Disconnecting alternators prior to welding

[blackrose]

Can anyone tell me which of these cables to disconnect from my alternators prior to welding?

 

I know that in normal circumstances one wouldn't bother, but I'm having my new skin tank welded in next week and it's within a couple of feet of the alternators.

 

 

 

The red stuff over the terminals is heat resistant silicone that I put on a few years ago. Someone told me I needed to cover them so that they couldn't be shorted out with a spanner, but I didn't have any rubber boots.

 

Thanks

Edited July 30, 2012 by blackrose

[RobinJ]

Can anyone tell me which of these cables to disconnect from my alternators prior to welding?

 

I know that in normal circumstances one wouldn't bother, but I'm having my new skin tank welded in next week and it's within a couple of feet of the alternators.

In the past I have simply turned off the isolators!

If you are worried, maybe take the positive feeds off the battery and clamp to the -ve/chassis/earth connection?

Will you have to move the batteries for access?

[blackrose]

In the past I have simply turned off the isolators!

If you are worried, maybe take the positive feeds off the battery and clamp to the -ve/chassis/earth connection?

Will you have to move the batteries for access?

 

Yes, I've done that in the past too, but apparently this doesn't protect the alternators.

 

Usually you wouldn't have to worry because I think any current would go through the hull to the earth clamp and not through the alternators, but because the welding is quite close to the alternators I'm not sure?

 

I don't need to move the batteries.

[bizzard]

Yes, I've done that in the past too, but apparently this doesn't protect the alternators.

 

Usually you wouldn't have to worry because I think any current would go through the hull to the earth clamp and not through the alternators, but because the welding is quite close to the alternators I'm not sure?

 

I don't need to move the batteries.

Take en off Mike and tape them up to be on the safe side, only a two minute job.

[Gibbo]

No no no no no no no.

 

All those suggestions are completely wrong.

 

Switching things off, removing bits, pulling the odd cable off here and there is just random meddling that will probably achieve nothing.

 

You need to isolate the electrical system from the hull. That may be as simple as removing two ground wires. It may also be as complicated as removing all the cables to the alternator(s), starter motor, glow plugs etc.

 

On the other hand, if you can be sure the skin tank welder man only puts his earth clamp on the hull next to the new skin tank, and his welding rod touches nothing except the hull and the skin tank, and you don't wrap the welding cables round cables in your electrical system then you don't need to do anything.

[blackrose]

 

On the other hand, if you can be sure the skin tank welder man only puts his earth clamp on the hull next to the new skin tank, and his welding rod touches nothing except the hull and the skin tank, and you don't wrap the welding cables round cables in your electrical system then you don't need to do anything.

 

Thanks Gibbo, that sounds like the best suggestion.

 

Mike

[PaulJ]

Good luck with new skin tank.I hope it solves your problem :-)

[DeanS]

I know someone who was doing some grinding near his engine. A spark hit a battery. It exploded. A frightening experience for him. I'd suggest taking whatever precautions you can to stop any welding sparks doing the same. Also remember if it's arc welding, when the guy puts the helmet on, everything goes dark..except the piece being welded...and he might forget what's in the vacinity...so blocking anything that might be exposed is probably a good idea?

[blackrose]

Good luck with new skin tank.I hope it solves your problem :-)

 

Cheers. I paid the bloke 70 quid for the tank today and it looked good. I asked him if he could weld it in for me next week with the boat in the water and he said he could do it for around the same price. £150 seems like a bargain to me compared to the two £500 quotes I had to do the job.

[blackrose]

I know someone who was doing some grinding near his engine. A spark hit a battery. It exploded. A frightening experience for him. I'd suggest taking whatever precautions you can to stop any welding sparks doing the same. Also remember if it's arc welding, when the guy puts the helmet on, everything goes dark..except the piece being welded...and he might forget what's in the vacinity...so blocking anything that might be exposed is probably a good idea?

 

Thanks for the advice. Perhaps I'll get a couple of fire blankets and use strips to cover my cables. The battery box has a ply lid so they should be ok. I'll have to find something bigger to cover the engine.

 

Edit: Just found some cheap welding blankets on ebay, so I'll use those.

