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Old 10th May 2012, 15:45   #1
v&v
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Default Electric welding in cars : How safe it is ?

My safari's bumper guard got snapped from the joint today morning. Went to FNG to get it welded(gas), but the guy was not available. Next to the shop there was an electric welding shop too.

He offered me to weld the same, said its safe to do it with battery -ve terminal removed.

I was a bit apprehensive as what would be the effect on battery,ECU and other electrical due to spikes. Finally got hold of another gas welding guy to get job done.

Now still the doubt remains is electric wielding safe on cars ? Has any body has done it ? Pl share your experience.
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Old 10th May 2012, 16:04   #2
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Default Re: Electric welding in cars : How safe it is ?

I had the exact same problem when I wanted to get fog lamp brackets fitted on my Xylo bull guard. The welder was the one who had done this multilple times for other customers and would have done it the same way suggested (disconnecting the -ve battery terminal). He was confident, but I was thinking about the multiple amps that would fry car electronics should anything go wrong. so NO to that!

The other option was to remove the bull guard altogether for the welding - lot of effort.

Finally - I got the brackets fabricated elsewhere. Regarding gas welding, the welder was of the opinion of paint damage due to higher heat near the welding point.
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Old 10th May 2012, 16:09   #3
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Default Re: Electric welding in cars : How safe it is ?

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Originally Posted by v&v View Post

He offered me to weld the same, said its safe to do it with battery -ve terminal removed.
I have never had the need to get arc welding done on my cars but do know that it is safe to go ahead with the battery -ve disconnected
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Old 10th May 2012, 16:15   #4
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Default Re: Electric welding in cars : How safe it is ?

Given proper precautions Electric Welding is probably as safe, if not safer, than gas welding.
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Old 10th May 2012, 16:36   #5
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Default Re: Electric welding in cars : How safe it is ?

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Originally Posted by v&v View Post
Now still the doubt remains is electric wielding safe on cars ? Has any body has done it ? Pl share your experience.
I don't know whether it qualify as a car or not, but for our baja buggy we have done a lot of electric welding. The only pre caution we took was to get the -ve terminal of the battery removed before welding as you have mentioned. Our juniors made a mistake of not removing the negative terminal and they cooked the ignition coil. There was no ECU in our buggy, but only a Ignition control unit, and was fine even after the umpteen welding work we done on it.

But hey, it was just a buggy an nothing much could possibly go wrong. I don't know how the ECU and other electrical stuff react to electic arc welding.
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Old 10th May 2012, 16:43   #6
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Default Re: Electric welding in cars : How safe it is ?

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I have never had the need to get arc welding done on my cars but do know that it is safe to go ahead with the battery -ve disconnected
I was also sure about it but didn't wanted to take the chance,after all a large amount of current is flowing though the body.
Said that just wanted to know if anybody has actually used it on modern cars and faced any issues ?


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Given proper precautions Electric Welding is probably as safe, if not safer, than gas welding.
Pl share the precautions to be taken while Electric welding.
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Old 10th May 2012, 16:46   #7
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Default Re: Electric welding in cars : How safe it is ?

The negative terminal of the battery is connected to the chassis (also known as chassis ground). However, it makes no difference whether it remains connected or not.

1. If you are worried that the welding current will ruin the battery - then it cannot. The welding current has no access to the positive terminal, and hence cannot flow through the battery.

2. If you are worried about the welding current ruining the other electronics, then again it cannot. The welding current will bring the potential of chassis to its preferred value (and all the negative lead of electronic items connected to chassis ground).
But again there is again no return path via the devices (no positive side to complete the circuit).

Keep in mind that electric arc welding is usually done AFTER stepping down the mains voltage to about 50V levels.
This is not really that far apart from your car battery voltage.


ECENADU - I am surprised that ignition coil would burn. Was the in and out leads of ignition coil both grounded? If so then how would it function??

Last edited by alpha1 : 10th May 2012 at 16:50.
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Old 10th May 2012, 17:53   #8
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Default Re: Electric welding in cars : How safe it is ?

V&v, thanks for bringing up the topic.

Most garages doing arc welding on your car disconnect the negative terminal of the battery. Usually, this is the only precaution needed. However, to be on the safe side, I prefer to disconnect the alternator lead and (after a short wait) also the ECM cable. That's it.

Just wrap the cable ends (battery, alternator, ECM) in plastic packets so they don't inadvertently touch metal and undo what you set out to do!

While the alternator or ECM is not usually damaged during arc welding (even if the battery -ve lead is connected), a current spike due to a faulty ground might hurt them - and they are expensive to fix. Better safe than sorry there. The best option is to double check that the grounding rod/clamp of the arc welder is firmly connected, and as close as possible to the place that is to be welded.

BTW, couldn't you have taken the bumper guard off the Safari, electrowelded it, and put it back again?

Edit: If this was the vRS, or some other high-end car (esp. autobox-equipped), there is a likelihood of having multiple ECMs - you would want to disconnect all of them.

Last edited by SS-Traveller : 10th May 2012 at 17:56.
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Old 10th May 2012, 17:55   #9
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Default Re: Electric welding in cars : How safe it is ?

Connect the ground clamp of the welding machine close to the welding point, that should ensure the welding current doesn't stray anywhere else. Disconnecting the batteries won't take that much of an effort, if you want to be on a safe side.
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Old 10th May 2012, 18:34   #10
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Default Re: Electric welding in cars : How safe it is ?

