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oldtimer Guest
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Posted: Wed Jun 30, 2010 11:16 am Post subject: Is welding detrimental to alternator wellbeing? |
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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: 4127 Location: South Cheshire
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Posted: Wed Jun 30, 2010 11:42 am Post subject: |
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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 Guest
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Posted: Wed Jun 30, 2010 1:32 pm Post subject: welding/alternator problems |
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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.
oldtimer |
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Kelsham
Joined: 18 Jan 2009 Posts: 349 Location: Llandrindod Wells Powys
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Posted: Wed Jun 30, 2010 4:29 pm Post subject: welding damage |
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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
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Posted: Wed Jun 30, 2010 4:42 pm Post subject: |
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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
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Posted: Thu Jul 01, 2010 12:14 am Post subject: |
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I disconnected the Maestro's battery but have never bothered when welding cars with dynamos - is it just alternators that a vulnerable then? _________________ Richard Hughes |
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michael1703
Joined: 22 Jul 2009 Posts: 349 Location: suffolk
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Posted: Thu Jul 01, 2010 6:49 am Post subject: |
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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 Posts: 1119 Location: Under the car.
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Jim.Walker
Joined: 27 Dec 2008 Posts: 1229 Location: Chesterfield
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Posted: Thu Jul 15, 2010 7:31 pm Post subject: |
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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. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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Farmer John
Joined: 18 Feb 2010 Posts: 181 Location: Manawatu NZ
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Posted: Thu Jul 15, 2010 8:37 pm Post subject: |
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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 Posts: 349 Location: suffolk
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Posted: Thu Jul 15, 2010 10:29 pm Post subject: |
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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 Guest
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Posted: Mon Jul 19, 2010 9:12 pm Post subject: |
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.
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: 4127 Location: South Cheshire
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Posted: Fri Jul 23, 2010 3:17 pm Post subject: |
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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 Guest
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Posted: Fri Jul 23, 2010 3:56 pm Post subject: |
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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
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Posted: Fri Jul 23, 2010 4:24 pm Post subject: |
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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. _________________ Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then! |
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