Automotive Load Dump

Somewhere here I have some papers. I'll see if I can find them.

Basics:

Series diode to disconnect from negative going transients... otherwise you fry substrates.

Series R + a zener to ground

-or-

As I'm fond of, a high voltage pass device to disconnect your circuits during anything over 18V.

At other times, like in ignition or alternator regulator, I just turn off the big-ass device during the transient because it can take the V's when off, and just series protect the low current stuff. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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I love to cook with wine.     Sometimes I even put it in the food.

This is old, but relevant

Rule of thumb seems to be that such components may need to handle a transient of up to +/- 50 VDC, in a "12-volt" automobile electrical system.

As a hobbyist I usually like to use a PTC "soft fuse" followed by a hefty Transzorb or other zener-ish device to ground.

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I think it depends a little on what it needs to do

can't what remember what app note it was but it basically had three strategies:

"dumb" npn preregulator that can handle the peak voltages. a problem when you need low drop out, such as for an ECU that needs to run at the low voltage when cranking

FET that disconnects the device when input voltage exceeds a limit low drop out but you don't want to turn off and reset your ECU when there's a voltage spike

The two in parallel, solves both problems at the cost of more parts

seems most of the automotive voltage regulators are rated for 40-60V

Wonder how big a load dump really is in modern car with 10's of amps of minimum load

-Lasse

I wouldn't be so sure about that. One guy reported that he drove about

800 miles in a European TDI (Volkswagen?) after the alternator died. During daylight, and with the radio off. Must have been one boring drive.

As for load dumps, per many documents the surge can reach well over 100V but that sounds a bit high. Even on aircraft where the nominal voltage is twice that of a car (28V) we usually do not have to stomach more than

80V. I usually try to let my stuff keep on working through such events. Much more pleasing to customers than simply letting it cut out.

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Regards, Joerg

http://www.analogconsultants.com/

impressive, 10A headlights + 5A? fuel pump must have been on the very limit

A guy I know that does AUDIs says they need to connect a charger to run a full test (20minutes?) on the automated tester

I can see how in the old days when the electric system was an ignition coil, lights and a radio you could get a huge change in load thus big spikes, but now when a car uses 10s of amps as soon as you turn the the key I'd think it is a bit different

indeed

-Lasse

During daylight. In the US we do not have to keep the headlights on during the day in most areas. I don't know what its fuel pump needs but most certainly not five amps.

That's a sad state of affairs. I had a big Audi station wagon in Europe and it's still traveling back and forth between Sweden and Germany. Will soon celebrate its 25th. It uses very little electric power during the ride. Maybe younger engineers should ask the older ones about the tricks of the trade :-)

I sure wouldn't want to buy such a car. But a load dump can also happen if a battery terminal comes off or becomes erratic. I've had that on a big fat Chevy truck. Those things were totally unfazed by load dumps. When I told the owner he said "Oh, then you grab the piece of wood from under the seat, pop the hood, whack the battery plus terminal a bit, then she'll start right up. And when it's a rough road and suddenly the headlights turn real bright, you'll have to do that again".

[...]

--
Regards, Joerg

http://www.analogconsultants.com/

Dunno how useful this is:

SAE J1113/11

Immunity to Conducted Transients on Power Leads

Scope This SAE Standard defines methods and apparatus to evaluate electronic devi= ces for immunity to potential interference from conducted transients along = battery feed or switched ignition inputs. Test apparatus specifications out= lined in this procedure were developed for components installed in vehicles= with 12-V systems (passenger cars and light trucks, 12-V heavy-duty trucks= , and vehicles with 24-V systems). Presently, it is not intended for use on= other input/output (I/O) lines of the device under test (DUT).

I haven't done any work on recent vintage cars but, in the '60's, it was not uncommon to experience 180-400V... lower voltages were of long duration and vice-versa... I learned a lot about automotive transients the hard way... like finding nothing but a melted silicon bead in a regulator autopsy :-( ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Well, you've got to place a TVS in there. Same in aircraft, the spec for short spikes is 600V for most stuff. But it's the longer duration surges, tens of millseconds, that kill stuff in a *KABLOUIE* fashion.

--
Regards, Joerg

http://www.analogconsultants.com/

SAE J-1113, ISO 7637, ISO 16750, ISO 10605

Also see ST Microelectronics TA0338, "Designing robust protection of automotive power rails against overvoltage and reverse polarity battery hazards"

Fig. 1 and Fig. 2 in the ST app note show surges according to the ISO standards -- they'll curl your whiskers...

--

Here is "my" thread from Jan 2007, hopefully link will work:

--

John Devereux

Just assume a nominal worst case of 50V being delivered to your black box. And protect it from reverse polarity as well..

Check the car wiring system if you are in control of the design of that also. Other devices on the bus may actually take most of the load dump, since they have transient protection also.

When I worked on automotive stuff, we had to comply with 150V for less than 100us (inductive open test) and 60V for less than 100ms (load dump test). Both figures for 12V system. Iso 7637-2 specifies simelar to ths (test pulse 2 and 5)

Cheers

Klaus

YOU may turn things off before some idiot puts a 48V charger on the car battery, but i bet many others will leave their radio etc on..

I remember an app. note from Intel in their Microcontroller databooks in the later half of the 1980's.

dig, dig, dig

Intel AP-125 Designing Microcontrollers Systems for Electrically Noisy Environments.

Mark Zenier snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)

See if these are helpful...

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Here are a couple of old ST app notes:

Pete

Begin with the battery, it is capable of hundreds if not thousands of Amperes for seconds. It has been part of the deal from the start. Then consider that the relevant standards require dealing hundreds of volts = for good chunks of a second today. Of course 20 A generators have been replaced by 80 to 140 A alternators as well.

?-)