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welding what needs to be disconnected


raymondh

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Disconnect the batteries.

 

Probably best to completely disconnect any ELECTRONIC devises ie radios, TVs, inverters, alternators etc.

 

ELECTRICAL stuff ie lights, water pump, etc will be OK just turned off.

 

Don't forget to remove flammable stuff from nearby. Also foam insulation produces the most poisonous fumes when burnt.

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Disconnect the batteries.

 

Probably best to completely disconnect any ELECTRONIC devises ie radios, TVs, inverters, alternators etc.

 

ELECTRICAL stuff ie lights, water pump, etc will be OK just turned off.

 

Don't forget to remove flammable stuff from nearby. Also foam insulation produces the most poisonous fumes when burnt.

 

This is one of those subjects that causes immense confusion. As you've just shown :lol:

 

Disconecting the batteries will do nothing to help prevent damage.

 

What OP needs to do is make sure the entire electrical system is disconnected from the hull. That is the only thing that guarantees no damage.

 

The only way to do this usually also involves removing all the cables to the alternator and starter motor.

 

Gibbo

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My apologies to have caused confusion.

 

I thought the words "disconnect completely" would be sufficient.

I suppose this is one of those occasions where if you're not sure what you're doing - don't do it.

 

My suggestion was intended to explain that unless you built the boat yourself, you cannot be sure that somewhere an earth has been made somewhere to the hull. The more so now with galvanic separators being used for shore power installations. In that case, IMHO disconnecting the batteries as well as all the other devices mentioned will isolate and protect the electrical system as effectively as is possible.

 

I don't like the idea of leaving batteries connected as a "soak". Stray currents through them may produce hydrogen and oxygen just itching to find a spark so that they can get back together again.

Edited by jake_crew
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In the car world its advised to leave the batts connected as it acts as a "soak" for any stray currents. Also have the welding earth as close to the weld as possible.

 

Justme

 

Cars/motor vehicles are different from boats in that they routinely use the chassis or body shell as a return conductor, boat wiring is not supposed to do that.

If the boat wiring really is only connected to the hull at one point, there's not much risk of electrical damage from welding on the hull, whether you disconnect stuff or not.

 

Tim

(who has just seen that this could be heading towards one positive argument for having the battery isolator in the negative :lol: though I haven't thought that one properly through yet)

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Cars/motor vehicles are different from boats in that they routinely use the chassis or body shell as a return conductor, boat wiring is not supposed to do that.

If the boat wiring really is only connected to the hull at one point, there's not much risk of electrical damage from welding on the hull, whether you disconnect stuff or not.

 

This is where it starts to confuse without thinking about it properly.

 

Assume you actually check and the installation does indeed only have one connection to the hull. It's safe so you leave it intact. If you now go and overplate the hull then the chances of damage to anything electrical are about as close to zero as it's possible to get.

 

But suppose you're actually rewelding an exhaust pipe into the hull. And further suppose that the engine isn't very well grounded and your first weld strike hits the exhaust and not the hull. You may well have just welded the prop shaft to the stern tube. Or an engine control cable into its sheath. Now that's nothing to do with the electrical system but it's something you know you need to watch for. But think about the alternator and starter connected to that engine. Due to the electrical system being bonded to the hull and the engine your welding current could go through the bond wires.

 

Likewise a heating exhaust where you could easily blow the negative power cable and zap the control box. And many other bits of kit.

 

I think it's probably easier to make sure the entire system is isolated from the hull (by use of spanners and a meter - maybe 15 minutes) than try to work out what the consequences will be of various mishaps whilst welding (maybe a week trying to work out all possibilities).

 

(who has just seen that this could be heading towards one positive argument for having the battery isolator in the negative :lol: though I haven't thought that one properly through yet)

 

LOL. Assuming it did actually completely isolate the entire electrical system from the hull you'd be right.

