# Drop 14.4v down to 7-9v......



## jabberwocky (Apr 30, 2008)

Quik one for you circuit guys.
I need a simple but reliable way to drop 14.4v from a cars battery, down to 7-9v.


----------



## fravak (May 16, 2009)

Do you know how much amperage you'll need?


----------



## bradbaum (Jul 26, 2008)

if you need less then 1 amp then just use a 7809 voltage regulator.

http://www.mouser.com/ProductDetail...M7809ACT/?qs=sGAEpiMZZMtzPgOfznR9QVMHHizqS70X

higher voltage goes in on the left pin, ground the middle pin, and then 9VDC comes out the right pin. Be sure to use a heat sink if you are more then half an amp.


----------



## jabberwocky (Apr 30, 2008)

Great..........
That looks like it will work.
Is this here the equivalent of said voltage regulator?
http://www.goldmine-elec-products.com/prodinfo.asp?number=A10450
I got a couple more questions for you all if ya dont mind.
I need a relay that can operate off of between 3-5volts DC, and switch on a current of between 12-14.4volts DC.
Im hoping to be able to purchase these from Electronic Goldmine if possible, since Im already about to order a few things from there.
http://www.goldmine-elec.com/Electronic 
I know I should be able to figure this out myself, but I believe in asking for help when not sure.
Thanks for the help.


----------



## hedg12 (Jul 6, 2008)

That's the same voltage regulator, it's just designed to be surface mounted. It'll work, but it might be difficult to attach a heat sink (which you probably need.) Hobby Engineering has the 7809 in a TO=220 package that might be easier to work with.

This relay from Electronic Goldmine should do what you want, & it's on sale to boot.


----------



## bradbaum (Jul 26, 2008)

You seem to mixing up the terms current and voltage.

Voltage is the level of the electricity (either AC or DC) and is measured in Volts (or Electromotive force (E)).
Current is the amount of flow through the circuit and it is measured in amps (I).
The other major player in the electricity game is Resistance (R) that is measured in ohms. This is the resistance the circuit has to current flow.
Power is usually a by-product of the circuit, it is measured in Watts.

The major formula used to calculate current/voltage/resistance and power is ohms law:

E=I*R, R=E/R, R=E/I

P=I*E, I=P/E, E=P/I

If you have a multimeter you can measure any two of these and calculate the others.

It is fairly important that you understand the relationships between the different aspects of electricity prior to messing with it.

For example the relay can handle the voltage, but if you are trying to light a pair of car headlights with it you will cook the relay because it can't handle the current.


----------



## hedg12 (Jul 6, 2008)

Sorry - just scanned the post & assumed he was drawing a low enough to be fed by the regulator. I guess if he's switching 12 volts it wouldn't be from the 9 volt regulator (doh)!
Sorry to give erroneous advice - I'll quit drive by posting now... 

Jabberwocky, what are you connecting to the relay?


----------



## bradbaum (Jul 26, 2008)

hedg12 - no need to be sorry, Your advice is good, we just don't have all the data to provide the correct advice.


----------



## jabberwocky (Apr 30, 2008)

Ok, so heres the idea.
I got a kit that lights up 6 leds, 2 by 2 in a sequential pattern when given the requested 9volts.
Id like to convert it to operate off a running(14.4volts) car battery, and instead of the 6 leds, id like it to trigger 3 "normal" taillamp bulbs.
I figured the best way would be to have the power that was triggering the leds, instead activate a relay for each bulb.
Any suggestions?


----------



## hedg12 (Jul 6, 2008)

Aah, I see. Progressive turn signals (kinda like the old T-Bird)? What you're attempting should work just fine. An 1156 draws a little more than 2 amps (right around 2.25), so if that's what you're using you'll need a relay with more current capacity then the one I referred to earlier. 

A couple of other things you'll probably want to look into, too - if you're hooking the coil of a relay to the output of your board, you'll want to wire a small diode across the coil to protect the circuit from back emf. A 1N4001 should do. Just hook it up so that the stripe on the diode is closest to the positive wire on the relay coil, and the other end is the ground. You'll also probably want to connect a small capacitor across the input and ground connections of your voltage regulator IC, too. Something like a .33mfd cap will help filter out any unwanted spikes from the cars charging system.


----------

