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fubar
20th Feb 2011, 12:24 AM
Title says most of it .
I recently purchased a 2005 ford transit cab chassis and need to weld some mounting plates on rear of tray and am wondering if I need to disconnect battery. I really dont want to as this will stop the stereo from working and I dont have code to restart it. I have received conflicting advice and am wondering if anyone here can advise

nihilism
20th Feb 2011, 12:38 AM
I would advise against it as it increases the chance of damaging any electronics in the vehicle if you leave it connected.
You can however purchase a surge protection device that you connect across the battery terminals which may allow you to weld safely with the battey still connected.

Master Splinter
20th Feb 2011, 12:46 AM
The correct answer depends on how lucky you feel....

More often than not, everything is fine. But one fried EMU or triggered airbag and you're down $600. Check your local car stereo place, they may be able to get a code for your stereo.

There are also little battery back up doodads (they plug into the lighter socket) that should keep power to the stereo while you disconnect the car battery.

However, if it's an aluminium tray and you are tig welding, I'd place disconnecting the battery at a much higher priority than if you were mig welding steel.

Claw Hama
20th Feb 2011, 08:37 AM
:wts: Expoloding batteries, burt out computers, not often but all possible.

steran50
20th Feb 2011, 09:22 AM
HI,
The Really Correct Answer is NO:no: as the Battery could Explode and not leaving out possible damage to the Vehicles Electronics. The Answer above is the same whether You are Arc, Mig or Tig Welding and probably even Plasma Cutting on the Vehicle. Think about it this way a car has a 12 volt Battery, some Batteries can take up to a 14.8 volt charge rate. For an example a Stick Arc Welder typically has a Voltage of 45 Volt and 70 Volts - Older Arc Welders were 50 volt and 80 volts. Imagine what that Voltage would do to the Car battery should it go through it for some reason.
Off the Subject a bit, Years ago when I was about 5 I was holding some Timber for my Dad whilst He was Cutting it with a Circular Saw. The Car Battery that was on Charge nearby suddenly Exploded - We were both Okay.

If You Contact Your Local Ford Dealer they should be able to Help You out with the Radio Code, providing it is the original Radio.
PLEASE PLAY IT SAFE AND DISCONNECT THE BATTERY!.

JUST A NOTE : For People thinking about the fact that You can Arc Weld with a Car Battery, Yes that is True. There is also a Danger there that if the Electrode sticks it will cause a Short Circuit and the Battery/s will Explode.

Bushmiller
20th Feb 2011, 09:30 AM
Yes you can. But don't under any circumstances:no:! On modern vehicles the computer would be the single item most at risk. Consider the measures we go to when jump starting. Special leads and allowing the charge to build up first amongst other things.

The very first time I welded on a vehicle, which was an early model Dyna truck, I did not have the benefit of anybody advising me to disconnect the battery. I think I blew every single light in the vehicle. I was probably lucky I didn't burn out the points.

Just disconnect the earth lead. Don't know what you can do about the code for the stereo.

Regards
Paul

fubar
20th Feb 2011, 10:17 AM
thanks guys I had only talked to 2 blokes one who said he had done it heaps of times with no problem the other who said similiar to you lot oh well really wanted to do the job today so now will wait till monday talk to ford re the code

Mathuranatha
20th Feb 2011, 10:52 AM
Have welded heaps of times [arc ac and dc]on white a few different vehicles , never any problem .But all were pre 85 so no hi tec electronics. :)

Grahame Collins
20th Feb 2011, 01:46 PM
As per the warnings above.

If there is no other choice place the earth return as close as possible to the area to be welded.

Unless you are considering a moon orbit without the benefit of the space shuttle, also check out the fuel tank.

How close is this to the welded area.?

If you can smell fuel don't weld ,its highly dangerous as its a vapour exposion that will kill you.

Does the fuel tank it or its ancillaries leak?

ok its a pain in the bum to drop the fuel tank in a lot of cases ,but the alternative is much nastier.

Check before you weld.!!

