Electrics Question (Curly one!)

[skronkman]

I take it the red light you mention is on the actual markfish unit? You are wiring the black and red wires directly to your battery supply bus and not the red and black wires from your gps/furuno, right?

It could be a faulty connection somewhere further up the wiring that gets disturbed by water or movement.

On dry land, watch the markfish light and try jiggling the wires near where it's wired in and further up circuit, see if it makes the light flicker, if so you have a loose connection somewhere.

Another test is using a multi meter on voltage setting, test the voltage on the black and red wires on the markfish where you wired it in (as close to markfish as possible) while on dry land. Record this number. Do the same while on the water. Do not disconnect the markfish for the tests, just touch the probes to the exposed wires where you joined them. Compare your numbers. They should both be pretty much the same and be between 11.5 - 14.5 volts (old battery and no motor running vs motor running). If your voltage is significantly lower when on the water then you have a power supply issue to that point in your wiring, possibly caused by water ingress, vibration, corroded wires, or some other unknown reason. You will need to trace back the issue to find the source of the fault. Remember, It could be a bad connection in either the positive (red) or negative (black) wires. your equipment must be turned on for this test to work (equipment draws current, creating the voltage drop).

You can just try and rewire your black and red wires to a different voltage source location too and see if that works for your markfish but you may still have a wiring fault somewhere that needs rectification or it can cause damage (possibly electrolisys if you have an alli hull!).

Good luck. Let us know how you get on.

Cheers

[Fish-cador]

Just keep the boat dry. I told there's a lot to write and check. LOL

[TheGreatestGoat]

Classic grounded connection. Dont get your boat wet.

Haha. Assuming the boat is wet, what am I missing? How is this affecting the circuit?

Hard to write it down here. I dont know how you wired it.

You are correct to say that the intermittent red light is a possible indicator of lack of electrical power.....current to be exact. Water, due to the minerals and impurities on it conducts electricity. It is possible that your power supply is getting electrical connection with the hull or engine when in water causing current to drain to the water which is grounded depriving your unit of current.

Check your + and - power leads. Look around and make sure there is nothing that can cause your "live" power lead to be in contact with water, directly or indirectly.

There are other things you can check. As i said, it's too much to write them all here.

Thanks all for the suggestions, will give some of these tests a go and report back. Worth noting is that the flickering is very pronounced on water but is still slightly noticeable when off (not enough to impact performance). However the flickering only occurs when Furuno is switched on, if it's just the Garmin then it's fine.

For what it's worth here is the wiring diagram that I was given, and also the way that I have rigged it up (if you see any issues with how I've done it, please let me know...)



Thanks again,
Goat

[Fish-cador]

Your solutions are easy.

1. Dont get the boat wet or
2. Dont turn on the furuno.

)

[Fish-cador]

Hang on. What kind of wiring is that?

Green is NOT battery ground. Green is supposed to be for neutral ground to dessipate stray current. Ideally, green cables should have zero current on it. If you have current on the green cable, something is terribly wrong.

[rb85]

http://www.mark.fish/how-to-install

What you have is not quite the same as the manufactures drawing? Although the drawing you have is supplied from somewhere

So we do not over confuse the situation there is no Neutral cable in this scenario as the voltages are all DC so it's only + or -.

Something is causing a voltage drop reading the drawings you supplied I would suggest lifting the Data out - and the furuno green - from the Battery - for a start and see if that helps.

Do all other electronics still work ok in boat when in the water?

[TheGreatestGoat]

http://www.mark.fish/how-to-install

What you have is not quite the same as the manufactures drawing? Although the drawing you have is supplied from somewhere

So we do not over confuse the situation there is no Neutral cable in this scenario as the voltages are all DC so it's only + or -.

Something is causing a voltage drop reading the drawings you supplied I would suggest lifting the Data out - and the furuno green - from the Battery - for a start and see if that helps.

Do all other electronics still work ok in boat when in the water?

Hey rb thanks for your reply. You're right in pointing out that the diagram displayed is different to that which ships with the unit. However, that diagram is directly from the manufacturer/inventor of the markfish because the Garmin units require a different wiring setup. However, they have gone cold on me, hence me asking on here.

It's a strange wiring setup due to the fact that the garmin negative doubles as a NMEA data ground which checks out in the Garmin manual which states:

"When connecting an NMEA 1083 device device containing one Transmitting (Tx) wire and one Receiving (Rx) wire each, the NMEA device must be connected to a common ground."

In an attempt to try and eliminate a potential cause, I re-wired the Furuno through the mains back to the battery and kept the markfish and garmin running their own leads directly back to the battery. However this did not help.

There is one piece of information in the Furuno manual that I don't quite understand but think might have some relevance to the problem, it states:

"For a boat with positive polarity DC power and the fish finder is grounded to the hull, external equipment cannot be connected directly to the fish finder is the signal line of the equipment is connected to ground."

Anyway, will try your suggestion and see how it goes.

Cheers,
Goat

[rb85]

Goat that makes sense the reason I say lift those wires off is they could be causing a drop in voltage for some reason it may not 100% solve your problem but may help in identifying where it’s coming from.

[Fish-cador]

Good find on that diagram RB.

That confirmed wiring issues. The data cable (green) should not be connected to battery neg. The green data cable most probably carries "positive potential" (+ voltage). Check the voltage between the green data cable and the battery neg to confirm.

"Grounding point" is generally called "earth ground", not battery ground. Earth cable is normally connected to an "earthed grounding bar" which should be totally isolated from battery or power leads. However, many connect battery neg to the same earth which is not the best way of grounding.

Green cable is generally accepted as ground wire to drain unwanted current to "earth". I wonder why markfish used green as the color of their data cable. That is just wrong!

[rb85]

It can be a dangerous game incorrectly grounding DC on a boat if it’s aluminium due to risk of electrolysis.

Personally I would not and I would be returning any negatives to a main point or to the battery post without worrying about it.

Remember we are not talking about a 240v residential installation so earthing is not something to consider unless your vessel is a little different to the average trailer boat.