View Full Version : is my hull live
Dignity
10-06-2015, 07:50 AM
I was removing the battery from the tinnie and I used some multi grips to loosen the wing nut on the positive terminal when I contacted the thwart seat and got a spark. Got out the multimeter and there is 12.5v between the positive terminal and the hull, now I have done a cursory check of all the connections and they are fine but before I start stripping everything especially where cable runs over any metal is this related to the motor being bolted to the hull, duh! I guess I can eliminate that by disconnecting the power to the motor, will give that a try but any other info would be appreciated.
Funchy
10-06-2015, 08:03 AM
its just the residual power of the Funch man after he spent the arvo in ya tub mate.... :-P
aussiebasser
10-06-2015, 08:06 AM
It's not live, it's earthed. Probably through the motor. It's not unusual.
McKnight
10-06-2015, 08:23 AM
The hull probably connects to the negative terminal of the battery (being earthed), the same is true for the chassis of cars.
Dignity
10-06-2015, 08:25 AM
its just the residual power of the Funch man after he spent the arvo in ya tub mate.... :-P
Was a pleasant afternoon, that 75 cm flattie gave you a run for your money on 8lb leader
Dignity
10-06-2015, 09:03 AM
I disconnected the power to the motor and the voltage dropped to 0.98v, why is this so, the power supply goes to a switch box with a master switch and even with this in the off position it still registers and all the wiring looks fine.
The 0.98 Volts would be a worry.
aussiebasser
10-06-2015, 10:16 AM
I'm sounding a bit like Tom Jones here, but again, it's not unusual. Some alloy boat manufacturers purposely earth the hull in an attempt to prevent electrolysis.
Noelm
10-06-2015, 10:32 AM
not too sure how you can get any voltage with the battery disconnected??
He said he disconnected the power to the motor not disconnected the battery noel.
This is going to be like herding cats.
macca3441
10-06-2015, 11:19 AM
If you're concerned, take the boat to a decent auto electrician to diagnose.
The hull will be earthed from the outboard, however, if the boat is wired correctly there should be no residual current through the hull!
As long as all circuits earth direct back to the neg of battery (and not through the hull), there'll be no issue!
Macca
Im not sure what your asking? you asking if your battery is connected to you hull?
- Disconnnect all power cables from motor and battery. Stick your meter on Ohms and measure continuity from your negative cables direct to your hull(anywhere on the hull is fine)
This will tell you if the boat builder has connected the hull to earth/negative(Some of them do)
So far we have...
Got out the multimeter and there is 12.5v between the positive terminal and the hull
I disconnected the power to the motor and the voltage dropped to 0.98v, why is this so
Dignity
10-06-2015, 12:45 PM
Guys, the hull is a quintrex WB 4.2, the wiring looks like it was initially installed by the local boat yard, i really dont know as i bought the outfit second hand. I just checked again and the voltage between positive on the battery and the hull is now 0.73v, the power to the motor has been disconnected. I will pull the switch panel apart over the coming days and separate all the connections and work my way through each one to see which circuit might be causing my issue, there are only anchor and running lights, bilge pump, sounder and a cockpit light so hopefully it shouldn't take long.
juggernaut
10-06-2015, 08:23 PM
Out of interest where's the -ve going from the batt, outboard and -ve bus?
I have a 2001 Quinnie 5m Sea Breeze and found they were all bolted together at the transom near the battery switch from the factory. Changed it when I rewired it.
Dignity
10-06-2015, 09:04 PM
Out of interest where's the -ve going from the batt, outboard and -ve bus?
I have a 2001 Quinnie 5m Sea Breeze and found they were all bolted together at the transom near the battery switch from the factory. Changed it when I rewired it.
The negative goes from the outboard and another lead to a bus inside a box, now there's another story. I can remove the gang of switches but getting to the negative bus is difficult as the hole to access it is the size of the gang switch and it looks a bit of a mess in there.