Safety always
Grahame

inverter_weld
20th Feb 2011, 09:03 PM
Hi All,

I have sketched a quick pic showing the relative current flows. If you can imagine the welding current shown in blue only flows in the chassis / frame / panels of the car. The actual car electrical equipment current shown in black uses the car chassis / frame / panels as a return path to the battery negative terminal.

http://www.tokentoolroom.com/images/carwelding.jpg

The car equipment current flows from high to low potential so from positive on the battery, via the fuse block, via the equipment (load) and via the return earth path (chassis, panels etc) back to the battery negative terminal.

If you are welding on a car then you are doing the same except your welding current flows from electrode to earth clamp, the load is the chasis itself, more specifically the end of the welding electrode. The only way it is possible for you to damage the equipment in your car is if the current path for your welding is a much higher resistance than the electrical circuit in your car (impossible due to it all being steel). A poor earth connection will not do it as the poor earth connection is localised and common to both scenarios. In short you cannot destroy anything ELECTRICAL in the car by welding other than by blowing it up or setting it on fire as Graham has pointed out due to fuel or sparks.

It is however a precaution often taken in case you put a hot (melts through plastic insulation) and live welding electrode onto a 12 Volt wire and inject a 70 volt open circuit voltage (http://www.tokentools.com.au/category28_1.htm)into a 12 volt system thus destroying many valuable car bits:doh:.

Regards
Pete (Tokentools (http://www.tokentools.com.au/category2_1.htm))

China
20th Feb 2011, 10:29 PM
As Pete says above, if you diconect the battery make sure your plug a computer saver into the lighter/power socket to stop it losing its memory.
Master Splinter whear can you get a air bag replaced for $600?

soundman
21st Feb 2011, 12:15 PM
Think about this......you old style reluctance welder (iron core transformer type) may only have an open circuit terminal voltage of 50 - 70 volts... but because of the reluctance of the coil, on strike up or lift off or the very action of the arc, very much higher voltage pulses or surges may occur.

Remember an arc has been the method of choice for producing big nasty voltage spikes since the beginning of electricity.

Likewise modern electronic welders or old sytle tig, may also have a base voltage of 50 to 70 volts ish..... but there may be a high frequency high voltage component to assist striking arc and smooth arc flow.

the above voltages may reach hundreds of volts, in the case of TIG lots more.

Now the all one earth argument.......well the chasis earth does have a finite resistance.......large amount of current flows.....there will be voltages resulting between certain points in the chasis.
Modern electronic cars have a multiplicity of sensors all grounded at different places on the chasis..many of these sensors may operate well below 12 volts.

Combine that with the forgotten high voltages...um not good.

Remember too that some car manufacturers are better at designing electronics to withstand the real world than others......some brands are known for their ECU's spitting the dummy without any provication at all.


If it is a modern car.....no question, disconnect the battery.

If I was tig welding on a modern car...I'd be realy thinking about yanking the ECU and anything else electronic too.

cheers

Vernonv
22nd Feb 2011, 11:06 AM
if you diconect the battery make sure your plug a computer saver into the lighter/power socket to stop it losing its memory.This is the bit I don't quite get - won't disconnecting one battery and then plugging another battery back in, negate the effect.

I can see that if the small battery explodes, it won't do as much damage as a big battery, but you are still not protecting all of the other electronics (if in fact they are in danger at all), by plugging in one of these devices.

welding
22nd Feb 2011, 03:28 PM
I think the hardest thing for people to wrap their head around is how current flows in a circuit. When welding on a car the only reason welding current would flow up the ground wire of a car's electrical device instead of directly back to the work clamp via the chasis is that the electrical device provided a lower resistance path than the chasis. For this to happen the current would flow via the device then via the battery and then to the work clamp. This is assuming the electrical device is turned on or permanently connected to the battery as in a clock / radio or ECU.

It is not likely that this scenario will ever occur as the chasis is always the lowest resistance, the electrical device will always have a resistance greater than the chasis as it is a device that does work and in order to do work you must use power and in order to use power you must have resistance. Power = Volts x Current and to get current, Current = Volts divided by resistance.

You can test the resistance of your chasis yourself. First touch your meter probes together and measure their own resistance, perhaps 0.2 to 0.3 ohms. Then measure the reistance across two points of your chasis within the reach of your meter probes. I bet you get the same reading :roll: that is because the resistance of your multimeter probes is higher than the chasis.

