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HDS 5 reading incorrect voltage....head scratcher

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HDS 5 reading incorrect voltage....head scratcher

Old 03-05-2012, 06:08 AM
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Default HDS 5 reading incorrect voltage....head scratcher

So I have a one year old battery, that measures around 12.6 when fully charged, on my multimeter.
My HDS says that the voltage is alot less, like 12.1 at the beginning of a trip and then down to the 11's after a couple hours.
What gives?

My theories are:
1. Voltage drop from a bad feed wire from battery to center console. Wire is pretty old.
2. A bad Diehard battery (tho its always started the boat and never is sluggish)
3. Bad HDS unit (which is a year old)
Old 03-05-2012, 06:19 AM
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I would probably trust that the HDS is reading the voltage that is is seeing where presented to it. My guess is that you have a 0.5V voltage drop from your battery to the HDS unit, resulting from the length / size of your supply wiring. If I am doing my math right this morning, a 0.5V drop from your 12.6 supply is about 4%, which would not be surprising. Does not matter how old the wire is (as long as the termination points are clean and not corroded), but rather the length and diameter of the wire. What does the voltage measure on your multimeter at the HDS unit?

Check out a voltage drop calculator such as the one here:
http://shop.genuinedealz.com/Store/Tab.aspx?tabid=2

Now, as to your battery level dropping over the the duration of a trip - dropping to the 11's - like 11.9 or 11.1? What else is running off that battery? Are you using a deep-cycle battery or a cranking battery or a dual-purpose?
Old 03-05-2012, 07:07 AM
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Duh, never thought to check supply voltage under the console. Going to go check that now.
The batt is a cranking battery, that the hds and running lights are off of. Think I should change to a dual purpose? Its only turning over a 25hp motor.
Old 03-05-2012, 07:15 AM
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Every Lowrance unit I have had shows the voltage slightly lower than a VOM on the battery.

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