Electrolysis question, 12V + hanging out there

[sbklf]

My hydraulic steering fittings hit the transom if the motor is tilted too high with the jack plate down. I set up a safety limit circuit but if I wire it the way I would like to, I will wind up with 12 volts + on the aluminum transom cap at all times (except when it is limited out). I run the boat in salt water mostly which I fear makes things worse.

-Will this set up an undesirable electrolysis condition?
-If the salt water washes over the motor and the transom plate, will it make the circuit?

I can wire it differently so voltage is only present when tilting or jacking but will have to use a different relay and latch circuit (more to go wrong). Did a quick drawing if it helps. It is not exactly what I did but it should get the point across.

 

[Silvertip]

Re: Electrolysis question, 12V + hanging out there

You probably have an issue right from the git-go. The relay being fed 12 volts in your system will be energized all the time since the hull of the boat (if metal) and the engine are already at ground potential. Remember, the ground cable from the engine to the battery makes anything it's bolted to at ground potential as well. Using metal parts to make a switch results in arcing that will over time prove unreliable. Why not use a waterproof switch and do this right. The switch should have some "overtravel" in it.

 

[sbklf]

Re: Electrolysis question, 12V + hanging out there

?
-The plate is not grounded.
-The current it takes to energize the relay will not cause enough arcing to be an issue.
-As I said, the picture is not exactly as it is installed. I have designed it for "overtravel"

This is just a safety to prevent from breaking off the steering fittings. I am aware of the limits and will not rely on it. The question is simple; Will this set up create an electrolysis condition.

You probably have an issue right from the git-go. The relay being fed 12 volts in your system will be energized all the time since the hull of the boat (if metal) and the engine are already at ground potential. Remember, the ground cable from the engine to the battery makes anything it's bolted to at ground potential as well. Using metal parts to make a switch results in arcing that will over time prove unreliable. Why not use a waterproof switch and do this right. The switch should have some "overtravel" in it.

 

[bruceb58]

Re: Electrolysis question, 12V + hanging out there

Will this set up create an electrolysis condition.

I think it might. I would modify so that voltage is present only during operation.

 

[seabob4]

Re: Electrolysis question, 12V + hanging out there

My hydraulic steering fittings hit the transom if the motor is tilted too high with the jack plate down. I set up a safety limit circuit but if I wire it the way I would like to, I will wind up with 12 volts + on the aluminum transom cap at all times (except when it is limited out). I run the boat in salt water mostly which I fear makes things worse.

-Will this set up an undesirable electrolysis condition?
-If the salt water washes over the motor and the transom plate, will it make the circuit?

I can wire it differently so voltage is only present when tilting or jacking but will have to use a different relay and latch circuit (more to go wrong). Did a quick drawing if it helps. It is not exactly what I did but it should get the point across.

What motor do you have? Most have the ability to limit "tilt" already on the motor. Unless your motor is kind of old, you can either use the motors built-in limiter, or, like a Merc Opti, buy the limit switch so that it's installed correctly.

12V- in the water, no prob. Add in 12V+? Prob...

 

[sbklf]

Re: Electrolysis question, 12V + hanging out there

It is a 98 Mercury 200 hp. I am not aware of the limit device, that would be nice. However, the jack plate position also needed to be considered. I think ideally, a sealed pressure sensitive plate across the top of the transom would be better than relying on an open connection like I wound up using. I wanted something that let the motor tilt up and jack down as high as possible in any combination of the two as well as the position of the steering. I finished it yesterday and it works good. My only concern is that the contact points will get dirty or covered with a patina like film and fail. I will post some pictures of what I wound up with later today.

What motor do you have? Most have the ability to limit "tilt" already on the motor. Unless your motor is kind of old, you can either use the motors built-in limiter, or, like a Merc Opti, buy the limit switch so that it's installed correctly.

12V- in the water, no prob. Add in 12V+? Prob...

 

[seabob4]

Re: Electrolysis question, 12V + hanging out there

sbklf,
Check out Mercury P/N 87-814407A 3. It will fit your motor.

 

[sbklf]

Re: Electrolysis question, 12V + hanging out there

Looked at it, as I said the allowable travel of both the jack plate and trim varies with the position of the other. This kit appears to have one setting only. I finished the installation and it works good and it will stop the motor no matter of the position of either and let it go as far (I have it adjusted to go within 1/8" of hitting the transom) as possible without hitting the transom. Thanks for the replies.

sbklf,
Check out Mercury P/N 87-814407A 3. It will fit your motor.

 

[chuckz]

Re: Electrolysis question, 12V + hanging out there

To eliminate the 12 volts on the cylinder all the time, supply the 12 volts through a diode from the trim up switch and through a diode from the jack down switch. 12 volts will only be present when either switch is actuated.

 

[sbklf]

Re: Electrolysis question, 12V + hanging out there

I don't quite understand. The voltage present is thru the limit relay, the trim and jack plate control circuits are isolated.

To eliminate the 12 volts on the cylinder all the time, supply the 12 volts through a diode from the trim up switch and through a diode from the jack down switch. 12 volts will only be present when either switch is actuated.

 

[chuckz]

Re: Electrolysis question, 12V + hanging out there

Disconnect the relay coil from the twelve volt source and instead connect it as follows:
When you press either the jack up or trim down 12 volts is applied to the control relay for each function. If you connect a diode from the terminal that gets "hot" when the switch is pressed to the limit relay coil, 12 volts will only be applied only when the switch is pressed. The diodes keep the jack up from actuating the trim down and vice versa.

You can do this at the relay by connecting a diode from the feed side of each of the NC contact to the coil. The diodes will be in parallel.

 

[The_Kid]

Re: Electrolysis question, 12V + hanging out there

My only concern is that the contact points will get dirty or covered with a patina like film and fail. I will post some pictures of what I wound up with later today.

You could always use a reed switch if you're worried about the contact points.

 

[sbklf]

Re: Electrolysis question, 12V + hanging out there

The circuit I ended up with uses DPDT switches keeping the limit circuit seperate from the jack and trim control. I wired it so the limit circuit is only energized when the jack or trim is used to avoid the 12 v + hanging out there condition. To include the trim switch at the motor, I used a diode to allow for one wire operation (had a spare in the wire harness). Here is a one line (kind of) of the circuit. Its messy and not as tidy as it could be, I will redraw it and put a copy in the boat for troubleshooting. The system works great. It allows for trim and jacking to within 1/8' of the fittings hittng the transome every time in any combination of positions. I will have to maintain the contacts at the transom and will consider adjusting it to 1/4" but for now will go with it. Thanks for the replies. Kevin