12VDC to 6VDC - Team Camaro Tech
Team Camaro Tech join team camaro
 
Camaro Parts at SS396.com     
GROUND UP & SS396.com         
Official Sponsor of Team Camaro
   

Auto Insurance



Registered users (free) do not see these large ads

Electrical & Wiring Troubleshooting electrical.

Reply
 
Thread Tools Display Modes
  #1  
Old Dec 23rd, 05, 06:27 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default 12VDC to 6VDC

Im installing something in my car that needs between 6 and 9 volts DC. Its an electric motor, fwiw. What is the best way to reduce the voltage (and amps?) from 12 / 13 VDC. I've tried diodes, but that doesnt seem to work.
__________________
John Fivian
68 327
Reply With Quote
Sponsored Links
Advertisement
 
  #2  
Old Dec 23rd, 05, 08:16 PM
HarleyD67's Avatar
HarleyD67 HarleyD67 is offline
Senior Tech

Harley D
 
Join Date: Oct 2002
Location: Sugar Creek,WI
Posts: 2,613
Default Re: 12VDC to 6VDC

How much power is this "THING" going to draw. Did you consider a power inverter. If it's something temporary go to Wal-Mart and get a basic 12V DC-120V AC adapter. Then plug in an AC- DC converter. Sounds hokey I know. But if it's temporary then it's cheep and easy. If this "THING" is more long term. Then go to Radio shack and build the same thing. Sorry, but it's the easiest way I know to drop from 12V-6V AND drop the amp's at the same time. Good Luck and don't let the "THING" get you.
__________________

"Be who you are and say what you feel, because those mind don't matter, and those who matter don't mind."-Dr. Seuss
We learn life's important lessons in kindergarten.

Harley D
'67 coupe 427SBC
60'1.7281/4-11.83@115.59
firstgens.com
Reply With Quote
  #3  
Old Dec 23rd, 05, 08:34 PM
JimM JimM is offline
Gold Lifetime Member

Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,119
Default Re: 12VDC to 6VDC

the best way is with a "zener diode" It will take a certain amount of figuring, but a resister in series with the load, and a 6 volt zener to ground from the load side of the resister will do it.
How much current is this motor going to pull?
__________________
JimM's firstgens.com Camaro Board

Jimragtop.com New website for my vert is coming together. Do ya like the slide show on the home page?
Reply With Quote
  #4  
Old Dec 23rd, 05, 08:54 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default Re: 12VDC to 6VDC

Thanks for the replys Harley and JimM - Not sure if it will help, but the "thing" is a radio shack DC electric motor. It runs on 9 to 18 volts. The back of the package says that the current load is 1.98A. I know the electric motor can handle up to 12 volts DC, but I want the RPM to be at the lower end of the scale (at max its 24000 RPMs no load, 128000 with load).

I had posted my hair-brained idea a few days ago about using the old AM radio, replacing the guts to operate a kill switch and using the on/off/volume switch to drive a linear actuator. I can build the actuator just fine I think (already have a mockup done) but the speed of the motor is too high. I've got all the wiring inside the volume switch to operate as an on/on switch to alternate the pos/neg to the motor, therefore driving the actuator out in the normal 'on' position and back in the normal 'off' position. I talked to the radio shack tech person on the phone and she said to use resistors (I am also using diodes to keep the power from coming back up the other set of wires when the switch is turned "off" which would keep the AM radio's light on, ok, thats confusing). Problem is, when I put 12 volts thru the resistor, nothing happens to the motor. When I test the resistor with my volt meter, I get the same volts as without the resistor (around 13). So even though the meter shows no change in voltage w or w/o the resistor, when I have it connected up, the motor doesn’t turn.
Sorry for the long post, but electricity, or more accurately, circuits, aren't my strong suit. I realized I was using the wrong term in my first post, I was told that a 1k ohm resistor is what I needed, no dice.
Heres a link to the motor, maybe theres some tech info on there that yall would understand that I clearly dont http://www.radioshack.com/product/in...entPage=search

Thanks guys.
__________________
John Fivian
68 327
Reply With Quote
  #5  
Old Dec 23rd, 05, 09:02 PM
HarleyD67's Avatar
HarleyD67 HarleyD67 is offline
Senior Tech

Harley D
 
Join Date: Oct 2002
Location: Sugar Creek,WI
Posts: 2,613
Default Re: 12VDC to 6VDC

You tested the volts through the diode, but did you test the amps as well. The motor may be getting the current just not enough power.
__________________

"Be who you are and say what you feel, because those mind don't matter, and those who matter don't mind."-Dr. Seuss
We learn life's important lessons in kindergarten.