Think about this for a moment, your battery at charge is 13.7V. A typical starter motor for a car would pull around 100 amps. On cranking the voltage would drop to aroun 10 volts. 3.7 volts is consumed by the internal resistance of the battery, 10 volts is consumed by the motor. The total resistance of the battery and motor and chasis combined is resistance = Volts divided by amps so 13.7 / 100 = 0.137 ohm. The reistance of the starter motor and chasis is 10 / 100 = 0.1 ohm. The way to determine chasis resistance is to measure the voltage between the starter motor case and the earth strap bolt on the chasis whilst cranking. You will find this value is extremely small hence a teeny weeny reistance can be calculated for the chasis.

Right everyone, clear as mud? But for safety you should always disconnect the battery before welding, it stops people using your car whilst your pride and joy welder is tethered to it:U

John

fubar
22nd Feb 2011, 04:09 PM
:oo: I use a kemppi 180 minarc so it would be real easy to drive away with it still attached of course the bottle is a bit bigger so maybe not
thanks John for the explanation

FenceFurniture
22nd Feb 2011, 04:18 PM
Hi Welding, if I could divert you attention for just a moment. This is nothing directly to do with welding, but a general understanding of electricity, and you sound like just the chap.

Power = Volts x Amps. I'm trying to make a correlation between the different components here. In high school (some 4 decades ago) my nigh on genius pal helped me to understand electricity with a garden hose analogy. He said think of the power as the total volume of water running through the hose (let's say litres per minute). The resistance was (or pressure increase/decrease I guess) was determined by the hose diameter (and with electricity the wire length as well). The current would be the pressure of the water, I think.

That leaves voltage, or potential difference for me to wrap my head around.My best estimate here is to substitute (say) a saline solution for the water. A stronger solution would equate to a higher voltage. This works in my head for the following reason:

Total salt flow per minute = solution strength x litres per minute of flow
which is the same as
Power = V x A

How am I going here? This has had me perplexed for decades (coz I didn't quite get Voltage even then!)

Regards, Brett

welding
22nd Feb 2011, 06:03 PM
Hi Brett,

Great analogy but I will change it a little and it will be a snap to understand.

The pressure is the voltage, the litres per minute is the current and the pipe diameter is the resistance.

In water terms ...... As you increase pressure and keep the pipe diameter the same you will increase the amount of water delivered.

In electrical terms ..... As you increase voltage whilst keeping the resistance the same more current will flow. Say a 12 volt supply and a 15 volt supply at 1 ohm resistance. The first will draw 12 amps whilst the latter will draw 15 amps.

Back to water. As you can see in logical terms also that increasing the pressure of water being forced into a pipe will increase it's velocity (flow over time) thus increasing the amount delivered to the outlet in the same time period.

You could expand this analogy further by then considering the battery to be a water tank, the amount of water is the charge, the more chrge you use, the less pressure you have, i.e the battery loses voltage as it goes flat.

John







Hi Welding, if I could divert you attention for just a moment. This is nothing directly to do with welding, but a general understanding of electricity, and you sound like just the chap.

Power = Volts x Amps. I'm trying to make a correlation between the different components here. In high school (some 4 decades ago) my nigh on genius pal helped me to understand electricity with a garden hose analogy. He said think of the power as the total volume of water running through the hose (let's say litres per minute). The resistance was (or pressure increase/decrease I guess) was determined by the hose diameter (and with electricity the wire length as well). The current would be the pressure of the water, I think.

That leaves voltage, or potential difference for me to wrap my head around.My best estimate here is to substitute (say) a saline solution for the water. A stronger solution would equate to a higher voltage. This works in my head for the following reason:

Total salt flow per minute = solution strength x litres per minute of flow
which is the same as
Power = V x A

How am I going here? This has had me perplexed for decades (coz I didn't quite get Voltage even then!)

Regards, Brett

FenceFurniture
22nd Feb 2011, 07:07 PM
That's great John, clear as a bell now. Thanks very much.

So, if I had a battery that is 3Ah, 18v, feeding a 500w drill then I could work out how many holes it will drill at full power, given that each hole took 5 seconds to drill.

