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'[EE] Vehicle load dump'
2007\05\23@174914 by luis antonio prata barbosa n/a

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Hi,

I need to do an overvoltage protection circuit for high current (30A)
needings.
It's for a vehicle powered circuit. Car or Truck (12 or 24v).

The "Load Dump" fenomenum makes car voltage up to 80v or higher.
The use of transorbs or proctection diodes require a series resistor that
dissipates a lot of power and/or generates undesireable drop voltage.

I didn´t find good single chip solutions for this high current scenario.

I've project a FET based circuit (attached) but I don't know if it will be
the best choice.

Do anybody have some suggestion ?

Thank you.

Luis.

2007\05\23@175141 by luis antonio prata barbosa n/a

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2007/5/23, luis antonio prata barbosa <spam_OUTluispratalistasTakeThisOuTspamgmail.com>:
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2007\05\23@190731 by Dr Skip

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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.

2007\05\23@194513 by Brent Brown

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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.brownKILLspamspam@spam@clear.net.nz


2007\05\23@200131 by Bob Blick

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> The "Load Dump" fenomenum makes car voltage up to
> 80v or higher.
> The use of transorbs or proctection diodes require a
> series resistor that
> dissipates a lot of power and/or generates
> undesireable drop voltage.

If you use a series polyswitch fuse and a big tranzorb
you can do pretty well.

Cheerful regards,

Bob

2007\05\24@045812 by Michael Rigby-Jones

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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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2007\05\24@114111 by Harold Hallikainen

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face
In a recent project where I have a 10F200 driving a FET driving a 12VDC
motor, I looked at various ways to get the 5V for the 10F200. Dealing with
automotive rated regulators turned out complex and expensive (big
capacitors required). The only load here is the 10F200 and the gate drive
to the FET (10F200 through a resistor), so I just did a zener regulator
(two series resistors, zener to ground, 1uF ceramic across the zener). I
think this should do fine in an automotive environment. The zener provides
reverse battery protection, the RC provides spike protection in case the
zener is not fast enough.

We'll see how it works!

Harold


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2007\05\24@171854 by luis antonio prata barbosa n/a

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What waveform will I have ? I mean, when "load dump" happens will be the
circuit cutted off ??? I need the circuit still working even during load
dump time (400ms)...

2007/5/23, Bob Blick <EraseMEbbblickspam_OUTspamTakeThisOuTsbcglobal.net>:
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> -

2007\05\24@183428 by Bob Blick

face picon face
The tranzorb limits the voltage by clamping. Your
circuit still remains powered. If there's too much
energy it will short circuit. Then the fuse protects
against fire.

It requires careful reading of spec sheets and some
testing to get the right combination, but then you
have something simple.

Does this application have a starter motor, do you
care about low voltage?

Cheers,
Bob

--- luis antonio prata barbosa
<luispratalistasspamspam_OUTgmail.com> wrote:

{Quote hidden}

2007\05\24@184609 by Gerhard Fiedler
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Harold Hallikainen wrote:

> so I just did a zener regulator (two series resistors, zener to ground,
> 1uF ceramic across the zener). I think this should do fine in an
> automotive environment. The zener provides reverse battery protection,
> the RC provides spike protection in case the zener is not fast enough.

With many digital components now working over a rather wide voltage range,
the zener diode seems to get new use as inexpensive regulator.
Specifically, I don't think there's much that can beat a double zener
circuit in terms of robustness for the buck -- if you have the headroom, of
course, and for lowish currents.

Gerhard

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