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Old 11-06-2014, 21:05   #1
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Voltage Drop

I have 12.2 at the battery and 27 feet down the 14awg copper wire the voltage is 11.96 with no load at a bus bar.

Is this drop what it should be? It seems excessive. I've used online calculators however they want me to enter an amp load where I had none.

Thanks.
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Old 11-06-2014, 21:31   #2
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Re: Voltage drop

With no load you should have no voltage drop. It should measure the same at each end of the wire.
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Old 11-06-2014, 21:42   #3
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Re: Voltage drop

What's the easiest way to trace down my problem?

Thanks
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Old 11-06-2014, 22:06   #4
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Re: Voltage drop

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Originally Posted by Ketchgould View Post
What's the easiest way to trace down my problem?

Thanks
What do you think your problem is?
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Old 11-06-2014, 22:45   #5
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Re: Voltage drop

As stated you should have no voltage drop for no load over that length.

Disconnect the power and measure resistance (aka continuity) in each section. Disconnect if necessary.

Look for black oxide in wiring, corrosion or visible breaks or crushed cabling. Wiggle the wiring while measuring.

Look first then measure.

You'll soon find where the problem lies.

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Old 11-06-2014, 23:09   #6
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Re: Voltage drop

If you have a voltage drop, some current must be flowing. Therefore the first question to be answered is what is still switched on, when you think everything is off.
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Old 11-06-2014, 23:57   #7
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Re: Voltage drop

Quote:
Originally Posted by Ketchgould View Post
I have 12.2 at the battery and 27 feet down the 14awg copper wire the voltage is 11.96 with no load at a bus bar.

Is this drop what it should be? It seems excessive. I've used online calculators however they want me to enter an amp load where I had none.

Thanks.
Have you disconnected the working end for this test? If you haven't the load unit (loght/motor/whatever) may have some parsitic resistance.

If you measure with the working end connected you are measuring parallel voltages - the voltage for the load unit and the voltage for the meter. These will be the same. The current draws will be different.

If you verify there is a ral votage drop then you are looking at a high resistance in the wire. You can troubleshoot the wire but why? Pull it and replace it.

If you want a science project run a replacement wire, hook it up in place of the current one and check the voltage.

Bottom line - Votage drop is either resistance or load.

BTW - Why is this important to you? Is there an underlying problem you are troubleshooting or did you wake up one day and say, "I wonder what the voltage drop is in that wire?" (just curious)
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Old 12-06-2014, 01:25   #8
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Re: Voltage drop

There's a load of questions I could ask to help sleuth things, but there are 2 most probable causes which spring to mind regardless.
- I don't know how old the wire is, but over time, unless the end fittings on the wire are incredibly well affixed & sealed, corrosion will creep (wick, more or less) into the wire, starting from it's ends. And of course, over time, corrosion grows... creating resistance.

Ideally, the terminal fittings would be both crimped & soldered onto the ends of the wire, & then sealed with waterproof heat shrink connectors. So that at either end of the wire, all you'd see would be the connector, with a small bit of well soldered wire protruding from under the seals on the wire's terminal fittings.
Such minimizes the creeping corrosion, more or less.

Also, how clean (corrosion free) are both; the end fittings of the wire, & the terminal blocks/fuse panels into which they're screwed? Ditto on the fasteners holding the ends of the wire's ends in place at both ends.
A little bit of corrosion there, is like corrosion on the terminals of the wire end fittings on your car's battery. It doesn't take a lot to impede the flow of electricity. And on both, a quick scrub with the Dremel with the wire wheel attachment rarely hurts regardless.

HTH
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Old 12-06-2014, 10:18   #9
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Re: Voltage drop

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...Ideally, the terminal fittings would be both crimped & soldered onto the ends of the wire...
A big negative on this. Crimp--don't solder.
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Old 12-06-2014, 10:54   #10
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Re: Voltage drop

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Originally Posted by UNCIVILIZED View Post
There's a load of questions I could ask to help sleuth things, but there are 2 most probable causes which spring to mind regardless.
- I don't know how old the wire is, but over time, unless the end fittings on the wire are incredibly well affixed & sealed, corrosion will creep (wick, more or less) into the wire, starting from it's ends. And of course, over time, corrosion grows... creating resistance.

Ideally, the terminal fittings would be both crimped & soldered onto the ends of the wire, & then sealed with waterproof heat shrink connectors. So that at either end of the wire, all you'd see would be the connector, with a small bit of well soldered wire protruding from under the seals on the wire's terminal fittings.
Such minimizes the creeping corrosion, more or less.