 

Gibbo

Edited by Gibbo
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Gibbo, your advice is well understood if you are welding something that can cause an arc between elements of the mechanical installation. But if I am doing some typical welding like just welding a bracket onto the hull, nothing to do with the engine or the stern gear, do the same precautions apply?

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Gibbo, your advice is well understood if you are welding something that can cause an arc between elements of the mechanical installation. But if I am doing some typical welding like just welding a bracket onto the hull, nothing to do with the engine or the stern gear, do the same precautions apply?

 

No. No problem can result.

 

There seems to be a general misunderstanding that arc welding does something funny and magical and can somehow cause huge currents in things by some mystical process. It isn't the case. As you've sussed out it's purely a case of where the welding current can leak to. You could. for example, (though I'm not recommending anyone does) fasten the ground clamp to a bolt on the the battery positive lead and weld the terminal without risk of damage to anything.

 

Hence....

 

Assume you actually check and the installation does indeed only have one connection to the hull. It's safe so you leave it intact. If you now go and overplate the hull then the chances of damage to anything electrical are about as close to zero as it's possible to get.

 

Gibbo

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No. No problem can result.

 

There seems to be a general misunderstanding that arc welding does something funny and magical and can somehow cause huge currents in things by some mystical process. It isn't the case. As you've sussed out it's purely a case of where the welding current can leak to. You could. for example, (though I'm not recommending anyone does) fasten the ground clamp to a bolt on the the battery positive lead and weld the terminal without risk of damage to anything.

 

Gibbo

many thanks

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This is one of those subjects that causes immense confusion. As you've just shown :lol:

 

Disconecting the batteries will do nothing to help prevent damage.

 

What OP needs to do is make sure the entire electrical system is disconnected from the hull. That is the only thing that guarantees no damage.

 

The only way to do this usually also involves removing all the cables to the alternator and starter motor.

 

Gibbo

 

So when I had some welding done previously (nowhere near any mechanical installations), and I just isolated the batteries, was I just fortunate that no damage occured to my alternators or batteries?

 

Once I even forgot to isolate the batteries! :lol:

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So when I had some welding done previously (nowhere near any mechanical installations), and I just isolated the batteries, was I just fortunate that no damage occured to my alternators or batteries?

 

Once I even forgot to isolate the batteries! :lol:

 

If a welding clamp is put the bottom ledge, then an anode welded on then even disconnecting the batteries is pointless. No damage is going to result anyway.

 

It's when you start welding things that can have an odd path back to the welder ground clamp that you've got be careful.

 

Gibbo

 

I think it is a bit like jump starting a car - officially you are supposed to disconnect the donor car's battery to protect it's delicate electrical circuitry, but in practice, nobody ever does it.

 

I'm still trying to work out where this idea came from. I can't think of a single reason why it would need to be done.

 

Gibbo

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I'm still trying to work out where this idea came from. I can't think of a single reason why it would need to be done.

 

Gibbo

 

 

I can.

 

When the first battery is so dead / flat that it pulls the good battery & its alt down so low that the second car still wont start. That said you still then have a car running on the battery of the other car so how do you disconnect the jump leads & reconnect the dead batt without blowing some thing.

 

 

Or just leave the engine running for 30 mins to charge up the dead car first if it will.

 

Edited to add

 

Just spotted that its the good bat that is being disconected so no I cant think of a good reason either.

 

 

Justme

Edited by Justme
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  • 1 month later...
This is one of those subjects that causes immense confusion. As you've just shown :lol:

 

Disconecting the batteries will do nothing to help prevent damage.

 

What OP needs to do is make sure the entire electrical system is disconnected from the hull. That is the only thing that guarantees no damage.

 

The only way to do this usually also involves removing all the cables to the alternator and starter motor.

 

Gibbo

 

 

Having done a lot of welding gas and electric, I would completely concur with Gibbo on this one, Hmm wonder why I prefer gas... Its no fun on and job having to disconnect multiple earths etc.

