Electricity is so weird - SailNet Community
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post #1 of 9 Old 06-27-2019 Thread Starter
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Electricity is so weird

Electricity is so weird.

I bought a rocker switch voltage meter that to measure two different voltage sources. When it arrived I noticed it had two positive leads and only one negative lead. Huh.

I have three different voltages in my system. The voltage coming out of the solar panel, the voltage that the solar controller is applying to the 24v battery bank (or if not charging, the resting voltage of the battery bank), and the 12v coming out of my DC-to-DC converter.

And sure enough, it doesn’t matter where I put the negative lead. You can put the negative lead on any negative part of my system, and it will read the voltage of where the positive lead is.

Huh.
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post #2 of 9 Old 06-27-2019
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Re: Electricity is so weird

Not so strange because if your boat is wired correctly, the ground reference for everything goes to a single point.

Think of it this way: 12V, 24V, 17V, etc are all different voltages, but each are referenced to 0V, 0V, 0V, etc - which are all the same voltages.

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post #3 of 9 Old 06-27-2019
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Re: Electricity is so weird

Back a while when things were 6 volt ,my dad ,who was handy but short on theory, needed12v for a new fangled radio. Connected up a second generator to charge the other battery. Output + went to old ground and new neg was separate and 12v below the existing + of existing battery,Voila ! 12 volts Radio worked good but zincs bubbled a bit.
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post #4 of 9 Old 06-27-2019 Thread Starter
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Re: Electricity is so weird

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Originally Posted by colemj View Post
Not so strange because if your boat is wired correctly, the ground reference for everything goes to a single point.

Think of it this way: 12V, 24V, 17V, etc are all different voltages, but each are referenced to 0V, 0V, 0V, etc - which are all the same voltages.

Mark


Now I'm wondering if I am wired correctly. I don't have any one ground. I'm wired like in the diagram: two wires out of solar panel to controller, two wires out of controller to battery and DC-to-DC converter, two wires out of converter to house bank.

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post #5 of 9 Old 06-27-2019
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Re: Electricity is so weird

Your solar charge controller (and DC converter) will likely have a common negative (ground) bus. So though you land the two black wires on different terminals, they are actually common.

If you are not sure, lift the wires and measure continuity from PV- to battery-.

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post #6 of 9 Old 06-28-2019
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Re: Electricity is so weird

There is almost assuredly a common ground reference point on the boat. The engine is always a good bet.

Mark
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post #7 of 9 Old 06-28-2019 Thread Starter
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Re: Electricity is so weird

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There is almost assuredly a common ground reference point on the boat. The engine is always a good bet.

Mark
It's a Catalina 22 no engine.

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post #8 of 9 Old 06-28-2019 Thread Starter
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Re: Electricity is so weird

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Originally Posted by fmueller View Post
Your solar charge controller (and DC converter) will likely have a common negative (ground) bus. So though you land the two black wires on different terminals, they are actually common.

If you are not sure, lift the wires and measure continuity from PV- to battery-.

Interesting. So although both my solar controller and my DC-to-DC converter have a negative in and a negative out, you're saying they're probably common. So the system would probably work if I connected both negatives to either terminal. Huh.

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post #9 of 9 Old 06-28-2019
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Electricity is so weird

Quote:
Originally Posted by Minnesail View Post
It's a Catalina 22 no engine.


... and no metal hull. A “common reference” is a matter of theory, on a plastic boat.

By your OP, it’s clear that all components in the system are tying the incoming to outgoing negative, treating it as a common node. Nothing surprising, there... these components are designed with the assumption they may be mounted into some vehicle with a metal negative-ground hull.

MSEE
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Last edited by DinghyRace; 06-28-2019 at 02:07 PM.
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