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Old 05-22-2018, 04:41 PM   #1
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Low voltage in the Pilot House

Hi All:
I have a KK Manatee. the Voltage in the Pilot house seems to be about 10.5 volts (measured on a reasonably high quality meter) This is regardless of whether we are on shore power, house battery or generator. The Power run from the Distribution panel to the Pilot house Sub-panel is reasonably short (maybe 15 feet) the overall wiring is not to my liking to the sub-panel, but I do now understand who i can have a 2.5-3 volt drop. Does anyone have any ideas where to start looking? (At this point I may run a larger pair of wires from the main panel to the pilot house and re-wire or replace the distribution panel up there)

Thanks
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Old 05-22-2018, 05:38 PM   #2
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I don't understand how you can have a 2.5 - 3 volt drop in 15 feet of cable unless it is grossly undersized. Is the voltage drop constant, or only when you have a major electrical load on the pilothouse panel?
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Old 05-22-2018, 05:43 PM   #3
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Undersized wiring and/or dirty loose connections can cause a voltage drop. I would check a wire sizing chart, West Marine or Blue Seas, then check every connection for looseness or corrosion.
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Old 05-22-2018, 05:52 PM   #4
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I don't know anything about electric stuff, so of course I will offer an opinion.


My I would first start at your distribution panel and check the voltage there. Then move towards your pilothouse and check at every connection along the way to see what the voltage is. My guess is that you will find spot where you get a larger voltage drop and likely a poor connection. If you find the run that has the voltage drop, and just cleaning the contacts doesn't solve it, then that would be where to consider running larger wire.


I may be completely wrong however....
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Old 05-22-2018, 06:15 PM   #5
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I don't know anything about electric stuff, so of course I will offer an opinion.

My I would first start at your distribution panel and check the voltage there. Then move towards your pilothouse and check at every connection along the way to see what the voltage is. My guess is that you will find spot where you get a larger voltage drop and likely a poor connection. If you find the run that has the voltage drop, and just cleaning the contacts doesn't solve it, then that would be where to consider running larger wire.

I may be completely wrong however....
No you are exactly right. That is how I would approach the problem.

Another, maybe easier thing to do that might find the problem quickly is to feel each connection along the route to the pilothouse. Any large voltage drop will cause the connection to be hot. Then fix the connection and the voltage drop may go away.


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Old 05-22-2018, 07:14 PM   #6
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No you are exactly right. That is how I would approach the problem.

Another, maybe easier thing to do that might find the problem quickly is to feel each connection along the route to the pilothouse. Any large voltage drop will cause the connection to be hot. Then fix the connection and the voltage drop may go away.


David

I like that idea! I would think it would have to be a very poor connection to create that much voltage drop and that should generate a lot of heat. BTW, finding the problem will not only solve some electrical problems in your PH, but keep the OP's boat from burning up.
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Old 05-22-2018, 07:20 PM   #7
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Originally Posted by Ftbinc View Post
Hi All:
I have a KK Manatee. the Voltage in the Pilot house seems to be about 10.5 volts (measured on a reasonably high quality meter) This is regardless of whether we are on shore power, house battery or generator. The Power run from the Distribution panel to the Pilot house Sub-panel is reasonably short (maybe 15 feet) the overall wiring is not to my liking to the sub-panel, but I do now understand who i can have a 2.5-3 volt drop. Does anyone have any ideas where to start looking? (At this point I may run a larger pair of wires from the main panel to the pilot house and re-wire or replace the distribution panel up there)

Thanks

Wire sizing ( VERY bad connection notwithstanding ) resulting in a voltage drop would be a factor IF there was a substantial load on that Sub Panel. At negligible or no load, there should be NO voltage drop in 15' of cable !!
Case in point, I can measure full battery voltage on a 18 gauge control circuit that's more than 35' away.



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Old 05-22-2018, 11:05 PM   #8
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The voltage drop may be in either the positive or ground lead. A very sure way to track it down is to run a temporary dedicated wire from the known good negative terminal on the battery to your meter. It can be small wire, there will be very little current going through it.

With the other meter lead, start probing the grounds you can reach from the pilot house back. It will help to have some loads turned on to aggravate the condition. The reading on the meter will be a direct reading of the voltage drop in the ground line, and you'd like it to be less than half a volt, preferably far less - one or two tenths of a volt is OK. If it is larger than that, keep moving the probe point towards the battery until you see the drop drop - so to speak. Now you are near the problem. If it just gradually disappears as you work towards the battery, then everything is simply undersized and adding up.

Now go back and do the same thing on the positive side: long temporary lead on the positive battery terminal, probing the positive network where ever you can get to it. Again the measured drop should be 0.5V or less. Work back towards the battery, same idea. It will not take very long to find the problem this way.
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Old 05-23-2018, 04:21 AM   #9
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Old 05-23-2018, 06:49 AM   #10
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The voltage drop may be in either the positive or ground lead. A very sure way to track it down is to run a temporary dedicated wire from the known good negative terminal on the battery to your meter. It can be small wire, there will be very little current going through it.

With the other meter lead, start probing the grounds you can reach from the pilot house back. It will help to have some loads turned on to aggravate the condition. The reading on the meter will be a direct reading of the voltage drop in the ground line, and you'd like it to be less than half a volt, preferably far less - one or two tenths of a volt is OK. If it is larger than that, keep moving the probe point towards the battery until you see the drop drop - so to speak. Now you are near the problem. If it just gradually disappears as you work towards the battery, then everything is simply undersized and adding up.

Now go back and do the same thing on the positive side: long temporary lead on the positive battery terminal, probing the positive network where ever you can get to it. Again the measured drop should be 0.5V or less. Work back towards the battery, same idea. It will not take very long to find the problem this way.



Very good good point re: the Negative ( - ) thanks for picking up on that ................ fb
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