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Having done a lot of welding gas and electric, I would completely concur with Gibbo on this one, Hmm wonder why I prefer gas... Its no fun on and job having to disconnect multiple earths etc.

 

I'm in a transition phase from gas to MIG, and just now I know why I prefer gas! I'm tidyer, don't have to grind off so much weld and I can see what I am bloody doing!!!

 

 

Richard

 

I love the smell of burning waxoyl in the morning...

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I think it is a bit like jump starting a car - officially you are supposed to disconnect the donor car's battery to protect it's delicate electrical circuitry, but in practice, nobody ever does it.

 

 

I'm still trying to work out where this idea came from. I can't think of a single reason why it would need to be done.

 

Gibbo

 

When my Brother in Law tried to start his Range Rover with jumpleads from a Jeep (this was in the US) the Jeep windows closed , the doors locked and the alarms and horn went off with the headlights flashing. No amount of intevention would stop it., we couold not even open the doors. We eventually had to get someone from the Jeep agents to unlock the jeep and re-set the system. When we asked him what had caused it he just said that it was part of the anti theft system, the electronic system, had sensed an "illegal" connection and responded in the way it was designed to , which was to lock a potential theif inside the vehicle.

Edited by David Schweizer
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When my Brother in Law tried to start his Range Rover with jumpleads from a Jeep (this was in the US) the Jeep windows closed , the doors locked and the alarms and horn went off with the headlights flashing. No amount of intevention would stop it., we couold not even open the doors. We eventually had to get someone from the Jeep agents to unlock the jeep and re-set the system. When we asked him what had caused it he just said that it was part of the anti theft system, the electronic system, had sensed an "illegal" connection and responded in the way it was designed to , which was to lock a potential theif inside the vehicle.

 

Now that is a distinct possibility. Makes perfect sense.

 

Doesn't explain why people were saying it 20 years ago though :lol:

 

Gibbo

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  • 1 year later...
If a welding clamp is put the bottom ledge, then an anode welded on then even disconnecting the batteries is pointless. No damage is going to result anyway.

It's when you start welding things that can have an odd path back to the welder ground clamp that you've got be careful.

Coming to this a bit late and agreeing with gibbo so all a bit risky, but I think thats it isnt it.

 

If your welding a fitting, onto the hull, no other complications then, the current will either flow through the hull to nearby clamp, or it will not.

 

But when as you gave as an example, your welding bits of engine related stuff, you could get flows through the alternator/propshaft/control cables etc at which point it all becomes far more open as to exactly what will do what.

 

*Also made FAQ topic.

 

 

 

Daniel

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Coming to this a bit late and agreeing with gibbo so all a bit risky, but I think thats it isnt it.

 

If your welding a fitting, onto the hull, no other complications then, the current will either flow through the hull to nearby clamp, or it will not.

 

But when as you gave as an example, your welding bits of engine related stuff, you could get flows through the alternator/propshaft/control cables etc at which point it all becomes far more open as to exactly what will do what.

 

*Also made FAQ topic.

 

 

 

Daniel

 

I'm just having a couple of fittings welded to the roof and onto the handrails at the stern.

 

Should I isolate the batteries, disconnect the hull earth bonds, or do nothing at all?

  • Greenie 1
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I'm just having a couple of fittings welded to the roof and onto the handrails at the stern.

 

Should I isolate the batteries, disconnect the hull earth bonds, or do nothing at all?

 

I would do nothing at all

However when I weld to the Barge I put the earth return on the bit that is being stuck on not onto the hull, this means that the return is through that and not the hull.

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... when I weld to the Barge I put the earth return on the bit that is being stuck on not onto the hull, this means that the return is through that and not the hull.

Which is actually more likely than any other workflow to potentially cause damage. If your torch touches the hull then current will attempt to find a circuit via the hull and/or any connected equipment to earth in order to complete the circuit back to the transformer. The earth should always be well connected to the hull.

 

Tony

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