38 replies to this topic

[haggz]

just to change topic slightly, i have been told to disconnect battery, + & - and disconnect the alternator lead. disconnecting the alternater will stop any chance of regulator being damaged. still a piece of electronic equipment so i wouldnt have been told that if it wasnt true. ( some one who reconditions them)
it would be interesting to know how many folk have had alternator/charging problems after welding their minis and put it down to faulty alternator.

[Sprocket]

While I see negative comments against my original suggestion to disconnect and remove any electronic equipment, all I intended to do was eliminate any doubt. Surely that it is not a bad thing

Back to the point.

The best example of electronics failure while welding, has to be in the TV series/ DVD "Long Way round" with Charlie Boorman and Ewan McGregor, when the frame on the cameramans BMW broke. They managed to get the frame welded in the next town, and promptly fried the electronics.

Why risk it? At the very least disconnect the battery

Edited by Sprocket, 17 September 2010 - 08:06 PM.

[sonikk4]

just to change topic slightly, i have been told to disconnect battery, + & - and disconnect the alternator lead. disconnecting the alternater will stop any chance of regulator being damaged. still a piece of electronic equipment so i wouldnt have been told that if it wasnt true. ( some one who reconditions them)
it would be interesting to know how many folk have had alternator/charging problems after welding their minis and put it down to faulty alternator.

I have always disconnected the battery both terminals and the alternator. I had previously answered to a similar thread to this and said the same thing but i also added that i done some exhaust welding on a Vauxhall Omega 2.5 and that had some serious bells and whistles on it and it did not affect it what so ever.

I have never disconnected a stereo and after welding on an awful lot of cars over the years none have ever failed. This is one of those things that do you disconnect absolutely everything just to be safe, some airbags have a facility to install a safety pin or be able to switch them off.

I personally have not heard off ecu's being fried, if its earthed correctly then it should be ok after all this is what we do on a/c to prevent lightning strikes from doing damage. We run some serious ECU's on large jet engines but because the unit is earthed and also the various parts of the electrical system are earthed numerous times they suffer no damage from lightning strikes. I know its not a Mini but the principle is the same.

How far do you want to go is the question you need to ask yourself, sometimes disconnecting things can have a detrimental effect if not done in the right sequence.

[MiniAlex]

You have got me thinking now ... I have to get the back end of my car welded soon! After its accident.
I had the front subframe welded up after I hit a pothole... the garage just disconnected the battery. My ECU is held in with two or 3 small bolts into the inner wing. It's an Spi Sprite ... When I took my ecu out before, its just got wires in the bottom that I can unplugg.
So when I weld the back end up I think I will now remove the ecu, just to be safe. I have always known to remove/disconnect the battery.


I need to get an answer for this question though.. (it's important!)
If I unplugg the ecu wires, take the complete ecu out, when I plug it back in.. will it still work? I get a bit nervous that it will reset itself or not work!!
Thank you
Alex

[MiniAlex]

Also forgot to say... when my local garage welded up my subframe, the car started fine afterwards & I never had any problems ecu wise (TOUCH WOOD!!!) Also I never knew to disconnect the alternator.
So when I weld the back end up, just to be sure. I am going to get this ecu disconnected, take the battery out (its out already!) and finally unplugg the alternator. This topic had made people a little nervous I think .. but ............... BETTER TO BE SAFE THAN SORRY!!

[munkey26]

Don't forget to wear rubber underpants and a bubble wrap suit

[andy159]

Don't forget to wear rubber underpants and a bubble wrap suit

is that just for welding or ur weekend gear lmao

[greenlantern101]

I have a 97 mpi cooper

I have just completed (ready for painting) cutting out the floor panels driver and passenger side and welding in new ones and cutting off both sills and welding in new ones.

All I did was disconect the battery.

The ecu is fine the airbag is fine, I drove it yesterday.

[mrsf15h]

I've got a SPI and had welding done on it numerous times over the last 5 years (front end, sills, floors, accident repairs etc).

Yes the battery has been disconnected and removed from the car, but I have never taken the ECU off.

Never had a problem over 5 years.

Still, better safe than sorry..I will be taking my new ECU off next time as it's going to be an aftermarket one....after tuning.