Quote:
Originally Posted by ecenandu View Post
I don't know whether it qualify as a car or not, but for our baja buggy we have done a lot of electric welding. The only pre caution we took was to get the -ve terminal of the battery removed before welding as you have mentioned. Our juniors made a mistake of not removing the negative terminal and they cooked the ignition coil. There was no ECU in our buggy, but only a Ignition control unit, and was fine even after the umpteen welding work we done on it.

But hey, it was just a buggy an nothing much could possibly go wrong. I don't know how the ECU and other electrical stuff react to electic arc welding.
The battery might also get damaged if connected as a minimum if 50 to 70 volts will be flowing through the system.


Quote:
Originally Posted by alpha1 View Post
The negative terminal of the battery is connected to the chassis (also known as chassis ground). However, it makes no difference whether it remains connected or not.

1. If you are worried that the welding current will ruin the battery - then it cannot. The welding current has no access to the positive terminal, and hence cannot flow through the battery.

2. If you are worried about the welding current ruining the other electronics, then again it cannot. The welding current will bring the potential of chassis to its preferred value (and all the negative lead of electronic items connected to chassis ground).
But again there is again no return path via the devices (no positive side to complete the circuit).

Keep in mind that electric arc welding is usually done AFTER stepping down the mains voltage to about 50V levels.
This is not really that far apart from your car battery voltage.
Most of the points taken, but lots of other electronics which are body grounded like most the accessories we add on, isn't there a change of getting them fried ?

Quote:
Originally Posted by SS-Traveller View Post
V&v, thanks for bringing up the topic.

Most garages doing arc welding on your car disconnect the negative terminal of the battery. Usually, this is the only precaution needed. However, to be on the safe side, I prefer to disconnect the alternator lead and (after a short wait) also the ECM cable. That's it.

Just wrap the cable ends (battery, alternator, ECM) in plastic packets so they don't inadvertently touch metal and undo what you set out to do!

While the alternator or ECM is not usually damaged during arc welding (even if the battery -ve lead is connected), a current spike due to a faulty ground might hurt them - and they are expensive to fix. Better safe than sorry there. The best option is to double check that the grounding rod/clamp of the arc welder is firmly connected, and as close as possible to the place that is to be welded.

BTW, couldn't you have taken the bumper guard off the Safari, electrowelded it, and put it back again?

Edit: If this was the vRS, or some other high-end car (esp. autobox-equipped), there is a likelihood of having multiple ECMs - you would want to disconnect all of them.
Thanks doc. As for taking off the bumper guard, the guy was reluctant to take out and was insisting it safe. That why i didn't get it done from him.

Even i too was concerned of the spike which might damage some thing and ending up with a dead safari at 42 degrees

The kind of desi transformers these guys use, man its scary.

vRs i cant even think of it, you know every morning i crank her, starts without a drama, i thank the god, another day without trouble. Must say my RS has not troubled me yet. "Touch wood"



Quote:
Originally Posted by ANUJ GEORGE View Post
Connect the ground clamp of the welding machine close to the welding point, that should ensure the welding current doesn't stray anywhere else. Disconnecting the batteries won't take that much of an effort, if you want to be on a safe side.
This is theoretically true but i feel the surge/spike will effect the entire space connected.

Last edited by v&v : 10th May 2012 at 18:36.
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Old 10th May 2012, 19:06   #11
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Default Re: Electric welding in cars : How safe it is ?

The end joints of the bull guard on my alto had rusted and the bolts were in no mood to come off. Went to a welder and asked if he could cut the part with a gas cutter. But as he did not have a gas cutter. He said he could cut the bolts with welding machine. He asked me to keep the engine on, while he cut through the bolts. Its been more than 10 months and no issues yet with the car electrical or battery.
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Old 11th May 2012, 10:49   #12
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Default Re: Electric welding in cars : How safe it is ?

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Most of the points taken, but lots of other electronics which are body grounded like most the accessories we add on, isn't there a change of getting them fried ?
Shouldn't happen, because grounding in a DC circuit usually means connection to -ve bus. For a circuit to complete and current to flow, the +ve side also has to be closed.

Now as far as I know, lights are controlled via separate switch, and rest electronics are controlled via ignition key switch.
If both are switched off, how can the welding current access the +ve side?

And when there is no access to +ve side, the current cannot flow.
(and OF COURSE, that's why they are called "switched off" while being connected to the internal car battery).

Same thing is applicable for the welding current! Its nothing different.
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Old 11th May 2012, 12:08   #13
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Default Re: Electric welding in cars : How safe it is ?

I get the point in taking precaution by removing the ECU connections and the like, but aren't these electronic parts already insulated enough from the rest of the chassis?

When i open the hood, i see all electrical and electronic parts inside well insulated plastic casing only connected with the things they should be connected with by wires. My question is how would they get subjected to surge of electricity unless there is a leakage somewhere? or am i missing something.

Last edited by mayankjha1806 : 11th May 2012 at 12:09.
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Old 11th May 2012, 12:21   #14
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Default Re: Electric welding in cars : How safe it is ?

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I get the point in taking precaution by removing the ECU connections and the like, but aren't these electronic parts already insulated enough from the rest of the chassis?

When i open the hood, i see all electrical and electronic parts inside well insulated plastic casing only connected with the things they should be connected with by wires. My question is how would they get subjected to surge of electricity unless there is a leakage somewhere? or am i missing something.
What the concern is , when Arc welding is done, if the battery is not disconnected then you are making a parallel connection of 50 - 70 volts.

For welding they will be using the car body as ground. So the electronics are exposed to higher voltage and surge.
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Old 11th May 2012, 14:31   #15
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Default Re: Electric welding in cars : How safe it is ?

To avoid any risk of the circuit completion removing the earth terminal prior to welding is an excellent precaution. So just do that and no more.
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