Entire 12v system FUBAR. Baffled of portishead...

[Reptile Smile]

In some ways it was very pleasant to spend the afternoon on the 'new' Hurley 20. I had a bilge pump to fit, and it was rather nice to be tucked up inside with the heater on and hoolie blowing outside...

On the other hand...

I'd left the wiring diagram for the cheapie all-in-one bilge pump, and the three way switch at home. Even do, I didn't think it would be beyond the wit of man to work out which way was up. Unfortunately, it was.

Couldn't get anything out of the bilge pump at all. Thinking it was faulty, I unplugged it, and connected it straight to the switch/negative bus. Nothing. In the end, out of desperation, I touched the ends to the massive starter-motor style cables that bring the battery power to the cabin and it turned fine.

This obviously limited the number of things it could be. Tracing it back from here, however, got even more confusing. The choc block bus bar was obviously rubbish, so I disconnected this, and took the 1 foot wire that closed the bus bar loop to the massive cable straight to the bilge pump. Still nothing. To clarify, it worked from the massive cable, but not from the end of the 1 foot cable connected to it. My multimeter said 12.68 volts from the massive cables, and 11.70 from the end of the 1 foot cable.

I suppose it retrospect I should have measured the current, not the voltage. Even so - I'd have expected the bilge pump to turn over on 11.7 volts..?

I also couldn't get *anything* else to work. No lights, nothing - I suspect because of the crappy common earth. The answer may well be to rip everything out and start again, though it don't know what gauge cables to use for what? And given even going back to barebones didn't work, I'm a little stumped. Any ideas..?

 

[neilf39]

If you got a 1v drop over 1 ft of cable with no load applied other than the minute load for the multimeter then I think it needs replacing, possibly badly corroded internally. I expect the internal resistance is so high that the current is so limited it won't deliver enough for the pump. Did you try using the meter to measure the resistance between the ends of the short cable?

 

[William_H]

If you got a 1v drop over 1 ft of cable with no load applied other than the minute load for the multimeter then I think it needs replacing, possibly badly corroded internally. I expect the internal resistance is so high that the current is so limited it won't deliver enough for the pump. Did you try using the meter to measure the resistance between the ends of the short cable?

+1 a digital voltmeter can almost smell a voltage that is not really there. I have had pieces of cable witha break in the middle often from corrosion througha pin hole in the insulation. good luck olewill

 

[VicS]

I'm a little stumped. Any ideas..?

You may well be facing an extensive rewire job.

But some more systematic testing may find a single cause for all your problems. A bad connection in some wiring that is common to all the things that don't work could be the cause. It could be in the positive or the negative wiring.

The ability of a digital multimeter to detect and measure a normal voltage through a bad connection in the way William_H describes can make a total fool of you if you are not careful. For trouble shooting like this a test lamp which will draw a significant current, can often be a better bet than a meter. Make one up with a car stop light bulb, or an old headlight bulb with one good filament, on a couple of leads.


IF doing any rewiring remember that not only must the wiring be heavy enough to carry the current involved safely it must also be heavy enough to carry it without excessive voltage drop. The longer the cable run the more important this becomes and you can end up needing wire much heavier than required to carry the current safely.

There are online calculators which will calculate wire gauge from the current and total wire length ( note that most require the total of positive + negative wires to be input)

 

[Fantasie 19]

You may well be facing an extensive rewire job.

...on a Hurley 20?

To the OP.. I'd be interested in the outcome if you decide to re-wire as I have the same job on my Hurley when I can get round to it.

 

[Rigger Mortice]

I had exactly the same problem a few years ago.
It turned out to be the Master switch. Once that was taken apart and cleaned up everything was fine.

It may be worth checking the resistance of different parts of the wiring (with the power switched off) to help locate the problem but I wouldn't be contemplating a rewire just yet.

 

[david_bagshaw]

I had exactly the same problem a few years ago.
It turned out to be the Master switch. Once that was taken apart and cleaned up everything was fine.

It may be worth checking the resistance of different parts of the wiring (with the power switched off) to help locate the problem but I wouldn't be contemplating a rewire just yet.

Had similar with a battery isolator switch.

If everything doesnt work, it is probably one of the big connections, battery posts get covered in oxide, that doesnt conduct. are you certain the battery has some capacity. earthing points are another potential problem

 

[blackbeard]

If you are not totally certain which bit of wire does what, then you will have to do either or (preferably) both of:
generate a wiring diagram for the boat (for a small boat shouldn't be too complex);
clearly label each bit of wire with a note saying where it goes to and what it does.
This can save unending grief.

If the wiring generally doesn't look too good then it might, as suggested, be easier to replace it rather than mess about with a rat's nest. Paying special attention to switches and connectors, also to earthing points. Shouldn't be too hard on a small simple boat.