Edited July 30, 2012 by blackrose

[steamraiser2]

Ummmm..... If your welder is welding within several feet of you batteries you will be well advised to take them out. Batteries give off hydrogen. A battery exploding is not a fun event

[blackrose]

Ummmm..... If your welder is welding within several feet of you batteries you will be well advised to take them out. Batteries give off hydrogen. A battery exploding is not a fun event

 

I thought they gave off minute amounts of hydrogen and the main issue was not allowing the gas to build up inside spaces - hence the need for ventilation. The engine space is vented and my deckboards will be up.

Edited July 30, 2012 by blackrose

[steamraiser2]

Hydrogen + ignition source = bang!

[blackrose]

Hydrogen + ignition source = bang!

 

Not quite.

 

Certain density of hydrogen + ignition source = bang!

 

From wikipedia: Hydrogen gas (dihydrogen or molecular hydrogen) is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume.

 

Hydrogen is lighter than air and given adequate ventilation it will escape, so I can't see how there could be a 4% concentration of hydrogen in the air in my engine space with the deckboards up and the batteries not charging. If that were the case then any spark from my alternators or when I've been messing about with battery cables (to remove batteries!) would have already blown the boat up.

Edited July 30, 2012 by blackrose

[steamraiser2]

.... or..so far... you have just been lucky

[bizzard]

Just make sure they're not on charge while he's grinding and welding.

[blackrose]

.... or..so far... you have just been lucky

 

You obviously misunderstood my last post...

 

If so far I've just been lucky, then every boater with batteries who hasn't blown themselves up has also just been lucky - including YOU!

 

After all, we have all produced sparks in our engine spaces without removing the batteries first.

 

Disconnecting cables and removing batteries itself usually produces sparks - so you've sort of defeated your own argument.

Edited July 30, 2012 by blackrose

[Timleech]

Just make sure they're not on charge while he's grinding and welding.

 

..& not recently charged, and well ventilated, and covered.

 

Tim

[blackrose]

..& not recently charged, and well ventilated, and covered.

 

Tim

 

The deckboards will be up and I'll waft something over the batteries to help the venting.

[tosher]

Cheers. I paid the bloke 70 quid for the tank today and it looked good. I asked him if he could weld it in for me next week with the boat in the water and he said he could do it for around the same price. £150 seems like a bargain to me compared to the two £500 quotes I had to do the job.

 

It sounds like a bargain to me if he is a good competent welder. I paid about £400 for my complete job. It was welded in ok with the boat still in the water and solved my engine cooling problems. Remember may have to increase the size of your coolant expansion bottle. --- tosher.

[blackrose]

It sounds like a bargain to me if he is a good competent welder. I paid about £400 for my complete job. It was welded in ok with the boat still in the water and solved my engine cooling problems. Remember may have to increase the size of your coolant expansion bottle. --- tosher.

 

Part of the reason it's cheap is that he said he'd make it from 3mm steel rather than the 4mm that I originally specified. But it looks well made and since it has anti-freeze inside and will be painted outside I can't see any problem with that.

 

Because it's made from 3mm plate, someone told me I should get him to run two vertical bars across the tank, from the baseplate to the counter to prevent the shape of the tank bowing out with the internal pressure. When I said this to the fabricator yesterday he just shook his head and laughed, saying that if the pressure is enough to bow the tank out then he wonders what sort of engine it is. I guess he's right. I have a 95kPa pressure cap on the engine's header tank which is less than 1 bar, or about the same as atmospheric pressure.

Edited July 31, 2012 by blackrose

[Justme]

I have a 95kPa pressure cap on the engine's header tank with is less than 1 bar, or about the same as atmospheric pressure.

 

 

Wont that be 1 bar above atmospheric pressure?

[blackrose]

Wont that be 1 bar above atmospheric pressure?

 

I don't know - is it?

 

In that case is 1 bar above atmospheric pressure enough internal pressure to bow out my tank? It's about 4' 3" long and 1' 4" high.

Edited July 31, 2012 by blackrose

[Timleech]

I don't know - is it?

 

Yes. Enough to make your tank bulge nicely

 

Tim

 

 

Mind you, if it's concave to follow the swim you might get away with it.

[blackrose]

Yes. Enough to make your tank bulge nicely

 

Tim

 

 

Mind you, if it's concave to follow the swim you might get away with it.

 

Yes, it's concave. So you think it might be a good idea to have a couple of bars welded vertically onto the baseplate & edge of the counter which butt up against the tank - about 1/3 of the way in from the ends of the tank perhaps? Or just one in the middle?

Edited July 31, 2012 by blackrose