12V Electrical Tie-in location???

R

rocket5979

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Hey I was wondering why our cars seem to have such high voltage? I see between 12.9 and 14.1 volts in the car. I looked around quite a bit the last few hours for threads in here and it seems to be the norm for our cars; however my other vehicle's elec system doesn't read so high??? I am going to be wiring something into my electrical system that runs off of 12V power source. Will this voltage difference cause a problem? Is there somewhere else in the car (preferably the cabin area) that I could find an actual 12V switched power source? I must admit that while I do know engines front and back, I am very very weak when it comes to understanding electronics. Thanks a lot for any and all replies.
 
14V is pretty typical for Automotive electrical systems. Remember, the only way to charge a 12V battery is to have more than 12V in the system.

Be more specific with your project. Products labeled as "12v" but designed for automotive use are typically designed to run off a 11-16V range. If you are running something else (say a computer) that is designed to run off a 12V power source that's going to be a different issue and you'll either need to purchase a regulator or power supply.
 
oh and if your other car is reading less than 13V while you are driving than you have an electrical failure coming REAL soon.
 
Sounds good guys. I figured I would be safe, but I just wanted to check with people who actually know a thing or two about electrical before wiring in my controller and blowing the poor little fella up. Thanks.
 
beaups said:
oh and if your other car is reading less than 13V while you are driving than you have an electrical failure coming REAL soon.
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very very true but I like to see it closer to 14v.
 
Rocket...just make damn good and sure you aren't tying into a computer system. That can and will cause other issues and could possibly damage a module or the ECM. Your best bet is to run a line from the fuse box using a safe circuit. Use an Add-A-Circuit that is readily available from Autozone, etc.

You're charging voltage sounds just fine to me. Automotive 12V batteries come with 6 cells...and each cell should hold 2.1 volts. Therefore, a fully charged battery with the surface charge removed should show 12.6 volts...and that's at the battery with all loads (cables) removed. You're alternator should output anywhere from 13.5 to almost 15 volts...with something between 13.9 and 14.4 being common. These measurements should be taken right at the battery. If it's not showing an acceptable charge at the battery, check it at the alternator and see if you have a voltage drop somewhere. Electronic regulators have become very sophisticated and the days of seeing wild swings in voltages with mechanical regulators are long gone.

Many race cars use 16V batteries for the extra cranking power of high compression engines. But these aren't recommended on a car with sophisticated electronics. However, many of the race cars do indeed use very sophisticated controllers, data acquisition computers, ignitions, etc and get by just fine. I don't know if they are stepping the voltage down for those items or not.
 
Most computers run off of 12 v DC...................

beaups said:
14V is pretty typical for Automotive electrical systems. Remember, the only way to charge a 12V battery is to have more than 12V in the system.

Be more specific with your project. Products labeled as "12v" but designed for automotive use are typically designed to run off a 11-16V range. If you are running something else (say a computer) that is designed to run off a 12V power source that's going to be a different issue and you'll either need to purchase a regulator or power supply.
Click to expand...

Most modern computers run off of 12V DC and 5V DC. Wiring computers into a car is actually very easy. The 12 volt side gets wired direct through a capacitor and the 5 volt gets wired through a stepdown transformer wired to the same capacitor. Most modern radio systems and DVD / Entertainment systems for autos are computerized and use the exact same components as your home computer.
 
bufordtpisser said:
Most modern computers run off of 12V DC and 5V DC. Wiring computers into a car is actually very easy. The 12 volt side gets wired direct through a capacitor and the 5 volt gets wired through a stepdown transformer wired to the same capacitor. Most modern radio systems and DVD / Entertainment systems for autos are computerized and use the exact same components as your home computer.
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and 2.5V-3V just case anyone is interested on the internal voltages of a PC.
 
