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

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.

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.

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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Not so. The original rectifier diodes are still used. Avalanche diodes are being added in a shunt path to limit any damaging induced voltages.

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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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?

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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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?

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.

Had one for a few years now.

Readywelder review.

Cheers Mick.

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

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?

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.