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Is welding detrimental to alternator wellbeing?
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oldtimer
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PostPosted: Wed Jun 30, 2010 11:16 am    Post subject: Is welding detrimental to alternator wellbeing? Reply with quote

I have only recently converted from dynamo so this would not have been an issue,but now I should like some learned member to confirm or deny what I have been told.If true is it all types of welding i.e. MIG, TIG and Arc
and just how simple/complex the precautions to protect the alternator.
My thanks in anticipation.
oldtimer
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Wed Jun 30, 2010 11:42 am    Post subject: Reply with quote

Hi

Its the diodes in the recitfier that don't like the voltage spikes that electric welding can generate, so just disconect the output plug and welding will be fine.

Dave
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oldtimer
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PostPosted: Wed Jun 30, 2010 1:32 pm    Post subject: welding/alternator problems Reply with quote

Thank you, uk Dave,for your help.It is sometimes what is fact and what is fiction is a problem that is not easily resolved.
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Wed Jun 30, 2010 4:29 pm    Post subject: welding damage Reply with quote

I can confirm that leaving the alternator connected when welding can destroy the diodes. I welded a TR7 and ended up having to replace the alternator.
I now remove the battery leads and the alternator plug. Further action with the welder has been ok.

regards Kels.
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Scotty



Joined: 23 Nov 2007
Posts: 883

PostPosted: Wed Jun 30, 2010 4:42 pm    Post subject: Reply with quote

I certainly would agree with Kelsham, - I realise to some it might sound a bit "belts & braces", but the car will be completely electrically dead, which in my view is no bad thing when working with electric welders or sorting fuel supply issues.
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Richard H



Joined: 03 Apr 2009
Posts: 2148
Location: Lincolnshire, UK

PostPosted: Thu Jul 01, 2010 12:14 am    Post subject: Reply with quote

I disconnected the Maestro's battery but have never bothered when welding cars with dynamos - is it just alternators that a vulnerable then?
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michael1703



Joined: 22 Jul 2009
Posts: 349
Location: suffolk

PostPosted: Thu Jul 01, 2010 6:49 am    Post subject: Reply with quote

i always disconnect but a mad professor i know swears that it wont do any damage.

recently when welding triumph stag i disconnected the earth lead before a mammoth welding session, after i had finished i was just tidying up when i noticed the interior light was on, i checked the battery to find the earth lead had flopped back on to its terminal and the battery had reconnected itself

no damage was done to the alternator, but i still disconnect batteries just incase
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baconsdozen



Joined: 03 Dec 2007
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Location: Under the car.

PostPosted: Fri Jul 02, 2010 10:51 am    Post subject: Reply with quote

It can definately destroy the alternator diodes,I killed one on my merc when welding the wings.Discnnecting it and the battery only takes a couple of minutes and you can weld till the cows come home with no damage possible.
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Jim.Walker



Joined: 27 Dec 2008
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Location: Chesterfield

PostPosted: Thu Jul 15, 2010 7:31 pm    Post subject: Reply with quote

There used to be a belief that jump-starting a vehicle with an alternator could destroy the diodes. I even remember buying a set of jump-leads which carried a warning to that effect.
Has anyone ever suffered from ignoring this advice?
I have seen lots of cars jump-started without disconnecting the alternator. I have not seen even one with any ill effects, unless the problem shows up later.

Jim.
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Farmer John



Joined: 18 Feb 2010
Posts: 181
Location: Manawatu NZ

PostPosted: Thu Jul 15, 2010 8:37 pm    Post subject: Reply with quote

Please do not take this as an "always do it this way", but had followed this debate for years until I found, on a USA agricultural engineering forum the following advice :-
" If you are worried about the alternator, take it off. If you fear for your battery, remove it. If you think your spare wheel is at risk, remove it."
That did it for me, but bear in mind that the earth clamp is as close to the work area as possible. On the same panel or fitting.The writer discussed the very early days of arc welding when a welder would work on, for example, a truck chassis with the earth clamp at one end of the truck and welding anywhere from one end to the other. Remembering that the electrode is alive all the time, unlike a Mig, merely brushing it on an improperly earthed electrical device, or worse still a live wre, there will be damage!
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michael1703



Joined: 22 Jul 2009
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Location: suffolk

PostPosted: Thu Jul 15, 2010 10:29 pm    Post subject: Reply with quote

no Jim, never had any problems jump starting either, cant see how it would

also... optimate market their charger saying a dead flat battery should be gradually charged and then maintained etc etc

but many vehicles that have completely flat batteries manage fine with a jump start which can instantly throw 40+amps at a dead flat battery rather than a gentle charge
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WLC4EVA
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PostPosted: Mon Jul 19, 2010 9:12 pm    Post subject: Reply with quote

.
The optimate is a lot kinder when it charges a flat battery than an alternator is Michael.

Batteries appreciate a bit of kindness.

Kind Regards, WLC
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Fri Jul 23, 2010 3:17 pm    Post subject: Reply with quote

There is a risk of blowing diodes with a jump start, but I think you would have to be quite unlucky.

The diagram below makes it easier to understand:



Alternator’s produce AC, the bridge rectifier (4 diodes in the diagram) converts it to DC, but as you can see from the wave form its a varying or chopped DC (a battery would just produce a straight line, no wave) . Alternator outputs have a bit more of a complicated waveform and there will be a regulator (not shown) that simply flattens the top of the curve. But it still Illustrates the potential problem....

When a car is jump started both alternators will be generating but probably not “in phase”, if they are not in phase the generators will be working against each other, this can generate quite high currents albeit for short periods of time.

So combined with the sudden surge’s that will occur as the “good” battery voltage suddenly changes from cranking voltage to normal etc could lead to diode damage, but I would think this risk is pretty low.

Dave
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WLC4EVA
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PostPosted: Fri Jul 23, 2010 3:56 pm    Post subject: Reply with quote

.
So, a wise man switches the donor car's engine/alternator off before he starts his engine then Dave?

And doesn't worry when he starts from a spare battery, or a dynamo equipped car?

Have I understood correctly?

Kind Regards, WLC
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Jim.Walker



Joined: 27 Dec 2008
Posts: 1229
Location: Chesterfield

PostPosted: Fri Jul 23, 2010 4:24 pm    Post subject: Reply with quote

It's only since the advent of the alternator that it has become normal practice to run the engine of the donor vehicle. The small increase in voltage and current with a dynamo wasn't generally thought to make much difference.
Curiously jump starting seems more common these days. Is that because there are more vehicles? Or because drivers then dare not park with headlamps blazing and everything possible switched on every time!? To the annoyance of moving traffic.

Jim.
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