Also, how clean (corrosion free) are both; the end fittings of the wire, & the terminal blocks/fuse panels into which they're screwed? Ditto on the fasteners holding the ends of the wire's ends in place at both ends.
A little bit of corrosion there, is like corrosion on the terminals of the wire end fittings on your car's battery. It doesn't take a lot to impede the flow of electricity. And on both, a quick scrub with the Dremel with the wire wheel attachment rarely hurts regardless.

HTH
Best practice (to ABYC standards) is to use marine wire, which has tinned conductors. Then there is no "creeping corrosion" to worry about. Another best practice is to use crimps that have adhesive heat shrink built in (GenuineDealz.com has the best prices), which seal totally. Finally, if you have a proper ratchet crimper, the crimped joint will be cold welded so corrosion can't really "creep in" anyway. These three practices will make for totally reliable connections.

Sounds like your boat was built by the French? Either that, or someone has been really cheaping out on materials when upgrading.

Soldering is not permitted according to ABYC regs - all connections should be crimped. This is because soldering can be brittle and eventually fatigue and break. Of course it can be unavoidable (got a couple of joints inside cables) but keep it to an absolute minimum and make sure the joints are well protected against strain.
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Old 12-06-2014, 11:36   #11
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Re: Voltage drop

The resistance of 14 ga. copper wire is 0.00297 Ohms per foot. The resistance of your 27 foot long wire is 0.08019 Ohms. The voltage drop from 12.20 to 10.96 is 0.24 volts. Current equals voltage divided by resistance. Either your circuit is conducting around two amps or your resistance is a lot higher than 0.08 ohms. Since you say there is no load on the wire, there is the possibility that there is a short somewhere up the wire but it must be drawing more than 2 amps (since its distance from the battery is shorter). If in fact you have a short conducting more than 2 Amps somewhere you had better find it right away.

It is much more likely you have a bad connection somewhere or a broken wire or corroded wire. You need to hook up the meter to read Ohms and test the conductivity of your wire. Disconnect the wire at both ends and measure the resistance. It should be 0.08 Ohms which is so small that your meter probably can't measure it. Remember, the resistance may be (probably is) in the connections at either end.
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Old 12-06-2014, 13:16   #12
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Re: Voltage drop

When you move the meter probe from one end of the wire to the other, are you also moving your ground probe? If so, some of the variation could be attributed to a variation in ground potential within your boat. Leaving the ground connected to the same point for both readings would eliminate that possibility.
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Old 12-06-2014, 13:21   #13
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Re: Voltage drop

You mention a bus bar. Are there other wires connected to the bus bar? If so, lift the end of the 27 foot wire and measure voltage of the wire only. This would eliminate potential loads on the bus bar affecting the measurement.
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Old 12-06-2014, 13:27   #14
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Voltage drop

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The resistance of 14 ga. copper wire is 0.00297 Ohms per foot. The resistance of your 27 foot long wire is 0.08019 Ohms. The voltage drop from 12.20 to 10.96 is 0.24 volts. Current equals voltage divided by resistance. Either your circuit is conducting around two amps or your resistance is a lot higher than 0.08 ohms. Since you say there is no load on the wire, there is the possibility that there is a short somewhere up the wire but it must be drawing more than 2 amps (since its distance from the battery is shorter). If in fact you have a short conducting more than 2 Amps somewhere you had better find it right away.

It is much more likely you have a bad connection somewhere or a broken wire or corroded wire. You need to hook up the meter to read Ohms and test the conductivity of your wire. Disconnect the wire at both ends and measure the resistance. It should be 0.08 Ohms which is so small that your meter probably can't measure it. Remember, the resistance may be (probably is) in the connections at either end.

Voltage drop is 1.24 volts, not 0.24. But if no current is flowing (as he claims), the resistance wouldn't matter. Not saying he doesn't have some bad connections somewhere, but there's gotta be current in this scenario, which needs to be eliminated to resolve.
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Old 12-06-2014, 14:03   #15
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Re: Voltage drop

I've seen voltage drops of more than that across a main battery switch!''

Bad connections and worn contacts ARE the resistance. No need for any current flow; these show up sometimes even with a just an extremely high impedence VOM.

Bottom line IMHO: check the connections, wire terminations, contacts, etc.

By the way, 12.2 volts at the battery is way too low. That's 50% discharged.

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