Welding work

[David Schweizer]

Our boat is booked into dry dock for blacking in August, and whilst it is in there, I am having some minor welding done to fill in a few corrosion pits.

 

Last time I had any work done, I seem to remember having to disconnect some of the electrics - Alternator and batteries? I am sure that Tim will know what I need to disconnect, but it would be useful for me to know just in case.

Edited July 17, 2009 by David Schweizer

[casper ghost]

Hi. I was always told to disconnect the battery master switch when welding, although I forgot once and nothing bad happened.

 

Casper.

[Gibbo]

This has been covered several times on this forum. But as usual the search engine doesn't help me.

 

I hear all sorts of crap about it........

 

"Just switch the battery isolators off" (won't make the blindest bit of difference).

"Disconnect the alternator output" (won't make the blindest bit of difference).

 

The only way to be certain is to ensure that the entire electrical system is completely isolated from the hull and that any electrical equipment being directly worked on (say an exhaust on an engine or diesel heater) has its electrical supply completely removed.

 

Doing anything less than this is just grappling in the dark and hoping for the best.

 

And having said all that, damage as a result of welding is rare. Even rarer with reputable boatyards. But when it does happen it often makes a big mess.

 

Gibbo

[casper ghost]

As Gibbo states, i've welded loads on my boat, only ever disconnected the battery master switch, never had any damage..

[dove]

Here http://www.canalworld.net/forums/index.php...&hl=welding

 

I've done loads of welding on my boats and others never bother disconecting anything and never had any trouble, not even with TIG with HF start.

 

Andrew

Edited July 17, 2009 by dove

[David Schweizer]

This has been covered several times on this forum. But as usual the search engine doesn't help me.

 

I hear all sorts of crap about it........

 

"Just switch the battery isolators off" (won't make the blindest bit of difference).

"Disconnect the alternator output" (won't make the blindest bit of difference).

 

The only way to be certain is to ensure that the entire electrical system is completely isolated from the hull and that any electrical equipment being directly worked on (say an exhaust on an engine or diesel heater) has its electrical supply completely removed.

 

Doing anything less than this is just grappling in the dark and hoping for the best.

 

And having said all that, damage as a result of welding is rare. Even rarer with reputable boatyards. But when it does happen it often makes a big mess.

 

Gibbo

This may be the one instance when my (as yet unchanged) negative isolation system could be of some advantage.

 

The battery earths all go to the isolation switch, if I switch that off, (or better still disconnect the cables) it completely disconnects all the battery negative connections from the hull and all the circuits.

 

I have run a test in the past, and with the switch off, the hull is definitely isolated so that should be ok, or am I missing something?

[WotEver]

This may be the one instance when my (as yet unchanged) negative isolation system could be of some advantage.

 

The battery earths all go to the isolation switch, if I switch that off, (or better still disconnect the cables) it completely disconnects all the battery negative connections from the hull and all the circuits.

 

I have run a test in the past, and with the switch off, the hull is definitely isolated so that should be ok, or am I missing something?

 

http://www.smartgauge.co.uk/earthing.html

[David Schweizer]

So what you are saying is that any connection to the hull (direct or indirect), should ideally be disconnected. The only connections between the hull and electrical equipment that I am aware of are the starter motor, heater glow plugs and the Alternator. Oh! and the instument senders, Oh God! there are probably more.

 

This will take all week to sort out and I will probably miss something. Given that it has had welding work done several times in the past and no damage occured, I guess that disconnecting the negative supply to the main circuits from the earth and disconnecting the alternator will hopefully be sufficient.

Edited July 17, 2009 by David Schweizer

[RLWP]

It isn't easy to find an authoritative answer on this on the internet. This is probably the best thread.

 

Richard

[Gibbo]

It isn't easy to find an authoritative answer on this on the internet. This is probably the best thread.

 

Richard

 

Hmmmm

 

That thread is absolutely full of all the bullsh*t I referred to earlier.

 

"Unhook the battery"............ "Disconnect the battery"........... "bla bla bla"..... It makes no bl**dy difference whether the battery is disconnected or not. It is completely and utterly irrelevant.

 

All you have to do is understand what the problem is. Unfortunately once you understand it you realise why it becomes impossible to give a clear answer on what to do that will cover all installations.

 

The problem is the welding current finding an easier path back to the ground clamp than the welder thinks it will. I've seen this happen with an exhaust on an Eberspacher. The welding current went down the exhaust, throught the control box and eventually down to the hull via the power cables. The mess it left was unbelievable. But of course everyone involved knew that couldn't happen because they had "unhooked the battery" which of course make no bl**dy difference. If they'd disconnected the electrical system from the hull it wouldn't have happened.

 

Gibbo

[Biggles]

I have welded my boat, and cars with arc, and mig and NEVER had a problem. I very wise precaution is to make sure the earth is well attached and as close the the area being welded as possible.

 

A screw clamp earth is better than a clip type. If there is nothing to get a good earth connection weld on a lug and cut it off after.

 

BTW I was a professional welder for 20 + years. Whilst I have only welded on my own boat, I have welded on 100's of customers cars over the years. Even ones with fancy computer systems and no problems encountered.

[RLWP]

Hmmmm

 

That thread is absolutely full of all the bullsh*t I referred to earlier.

 

"Unhook the battery"............ "Disconnect the battery"........... "bla bla bla"..... It makes no bl**dy difference whether the battery is disconnected or not. It is completely and utterly irrelevant.

