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the12volt`s installbay - Mobile Electronics Forums the12volt's install bay / Miscellaneous - Off Topic

Subject Topic: welding surge protector

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shirker
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Posted: May 22, 2011 at 7:58 AM - IP Logged
Link to Post  Post Reply Quote shirker

Done some searches,nothing relevant that I   could find,not that that proves anything....but,

welding surge protectors....whats inside them?What are they? I know what they are FOR,and wgy and when etc etc,but a few of us on a landrover forum want to know whats in 'em.

Theres the type that clips onto your battery,like jump leads,big crocodile clip things with a box the size of a cigarette pack or smaller then theres the type that plugs into your cigarette lighter socket.

When welding cars with MIG or other electric processes we have always been told to at least detach the neg terminal of the battery,or even the alternator (to preserve the diodes) and this of course leads to a break in power supply to various things that dont like that.Thats where the little plug into your cigarette lighter socket thing comes in - really just a backup power supply so there is no break whilst battery is off.But then we hear stories about ECUs/ ECMs,whatever,being cooked by welding,or even the battery.Thats where surge protector clip on thing comes in.Theres a couple of issues here ; many claim that they are not needed since the vehicle handles much bigger voltage and current at times as it is,and then some say that the battery is the ideal dump for a current and/or voltage surge and thus to leave it on.Whatever,we are familiar with the arguments,have followed them and everyone has an opinion,many of them even backed up by facts !

What we dont know,is what is inside those little boxes...MOV (metal oxide varistors)?Bloody great cpacitors?Coils?What?What?WHAT?

thank you for your time,the shirker
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oldspark
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Posted: May 22, 2011 at 1:17 PM - IP Logged
Link to Post  Post Reply Quote oldspark

Usually MOVs.
And usually you won't know if or when they have blown. (Same for surge protected jumper leads.

At least for welding you can just disconnect the battery...
( Or have they changed that advice? - ie, remove the battery+ which means you must also have removed the battery- )
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shirker
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Posted: May 23, 2011 at 6:01 AM - IP Logged
Link to Post  Post Reply Quote shirker

I was hoping you would answer this one mate ! Theres a lot of mixed opinion on this issue right now,even amongst auto-electricians,see here-

http://retrorides.proboards.com/index.cgi?board=general&action=print&thread=63958

and also here -

http://www.ukwelder.com/forum/index.php?showtopic=6629

so us in the landrover club are debating at present.I have not had any trouble,so far,with just disconnecting the battery neg or both,if feeling timid.Mind you,my newest vehicle is 98 so,however,it does have a fair few ECMs.Newer vehicles with multiplexing cable shares,I know nothing of other than that they exist.
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oldspark
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Posted: May 23, 2011 at 9:32 AM - IP Logged
Link to Post  Post Reply Quote oldspark

LOL! I was going to suggest Wiki re your "a lot of mixed opinion...", but then I briefly checked the links.


I do have an article about it somewhere (from decades ago) that explained the issue - it said that the +ve should be disconnected.

However either I have forgotten its "electronic & ionic" detail, or I have outgrown it.

As per one of those link repliers, I too reckon you would have more problems with the battery disconnected. I certainly know of welding without any disconnection, but maybe it's a "just in case" thing or restricted to certain situation. (EG - I used to laugh at the old myth about leaving jumper batteries connected for a while after starting the flat-battery vehicle UNTIL ~2 years ago when I started using Bosch alternators! Bosch had IMO pathetically weak power diodes.)


As I recall, the welding spike thing was for electronics (not the battery), and probably therefore the alternator since that had the only "electronic" (solid state) component in the vehicle back in those days.
But I thought it was better connecting the 2 battery cables together to help short out any induced spikes rather than having one side floating. IE - since you have to disconnect the battery- before disconnecting the battery+ (ie, the usual DC safety requirement to isolate "chassis" before touching the hot polarity), you then connect the two cables together. (In practice I would have merely disconnected the -ve battery cable and then clamped it to the +ve battery terminal and its still connected +12V cable.)