3Ah = 10800 amp seconds
18v
500w
5 seconds per hole

Amps per hole = 500/18 = 28 (rounded up)
Amp seconds per hole = 140
holes per charge = 10800/140 = 77 holes

I tink dat's roight!

Regards, Brett

welding
22nd Feb 2011, 08:34 PM
Hi Brett,

Not quite. Ampere hour is a measure of the ability of the battery to discharge over a 20 hour rate. A 3 Ah battery can effectively supply 150 milli amps per hour for 20 hours before it's voltage starts to dip dramatically and it is considered to be flat. A 3Ah battery is very small in capacity, about half of the capacity in Ah of what you typically find in a domestic alarm panel but they are 12 volt.

If you are running a 500 watt load off this 18 volt battery you would be pulling 500W/18V amps, this is 62.5 amps from the battery. I dare say you would be lucky to drill one or two holes. Remember that the quoted charge dissipation rate is 150 thousandths of an amp (150 mA) per hour for 20 hours and suddenly it is being asked to pump 416 times more power at 62.5 amps which is way over the top.

A suitable battery would be as follows

62.5 amps x 20 hours = 1250 amp hour. One hole per 5 seconds is 20 hours divided by 5 seconds is 12 per min x 60 min x 20 hours = 14400 holes per charge. Your average car battery is 12 volts at 45 Ah so an 18Volt 1250 Ah battery is something in the range of a very large forklift array.

Moral of the story, use an extension lead and a 240 Volt 500 watt drill or else a generator.

Regards
John

FenceFurniture
22nd Feb 2011, 08:52 PM
Ok, thanks John

soundman
23rd Feb 2011, 11:54 AM
There is a failure in understanding here.

Firstly forget that the chasis or any other part of the vehicle or wiring is an earth or common of any form......once we start welding it is simply a conductor with no particular status.

All the electrical wiring and all the metal body simply presents a complex network of paralall paths.

because the system runs at 12 or 24 volts everything is a low resistance, every lamp, motor, solenoid relay or even the battery its self can present a low resistance path between these paths

If there are several paralell paths (in any curcuit), current will flow in all of them.....it matters little how much lower or higher the resistance of each path is...SOME current will flow in each.

The voltage across each path will be the same.....the relative resistance in each individual path will form a voltage divider and that will determine the voltage that will occuer at a given point.

so if there is 70 volts (or a couple of hundred volts TIG) across the combined paralell paths and your ECU happens to be in one of those paths......regardles of the current flowing in that path it might cop a dose of excess volts.

Mostly it is voltage not current that will snot our electronics

The above complex system is realy beyond practical analisis, especially the simple reasoning above.

There are two main reasons we disconnect the battery in a modern car.
1. to remove the common link between the whole positive distribution system and the chasis/earth system.....the battery may act as a low impedance link or a high impedance link...ya just don't know..it depends on which paralell path it ends up in.

2. to de energise all the electronics..... because if they are not powered up they have a far better chance of survival.

Welding on a motor vehicle is very much a lottery.....ya simply can not properly analise what is going to happen.

Disconnecting the batter is just a simple, easy and reasonable precaution that may help in some situations.

What will help is to always place the welding earth as close to the weld as possible and to make as good a contact as possible...... but isn't that a fundamental rule of welding..........and be incredibly carefull

personaly If I have a choice I will remove the item rather than weld on the vehicle.

If it was my car and it had funky electroncs and I had no choice but to weld on the vehicle.....I'd yank the ECU and unplug the radio and anything else from the harness.

This issue is bigger than just disconnecting the battery.

Now think about this one.....we are welding on a set of brush bars on a 4WD, the battery is removed, the radio is still connected as normal.
The brush bars are connected solidly to the chasis.....the earth clamp is near by as it should be
.
Being a little careless and half blind because of the mask....we accdentaly strike arc on the guard or the sill or something else connected to the body.....the boddy is mounted on rubber blocks and has a token effort earth strap bonding the chasis to the body.
One of the paralel paths

Now the aerial is mounted and earthed to the guard... one of the paralell paths is..from the body, thu the aerial earth connection along the coax to the radio, in one end of the PCB and out the other ( no back strap or chasis earth connection for the radio) along the negative supply wire of the radio and into the negative electrical common for the dash....and back to the battery...AHH but what else in the dash is connected to the negative common....so what could we possibly snot here.

