>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of Brent Brown
>Sent: 24 May 2007 00:45
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE] Vehicle load dump
>
>
>On 23 May 2007 at 19:07, Dr Skip wrote:
>> I've heard this talked about here, but how real is it? In cars from 
>> 1964 to 2006, I've had all sorts of devices on the 12v system, most 
>> without any fancy protection, and many fairly sensitive, and 
>none ever 
>> suffered. I would think the lead acid battery would sink any spike 
>> that came along and the worst you might get is some hf noise 
>far from 
>> the battery. Off hand, I can't think of any switched inductances or 
>> capacitance that would cause it, and even then, it would have to be 
>> far from the battery I'd guess. Is it a myth?
>> 
>> luis antonio prata barbosa wrote:
>> > The "Load Dump" fenomenum makes car voltage up to 80v or higher.
>
>Yes, it can and does happen, but perhaps not everyday. Worst 
>case is when battery 
>is flat and vehicle is jump started from another. Once started 
>the vehicle alternator 
>is then pumping out 60 amps or so doing it's best to try and 
>charge one maybe two 
>flat batteries. If the jumper cables are then removed 
>disconnecting the heaviest load 
>(load dump), the alernator output voltage goes through the 
>roof (momentarily) until it 
>settles down to the new load requirements. Specs are available 
>of typical load dump 
>waveforms (can't think of the standard number(s) off hand) so 
>you can design for 
>this, but it does take quite some effort.


Worse still is one of the battery connection getting intermittantly made and broken whilst the engine is running, e.g. due to corrosion in crimped connector or broken cable etc.

Regards

Mike

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