What has happened is whoever built the box put it all together with glue and screws and then glued carpet all around. I had a go today and stripped the carpet off the bottom of the box, removed the screws and can't progress any further. Looks like a hack job tomorrow, don't have time to build a new box just now so will have to be easy on it so that I can rebuild it temporarily.
aussiebasser
11-06-2015, 08:03 AM
Quintrex liked to run the earth to the hull. It prevented the hull from having a positive charge if a wire shorted on the hull. The positive charge would create some corrosion issues. By earthing the hull, if a positive wire touches the hull a fuse will blow. Most outboards automatically earth the hull now, so I'm not quite sure why people take away the earth wires to the hull.
With the motor already earthed by adding a second earth to the hull opens a can of worms to allow current flow through the hull itself.
groverwa
11-06-2015, 10:35 AM
This may not help but is the multimeter a digital or is it analogue? A digital mm will measure residual voltage as it does not drain current where as an analogue mm will drain current and result in showing no voltage.
When we in Telecom first got digital meters I remember working on an exchange rectifier/ distribution system that with the rectifier turned off and disconnected from the battery still showed 52 volts on the rectifier output where should have been nothing. When an analogue mm was used we saw the voltage decay to zero as this mm drained the capacitors in the rectifier
Dignity
11-06-2015, 11:45 AM
This may not help but is the multimeter a digital or is it analogue? A digital mm will measure residual voltage as it does not drain current where as an analogue mm will drain current and result in showing no voltage.
When we in Telecom first got digital meters I remember working on an exchange rectifier/ distribution system that with the rectifier turned off and disconnected from the battery still showed 52 volts on the rectifier output where should have been nothing. When an analogue mm was used we saw the voltage decay to zero as this mm drained the capacitors in the rectifier
I checked an hour or so later and still had residual current, does the multimeter hold this current after it has been switched off.
Working through a small hole is no fun and I am getting weird readings. Turn on the led anchor lights and running lights and a small delay before they come on, turn the switch on to supply power to the sounder (not actually turning sounder itself on) and both led systems shut down but turn the bilge pump on and they fire up again. Tried measuring the voltage and I am only getting 6.5v to the switches but I can't access the main switch as instead of cutting a nice large hole whoever made this box bore 2 smaller holes just big enough for the terminals to poke through, certainly they had no idea of what they were doing and didn't want to add to the system. Looks like I will just hack the box apart and make a new one up and do a complete rewire.
A question, I checked the switches out and most read 1.1 or 1.2 ohms across the terminals when in the on position but one of them reads 1.7 ohms, should I replace this one.
Dignity
11-06-2015, 06:51 PM
OK, had half an hour spare and needed all of it to get the box apart without totally destroying it. The wiring underneath was a bit of a mess, there were 3 sets of fuses with 15 amp fuses in them so the items in question would have fried first before the fuses blew, the negative wiring was all connected to a bus bar with screw fittings yet whoever built the box decided in their wisdom to crimp cheap lugs onto them then screw them down ????.
I put the battery on charge this morning and considering it is about 4 years old it came up as 12.9 volts.
1. Next step pull the box apart, found a mess of wires etc. make sure all connections are on, some were loose. Check the voltage on the other side of the master switch and only get 12.5 volts , not a lot of drop but enough to maybe be concerned.
2. Check the other switches and 12.5 getting to all of them on both sides (when On that is) .
3. Interesting that if I turn on the LED's then try the Sonar switch (not turning the sonar unit itself) the LED's go out, remove the sonar and turning the switch on has no effect.. Same thing if I first put on the LED's then turn on the bilge the LED's go out.
4. Turn either sonar or bilge pump on first and LED's will work.
5. I am now totally confused, why would the LED's go out when the switch for the sonar is On but the unit itself has not been turned on, is there some sort of feedback or whatever the terminology is happening.
Attached is how the wiring is set up, I have checked where possible that the wiring is definitely positive or negative without pulling everything apart.
High inrush current causing voltage drop, by pass the main switch and try it.
Dignity
11-06-2015, 07:38 PM
High inrush current causing voltage drop, by pass the main switch and try it.