Yeh welding on vehicles is something I would rather not do...and if I had to I'd want to be incredibly carefull.

What is an ECU or dash cluster worth for your car.



cheers

welding
23rd Feb 2011, 03:10 PM
Hi Soundy,

I just wanted to clear something up.

The length of the welding arc is a function of it's electrical potential so the 60 - 70 volts is not in the chasis but between the chasis and the tip of the electrode. This is also the open circuit voltage, once you strike the arc and start current flowing, the arc voltage drops to around 20 - 25 volts but again this is the potential difference between the chasis and the tip of the welding electrode.



John

soundman
23rd Feb 2011, 04:04 PM
Yes but those are " nominal" voltages. These steady state voltages are probably the least harmfull.

There may be very much higher voltage spikes at the time of strike and lift off...particularly if it is an old style iron cored welder....if the arc is spluttering or discontinuous these spikes may be repeated many times in a second.

In the case of TIG....the high frequency high voltage component may disapear or be substantialy once the arc is established.....But the instant of strike up or lift off those voltage will be there and that is plenty

It only takes a single instantanious incident to snot a semiconductor, something that takes a fraction of a second.

Some semiconductors, Cmos devices take very little to damage, and some power diodes have very poor reverse voltage tolerance.

Blowing the diodes in the alternator is not an uncommon welding damage in vehicles......

Remember too that large amounts of our logic and microprocessor semiconductors operate on 5 volts sometimes less......the the normal power supply route may be well protected by voltage regulators and surge supression, but the sensor inputs and the earth plane of this equipment may not be.

Hell quite a lot of automotive and marine equipment does not even have rudimentary reverse voltage protection, you can comprehensivly snot these items with 12 volts the wrong way arround.



cheers

soundman
23rd Feb 2011, 04:19 PM
Oh... just think on this too.

We have an earth clamp on one end of a chasis...we strike arc on the other end of the chasis..at the time of striking arc....what is the voltage in the middle of the chasis.

The earth path, any earth path has a finite resistance, and there fore presents a voltage divider.

If something is "earthed" to the chasis nearer the striking point...that earth point may have say 50 volts of the available 70 volts compared to the end of the chasis with the earth clamp connected...this does not account for spikes.

Say we have a brake sensor on the rear brakes that derives its earth from the rear of the chasis and the brake CPU is at the front of the vehicle and derives its earth near the earth clamp....there is now 50 volts between the sensor earth and the cpu earth this means there may be 50 volts across the the interface in the cpu and the sensor live terminals.....SNOTTED
cheers

welding
23rd Feb 2011, 07:34 PM
Hi Soundy,

I have read your post and digested the information however have you considered that the resistance of steel is between 1 x 10^-7 ohms per meter and 10 x 10^-7. If we take the mid point of the general 5 meter car and assume you are welding at 80 amps the voltage present at the mid point would be 0 volts plus (2.5 x 10^-7 x 80 amps) which is 0.00002 Volts. At the other end of the resistive scale it would be 0.0002 Volts

You need to add the voltage to the zero volt reference as the earth clamp is bonded to the car. The potential (70 volt bit known as an electrode) is located away from the car at a distance (several millimetres) as it is being used to weld.

You also cannot call this a voltage divider. It is a circuit comprised of several in series components, welder itself, the cable to the rod, the rod, the arc, the chasis, the return earth cable and each component has a resistance. Using ohms law V = I x R and considering you have the same current passing through all of these parts as they are in series, you can multiply the different resistances of all of the these parts by the current and added up they will be equal to the total voltage available by the power source under load.

Please don't take my word for it. Bolt both the positive and negative outlets of your welder together with a bridge (steel or copper bar of suitable diameter to conduct the current) and run at full amps and measure the voltage and current across the bridge. This will give you a reading that can be used to calculate the internal resistnce of the welder.