bufordtpisser said:
Most modern computers run off of 12V DC and 5V DC. Wiring computers into a car is actually very easy. The 12 volt side gets wired direct through a capacitor and the 5 volt gets wired through a stepdown transformer wired to the same capacitor. Most modern radio systems and DVD / Entertainment systems for autos are computerized and use the exact same components as your home computer.
Click to expand...
Not a very accurate post. I'm not sure what you are stating though. Computers externally run off 110-240VAC. Internally, there are several feeds from the power supply. 3.3V, 12V, 5V, 1.8V etc. Each of these go to different components of the PC (system board, hard drives, etc.). The 12V feed is used primarily for drives (HDD's, CDRW's, etc.). There is VERY VERY little voltage fluctuation tolerance in the other components. Most PC power supplies can nail these voltages down within 1% of their target. The 14.4V automotive electrical system would TRASH most of a PC's components...capacitor or no capacitor. I have seen small voltage regulators out there that will output 12v however they can't dissipate much heat so they have a very low power output. Certainly not the 100-300 watts a PC will need.

Lastly, while DVD players/nav systems are computers, they have very little in common with your home PC and very few shared components...if any at all.
 
I think Bufordtpisser was talking about using a power converter not a capacitor. Even though it is not very effiecient to go DC to AC back to DC. As 2001LS8Sport mentioned race instruments run off 14V or more but I would assume they have internal power supplies to designate the proper voltages to their different components. Or are designed differently to run off 12+ volts.
I misunderstood what Buford was saying about PC's and DVD/entertainment systems. I agree with Beaups they share components but are a completely different device.
 
Please help ASAP

Another quick question about switches and wiring an on off switch somewhat together with a momentary push button.


Here is my plan, let me know if there are any flaws or other electrical no-no's. I wire the positive side of the on/off switch to a ignition switched + power source and the other side of the on/off switch to a ground. On the ground side of the on/off switch is where I wire my positive side of a momentary push button switch so that the momentary switch can only be powered up when the on/off switch is flipped up and the momentary button is also depressed. Then of course the other side of the momentary switch is wired to its respective piece of equipment that it is activating and so on to its ground.




This is what it would look like? I dont think I will be creating any ground faults or anything of the such but I figure I would ask someone a little more knowledgeable in electrical work. Thanks.

Elec Diagram.JPG
 
Hey its been a while since I've wired some stuff, but your verbal and the drawing don't exactly seem to be the same.
 
How much power do the "controller" and the "equipment" need? You don't want to tap off any 12v source that is say 15amp and then pull serious power threw it, you'll blow the fuse and more. You may want to have a relay with power straight from the battery, fused of coarse, as the power for the devices with a proper fuse and gauge wire. Get the ignition source anywhere its power can be minimal as it only has to trigger the relay on. With the relay triggered on it'll power the "controller" and provide the power for the "equipment", with the push button. Its a simpler and safer way to do it. I would need to know a little more to give you better direction.
 
Here are two quick schematics I drew in paint. Use the relay if you are pulling more amps then your toggle or push button can handle

new push.gif


new relay.gif
 
WAIT!! Why are there three wires to the toggle in your drawing Rebel? Unless the switch is lighted, there should only be two on a single pole single throw switch. If it's lighted, then yes...you COULD need a ground depending on the design of the switch.

Rocket, on your drawing, you have 12V going to the controller when the toggle is on...and zero when it's off. You have 12V to the momentary switch (purge?) whenever the toggle is on and zero when it's off. Your "equipment" (you sly dog!) will then have 12V whenever the toggle is on and the momentary is closed. Make sure your momentary switch is normally open...they make them both ways.

Whenever I control power to electronic equipment, I much prefer using down side switching. (aka ground side switching) You have your fused power source constant to the equipment and switch the ground from open to closed to control it. This is a MUCH safer way to control delicate and sophisticated electronic equipment because it all but eliminates any spiking that can occur from switching the positive side....and this method in fact is used by the automotive manufacturers to control most of their electronics. Dealing strictly with the controller...you would place the switch on the ground wire and wire the positive direct. PM me and I'll tell you how to do it all with ground side switching. It's worth it in my opinion.
 
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