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Understanding the electrical

Troubleshooting, repair, and how-to's related to marine systems.

Understanding the electrical

Postby latitudes » Wed May 27, 2015 1:00 pm

So I have finally gotten a few trips in where I didn't cross wires, and have learned to play with crab pots. So now I am moving on to trying to figure out line voltage, boat voltage, etc. I purchased a Russel black box unit and have it hooked up. Everything is isolated with the proper hose on both ends, UHMW bases, and nylon bolts and nuts. When I turn the Russel unit on to the "read only" function, it reads a little over 0.4 volts. When I check the wire with a Fluke meter (ground to rudder post, hot to wire) it is a little over 0.5 volts. I turned the Russel box to continuous feed at 0.6 volts and the wire was over 0.7 with the Fluke.


So, A few questions......
Should the readings be the same or is it normal for them to be different?
I have heard of "boat voltage" but don't know how to measure that or what it should be
I have also heard of people who have had Russel come to their boat and get it dialed in. Does he still do that?

Any help would be greatly appreciated. Hopefully we'll catch a bunch one day!

Joe
latitudes
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Re: Understanding the electrical

Postby Crawfish » Thu May 28, 2015 7:37 am

Flukes are a good meter, I would be inclined to believe it over another testing method. Maybe you have a dirty connection on your black box and your losing a tenth of a volt?

If you are looking for your "Hull Potential" you need to have everything shut off while sitting at the dock lines in the boat. Take a reference wire which is typically a piece of trolling wire around 9' to 12' long and put it over the side into the water. Touch the reference wire to one of your Fluke leads and your other Fluke lead to your bonding system and you will have your hull potential.
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Re: Understanding the electrical

Postby Lulu » Thu Oct 22, 2015 12:41 pm

Latitudes, you are measuring several different and independent functions. Voltage on the rudder post should have no interaction with the gurdies if they are truly isolated. Voltage on the wire without the box turned on is normal. Reading at the box when on will be different than the actual wire voltage.

Voltage at the rudder post, if incorporated to the vessel's bonding system, should read zero. What you are reading is the galvanic activity between the metals on your boat, i.e. rudder, zincs, keel cooler(s), prop, shaft, engine, etc. .500V is low for a troller unless the vessel is less than 30 feet and fiberglass.

Standing voltage on the gurdies is normal. The voltage is created between the copper in the bronze gurdies and everything it touches like SS troll wire, splicing sleeves. .400 is high but not a disaster. Usually happens when the gurdies and wire are wet from the morning fog or dew. You can reduce the standing voltage by keeping the mounting plate clean, especially the green stuff which is fillings from the gurdie brake system, minimize the number of wire splices (which are generally brass), use new wire, do not use not non-conductive material as filler on the spool (connect the wire directly to the spool with a #10 SS sheet metal screw). The non-conductive filler eventually absorbs or collects salt water becoming a source of lost hair and immature outburst of rage.

Voltage reading at the box is not going to be the same as the line voltage. Depending on the length of wire from the box to the gurdie, splices, water tight connections to the gurdies, etc the box voltage will be different. Measuring line voltage (I've learned) should be at the wire. For instance on my vessel, a box reading of .498 equates to a line voltage of .550
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Re: Understanding the electrical

Postby Lulu » Thu Oct 22, 2015 12:46 pm

Crawfish is correct with a reading at the dock. But there are three other important readings: voltage spike when the engine is turned on, hull potential with the drive train engaged at the dock. And, hull potential while trolling. They are all different and tell you something about your vessel's electrical footprint.
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