Then repeat again with the chasis of a car. You will find the same reading. The reason is that the .00002 volts or 0.0002 Volts depending on the steel in your chasis will not be measurable by your multimeter.

John



Oh... just think on this too.

We have an earth clamp on one end of a chasis...we strike arc on the other end of the chasis..at the time of striking arc....what is the voltage in the middle of the chasis.

The earth path, any earth path has a finite resistance, and there fore presents a voltage divider.

If something is "earthed" to the chasis nearer the striking point...that earth point may have say 50 volts of the available 70 volts compared to the end of the chasis with the earth clamp connected...this does not account for spikes.

Say we have a brake sensor on the rear brakes that derives its earth from the rear of the chasis and the brake CPU is at the front of the vehicle and derives its earth near the earth clamp....there is now 50 volts between the sensor earth and the cpu earth this means there may be 50 volts across the the interface in the cpu and the sensor live terminals.....SNOTTED
cheers

chrisp
23rd Feb 2011, 07:45 PM
I have read your post and digested the information however have you considered that the resistance of steel is between 1 x 10^-7 ohms per meter and 10 x 10^-7. If we take the mid point of the general 5 meter car and assume you are welding at 80 amps the voltage present at the mid point would be 0 volts plus (2.5 x 10^-7 x 80 amps) which is 0.00002 Volts. At the other end of the resistive scale it would be 0.0002 Volts

John,

I'm being pedantic here. I think you are confusing resistance with resistivity. Resistivity is a property of the material, whereas resistance is a property of the resistively of the material and its geometric shape.

Have a look at Electrical resistivity and conductivity - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Resistivity)

soundman
23rd Feb 2011, 08:17 PM
Ya still fail to understand.... the current the welder is set to and the suposed current flowing after the arc is struk is irrelivent.

0 volts at one end of the chasis 50 volts at the other end of the chasis....what is the voltage in the middle... not steady state....Instantanious.

If what you are proposing is the whole story it should be imposible to harm any electrical or electronics in a car with a welder.

It is well established that it is possible to, damage batteries, alternators, and modern electronics in motor vehicles with a welder.

Situations are never ideal.
Cars are made up of many joined parts.
are the joins in the chasis, welded riveted or bolted, how continuous are those joins.......is what you are welding on electricaly well bonded to the chasis.

when the end of that welding rod is grounded to strike arc...does it make a perfectly smooth step from the open circuit voltage to the welding voltage, what about when you lift off...how much back EMF does that big choke (the welder) generate.

remember even a straight bit of wire has some inductance..so does a chasis.


In the majority of cases where there is a good solid low impedance earth path......... there will probaly be no problem....... but in a situation where there is some sort of non ideal situation......SNOTTED.

How about a real situation.
Aluminium boat, bare...sitting on the damp grass......earth clamp on the stern...... bloke tig welding not far from the earth clamp..me holding a patch in place with an insulated screwdriver with a gloved hand.......unfortunately I am sitting on the damp grass and I lean against the boat.....I get a tingle thu my shirt.......nothing major....but an indication of earth potential rise even though there is a short low impedance earth path.

cheers

welding
23rd Feb 2011, 08:38 PM
You are right.

I did a quick calc before the post and using 0.9mm steel thickness with 5 metres length and roughly 5 metres circumference the multiplier was 1.111 etc so I just used the resistivity value as the resistance. My error for not wording correctly.

John



John,

I'm being pedantic here. I think you are confusing resistance with resistivity. Resistivity is a property of the material, whereas resistance is a property of the resistively of the material and its geometric shape.

Have a look at Electrical resistivity and conductivity - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Resistivity)

welding
23rd Feb 2011, 08:46 PM
Eddy currents and skin effect (not your skin but the skin of the ally), induced in the aluminium due to current flow as your friend was welding with AC current. It would not have occured with DC.

John :)



How about a real situation.
Aluminium boat, bare...sitting on the damp grass......earth clamp on the stern...... bloke tig welding not far from the earth clamp..me holding a patch in place with an insulated screwdriver with a gloved hand.......unfortunately I am sitting on the damp grass and I lean against the boat.....I get a tingle thu my shirt.......nothing major....but an indication of earth potential rise even though there is a short low impedance earth path.

cheers

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