# convert 12v dc to 6v dc

ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 3:29 PM / IP Logged

how do you change 12v DC to 6v DC? what resistor or potentiometer would that require?

Would a voltage regulator work? (where would I find one?)

what would be your guess at a normal average sized car battery's current? current is measured in amp-hours correct?  so how many amp-hours?   how much wattage does it put out?

sorry I didnt look it up on my own (or am too retarded to do so)

Thanks Alot!

megaman
Copper - Posts: 386
Joined: June 24, 2008
Location: Montana, United States
Posted: August 22, 2008 at 3:47 PM / IP Logged
what are you attempting to do?
ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 3:51 PM / IP Logged

I'm just trying to change 12v dc from my motorcycles battery to a 6v DC input on my bike's computer.  My bike will not work without this 6v DC input

Thanks alot!

KPierson
Platinum - Posts: 3,539
Joined: April 14, 2005
Location: Ohio, United States
Posted: August 22, 2008 at 3:54 PM / IP Logged

If you need a power supply a resistor won't work, if you need a voltage reference you can go that route.

They make an adjustable voltage regulator, an LM317.  You control the output voltage by selecting a few external components (there are calculators available on the net to help with this).  An LM317 should get you about 1 amp of power.

All car batteries are different and it would be pointless to design something off the "average" storage capacity of all car batteries.  You should be able to take the make and model of your battery and find out how much reserve capacity it has.

Kevin Pierson
ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 4:27 PM / IP Logged

lets just assume my motorcycle battery is...   600 cold cranking amps.

how much watts could it produce?

what would be the Amp-Hour?

reserve?

I will get my battery's exact stats tomorrow.

Will try to order one of those LM317s but it would be cooler if I could just make one out of resistors

Last night I metered my battery,  it was at 12.59 Volts,  I hooked up 20x  100Ohm resistors and got my voltage down to 11.99V.   I'm sure with enough or the right kinds of resistors I could get 12v DC down to 6v DC.

thanks alot!

ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 4:36 PM / IP Logged
ezrollin wrote:
 Last night I metered my battery,  it was at 12.59 Volts,  I hooked up 20x  100Ohm resistors and got my voltage down to 11.99V.   I'm sure with enough or the right kinds of resistors I could get 12v DC down to 6v DC.

by that logic it would take me 200 more of those  100 ohm resistors to arrive at around ~5.99V

Is my logic flawed?

KPierson
Platinum - Posts: 3,539
Joined: April 14, 2005
Location: Ohio, United States
Posted: August 22, 2008 at 4:54 PM / IP Logged

Resistors resist current, not voltage.

If you took two 100 ohm resistors and wires them in series (one end to the other) then connected them to the battery you'll end up with almost 6vdc exactly if you measure from the middle of the two resistors to ground (a standard voltage divider circuit).

However, you'll have basically no current at all to power anything, and as you load the circuit the voltage will start to drift.

You could take the voltage divider circuit and add a couple transistors to it to increase current capacity, but why not just buy a voltage regulator and be done with it?

Also CCA isn't what you need, you need reserve capacity.

Kevin Pierson
ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 5:47 PM / IP Logged

To find the voltage across a component with resistance Ri, use Ohm's law again:

<_i \,[/itex]

where I is the current, as calculated above. The components divide the voltage according to their resistances, so, in the case of two resistors,

V1   =    R1

V2   =    R2

[/QUOTE]

How come when I connect 20    100ohm  resistors end to end (using a 12v dc battery)  I end up with 11.99Volts?

thanks alot for the info!!

KPierson
Platinum - Posts: 3,539
Joined: April 14, 2005
Location: Ohio, United States
Posted: August 22, 2008 at 6:03 PM / IP Logged
Where are you measuring voltage from?
Kevin Pierson
ezrollin
Copper - Posts: 59
Joined: August 22, 2008
Location: Texas, United States
Posted: August 22, 2008 at 6:24 PM / IP Logged
KPierson wrote:
 Resistors resist current, not voltage.If you took two 100 ohm resistors and wires them in series (one end to the other) then connected them to the battery you'll end up with almost 6vdc exactly if you measure from the middle of the two resistors to ground (a standard voltage divider circuit).

I guess I'm not understanding,  (sorry if it seemed like I wasnt listening to you)  is there any way  you could make a quick Paint drawing?

I hook negative voltage meter to negative battery post.

I hook resistors to battery positive then voltage meter positive to the last resistor.

(if that makes sense?   I can make a quick paint drawing no problem!)

I really wanna get the voltage Regulator!

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