Harley D
'67 coupe 427SBC
60'1.7281/4-11.83@115.59
firstgens.com
Reply With Quote
  #6  
Old Dec 23rd, 05, 09:04 PM
JimM JimM is offline
Gold Lifetime Member

Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,119
Default Re: 12VDC to 6VDC

12v---switch---3 ohm, 10 watt resister----x------motor-----ground
.................................................. .........|
.................................................. .........|
............................................6 volt, .25 amp zener diode
.................................................. .........|
.................................................. .....ground

The resister will be big, the kind in a metal case with fins, and will do most of the work. The 3 ohms is based on your motor wanting 2 amps @ 6 volts. At 2 amps, the 3 ohm resister would drop the cars 14 volts to 7, the zener would do the rest.
Current thru the motor depends on coil resistance, input voltage, and load, it will take some experimenting to get exaclty the right resister. I would use a pretty "strong" zener, rated at a couple of amps, at least while dailing in the circuit. If the initial resister value was too low, it could overload the zener.
__________________
JimM's firstgens.com Camaro Board

Jimragtop.com New website for my vert is coming together. Do ya like the slide show on the home page?
Reply With Quote
  #7  
Old Dec 23rd, 05, 09:12 PM
69-er's Avatar
69-er 69-er is offline
Gold Lifetime Member

Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 854
Default Re: 12VDC to 6VDC

This is kind of long, but bear with me.

You can use a simple resistor circuit to reduce the voltage in a circuit.

First, you need to know the current draw, in amps, of the component and how many volts you need to drop from 12 volts, (3 to 6 volts in your case). Using Ohms Law, divide the voltage drop by the amperage draw of the component. This will give you the required resistance to use in the circuit.

Now, since there only so many standard resistances that are available, try using 3 volts in one calculation, then 6 volts. If a standard value of resistance falls within your two answers, use that value. It will get you in the range of of 6 to 9 volts the component requires to operate.

If you find a resistor that will work, now you have to determine if it will handle the power, in watts, the component draws. If the resistor is too small, it will overheat. (you can always go bigger with the wattage rating of a resistor). To do this, take the voltage drop that worked in your resistor calculations and multiply this voltage by the amperage draw of the component. This will give you the minimum wattage rating of the resistor.

Remember, this circuit will only work with a component that draws the same amperage as the one you have now. Any other component that draws a different amount of current will change the voltage going to the component.

If you can't find resistor that will work, you can build a voltage divider. It's a little more complicated, but you can get the required voltage very close to what's required. Having a range of 6 to 9 volts will help in both methods.

Let us know if this makes sense!

Larry
Reply With Quote
  #8  
Old Dec 23rd, 05, 09:15 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default Re: 12VDC to 6VDC

Holy smokes - you guys are fast - thank you very much. JimM, your diagram makes perfect sense. I think I need a electronics for dummies book. I didn't realize that the resister went connected between the pos and negative. I'll have to go by radio shack tomorrow (wonder if they’ll be open). So do you think three of these http://www.radioshack.com/product/in...entPage=search in series would work, then with the zener after that? Its a 1ohm resister.
__________________
John Fivian
68 327
Reply With Quote
  #9  
Old Dec 23rd, 05, 09:21 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default Re: 12VDC to 6VDC

Larry - thanks for the info, let me see if I've got this right:
I have a motor that I want to use at 6 volts and it requires 2 amps,
So I need a 3 ohm resistor with a wattage rating of 12 watts?
Which would be three of these: http://www.radioshack.com/product/in...entPage=search netting 3 ohms / 30 watts

you guys are GOOD
__________________
John Fivian
68 327
Reply With Quote
  #10  
Old Dec 23rd, 05, 09:44 PM
69-er's Avatar
69-er 69-er is offline
Gold Lifetime Member

Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 854
Default Re: 12VDC to 6VDC

You got it. But you might have to use a 3.3 ohm resistor, as that's the nearest standard. It will run the motor a little slower than 3 ohms.

12 watts will be a hefty resistor. You will need a large (physically) resistor, probably a wire wound type that can handle the heat generated by the current flowing through it. When it comes to power resistors, the standards don't always apply. There are 5 ohm power resistors, not a common value of the small 1/8 to 1 watt resistors. I don't remeber seeing a 3 ohm power resistor. I think you need another way to do this.

Jim's version with the zener might be better.

Also remember that the 1.98 amp rating is at what voltage? That changes everything. Experimentation might be needed to get the right speed you need. Nothing can be simpe, huh? If the motor current was way smaller, it would prbably be easier to do this.

