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Car power supply overvoltage protection

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eem2am

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car battery protection from overvoltage

Hello,

Cars use a battery which is charged by an alternator to supply the electrical facilities.

However, if many of the car’s electrical devices are turned off at the same time, then the alternator’s coils are engorged with energy and must dump this energy into the battery and external circuitry.

-This can result in “Automotive Load Dump” with voltages at the battery terminals going to as high as 80V.

“Automotive Load Dump” can be especially severe just after the car has been started.

All of the electrical devices in the car (eg lights, radio etc) must be protected from this 80V overvoltage.
That is, each circuit has its own transorbs etc.

-Instead of having to have such protection on every single circuit attached to the battery, would it not be preferable to simply put a big transient suppression circuit on the alternator and that forget about having to do it on all of the individual circuits connected to the battery?

It seems ridiculous that , for example, car headlights must be designed to withstand 80V overvoltage transients.?
 

leomecma

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vehicle battery over voltage

It's not possible, this overvoltage has very high energy not concentrated in unique point, then are no place to put it that you will protect all circuits. The effect of each inductive load as more intense just near of the load that generated the dump. For example, if you see the waveform in ignition coil supply line, you can see very noise line, but in other parts of the same +12V line, you don't see the same noise, this is because the noise is high frequency and the car network appear how a distribuited parameters, very dependent of impedance.
 

betwixt

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car overvoltage battery protection

Prove it for yourself.
Take a heavy duty 80V power supply and connect it across a car battery then see how much current it draws. Don't stand too close when you switch on.

Seriously, transients can be produced by the alternator but be realistic. Look at the sources of voltage and their power capability, then look at the loads around a typical car. There are some inductive devices which can produce back-EMF or short voltage spikes but they are normally filtered anyway. As Leomecma states, they are distributed around the wiring and in almost all cases, sensitive equipment in the vehicle is fed directly from the battery anyway. The battery is like a massive (hundreds of Farrads) capacitor sitting across the supply so excessive voltage quickly gets absorbed quite safely.

Brian.
 

willi65

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overvoltage protection automotive

Hi

sorry i not understand u...what u want ..or what ur target
All Car Radios ec. must be approved ISO7636-2 (must cheked the wright ISO)..
The load dump can be at 12V 200V for 200ms and high power..
U can protect with an active clamping and some Suppressors and capicators..

Willi
 

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