Although Cars Use 12v Batts, What Is The Highest Voltage I May See?

[Anton green 12 1 Cars]

Although cars use 12v batts, what is the highest voltage I may see?

I am thinking of running a voltage display panel in the car which is rated at 15v maximum input power and would like to know if it is likely to last.?

[Sandy 189]

Over 14 during charging isn't unusual.

[Rob_the_Sparky 9]

14.5 under charge, could go higher if the regulator isn't happy. 15V is possible but unlikely if the alternator is healthy.

[Beastie 1]

15V is possible but unlikely if the alternator is healthy.

 

I've seen a Volvo putting out 17.5 volts. It had been blowing bulbs regularly and by the time it came to me the day - running light fuse holder had melted.

[Rob_the_Sparky 9]

Yeah, I had one blow every bulb in the dashboard for the same reason. Made night driving more "interesting"! Reason was a duff regulator in the alternator though, not something that happens too often.

[Sam 4]

13.5-14.5 while charging is the good zone for a healthy alternator. My friends 106 was kicking out 18 volts once and the battery was bubbling and smelling awful, the regulator on the alternator was dead basically.

[Anton green 12 1 Cars]

Thanks all.

I fitted an alternator about 3 months ago, so I'm going to go ahead and order the panel.

Edited December 21, 2006 by Anton green

[gizzmo 3 1 Cars]

Although cars use 12v batts, what is the highest voltage I may see?

I am thinking of running a voltage display panel in the car which is rated at 15v maximum input power and would like to know if it is likely to last.?

some of the cheap multi meters that avaliable arn,t so accurate so i would only use it for indication purpose only. i am industrial electrician my meter £200 an calibrated every year but only use for indication purpose good battery should put around twelve volts engine not running turn engine on voltage should lift,rev the engine and the voltage will alter depending on the engine revs good alternator.

[Anton green 12 1 Cars]

no worries. I'll be using the meter to keep an eye out for any unusual readings(!), and not worried about it being super accurate.

 

If anyone wants to do the same as me, the guy sells a lot of these at once on ebay, so dont bid mine up -just bid on one of the other exactly the same panels he has for sale.

[Rob_the_Sparky 9]

some of the cheap multi meters that avaliable arn,t so accurate so i would only use it for indication purpose only. i am industrial electrician my meter £200 an calibrated every year but only use for indication purpose good battery should put around twelve volts engine not running turn engine on voltage should lift,rev the engine and the voltage will alter depending on the engine revs good alternator.

 

That depends on what you call accurate though, cheap nasty meters are fine for most home use purposes. Professionally I too use expensive calibrated meters but I wouldn't recommend them to the hobbyist. Just too much cash for the amount of use they will see.

 

Rob

[Anton green 12 1 Cars]

14.5 under charge, could go higher if the regulator isn't happy. 15V is possible but unlikely if the alternator is healthy.

Rob, what would be an ideal component to use, just to bring the voltage down a little? The panel will run off any voltage between 5 to 15 volts, so if I simply solder in another component in line with its live feed would this be a viable way of being extra careful? Cheers

 

Anton

[Rob_the_Sparky 9]

A voltage regulator is probably best, maybe a DC-DC converter. Regulators can get quite hot and can need a heat sink, depending on the amount of power used, DC-DC converters are more efficient (less heat) but finding one with the right input and outputs could be more tricky. A 9V voltage regulator looks good, but will drop 3 to 6V depending on the input so may get quite warm and need a heat sink or if you are careful could be bolted to the car. The bit to bolt it on can often be live, creating a short if bolted to the car so check the datasheet.

 

However, check the display specs. If it is normal to operate upto 15V then absolute max voltage will be above this. E.g. it won't (certainly shouldn't) blow at 15.1V. I'd expect 10 to 20% over voltage to be withstood without damage, but that does assume good design practice...

 

Rob

[Anton green 12 1 Cars]

Thanks Rob, the panel will be on a swich and not run continuously for more than about 5 mins I should say. So having taken what you said about 'it shouldn't blow if it strays slightly over 15V assuming good design practice', common sence says I am good to go ahead if I do common sence things like fusing and not putting the heatsink anywhere heat may be an issue etc.

[Rob_the_Sparky 9]

Regulators drop power based on the voltage drop and current. E.g. if dropping from 15 to 9V and load is 1A then you are looking at getting rid of 6Watts. That would get hot. However, if your display only uses 0.1A then you are looking at 0.6Watts, not very much heat...

 

Rob

[Anton green 12 1 Cars]

very good point there.

 

V = I x R

 

Im a touch rusty at electronics. I'll thrown my multimeter over it, but I dont think it should be an issue as it uses LEDs to form a display. time will tell tho!

Edited January 8, 2007 by Anton green

[Rob_the_Sparky 9]

Sorry if that was a bit noddy, you never know what experience people on here have so try to keep it simple

 

P.S. I think there is a hgh chance you will be fine without a regulator (but no guarantee).

[Anton green 12 1 Cars]

I installed the voltage meter where the ashtray is in the 205 dash. I can fold it away neatly out of sight. The picture was taken in the dark, but you get the general idea. Im going to colour code it black now, instead of the light grey which the metal I used was coated in.

 

[Neosophist 0]

That looks jazzy!

 

All you need now is a flux capacitor and your all go.

 

..my astra gte's digidash voltage meter only goes upto 15v but usuall stays around 12.7