Like I said, I can't recall the detail of the old theory, but I suspect it's one of those dumb ones that sounds good but is (usually) completely stupid in practice if not outdated. (IMO other examples are hydrogen gases at the +ve battery terminal, or that fridge or freezer condensed frost/ice is poisonous.)


But lots has changed... MIG, TIG etc welders are in use. Welders use inverters. Vehicles use electronics, though they are usually protected against spikes - at least on power circuits. (Their signal and sensor circuits may not be protected, but disconnecting the battery won't prevent that - in fact it will remove the common "rail clamping" protection that is usually used - ie, like a relay coil's reverse biased diode to quench spikes, electrical interfaces usually have reverse biased diodes from the input or output terminal to the +ve & -ve supply rails.


But as to vehicle voltages and currents - sure, 200V spikes are typical, but a mains referenced welder (we have 230VAC here), and (say) 40A to 120A currents along paths that normally do not have that current concentration... that could be a problem. (IE - starter motors may be 400A, but it has good cabling etc. Run 30A@70V across a short section of panel or chassis with some nearby cable to a sensor... it only takes a few uA to wreck an O2 sensor!
Not that that will ever be as bad as Hawaii in the 1960s!)


If I find that article I'll let you know. I think it was from Electronics Australia, probably the 1960s or 1970s.
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howie ll
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Posted: June 03, 2011 at 10:13 AM - IP Logged
Link to Post  Post Reply Quote howie ll

Peter, how relevant I don't know but I was called out to an oldish Lexus (the big one) where the owner had only one key and the security light was on. It was pouring down (England, remember?) and we left it with "have it towed to the nearest Lexus dealership and let them programme two new keys". Then I remembered what a bunch of ignorant plonkers they are and on a friend's advice I went back and joined the terminals for about 20 seconds, actually disconnected only the neg and joined it to the pos, bingo, job done.
Funny I was always taught on jump starting to keep the donor engine running and connect pos first, disconnect neg last.
N.B. Most of the body shops I work with use spike protectors but those guys probably know less about car electrics and why are they doing this than my grandson's gerbil.
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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.
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oldspark
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Posted: June 03, 2011 at 7:55 PM - IP Logged
Link to Post  Post Reply Quote oldspark

Yet again, great story.
And IMO another one of those DIY "why not try" solutions. Although some need to be careful of other batteries or maybe big audio caps, and being aware that EMS's power relay will be off (but we are talking here of security which is permanent +12V, not IGN).

But for security systems, what if something has "latched" that can be reset by ensuring a power disconnect (at least) if not a terminal shorting (to discharge caps or static etc).


Jumpers - connect pos first (yes) and therefore neg last.

But disconnect neg last? Doesn't that strike you as strange - ie, they wanted the neg (ground/earth) NOT connected when connecting the pos, yet don't mind neg still being connected when removing the pos?

I know there are lots of strange teachings - some of which are totally R's about because someone forgot the "not" etc.

And I once saw a 12 line "Rule" for what to do. It was then that I came up with my version which replaced those 12 rules - namely (and in "Universal" format for +ve & -ve grounds):
Whenever you work on the hot, the chassis/ground must be disconnected.
(Or whatever wording I used - I think I wrote it better once.....)

IMO even if you forget the sense (polarity) of that rule, if you remember the concept, you can work it out.
Namely that if your spanner when undoing the battery ground terminal also touches the chassis, what happens? Nothing.
If your spanner when undoing the battery hot terminal also touches the chassis, what happens? BANG!
Therefore undo & disconnect the chassis terminal BEFORE doing anything else, and reconnect last - ie AFTER everything else is done. IE - whenever working on the hot, the chassis is disconnected.   

(IMO simple if you can picture the issue. But bluddy complex if you try to describe it.)



BTW - sometimes there is some logic to certain things like (say) disconnecting neg last, but often such logic is IMO flawed.
And other times, though not incorrect, it has little practical significance (not a good example, but eg, connecting the neg battery terminal because hydrogen gas is at the pos terminal.. Yes - all six +ve terminals in a 12V battery, ie, every vent or the single vent etc). Maybe a better such example was the "disconnect the pos" for welding - if only I could remember the electronic reason for that "rule".
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