And finally.....DC welding off your vehicle.

Submitted: Friday, Oct 04, 2019 at 19:03
ThreadID: 139147 Views:1166 Replies:5 FollowUps:13
I have over the years had to use my vehicle batteries (24volt) to weld up the odd running repair. I have always disconnected the battery bank (two 12 V batteries) from the vehicle because of the fear of doing some sort of damage to the vehicle electrics. What damage I don't know; just better safe than sorry.
Further, I have always wondered how I would go leaving the batteries connected and the engine running to keep charging the batteries but when out in the desert, I've never been game enough to try. Thoughts?
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Reply By: Member - nickb "boab" - Friday, Oct 04, 2019 at 20:30

Friday, Oct 04, 2019 at 20:30
That would be handy ( 24volt vehicle) , just connect your welding lead & way you go as long as you have got long leads ..
always been surprised how little welding takes from your battery's
Cheers Nick b
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Reply By: IvanTheTerrible - Friday, Oct 04, 2019 at 20:35

Friday, Oct 04, 2019 at 20:35
Connected or disconnected you still run the risk of destroying a battery. The risk that is worse now with the shitty crap batteries on the market. In the middle of nowhere the vehicle would have to be absolutely disabled before I would be using the batteries for anything other than starting the vehicle.
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Follow Up By: GerryG - Friday, Oct 04, 2019 at 20:45

Friday, Oct 04, 2019 at 20:45
That's been my thoughts Ivan. Just thought I'd run the idea past "the lads" while I'm home and not out in the sticks.
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Reply By: Member - Boobook - Friday, Oct 04, 2019 at 21:06

Friday, Oct 04, 2019 at 21:06
I would not even think about thinking about welding from batteries connected to the vehicle. Hundreds of amps to none suddenly can cause massive voltage spikes, hundreds or thousands of volts. Even the battery leads could act like an inductor.

The odds of zapping the electronics are lower than the Melbourne cup favorite.

I'd totally disconnect the batteries from the car before starting to weld personally.

Tony
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Follow Up By: RMD - Saturday, Oct 05, 2019 at 08:07

Saturday, Oct 05, 2019 at 08:07
Welding from a 24v system wile running will cause the voltage spikes Tony mentioned. Since most vehicle electronics have reverse voltage tolerance of components only spec'd to be above normal vehicle events, the sudden full alternator output which is suddenly not required when the arc stops or during when the rod sticks and releases, will cause the alt voltage to flare to high values.

A 12v alternator system will peak at well over 100v so a 24v system will most likely be higher than that. That is only the momentary flare of uncontrolled regulator action. Normally no sudden changes happen while the alternator is charging, those which do happen are well within design limits.

If likely to need it, I carry a Honda generator Eu20 and a small inverter welder which will weld far better than batteries can.
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Follow Up By: HKB Electronics - Saturday, Oct 05, 2019 at 20:20

Saturday, Oct 05, 2019 at 20:20
I agree with the above but as a matter of interest modern alternators these days are using Zener diode type devices for the rectifiers. These devices break down when alternator overshoots occur and limit the alternators output levels to safe levels. See "avalanche devices in alternators"
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Follow Up By: Allan B (Sunshine Coast) - Saturday, Oct 05, 2019 at 21:46

Saturday, Oct 05, 2019 at 21:46
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Not so. The original rectifier diodes are still used. Avalanche diodes are being added in a shunt path to limit any damaging induced voltages.
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Allan

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Follow Up By: HKB Electronics - Sunday, Oct 06, 2019 at 12:00

Sunday, Oct 06, 2019 at 12:00
Alan I suggest you refer to figure 4 in the linked doc:

Alternator schematic

From another doc :

"Abstract
The alternator "load dump" problem has become more serious with the increased use of electronic modules in today's "hi tech" automobile designs. An alternator rectifier device has been developed to contain the unwanted alternator voltage excursions that might occur should a connection become intermittent during a high charge rate cycle. These new avalanche rectifiers have been designed and constructed to withstand the hostile automotive environment. They are rated to operate as normal alternator rectifiers, and when required, will operate in a zener avalanche mode to clamp the alternator output voltage level to under 40 volts. The performance of these new rectifiers under load dump conditions is examined as well as the normal forward voltage drop versus current flow. The use of the avalanche rectifiers in the alternator design allows the automotive engineer to reduce the cost of protection for every individual electronics module in the vehicle."

The schematic of the alternator for the Toyota 200 series only shows 6 avalanche diodes in the rectifier bridge, the Prado is the same.
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Follow Up By: Allan B (Sunshine Coast) - Sunday, Oct 06, 2019 at 13:46

Sunday, Oct 06, 2019 at 13:46
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Leigh, thank you for drawing my attention to that article by Dan Eddleman of Linear Technology. I had not before seen it.

As I understand the situation, moves to limit alternator output using avalanche diodes were initiated but not universally accepted as the reverse voltage of 35v was still undesirable to be presented to many onboard electronic modules of modern vehicles. With the proliferation of these modules it becomes economically unacceptable to equip each module with adequate protection.
Typically, these modules were limited to accepting over-voltages in the order of 20v and their internal voltage suppression needed to shunt anything over that which placed excessive demands on their internal TVS devices. With device suppression set at 20v they acted before the avalanche diode breakdown of 35v and accordingly were called upon to handle the entire over-voltage and over-current presentation from the alternator.

