What you really want is a self biasing voltage regulator or a Zener diode.......you could build a voltage divider by using two like resistors ..and tap your load between the two resistors and ground to get six volts (around 7 actually) the size of the resistor is only a consideration of how much current you need for your device.......for 3V you'ld use a resistor of a given value and two resistors of half that value .....tap between the large and small resistors for 6V and tap between the two small resistors for either 9v or 3v depending on which end was at ground.

If you have a simple resistive device you can check it's resistence with an ohm meter and size the resistor so that it is 3X the value of the load for 3V(device grounded) or equal to the load for 6V.......keep in mind that you're actually dealing with 14.5+/- volts in reality.

As self biasing regulator or a Zener would be the way to go here .....these will maintain the correct voltage under different applied voltages.......but I guess you can do it with resistors.

Anyone have anything better to offer this man in need?

GeeAea

Figures don't lie ....... but liars sure do figure.

 

What are you trying to power at 3 or 6 volts? As GeeAea stated, a lot depends on the load. The problem with resistor is, if the load changes, the the resistors need to change. A zener will work, assuming that the load is not to high....the math is simple....if you want to drop 12v to 6v, then you need a 6v zener...and if the load is 1 amp, then the zener needs to be at least a 6 watt device (6v x 1A = 6 watts). However, on most vehicles, the actual voltage is going to be more like 14vdc...So to be really safe, you need a DC to DC converter....something that Radio Shack may not have.

Let us know what your trying to do and we might be able to give you a better solution.

John......southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Locker, Solid Axle's, Durabak

 

I'm building a console that will turn on lights, winch, P.A. System, and any other stuff I can think of bolting onto my CJ. I have a 12 port box that I'm using and I bought a switch (on-off-on) that handles 20amps. I'm using relays for any thing that will draw major power (like CJDAVE suggested). And I intend to make the whole thing removable, so it won't get stolen. I have 3v led lights that connect to the switch to show that it's activated. The 6v comes in for a plug that I want to connect to an FRS radio (walky-talky). It runs off four 1.5volt AAA batteries. I don't know the amperage of the batteries, but I was told that the FRS radio will only pull the amps it needs.

If I pull the power from the alternator won't I get a clear 12v? I intended to run a cable from where ever the ignition power comes from. After following the other post ("Electrical Reality Check") it seemed there was too much running through the ignition.

I will post the schematics and pictures of the unit when I'm done, but I'm facing a big learning curve (like everything I do on my Jeep). Thanks for all the help guys.

'83 CJ7 258 i6 31x10.5 3in. lift? /wwwthreads_images/icons/cool.gif

 

Hey jeep head,
why are you making this more diffacult than it needs to be.....
Radio Shack sells 12v LEDs' in 3 different colors ( red, yellow, green ) so you can eleminate those resistors,
as for your FRS they should also sell a adaptor cord that plugs right into your cigarette lighter. Another thought
would be to get lighted toggle switches, ( they light up when activated ) then you could eleminate those LEDs' altogether

Just an idea
Mike

 

I would use 12 volt lights instead or an LED with the approproate dropping resistor. The problem with a filiment type bulb is that the resistance changes as it warms up. So, if one sixe resistor works when you turn it on later after the lamp warms up it may require a different resistor. An LEN does'e change and there are many different types and colors you can use. Alot of times the ones that you buy from Radio Shack come with bezels and a chart for what dropping resistor to use. Otherwise, I would use 12 volt lamps.

For the 6 volt device Radio Shack or other electronic sections at discount stores sell adapters for cigarette lighters that convert from 12 volts to 3 volts, 6 volts, and 9 volts, etc. I would buy one of there, remove it from the case, and solder your own wires to it.

The reason a resistor will not work is that a resistor is not for dropping voltage but limiting current. The fact that it limits current will cause voltage to vary with load. When you tried to key up the radio the current woud go up and the voltage to the radio would go down and then the radion would not work.

Good Luck - email me directly if you have any questions elecdir@washingtonnc.com

O|||||O
/wwwthreads_images/icons/crazy.gif A conclusion is simply the place where you got tired of thinking. /wwwthreads_images/icons/tongue.gif

 

If the voltage drops down to 12v, then the altinator is not working. A fully charged battery actually sits around 13 volts, and the altinator puts out (or should) about 14 to 14.5 volts. If it goes over 15 then you take a chance of damaging the battery.

If Radio Shack has the 12v LED's go that way, if not, use a 9v zener. Each LED pulls about 5ma...so a 1 watt zener will be fine........and use the adapter for the FRS....the current draw will vary too much to use resistors...

One other piece of advice....if your going to hook up some relays, mount them on the inside of the engine compartment near the starter solenoid and use a feed from there....make sure you fuse the feed. Then use acc power to energize the relays. If you try to pull power from inside the cab, you will most likely start blowing fuses...plus the voltage drop will hurt performance.

John......southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Locker, Solid Axle's, Durabak

 

Thanks for the info. I have about 100 of these LED lights and I'm itchin' to use them. They came with the frame of the box I'm using. Anyone could use the cigarette adapter for the FRS, I want this to be different. I use the cig outlet for my CB handheld. I looked at the switches with the lights in them and they look chinchy. I'm not running a pretty boy Jeep here. This baby needs steel, I want to hit the damn switches while climbing a hill.
Again, thanks for the help.

'83 CJ7 258 i6 31x10.5 3in. lift? /wwwthreads_images/icons/cool.gif