[MiniAida]

I'm wincing reading all this.
Sprocket - I have acted on your advice many times with my SPi and always found it helpful.
That said, I've just repaced my o/s sills with a mig and forgot to disconnect. Luckily she started when I turned the car round to do the other side.
I have now disconnected the battery, main relay & ECU.
It just isn't worth the hassle of trying to fault find if you can't get the thing started. Sprocket is absolutely right.

Let's try & remember this is a forum for like minded people.

[David Wayne]

Where and what is the SRS (is that the sensor for the airbag?).
Anyway this does comply with what I've heard about welding on a car with an ECU.

This is almost 2 years past the asking date, but:

SRS = Supplemental Restraint System AKA the airbag and deployment system

[Jake Didsbury]

All my welding on mine is gas welding, it warps but hell of a lot stronger no need to mess with the electronics

[Mini_Magic]

Why risk it? Probably a 5 min job to disconnect and gives you peace of mind.

[darlio]

If i took it to a garage would they remove the ecu etc??

[Vonski]

IMPORTANT.

If you do not know what you are doing, or are in any way unsure then you should NEVER under any circumstances do anything to any component of the airbag (SRS) system.

I find it highly dubious that sprocket is advising people to remove the airbag ecu from their car.
Here is why...

Airbags are intended to deploy in an accident, and as such are designed for the occupants to be moving into the airbag in a fairly specific way (think of all those videos showing crash test dummies)
If you are working on your car, kneeling outside the drivers door and leaning across the drivers seat to access something when the airbag deploys then it would hit the side of your head at a nasty angle. This can BREAK your neck such is the force that it deploys at.
This is why you must not mount rear facing baby seats in the front of a car, and if you do then you must deactivate the passengers airbag using the deactivation switch, which is so clearly marked that even an idiot can't miss it. Otherwise a deploying airbag would snap the baby's neck.
This is also one reason that wearing a seatbelt is important. Not only does it restrain you in an accident, but it also ensures that you hit the airbag in the way that the designers expect you to.
When you hit an airbag the designers are expecting you to be carrying forward momentum because you are in a crash. They also expect you to weigh somewhere between 50Kg to 120Kg or thereabouts. It is highly unlikely you will weigh less, being a person of driving age, and if you weigh more then the airbag will not be as effective at saving you. So your forward momentum can be approximately calculated, which the designers have done. Should you be stationary, doing repairs around the airbag when it deploys then you have no forward momentum to counter the violence with which the airbag inflates. Instead, your neck, or other body part, absorbs all the energy of that force, which is why it can even break an adult's neck.

When i replace airbags or seatbelt pretensioners at my work then we must, by law, detonate them before disposing of them. The sodium azide charge in modern airbags replaces the dynamite charge that was used for a short while in the past. Either way, that charge is High Explosive and must be transported suitably marked as hazardous high explosive contents.
These things detonate with one H**L of a loud bang in the workshop, and shock anyone who has never seen it before. This is how i impress the importance of what i am saying on a young appretice.
I hope that this makes people realise how dangerous an airbag system can be.

Now...
If you disconnect your car battery in preparation for welding, then you disconnect the airbag ecu...........
BANG.
It is possible, but not certain, that the airbags will deploy. The ecu has capacitors within it that store charge for a period of time so that it can still deploy the airbags if the car's battery has been smashed in an accident. It can also deploy the airbags without a signal from the sensors (since they might be faulty). Any voltage, even millivolts, even for the briefest period of time can be interpreted by the ecu as a reason to set off the airbags.
Don't misunderstand me, the airbags will never deploy randomly, and the default state of the ecu if in doubt is to disarm the system. However, if you try using a multimeter to check the system without safely disarming it first (multimeters give out a small current to calculate resistance), or you disconnect something without following the correct safety procedures then you may well be triggering the system without knowing why or how.

I am NOT going to explain how to safely disarm the system, as you shouldn't even be thinking about working on it!
Earlier in this thread people have mentioned better safe than sorry. Very true, and i would rather keep my body parts intact than save money on the cost of a new airbag ecu!
(Although welding can be safely carried out without disconnecting any ecus! just disconnect the battery positive.)

Sorry for the long post, but its important for your safety.
Happy repairing.