I Didn't Know 12v was so Sensitive

[Vincentc]

I completed the install of a Maxwell RC-10/8 yesterday just before everyone came aboard for our 4th of July trip to the Island. When I attempted to crank the port engine, nothing happened when I turned the key.

Since I had incorporated a breaker in the old windlass wiring, that connected to the port battery bank rotary switch and required my removing the windlass connection to the switch, I guessed I had done something to cause this. I looked at, studied and tested the switch connections. Good voltage at the "in" post at the bottom of the switch and at the lug connected to the fwd post at the top of the switch. There was no voltage at the battery cable lug connected to the aft post at the top of the switch. I checked the fuse at the switch (the same one which stranded me at the fuel dock a month or so ago) and the fuse was good.

The lugs for the windlass cable and the engine starter cable are connected to the aft switch terminal. I removed the windlass cable lug, replaced the nut, and we had power to the engine. I then reconnected the windlass cable lug and tighted everything up and again had power at the engine.

We went to the West side of Sand Island, since the waves were out of the NNE and the SE, this was the only protected anchorage I could think of between Horn, Petit Bois and Sand. We anchored between my brother-in-law's totally redone Gulfstar 43 trawler, "Ali Cat III" and good looking Hatteras convertible "Patience" out of Orange Beach, and had fine time, distracted only by the presence of an oil boom blocking our access to the excellent anchorage in the indention on the West side of the Island. The boom was not stopping any oil and the cove, it was intended to protect, has the same sand beach, without any grass, as the rest of the unboomed island. After another 7 hours on the coastal waters, I am pleased to report, we have not seen any oil while boating, though one of my daughters did report finding a few tar balls on the South side of the island.

We stopped and restarted the port engine at the island and again when we anchored to watch and enjoy the fireworks display at the Pascagoula city pier.

Everything worked fine, including the new windlass with its rope and chain rode; but, I am now wondering why the battery switch/connections are so touchy. The 1/2 inch nut holding the engine and windlass cable lugs was snug, but not extremely tight, but it is now as tight as I could make it with a 3/8 driver and a 3/4" socket.

Do I have a problem, (other than my mechanic) or is this the nature of 12v systems?

Thanks for your input.

[MikeP]

Sounds like either a dirty/corroded connection at the lug or a bad cable. A cable can have a faulty joint at the point where the connector is attached where twisting it can make the connection. It can also be damaged internally with the same result - moving/twisting can make/break the connection. I suppose the switch itself could be faulty/intermittent but that seems unlikely. I'd look carefully at the specific wires/connections in the affected circuit.

As far as cleaning the connections at the lug - disassemble, clean connectors/lugs with De-Oxit or something similar, coat connectors/lug with dielectric grease and reassemble. The connections need to be tight in accordance with the size lug/nuts/screws but not any more than what I'd call "normal" tightness (whatever the heck that is) or, if you have them available, tighten to the published torque settings. They certainly shouldn't need to be as tight as you can possibly make them

A voltage drop test is very helpful in finding poor cables/connections. Do an internet search on "voltage drop test" if you are not familiar with doing one. There's plenty of info on the procedure. It will identify problems with cables/connector current-carrying ability whereas a resistance test with an ohm/multimeter tells you very little, especially about high current circuits.

Good luck

[Vincentc]

Mike,
Considering your comments, I would guess it is a problem at the connection rather than the wiring. There was no voltage at the lug connection to the switch. Think I will clean the lugs and apply di-electric grease.
Thanks

[REBrueckner]

It's possible the switch wiper itself is sensitive to the location of the handle position. My big black Guest switches, original equipment, stay engaged for about a 1/4 turn (a lot)...Other types of switches require the handle to be in the exact postion to make contact.

[Genesis]

Those big GUEST switches have a habit of losing conductivity over time. I had to replace two of them on my boat when I owned her - they're expensive too.

Often when they do this they'll pass enough current that low-load things run just fine, but as soon as you hit something like a windlass or starter its "lights out."

If you can get it to do it again get in there with a meter and you'll find the place where the 12v just "disappears." That's where the bad connection is; don't be surprised if it's in the switch.

[fixin-to-cruise]

There's a good chance that when you put the windlass cable on the battery switch you reoriented the contacts inside the switch. The contact is like the head of a bolt but made of plated copper. I'd recommend disassembling the switch and cleaning the contacts with sandpaper. Be sure to disconnect the battery and take a picture or sketch the everything before you take it apart. If the contact is bad you might be able to talk the manufacturer into sending you the part if you find the right tech support person.

[MikeP]

Good info re the switches; I had no idea they could be so problematic!

[REBrueckner]

Anybody take a black OEM Guest switch apart?? What's inside??


Some types have the front and back case riveted together, but drilling out the end permits disassembly...and a proper size bolt can be used to reassemble. I took a smaller red PERKO apart many years, ago, fixed whatever was wrong, but I don't remember the nature of the mechanism inside.

The only thing Iever did with my OEm Guests was to rotate the switch whenver I was checking batteries....then of course sometimes I'd accidentally brush against them when crawling around......I learned to check the position before exiting my cramped YF engine room....better called a "crawl area"....

[fixin-to-cruise]

I took 2 Guest switches apart to replace broken knobs (got 'em free from Guest) and have taken others apart in the past. Often you can swap the contact "bolt" around or turn it 180 degrees and have a new contact surface. I think you will find screws on most of them. I did the same kind of thing with the $300 battery parallel contactor.

[TROUBLE]

what type of windlass did you remove from the boat?
Art (TROUBLE)