Accordingly, more sophisticated protection circuits were developed to meet the demands of ISO 7637-2 and ISO 16750-2 Compliance and the quoted Linear Technology proposal is but one of these.

There is no doubt that the electronics of modern vehicles has placed great demands on the performance of their power supply systems.

I would like to read more of the "another doc." that you referred to. Can you provide a link to it?


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Allan

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Follow Up By: HKB Electronics - Sunday, Oct 06, 2019 at 16:34

Sunday, Oct 06, 2019 at 16:34
Alan there is a wealth of information out there if you search for the use of avalanche diodes in automotive alternators as I wrote above.

This types of alternator is being used extensively in Europe, one manufacture I looked at in Italy recently showed approximately half of the many OEM and replacement alternators they manufactured for different makes and models had avalanche rectifier diodes which I must admit did surprise me. I was even more surprised to find Toyota had introduced this type of alternator into the 200 series a few years back, and more recently into the Prado.

It will be interesting to see if switch mode controlled rectifiers in alternators will make it into vehicles before electric vehicles become the norm:

Electronic controlled rectifers

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Follow Up By: Allan B (Sunshine Coast) - Sunday, Oct 06, 2019 at 17:00

Sunday, Oct 06, 2019 at 17:00
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Leigh, it is hard work to keep up with technology in general and automotive electronics in particular.

As an example, the first reference you provided from Eddelman was published in 2015 and the second from Perreault/Caliskan in 2000, so neither can be relied upon to represent the current state of the art.

Who knows what is happening in the development labs today and about to be launched tomorrow?
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Reply By: Member - PhilD_NT - Sunday, Oct 06, 2019 at 00:04

Sunday, Oct 06, 2019 at 00:04
I know these are definitely more expensive than the basic way being described here but have any of you heard of these things and would like to comment.

http://www.readywelder.com.au/readywelders/

By the way, they do have a comment saying not to leave batteries connected to car while doing the welding.

Decades ago while the Stuart Hwy still had the 900km of dirt in Northern SA I had a workmate that carried a small oxy acetylene kit with him when going South and used it to cut off leaf spring parts from a wrecked vehicle and repaired his boat trailer.
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Follow Up By: Member - nickb "boab" - Sunday, Oct 06, 2019 at 06:37

Sunday, Oct 06, 2019 at 06:37
Phil The readyweld spool mig welder would probably suit people that aren't much of a weld and they are very expensive $$$ when i piced them after watching the show . ( us made )
Stick welding with batteries arn't easy to do for novice .P.S remember those days of stuart hwy.
Cheers Nick b
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Follow Up By: Mick O - Sunday, Oct 06, 2019 at 11:00

Sunday, Oct 06, 2019 at 11:00
Had one for a few years now.

Readywelder review.

Cheers Mick.
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Follow Up By: Member - JOHN C16 - Sunday, Oct 06, 2019 at 21:36

Sunday, Oct 06, 2019 at 21:36
I have got one too. Works well. As I am sitting in hospital awaiting a pacemaker there might be a cheap one available to a good home soon . Keep an eye on ExplorOz classifieds.

Cheers, John
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Reply By: Allan B (Sunshine Coast) - Sunday, Oct 06, 2019 at 08:38

Sunday, Oct 06, 2019 at 08:38
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If welding from batteries it is essential to fully disconnect the batteries from the vehicle, both positive and negative.

Even though using a heavy cable for 'weld earth return' to the battery, if the car negative is left connected then the weld current will also seek alternate return paths that can cause havoc with excess currents through car earth wiring connections.
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Allan

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Follow Up By: RMD - Sunday, Oct 06, 2019 at 10:50

Sunday, Oct 06, 2019 at 10:50
I consider the alternator avalanche diode saving isn't really for an alternator. If it was a problem then most alternator rectifiers would be continually failing on a daily basis. Probably the inclusion of such diodes is to save the ever increasing proliferation of electronic thingo's in modern vehicles. Unless the alternator is suddenly disconnected from the battery and it's regulator left to wander in the wilderness, the voltage spikes are generally under control, ie, within normal tolerable limits. When you get a piece blown out of an integrated circuit and you can see inside it, it points to overvoltage. Induced Reverse voltage, does it rise to alarming levels?
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Follow Up By: HKB Electronics - Sunday, Oct 06, 2019 at 17:00

Sunday, Oct 06, 2019 at 17:00
The overshoot protection is to protect the vehicles electronics not the alternator. Cars electronics are designed to handle normal transients that occur with lead acid/ alternator setups but having another level of protection doesn't hurt.

I have seen what happens when the voltage regulator fails and the battery is disconnected from an alternator that does not have any in built protection, any electronic equipment that was turned on is destroyed, headlight filament are vaporised etc.

Reversing the voltage turns the rectifiers on, the load then becomes the stator windings and the alternator goes up in flames. Other cars electronics may also be protected by a diode that will conduct and possibly either destroy itself or blow a fuse, if either of the devices is internal to the module the user is not going to be able to fix it. Reverse voltage will kill most electronic devices if the are not designed to handle such an occurrence.

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