car voltage

[andrew8485]

Hey, I am currious how you guys make electrontics for a car when the voltage can differ by more than 2 volts at any two points in time because a cars voltage can vary from 12-14.5v. just wondering

 

[crust]

For systems that need a constant supply, usually a regulated power supply is used.

 

[iso9001]

Crusts answer is right for power supply, As far as getting and sending signals,

All (except a VERY few) the sensors run on 5V... The entire car has a system of 5V Ref wires running around... so thats easy.

As for the other stuff, its all 12V. Gas Tank Pump, ignition coils, airbag squibs, stereo, power windows/locks/seats, etc etc

That is in all the car's I've worked on. I bet there are some bmws or mercs that have oddball stuff in them.

Bewarned though, there is a SERIOUS push for all cars to be 48V in the next few years. (inevitable)

But for now, you SHOULD be fine w/ 12V... Unless your trying to do somthing directly w/ the battery or starter

 

[stevez]

I read an interesting article, written by the people who design automotive electronics. Voltages as high as 60 volts might appear - maybe not long duration but in some situations a millisecond is long enough to do damage. That doesn't mean that everything has to operate as those higher voltages but the possibility must be accomodated/tolerated - or you accept the resulting damage. In my own vehicles it is normal to see some very high voltage spikes, of very short but measurable duration.

It is myunderstanding that the new standard will be 42 volts - whether 42 or 48 the whole point is higher voltages for smaller wires or more power delivered without increasing the wire size. Also heard that starter and alternator will be one unit with power electronics to make the appropriate adjustments.

 

[andrew8485]

all very intresting, how ever one post said regulated power supply but how is this done (I am a newbe) because if you use a resistor or something else which causes restance the amount of resistance will change acording to voltage applied. and in stuff like a cb radio, Fm radio, radar dector that voltage change could dramaticly change the way the componet works. In these devices are there circuts that measure the amount of voltage and determine the amout of resistance need to be applied to get a certain voltage. thanks again the above stuff was interesting tho

 

[mattg2k4]

An easy regulated power supply uses a linear regulator like the 7805 which when hooked up with filter caps will provide a stable 5v power supply when it is input with over 7 volts or so (you can check the datasheet).

 

[Exo]

all very intresting, how ever one post said regulated power supply but how is this done (I am a newbe) because if you use a resistor or something else which causes restance the amount of resistance will change acording to voltage applied. and in stuff like a cb radio, Fm radio, radar dector that voltage change could dramaticly change the way the componet works. In these devices are there circuts that measure the amount of voltage and determine the amout of resistance need to be applied to get a certain voltage. thanks again the above stuff was interesting tho

Mostly, a Zener diode is used to stablize the voltage (for example at 5V)
see section 5.3 on this site to see how this works

This stable voltage can then be buffered using a transistor in emitor follower configuration

Such regulators are available in a single IC-package nowadays
like a 7805 like said above

 

[andrew8485]

thanks a million guys I appricate it thanks

 

[Eclipsed]

I would recommend using regulators designed for automotive use such as the LM2937 from National.They can handle reverse polarity,jump starting, and load dumps -50v/+60v.I usually use a 43v Zener with them too. www.national.com has some pretty good info and circuits on using their regulators too.