Larry
Reply With Quote
  #11  
Old Dec 23rd, 05, 09:52 PM
69-er's Avatar
69-er 69-er is offline
Gold Lifetime Member

Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 854
Default Re: 12VDC to 6VDC

Forgot to add: The wattage of these resistors might be a little small. It's always a good idea to go bigger than what's required. You have the right idea by placing the three resistors in series to get 3 ohms, but the wattage remains the same. Since the same amount of current will be flowing through each resistor, then the power will also be the same for each resistor.

Now, if you put three, 9 ohm, 10 watt resistors in parallel, that would give you a total of 30 watts at 3 ohms. See if they make a 9 ohm resistor. Maybe a 10 ohm would work too. That would put you at 3.33333... ohms.

Larry
Reply With Quote
  #12  
Old Dec 23rd, 05, 10:12 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default Re: 12VDC to 6VDC

Larry - I think I understand, I wasn't taking into account the parallel vs series in that the wattage wouldn't change if in series, the first one would cut it to 10 watts and the following wouldn't do anymore. They do have a 10ohm / 10 watt resistor at R/S. You guys mentioned that the resistor would physically be large, while I know the R/S website doesn't really put it in perspective, the 10o/10w resister don’t seem 'large' (I'm picturing a voltage regulator sized resistor). This is a generic pic of the 10o/10w at R/S. http://www.radioshack.com/product/in...entPage=search

So, put those 3 in parallel and still use the zener diode after that? If you've got the time, I'd love to know the science behind why 3 1ohm resistors would net 3 ohms, but 3 9ohm resistors parallel would result in 3 ohms (or did I get that wrong? lol). You guys are teaching me a ton tonight, I really appreciate it.
__________________
John Fivian
68 327
Reply With Quote
  #13  
Old Dec 23rd, 05, 10:16 PM
JimM JimM is offline
Gold Lifetime Member

Jim
 
Join Date: Dec 1999
Location: Yorkville, Illinois USA
Posts: 22,119
Default Re: 12VDC to 6VDC

You might just dummy it up, using the 3 1 ohm resisters and see what you get. What's the voltage at the motor and how hot are the resisters getting. Buy 4, start with all of them, and if you don't get enough voltage take one out, etc. The zener will put it at 6 volts and keep it there, but you gotta get close with the resisters or the zener will get too hot and burn up.

When i did my tach filter, I dummied it up on a breadboard so I could easily juggle the parts till i found values that worked. Once i had a functional circuit, I put it in a neater package.
__________________
JimM's firstgens.com Camaro Board

Jimragtop.com New website for my vert is coming together. Do ya like the slide show on the home page?
Reply With Quote
  #14  
Old Dec 23rd, 05, 10:27 PM
69-er's Avatar
69-er 69-er is offline
Gold Lifetime Member

Larry
 
Join Date: Oct 1999
Location: Alamogordo, NM, USA
Posts: 854
Default Re: 12VDC to 6VDC

It does seem smaller than I envisioned it. I think those resistors are about 1" long.

I'm not too sure about the zener diode, ask Jim about that.

There are formulas for calculating the total resistance in a circuit when using resistors in parallel. When using resistors in series, you add the the resistance values to get the total resistance.

In parallel, if all the resistors are the same, you simply divide the number of resistors into the resistance of the each resistor. For different values, this one way of doing it.



On a calculator, just take the reciprocal of each resistor and add them together. Then take the reciprocal of that answer to get the total resistance.

Larry
Reply With Quote
  #15  
Old Dec 23rd, 05, 10:41 PM
JHunter JHunter is offline
Senior Tech

John Fivian
 
Join Date: Dec 2003
Location: Fredericksburg, VA
Posts: 785
Default Re: 12VDC to 6VDC

So, maybe this will work?

Only problem I see now, is the only zener diodes at radio shack are 12v / 1watt or 5.1 volt / 1 watt. Although, lets see if I learned anything, could I then put 10 (or so) of the 5.1 volt / 1 watt zeners in parallel, resulting in 5.1 volt / 10 watt?

http://www.radioshack.com/search/ind...=zener%20diode

EDIT: Larry, JimM and Harley - thank you very much for the help tonight, you guys are awesome. Larry, thanks for the diagram for the resistance factor, it makes more sense now. I think I'll do like JimM suggested and spend a little time at R/S, bring home some toys and start tinkering. At least now, I actually have a grasp of what the different items do. Thanks again guys, you rock!
__________________
John Fivian
68 327
Reply With Quote
Sponsored Links
Advertisement
 
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -7. The time now is 11:17 PM.



Camaros.net - © 2009 AutoForums.com