I'd love to have someone explain how a 12 volt system is better than a an original 6 volt wiring system with LARGER wire than a 12 volt system. Twice the voltage going through SMALLER wire. It is all a total mystery. Bob
Maybe not always "better", but the idea is to have more voltage (pressure) and less amperage (flow). Either can work fine, if well designed and in good condition. And remember that smaller wire is cheaper to make and use, so when multiplied by millions of cars rolling down the assembly line, that's profit.
If whatever you wish to call the stuff in the wire were automobiles on a highway wouldn't traffic flow faster on MORE lanes = FAT wire than two lanes? Bob
It's all about voltage drop.... Now, if both systems are in excellent condition there really isn't any difference between them. The 12V system will be cheaper to build because you can use smaller wire and lighter-duty switches because for the same function the current is cut in half. But that's still not the main reason a 12V system is 'better'. The real problem is that a 6V system is much more sensitive to voltage drops, particularly at connections. ANY electrical connection will degrade over time due to corrosion or switch contact wear, or have a small inherent resistance, the amount can be very small but it still affects the system. Let's do an example... Voltage drop can be calculated with the formula VD (voltage drop) = I (current/amps) x R (resistance). Note that circuit voltage has nothing to do with the drop; this will be the same for any circuit with a specific load and resistance. So for a headlight circuit that has two 60 watt lamps, the 12V circuit will need ten amps, the 6V circuit will need double, or 20 amps. So let's say that the connections have degraded slightly and we now have an additional .1 (one tenth) ohm 'extra' resistance in the circuit. Plugging the circuit amps and resistance into the formula, this will give you a voltage drop of 1 volt with a ten amp load or a 8.3% drop in your 12V. Now do the same with the 20 amp load; the voltage drop doubles to 2 volts, but because you only have 6 volts in the circuit, the drop is now 33% or four times the amount the 12V circuit will see. This is why a 6V system is inferior to a 12V....
Steve is providing a lot of valuable information in this thread. Thank you. This info is well thought out. I have wired airplanes, and the process is the same but different (rules and appearance, etc.)He has presented info that even I didn't think about. Its not the bigger smoke cloud, it is a larger amount of magic smoke that escapes.
Ok, a couple of housekeeping items to take care of before moving on. First, I've gone back and added to my last post about overcurrent protection of the feeder wire. If you're planning on overcurrent protection on that, you should read this. Also, it's come to my attention that the link to the crimpers in post 128 is no longer good and worse yet, they have apparently discontinued that particular crimper. So here's a couple of alternatives.... http://www.amazon.com/Tools-VISE-GRIP-Crimper-10-Inch-2078310/dp/B001LOVEGS/ref=pd_sim_469_3?ie=UTF8&dpID=31DOLIWgB3L&dpSrc=sims&preST=_AC_UL160_SR160,160_&refRID=09Q6P17EME6X14MPJC40 This is almost the same as the one I originally linked to.... http://www.amazon.com/GB-GS-388-8-Inch-Crimping-Electrical/dp/B00079LN1Y/ref=pd_sim_469_4?ie=UTF8&dpID=313WFP47RTL&dpSrc=sims&preST=_AC_UL160_SR160,160_&refRID=1RJ2VVZNN9SYB3N9MSMB Slightly smaller, and one less crimp size, but less money.... And a hopefully printable worksheet like I showed in post 106 to help you figure your loads. I put the most common items on there but left blanks to write in anything extra...
Steve, I don't want to pull you off track, but I am currently planning a wiring project and would like to use a relay for my high and low beams. My question is, can I use NOS Delco Remy horn relays for headlight relays? I would rather use these than modern styled relays, but only if they are within design limitations. What is your opinion. Mike
The old horn relays are designed for a grounding switch, so you'd have to do some figuring out how to make it work... Is there something special about your headlights that requires a relay? Ordinary dimmer switches work with ordinary headlights, they last for decades.
I have a GM style headlight switch with a "parking" and a "on" position. I was going to use the "parking" position for low beams and the "on" position for high beams. I'm out of floor board space for a dimmer switch in the T I'm working on. Mike
I've seen recommendations for relays with halogen head lights. Something to do with their high initial load when they're turned on.
If you can find an AC blower relay from a 1960s GM car, that would have the look you want, and the function you need. I never had any issues with halogen headlights (normal replacement sealed beams) and dimmer switches. again, this is over decades of use.
over-sized wire will be just that....over-sized, and can actually handle the current flow better than thing gauge wire, but costs more and takes up more space in the wire bundles.
Squirrel, I went with your suggestion when I asked about using a NOS Delco Remy relay for a headlight relay. I went with a new 3 wire dimmer switch. I found space for it at the base of the seat. I can hit it with my boot heal or reach down and tap it. I didn't have space for another relay even if it would have worked. Thanks.
Wow....all this talk about jigawatts gives me a headache but I'm in. I'm doing everything else on the car myself so I'm not stopping here. Glad I found this thread.
I too was debating kit or scratch built. Since I won't even have wipers, I decided to go from scratch, BUT apparently not scratch built enough! I bought a five toggle switch panel from Summit with each switch fused (20A) and each with an indicator light. Upon receipt it appears to only have 16 ga wire. If I read Steve's de-rating to 80% properly there isn't much I could run through this panel without using relays. I'm thinking now that I should have bought individual switches that are rated for more than a de-rated 16 amps and wire of heavier gauge than skimpy 16.
The biggest amp load would be a fan and lights. I could put the dash lights on a separate switch and run LED tail lights I suppose.
20 Amp Circuit Breaker Question: Why is one post on the breaker copper (or copper plated) and the other post not?
Just found this thread, Steve. Your explanations and attention to detail, including the check lists are very helpful.
Always thought it was kinda like a "color" code so you didn't have to read the small letters to know which stud was batt. and which was load.
It seems to me that heat is what trips it and does electricity flowing through in one direction vs the other create more heat. Just a curiosity point.
I think it so you can identify whether you should have power to the + side when checking without the fuse in place.
The Jalopy Journal
