Any advice please

[Pug808]

Hello everyone,

I've to cut some steel off a truck and ill be using a plasma cutter, ill be disconnecting the batteries but I'm wondering is there anything else I should do to be on the safe side I don't want to case any ecu / electrical damage ?

Thanks in advance for any help or tips.

 

[JohnRUFC]

As a car guy I can tell you once you've disconnected the battery the ECU will be isolated. The rubber wheels should also Earth the car so as not to cause any damage.

But I'm sure one of the Pro's will be along shortly to advise!

 

[gordon stephenson]

Make sure that you have good clean/bright metal connect the earth/work clamp to and keep it as close to the cutting area as possible.

 

[Davek0974]

The rubber wheels should also Earth the car so as not to cause any damage.

Err, no, the rubber is non-conductive and will isolate the car

Make sure that you have good clean/bright metal connect the earth/work clamp to and keep it as close to the cutting area as possible.

This is the vital part

 

[rtbcomp]

As a car guy I can tell you once you've disconnected the battery the ECU will be isolated. The rubber wheels should also Earth the car so as not to cause any damage.

........

The only way to isolate the ECU is to disconnect it.

Not sure what you mean with the rubber wheels thing.

 

[JohnRUFC]

My FIA blue book states that an approved kill switch fitted between the battery and all components will isolate the electrics and stop the engine from running on. I was just going from that however I would love to know how you get any kind of electrical reading from the ECU while the battery is disconnected, as to the rubber wheels all I can say is blonde moment! But I'm sure I read that having it on the rubber wheels while welding or cutting is safer? Any one expand on that or have I dreamt it?

 

[rtbcomp]

You won't get a reading from the ECU - you stand a chance of putting voltages into it. When you weld electric current will flow all over the body between the 'earth' and electrode. To reduce these extraneous currents keep the 'earth' as close to the bit you are welding as possible, as mentioned above.

Disconnecting a battery with a kill switch will cut the supply to the ignition circuit, in some cases the alternator could keep supplying the electrics and the engine would keep running. If it were down to me I'd design a kill switch that isolated the battery (for fire safety) and at the same time cut the ignition with separate contacts.

The rubber wheels could introduce a hazard when welding. If the welding set develops a fault such the welding 'earth' and mains earth became connected current could find its way through the person doing the welding, if say he's kneeling on the ground.

I put 'earth' in quotes - what I really mean is welding current return.

 

[blenkie1]

The computers on our machines cost over 14,000 and they will be damaged if you start welding. There is a isolater we use and have a surge protector connected to the + on the battery and earth onto the chassis which is a must. If it's a wagon look out for air pipes. You will know when you burn through one when it starts hissing.

 

[premmington]

Damage to car electronics! Even thou I have owned AC-DC TIG welders with HF arc ignition functions, I always use the lift start or scratch start arc ignition modes when welding, in situ on cars. Old wives tales about removing the battery and disconnecting the alternator terminals are history. Capicitors will absorb energy if they are in the earth path of the welding circuit. Never-ever use welders with HF, hot start or anti stick functions on vehicles. As they can damage the cars electronics. Removing battery leads or using anti-surge clamps does not really reduce the risk. Positioning of the welding earth clamp as near to where you are welding as possible will reduce the risk of damage to electronic modules. The only safe method is gas welding using oxygen and acetylene. Most modern arc type welder have very high OCV voltages, stray HF energy gets everywhere. Ocy-acetylene welding leaves you with only one risk, which is setting the car alight. If something needs welding on a car and you can remove it, take it off the car and weld it away from the car!

 

[brightspark]

As a car guy I can tell you once you've disconnected the battery the ECU will be isolated. The rubber wheels should also Earth the car so as not to cause any damage.

But I'm sure one of the Pro's will be along shortly to advise!

rubber wheels earth the car
rubber tires insulate

 

[ajlelectronics]

Wow, there really are some old wives tales still doing the rounds! If you are concerned, then disconnect the battery and short the live to earth. Snake oil "surge protectors" are just that. Personally, I wouldn't bother with any fussing and would just get on with it.

 

[Robotstar5]

If it were down to me I'd design a kill switch that isolated the battery (for fire safety) and at the same time cut the ignition with separate contacts.

Available here

 

[premmington]

Wow, there really are some old wives tales still doing the rounds! If you are concerned, then disconnect the battery and short the live to earth. Snake oil "surge protectors" are just that. Personally, I wouldn't bother with any fussing and would just get on with it.

As an Auto electrician. My thoughts are as follows!

1. You maybe better to leave the battery on, as if any stray HF will get absorbed by the battery.

2. Surge protectors cannot absorb anything like the amount of energy a huge lead acid battery can.

3. Electricity takes the path of least resistance, so place the earth clamp on a cleaned up point near to where you are welding. Is always best practice.

Hold this thought, a modern car may have up to 75 clustered ECU modules! Removal of ECU units for a welding job is not practical.

4. It is also considered best practice by some manufacturers to only weld on a car with a fully charged battery, not a battery with a low state of charge. Due to higher risk of HF being absorbed.

5. The risk with solid state ECU unit damage is inductance. Introducing stray voltages down cables it is not designed to go, into capacitors trying to absorb this energy. Removing the battery and draining down these units leaves them in a state where they are ready to draw energy. Leaving the battery on, maybe safer in the long run! There are several schools of thought on this in the automotive industry. It is a grey area. Nobody will come out and give clear guidance due to the risks of getting sued if it is wrong.

6. Alternator regulators can blow, trying to regulate stray welding voltages. I have only seen one failed alternator attributed to welding in thirty years in the trade.

7. Personally I think the biggest risk is HF start TIG, hot start and anti stick functions on MMA welders. Standard constant voltage MIG sets and wound coil MMA welders, just maybe safer on cars. As you don't get the high OCV starts.

It is a grey area, battery disconnected or not!

In the real world of car repairs, sometimes removing the battery can prove more hassle than it is worth.

Yes there is a risk of damaging solid state modules on cars when welding. But statistically it is low.

So thus my previous point. The only electrically safe welding process on a car is gas welding!

I have seen more damage to car electronics caused by battery chargers than welders. Big wound coil battery chargers connected to the mains connected to really flat batteries, when the current surges in the voltages ramps up and stays up. Now I would always advise removing battery leads to charge a car battery (but nobody ever does).

 

[ajlelectronics]

As someone near me who reduced their car and garage to a smouldering pile would attest, really you should remove the battery from the car and place in a well ventilated area to charge it

How about when it is charging at 50A plus in the car?

 

[rtbcomp]

^^ It only charges at that rate when it needs to, the alternator gives a regulated output whereas cheap battery charges are unregulated, so the output voltage rises as the current drops, leading to overcharging.

Also when a car is moving the gasses are ventilated, but they can build up in a garage.

I experienced this myself with a battery that overcharged, my workshop was filled with hydrogen sulphide, an explosive gas.

 

[Old Dog]

Disconnect battery leads and join the positive lead to the negative lead. Keep the welder earth lead on clean metal close to the welding area.

 

[Robotstar5]

Now I would always advise removing battery leads to charge a car battery (but nobody ever does).

I've always removed the battery from the car to charge it, probably because I've never been able to get the car in a garage to charge it

I do leave the battery on the bike connected while it's plugged into the Optimate maintenance charger, never had any issues even when it was connected for 6 months.

Another one is connecting jump leads directly to a flat battery instead of negative to a good engine earth point, although I once watched a used car dealer invert a good battery over a flat one so the terminals touched to jump start it