A basic, possibly embarrassing, question 12 DC wiring ......

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NealB

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Would it be sensible (ie safe and reliable) to take the power for an echo-sounder by wiring its two cables to each terminal on a push button starter switch, or a push button stop switch?
 
You can only put a switch in one wire or the other, usually the red positive one.

The negative black wire needs to be connected to a grounding point eg on battery negative or a terminal strip.
 
MoodySabre said:
All my instruments are wired to one Instruments switch in the panel. Why switch is separately?
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I'm looking at ancient wiring (1966), probably adapted by several owners over the decades.

There isn't an 'instrument' switch on the panel. The instruments are potentially 'on' as soon as the domestic batteries' master switch is 'on'.

The instruments are then switched on/ off using their individual power switches.

I'm thinking of fitting a new, basic, echo-sounder, and the easiest place to pick up 12 volts would be to wire it across either the engine start, or the engine stop, button (let's say it's the 'stop' button to avoid repetition).

ie when the stop button isn't pressed, the echo-sounder will work, and the engine will continue to run.

When the stop button is pressed, the engine will stop, and the echo-sounder will keep working ........ I think!

ie when the stop button is pressed, the stop solenoid and the echo-sounder are momentarily in parallel.
 
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MikeCC said:
You can only put a switch in one wire or the other, usually the red positive one.

The negative black wire needs to be connected to a grounding point eg on battery negative or a terminal strip.
Click to expand...

Please see my reply to MoodySabre (#4), where I hope I've explained my thinking more clearly.
 
In short, no. The switches are simply making a circuit when pressed, so connecting your echo sounder to both pins of the switch (if that is what you are asking) will put the echo sounder in the original circuit in parallel with the switch. So current will flow from one pin, into the echo sounder (which will pinch some of the power on the way through) back to the other pin and then to (in your example) the stop solenoid, which wants the power the echo sounder has already pinched. So neither are likely to work with the switch off, and with it on the solenoid will work because you will have bypassed the echo sounder, so the solenoid gets all the power again.
 
It's your use of "across" that doesn't make it clear. As said by Mike, it is just the red (positive) that is switched. If you are just tacking on to the positive feed to the engine switch then that's ok but it is not switched on it's own account. The negative is just needs to go to ground anywhere - if that is by tacking it on to the black wire on the back of the engine switch then ok. It's not tidy but it should work.

Your ancient wiring by several owners over the decades has just got another twist!
 
Jungle Jim said:
In short, no. The switches are simply making a circuit when pressed, so connecting your echo sounder to both pins of the switch (if that is what you are asking) will put the echo sounder in the original circuit in parallel with the switch. So current will flow from one pin, into the echo sounder (which will pinch some of the power on the way through) back to the other pin and then to (in your example) the stop solenoid, which wants the power the echo sounder has already pinched. So neither are likely to work with the switch off, and with it on the solenoid will work because you will have bypassed the echo sounder, so the solenoid gets all the power again.
Click to expand...

I'll try drawing a pic!
 
Thanks, folks, for taking the time to answer this numpty.

Jungle Jim's post (#6) has explained in terms that even I can visualise clearly: phew!

Back to the drawing board, and poking around on board tomorrow.

I'm glad I was brave!

(and thanks for not laughing too overtly).
 
My services as a consultant are available until Monday. My fees are, I think, quite reasonable (coffee will suffice, beer gets the platinum service :D )
 
Thanks, Bru ...... we had, by our standards (please, no comments needed!), a high achieving day today.

So I've been girding my loins for tomorrow's battles.

If you see smoke from the marina, it might be me doing sumfink silly.
 
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What you propose won't work.

One of these would be a simple solution, providing a switch and circuit protection in one package:

Thermal Magnetic Circuit Breakers | RS Components

Wire the negative directly to a suitable negative (busbar or whatever), find a positive that's only on when the isolator is on and connect a wire from it to one terminal of the switch, the other terminal goes to the echo sounder. Press it for on, press again for off, if there is a short/overload it pops out and breaks the circuit.
 
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