Disconnecting battery?

[Beeezer]

ive a 04 merc sprinter I’m making into a camper.
I want to weld a few brackets in the back for a fold up bed.
My question.... can I just disconnect the battery and get on with it??
Or should I be using some bit of kit to stop electrical gubbins frying??

Cheers.

 

[grim_d]

I've never disconnected the battery to weld a vehicle. Just get the earth as close as possible to where you are welding so the only place it goes is through that.

 

[steviec_lj]

On my Vito, I just removed the battery and cracked on. No issues

 

[jpmillermatic]

Its up to you...as said, keeping the earth as close as possible to the welding area is okay....but if welding near the ECU, I might disconnect the battery AND the ECU for peace of mind...but that is probably overkill....

JP

 

[normspanners]

Nowadays you are asking for problems disconnecting batteries I have just spent a week working on 4 cars that had caused allkinds of issues because of disconnected or flat batteries.
you can loose steering settings ecu adaptions etc etc etc!
it used to be the first thing you were taught as a apprentice ------ disconnect the battery ----------now its the last thing you want to do !"!

 

[normspanners]

VW Golf and the like are prime for it two cars ended up having all REAR wheel bearings!!! replaced because the batteries were removed for repair !!! one head gasket the other clutch because when re-adapting the ecu wants perfect readings which the old bearings wont give !
How do you explain that-------- to an angry customer !! oh it needed several hundreds more now coz we disconnected the battery to fix the first problem .

 

[p0689109]

What readings from the bearings was that being monitored then?

 

[Hopefuldave]

What readings from the bearings was that being monitored then?

I'm guessing but - ABS sensor pulses, waveform off a bit due to bearing wear?

Too clever for their own good, these modern cars...

Dave H. (the other one)

 

[p0689109]

That was what I thought it would be thought I would ask in case it was somehow measuring the actual bearing somehow!

 

[brightspark]

current takes the shortest path so keep the return as close to the torch and there isn't a problem .it cant wander along your car and damage anything it has to have a loop circuit catching a wire with your welding tips a different matter and that's down to being careless

 

[normspanners]

I'm guessing but - ABS sensor pulses, waveform off a bit due to bearing wear?

Too clever for their own good, these modern cars...

Dave H. (the other one)

well yes and no the bearings were perfect its the hubs that rust and the magnetic ring becomes deteriorated, although it still works and gives a speed reading it is not reliable enough to calibrate the ecu

ABS ASC ATC steering angle etc, all have to concur, so if the steering sensor is a couple of degrees out from straight the asc sees the car as skidding and can apply the brake to one wheel.

 

[normspanners]

That was what I thought it would be thought I would ask in case it was somehow measuring the actual bearing somehow!

Merc sprinters now have a reading to the ecu telling it the calculated air gap between the reluctor ring and sensors !! and can tell if it is rotating forward or back.
I had one a few weeks ago with an abs fault and it was the road spring locating nipple had sheared and the rear axle had moved backward a few mm on one side, and it knew.
The abs can sense it the tyres are at different pressures due to the different rolling radii

 

[8ob]

I have always used a Sealy surge protector, not sure what it does if anything but have never had any issues. https://www.sparkswarehouse.com/pro...MIqqXCyKmz2wIVhZ8bCh0jPAfnEAQYBSABEgI1ivD_BwE

Bob

 

[brightspark]

I know how a domestic surge protector works. its connected to live and neutral any surge in voltage and it sends the excess current down to earth . stick a megger on a circuit and it shows as an earth fault as its a surge theres only 2 wires on on the car one so cant explain

 

[Pigeon_Droppings2]

I always thought they were just capacitors which stored the excess charge.

My volvo was a nightmare...I used to have to leave all the lights on when removing and refitting the battery!! The design is deliberately complicated...a brake control module was £1,200 because it had to be coded to the car....and of course old modules couldn't be recoded (wonder who thought of that one!)

 

[anto44]

I do a lot of welding on cars and only diconnect the battery on very old cars. On anything newer thats fitted with electronic control units I leave the battery connected and use a surge protector like the one 8ob posted. I've done a good bit of training on welding on modern vehicles and have done welding on cars fitted with over 100 separate control units and never had an issue.
A few years ago i had a vw golf that I bought crashed and was breaking for parts, ECUs for these are worth nothing as they don't give problems so I started the car and left it idling. Then I put the earth clamp of my mig onto the ecu case and welded my name into the case of the ECU. It idled perfectly the whole way through the weld and there was no faults stored in the ecu when I checked it afterwards.

 

[Beeezer]

Cheers chaps, I will speak to the local garage and see if I can borrow one of these gadgets over the weekend.

 

[normspanners]

a brake control module was £1,200 because it had to be coded to the car

Quite a lot of you would think of as mundane stuff is registered to the car or 'coded ' and has to be 'virginised' if poss before being fitted to another vehicle you cant just update the code, sometimes you have to change the whole series of items in the loop, even if if you want to change only one item, because items will only 'talk' to others with that code, that are in the loop. the steering and brakes for instance are linked and both linked to the engine ecu to reduce power if it sees a fault or thinks it sees a skid shown with either.

 

[8ob]

Dont know quite what goes on inside these but it does not give a reading with an ohm meter, maybe they come alive when connected

 

[Pigeon_Droppings2]

I think inside they are capacitors which absorb the voltage spikes and smooth them out I think....if you connect it across a battery and then take it off and stick a volt meter on it I wonder if it would briefly register voltage discharge?

I looked into fitting a permanent one to my volvo because it had a habit of blowing bulbs, they have a bit of a reputation for electrical gremlins...then again it now has around 200k on the clock so I think we can forgive them...those d5 5 cylinder diesel engines were amazing....40+ mpg in a car that size!