 

Gibbo

 

True, but on balance there were more posts in that thread about why it could be OK not to disconnect everything than in many of the other threads I checked out. Some sensible bits on where to attach earth connections when welding too.

 

As far as I can see, like anything else, if you think about what you are doing rather than blindly following some ancient "rule" you will be OK. In this case, think about how the current is passing from the tip to the earth cable.

 

The problem is the welding current finding an easier path back to the ground clamp than the welder thinks it will. I've seen this happen with an exhaust on an Eberspacher. The welding current went down the exhaust, throught the control box and eventually down to the hull via the power cables. The mess it left was unbelievable. But of course everyone involved knew that couldn't happen because they had "unhooked the battery" which of course make no bl**dy difference. If they'd disconnected the electrical system from the hull it wouldn't have happened.

 

because they wouldn't have had a circuit and no welding would have taken place?

 

Richard

 

Did laugh at the suggestion of removing the fuel tank though...

Edited July 17, 2009 by RLWP

[David Schweizer]

Hmmmm

 

That thread is absolutely full of all the bullsh*t I referred to earlier.

 

"Unhook the battery"............ "Disconnect the battery"........... "bla bla bla"..... It makes no bl**dy difference whether the battery is disconnected or not. It is completely and utterly irrelevant.

 

All you have to do is understand what the problem is. Unfortunately once you understand it you realise why it becomes impossible to give a clear answer on what to do that will cover all installations.

 

The problem is the welding current finding an easier path back to the ground clamp than the welder thinks it will. I've seen this happen with an exhaust on an Eberspacher. The welding current went down the exhaust, throught the control box and eventually down to the hull via the power cables. The mess it left was unbelievable. But of course everyone involved knew that couldn't happen because they had "unhooked the battery" which of course make no bl**dy difference. If they'd disconnected the electrical system from the hull it wouldn't have happened.

 

Gibbo

 

Right, It doesn't make me feel any better, but I do undersand that.

 

The work I am having done is directly to the hull (no equipment) and is quite a long way from the batteries and engine, where all the hull/earth connections are located. If the welder ensures that the AC hull connection is good, and close to where he is working, does that reduce the risk of the welding current seeking an alternatinve longer path?

 

I am beginning to sound ike Frank the tortoise on Creature Comforts with his " I am a bit of a worrier"

 

edited to add whilst I was messing about :- Biggles reply helps to confirm my assumptions.

Edited July 17, 2009 by David Schweizer

[GUMPY]

Just make sure that the earth lead from the generator is connected as close as possible to the spot to be welded.

Quite often I have put the earth onto a piece if angle Iron and then welded that to the hull next to where the work is being done

This means that for the first weld there is very little chance that the current can go back through the hull and for all the welding you need to do the earth is then within a few inches of the weld and on the same plate...........

 

Having said that if you do this and it goes wrong I am not responsible

[Gibbo]

The work I am having done is directly to the hull (no equipment)

 

In that case there is no need to disconnect anything. You could even leave everything switched on and running without a glitch

 

Gibbo

[WotEver]

Edit to remove post because Gibbo had said exactly the same thing while I was typing.

Edited July 17, 2009 by WotEver

[David Schweizer]

In that case there is no need to disconnect anything. You could even leave everything switched on and running without a glitch

 

Gibbo

That is very gratifying, thanks.

 

There is clearly something to be said for having a simple boat, with very little extra equipment.

Edited July 17, 2009 by David Schweizer

[Guest]

In that case there is no need to disconnect anything. You could even leave everything switched on and running without a glitch

 

Gibbo

So is there no need to bother diconnecting when welding anodes on?

Cheers.

[Biggles]

So is there no need to bother diconnecting when welding anodes on?

Cheers.

 

 

Nope as far as I am concerned.

[ThePiglet]

A screw clamp earth is better than a clip type. If there is nothing to get a good earth connection weld on a lug and cut it off after.

But how do you weld on the lug without the earth clamp?

[WotEver]

But how do you weld on the lug without the earth clamp?

 

Gas bottles

[Biggles]

But how do you weld on the lug without the earth clamp?

 

 

I think this is the answer you are looking for all be it the question is worded slightly wrong.

 

Its simple it you think about it, and it has already been mentioned but here it is anyway.... the big reveal....... You attach the earth clamp to your lug first which you then weld to the job. In this case a boat. By so doing you make the lug part of the work piece.

 

But to answer your question exactly you can't. You have to have a return.

[Gibbo]

So is there no need to bother diconnecting when welding anodes on?

Cheers.

 

No. No need or point.

 

Gibbo

[gazza]

pedant alert.....

 

just a small point, what you are refering to as an earth is actually the work return. a sperate earth should be fitted to the job being welded. but this is seldom done.

 

biggles is correct, a clamp with a screw gives a better electrical connection than a spring type croc clip work return. a poor connection can lead to a lot of heat build up and voltage drop with a spring loaded clamp.

welding a small lug to attach the work return to is also good practice.

 

stay safe boys and girls

[WotEver]

just a small point, what you are refering to as an earth is actually the work return. a sperate earth should be fitted to the job being welded. but this is seldom done.

 

Indeed, but isn't the work return connected to earth within the welder anyway?

 

I'm not suggesting that a second safety earth shouldn't be used, but am I right?

 

T.