Battery Jump Leads

[John Orentas]

just for fun, try driving your car into the river at any convenient spot with a depth of about 6ft, with the lights switched on. jump out as it sinks and watch how long the lights stay on.

 

no sparky kerpuff bang stuff. no shorting through the water. clearly 12VDC does not prefer water as a conductor.

 

 

Different thing altogether, the 'live' bits in contact with the water in your example are tiny, a few square millimetres at most. The contact area of the zero volts from a boat hull in my example is the size of a tennis court. I still think my little theory would work even though our captive genius thinks otherwise (well he would wouldn't he).

[ChrisPy]

Different thing altogether, the 'live' bits in contact with the water in your example are tiny, a few square millimetres at most. The contact area of the zero volts from a boat hull in my example is the size of a tennis court. I still think my little theory would work even though our captive genius thinks otherwise (well he would wouldn't he).

obviously your hypothetical boat does not have a blacked bottom

 

don't understand the single wire 240VAC theory though John. possibly confusion with the fact that the mains neutral and the earth are tied together at the local substation, but that makes it 2 wire plus the lawn, not single wire plus the lawn.

[John Orentas]

don't understand the single wire 240VAC theory though John. possibly confusion with the fact that the mains neutral and the earth are tied together at the local substation, but that makes it 2 wire plus the lawn, not single wire plus the lawn.

 

 

More common these days the neutral and earth are connected in or just outside your house. Many modern houses have nothing more than a fancy earth spike with the neutral and earth connected to it. The 230 volt live comes from the substation as a single conductor.

[Gibbo]

More common these days the neutral and earth are connected in or just outside your house. Many modern houses have nothing more than a fancy earth spike with the neutral and earth connected to it. The 230 volt live comes from the substation as a single conductor.

 

And the neutral as another single conductor.

 

Gibbo

 

Different thing altogether, the 'live' bits in contact with the water in your example are tiny, a few square millimetres at most. The contact area of the zero volts from a boat hull in my example is the size of a tennis court. I still think my little theory would work even though our captive genius thinks otherwise (well he would wouldn't he).

 

12 volts difference between two 70 foot narrowboats, with blacked sides and bare baseplates, parallel, 2 feet apart, in a 5 foot deep canal of average pollution will produce a current between them of about 1 amp.

 

If a starter motor requires 9 volts to spin the engine, that leaves us 3 volts to play with. Assume the starter requires 200 amps, then the conductive path through the hull and water is approximately 800 times too poor. Move the boats to within an inch of each other and it is still 600 times not good enough.

 

It would be like trying the jump start the QE2 with speaker wire.

 

Gibbo

Edited June 25, 2007 by Gibbo

[mayalld]

More common these days the neutral and earth are connected in or just outside your house. Many modern houses have nothing more than a fancy earth spike with the neutral and earth connected to it. The 230 volt live comes from the substation as a single conductor.

 

Utterly wrong!

 

There are ALWAYS at least two conductors on the supply from the substation. The only variation is in how far the 3rd (earth) conductor goes;

 

TT - earth conductor terminates at a local earth spike

TN-S - earth conductor goes all the way to the substation

TN-C-S - earth conductor is connected to the neutral at the company fuse (PME)

 

Most new installations are TN-C-S

[RupertG]

More common these days the neutral and earth are connected in or just outside your house. Many modern houses have nothing more than a fancy earth spike with the neutral and earth connected to it. The 230 volt live comes from the substation as a single conductor.

 

That's... not how I understand it!

 

The last time I got involved in ground conductivity, I was burying some radials to provide a good earth plane for an antenna. Needed quite a few, because the earth (which was pretty standard soil) really wasn't that conductive. The best thing to do, I was told, was to put many square yards of chicken wire under the surface, but at that point I hit the limits of enthusiasm (not least of the co-owner of the garden, whose fondness for matters Marconi was somewhat less than mine...)

[blueprince]

In reference to matters electrical, 3 phase 32a current is different from most things on a boat, which current are you talking about when you talk about ground conductivity? It's ok for 230Kv (NOT 230v, 230,000v) and smaller 55Kv sub-stations, but not for boats. Even marconi had to use higher frequencies.

 

As for the petrol only leads, I know some petrol engine leads come with 'slow blow' connectors, to minimise or avoid sparking in the event of a crash or dead short, these are usually shown by a thickening of the connectors near the battery. These can often blow at as low as 60a and in a cascade up to 120a, and so don't work on diesels. They've usually got electrical codes on the side, and it's worth trying to understand them. They're really only a feature on cars, but you don't say where the leads come from.

 

If they do melt, it peels off quite nicely if you let it cool, really don't bother when it's hot.

 

blueprince (a.k.a. 'stumpy')

[chris w]

With reference to the conductivity of canal water and the impedance between a hull and ground, Allan Jones ("Keeping Up") and I made extensive measurements, inter alia, on his boat some months ago in this regard.

 

For a 60ft NB, with unpainted baseplate, moored in about 4 feet of water the figure came out to be around 3 ohms. Ergo, any idea that one could use this path as a return path for current in starting the engine is nuts. Just run Ohms Law to see why.

 

Even with internal resistances in lead acid batteries being as low as 20 milliohms, starting an engine will cause a 2-3 volt drop. In fact, one test of a fully charged battery, is to start the engine and monitor the volts drop; if the volts drop to below 9v the battery is most likely cream-crackered due to its internal resistance being too high. Note that just because a battery appears fully-charged (~12.6v) it does not necessarily make it a good battery (analogous to having a full lock of water with a jammed sluice gate. Lots of water, no way of getting it out).

 

Chris

[Radiomariner]

In reference to matters electrical, 3 phase 32a current is different from most things on a boat, which current are you talking about when you talk about ground conductivity? It's ok for 230Kv (NOT 230v, 230,000v) and smaller 55Kv sub-stations, but not for boats. Even marconi had to use higher frequencies.

 

As for the petrol only leads, I know some petrol engine leads come with 'slow blow' connectors, to minimise or avoid sparking in the event of a crash or dead short, these are usually shown by a thickening of the connectors near the battery. These can often blow at as low as 60a and in a cascade up to 120a, and so don't work on diesels. They've usually got electrical codes on the side, and it's worth trying to understand them. They're really only a feature on cars, but you don't say where the leads come from.

 

If they do melt, it peels off quite nicely if you let it cool, really don't bother when it's hot.

 

blueprince (a.k.a. 'stumpy')

 

 

Well there you are Maveric. I did not know about "slow Blow" connectors. Seems extremely plausible, and the most likely answer to your original query

 

Radiomariner

[Maverick]

Well there you are Maveric. I did not know about "slow Blow" connectors. Seems extremely plausible, and the most likely answer to your original query

 

Radiomariner

 

 

Thanks for your help my friend. Appears my original question got Hi-jacked as so often happens on here. I doubt very much these particular leads will have a slow blow connector fitted as they are only £3.99 per set so unlikely to have anything so fancy added but I will check Decided to just go for it and keep an eye on them for overheating etc.

Edited June 27, 2007 by Maverick