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.

-- 
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brown@clear.net.nz


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