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Old 07-14-2019, 06:09 AM
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Originally Posted by Casador68 View Post
I have cummins 6bt and I think the battery is way to small its a bit bigger than a car battery.thankyou for the info mikie.i need to stop being so cheap
NO!

Buy cheap like so many do. Then come here and complain about product XYZ being crap. Disparage the battery maker. Many will pile on. Great sport.
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Old 07-14-2019, 06:25 AM
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at least i know im cheap mikie mentioned an 8 d and brought home the reality of what a crappy little battery I have!
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Old 07-14-2019, 07:21 AM
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To save your back lifting - you can hook up a bunch of smaller batteries in parallel to add up to the cranking amps or amp hours you need
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Old 07-14-2019, 07:42 AM
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Originally Posted by mickt243 View Post
To save your back lifting - you can hook up a bunch of smaller batteries in parallel to add up to the cranking amps or amp hours you need
Not here on THT you cannot. It is the kiss of death. Particularly if one battery was made in January 2019 and the other was made in February 2019. They will be incompatible and cause all sorts of mayhem.

But in the real world it can work just fine.
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Old 07-14-2019, 07:51 AM
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13.8 is likely perfectly acceptable. Not all alternators have the same set point. Fairly wide spread actually. Your battery needs to be sized to your starter primarily. On a 6bt I would match whatever early 90’s Rams ran.

If you see a part number on the alternator, I can likely look up what the set point specs are. PM me of so, as I may miss thread updates. In the business and have access to pretty good lookup info.
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Old 07-14-2019, 07:51 AM
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It's all about the CCA's
8D's are tough to manage because of the weight
Perhaps consider 2 Group 31's
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Old 07-14-2019, 07:56 AM
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Originally Posted by tvguy243;12720756[b
]It's all about the CCA's[/b]
8D's are tough to manage because of the weight
Perhaps consider 2 Group 31's
Since we are talking about a marine application why wouldn't MCA's be what it is about?
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Old 07-14-2019, 08:33 AM
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thanks will take a photo it will be useful to know
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Old 07-14-2019, 04:57 PM
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Originally Posted by alloyboy View Post
Since we are talking about a marine application why wouldn't MCA's be what it is about?
it's a matter of degrees

Same concept
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Old Yesterday, 11:32 AM
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Isn't it amazing how fast these subjects get out of hand
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Old Yesterday, 11:37 AM
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Originally Posted by alloyboy View Post
Not here on THT you cannot. It is the kiss of death. Particularly if one battery was made in January 2019 and the other was made in February 2019. They will be incompatible and cause all sorts of mayhem.

But in the real world it can work just fine.
For sure. Shooting from the hip, pretty sure a pair of 31's is basically the same capacity as an 8D, all else being the same. I would go with a pair of 31's all day long, even though they are likely a bit more money, just to save my back. Wrestling an 8D is no joke.
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