Thanks Fed, I figured the master switch needed replacing considering the drop in voltage, I will give it a go tomorrow. What I don't understand is why when the sonar is switched off why the sudden inrush of current when the supply switch to it is switched on, to me it appears that there must be some sort of leakage. I have very basic knowledge of electrics so the issues I am having is beyond me.
scottar
11-06-2015, 08:36 PM
In most modern electronics, capacitors are used in the power supply for filtering. When first hooked up these capacitors "charge" at sometimes quite high currents until they are at the supply voltage. As an example, I had a Navnet 3D system that was giving me issues when coupled with a fully electronic, programmable voltage distribution system. The current limiting was programmed at 20 amps. The Furuno system was spec'd to only draw 15 amps but the momentary inrush current was enough for the whiz bang voltage system to have a hissy fit and throw it's hands in the air and switch the power off - even though the 15 amp fuse didn't blow (due to the duration of the spike being too short to generate the required heat to melt the fuse wire).
Dignity
11-06-2015, 08:51 PM
Thanks Scottar, it kind of makes sense, the end result is that I will rebuild the box and really tidy up the wiring and get rid of those unnecessary crimps in the process, I guess the high resistance of master switch didn't help.
Dignity
13-06-2015, 11:31 AM
Update, a jigsaw was used to cut the bottom of the box off, I had a blade that went just deep enough, the box was definitely built to never ever be pulled apart for either maintenance, how would you replace the fuses, or to add a component. What a mess, the negative bus bar was sitting directly under the switchboard and most of the positive crimps were uninsulated so if one dropped off, and some were a little loose, it would have dropped directly onto the bus bar.
After much testing there is one switch which has more resistance than the others and as I had a spare I replaced it. The main switch (One of those battery security/isolation switches with the red quarter turn key) was faulty, initially I got 0.5 voltage drop across the terminals, but a couple of times it was around 6 volts so it is now out. I will wire the positive direct to a closed in bus and will install some Anderson plugs at the battery end for both the motor and accessories, I prefer it this way as my battery charger has been modified to end in an Anderson plug and at the end of the trip I just separate the ones in the boat, plug in the charger and everything else is isolated.
If I get a chance next week I'll make a new box, one that allows easier access, I hope I should only need that for adding additional circuits.
This is what I'd do Dignity.
1) Get rid of the wingnuts.
2) Find out where the second earth to the hull is coming from.
3) Bolt the motor leads directly to the battery. (no plug)
4) Use a bolt in fuse at the battery for the accessories. (no plug)
5) Clean everything up, lightly Vasolene & tighten securely.
6) Disconnect the battery negative between uses.
7) If you really feel the need to a plug on your charger check out the ctek comfort leads.
Dignity
13-06-2015, 02:48 PM
Fed, I will probably follow through with most of the suggestions, I do have some special grease that promotes good conductivity which I use instead of Vaseline. I had a look at the ctek comfort leads and the new ones look good as they appear to be well sealed, I don't envisage a problem with Anderson plugs as the connection is looped inside the battery box and I use the grease I mentioned on the connections.
I have been looking for where there might be an issue with the negative, most of the wiring is in conduit so I have concentrated so far on where the cable enters and exits the conduit but so far looks OK but that's not to say there could be joins inside. Next I'll have to check all the connections to the accessories although the running lights have been pretty well sealed.
When the motor is connected to the battery I still get 12+ volts from the battery to the hull so I am assuming because the motor is bolted directly to the hull this is the origin of the reading I getting, is this normal or should I be looking for an issue with the electrics in the motor.
When the motor is connected to the battery I still get 12+ volts from the battery to the hull so I am assuming because the motor is bolted directly to the hull this is the origin of the reading I getting, is this normal or should I be looking for an issue with the electrics in the motor.
Completely normal & desirable, according to Mercury this will allow the motor anodes to also offer protection to the alloy hull. It's the second earth connection that's a worry especially as it's an "odd" reading.
aussiebasser
13-06-2015, 05:27 PM
That 12 volts is proving that there is no voltage in the hull, it's all in the battery where it belongs.
Dignity
13-06-2015, 05:44 PM
Completely normal & desirable, according to Mercury this will allow the motor anodes to also offer protection to the alloy hull. It's the second earth connection that's a worry especially as it's an "odd" reading.
Fed, it isn't much but something must be causing it, I'll keep chasing till I've eliminated everything, must be a stray wire somewhere.
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