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Old 20-03-2010, 11:03   #1
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Voltage Drop at Panel

Hello All!
A big thanks ahead of time for your comments.

My Beneteau 49 has a factory installed Siemens battery monitor at the D/C distribution panel. With a 30 amp draw from battery bank (4x200ah Deka 4D AGM batteries that are less than one year old) the monitor shows 11.7v whereas the batteries show 12.44v at terminals (using portable volt meter). There is a 6awg wire attached to the positive post at back of distribution panel. I assume that this voltage drop is not good. Where do I go from here?
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Old 20-03-2010, 11:14   #2
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Check the voltage at the pannel with the portable volt meter. The Siemens may well be reading low and the portable volt meter high.
If the difference is still high try at any inermediate points such as the battery switches. Isolate the drop further by checking the + and negative seperately.
A quick alternative is to feel all conections with your hand. If you are loosing 0.7v at 30 amps that is 21 watts someting will be getting warm.
Finally 6awg sound a bit thin. How long is the run and I can calculate the expected drop just from the wires.
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Old 20-03-2010, 11:20   #3
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6awg runs for about 6 feet.
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Old 20-03-2010, 11:37   #4
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Measure the voltage drop across each live connection in the circuit, while it is under load (see below).

Assuming a maximum permissible 3% Voltage Drop (0.36V), #6AWG Cu. Wire is good for about 900 Amp/Feet at 12 Volt nominal.
900 A/Ft 30A = 30 Feet Round Trip (Pos + Neg)

Wire Size Chart.1 - Read /w "Ohm's Law & You" Cruisers & Sailing Photo Gallery

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Wire Size Chart.2 - Read /w Wire Size Chart.1 & "Ohm's Law & You" Cruisers & Sailing Photo Gallery
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Old 20-03-2010, 14:02   #5
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Quote:
Originally Posted by Wakadui View Post
6awg runs for about 6 feet.
Assuming the out and return (+ and - wires togetether) is 12 feet at 30A the voltage drop is 0.23V
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Old 20-03-2010, 14:55   #6
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Assuming the house batteries are all in parallel, is each voltage the same at the battery posts ? I found with my Lagoon / Beneteau there is a well hidden fuse 350a, at each battery terminal. I had one blown. Even so replacing that I still have .5v difference on the display to the batteries. Does anyone know how to adjust the display value. ?
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Old 20-03-2010, 17:16   #7
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+1 to what Gord said, but remember to check each connection on the ground side of the circuit as well as the hot side.
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