calling electrical ppl - general questions

[jt1583]

ive been having trouble with both sets of electrical gauges ive bought and am about to wire my fans up and want to make sure i understand the basics

*i have 2 gauges, currenty both are wired up to my radio ACC wire, will this effect the gauge at all, say, through off the signal/cause problems, should I be using an independent battery source. basically, what are the rules on sharing wires?

*ill be wiring my altima fans up soon and I know there are 2 power wires for each fan, im going wire up one wire from each fan so they receive power with car running (on low) and the other two to switches, so it can be on high with the car running or low with the car off. this question pretty much reverts back to the first question, I dont think I should be using fuel pump relay as a voltage source for my fans like i see in some of the writeups. here is one of the ideas i thought up, but it involves almost as many fuses and relays as there are in my engine bay, im wondering if it has to be this complicated to remain safe and reliable.

[g6civcx]

My comments:

1) You may want to let the people know what car this is so they know what they're working with. At least give us year/make/model.

2) Current flows from the battery to the fusebox, through a fuse, then to the accessory power. There are generally 2 rules when it comes to piggy-backing circuits like this:

a) Will you exceed the capacity of the circuit by drawing too much current? There are 3 things to consider:

Power - measured in W
Voltage - measured in V (should be 12, but sometimes it fluctuates slightly)
Current - measured in A

Power = Voltage X Current

Every piece of electronics has a power rating. It tells you how many Ws the device consumes. For example, a typical light bulb usually consumes 27W. What this means is when you hook it up to a 12V power source, it will draw some current. The amount of current is calculated as follows:

Power / Voltage = Current
27W / 12V = 2.25A

So this bulb will draw roughly 2.25A if it's getting a steady 12V source. Note that this is maximum draw, and nominal draw may be slightly less.

The reason you have fuses is because sometimes a device may draw too much current. It will cause the circuit to overheat and possibly catch fire or damage fragile electronic components.

If you put a 3A fuse in front of that bulb, if the bulb pulls more than 3A the fuse will break and disconnect the bulb from the power source. If you put a 1A fuse, the bulb will burn the fuse under normal use.

So take all the power ratings of all the devices you intend to run on the radio accessory wire and add them up. These numbers should be printed on the back of the gauges and radio. If you can't tell, check with the manufacturer of the gauges.

Add them all up. Then divide by 12V and see how many As you get. Then trace down the wire to the fusebox and see how many As the fuse can hold. If you have more current pull than the fuse, you will blow it out under normal use.

Keep in mind that voltage isn't always 12V, and sometimes it fluctuates a little bit. So you want a fuse that can support enough current pull and don't cut it too close.

We can't tell you how many Amps your radio ACC fuse is because you didn't tell us what car this is.

b) The actual wire is measured and classified as gauges. Your interior accessory wires are typically 16 gauge, but again you didn't tell us your car so we don't really know.

For a given wire gauge, if you try to run too much current through it the wire will overheat. How much current the wire can support depends on its size/gauge. Too much current and resistance will increase. A lot of heat will be produced and possibly failure/fire will ensue.

Imagine people running down a narrow hallway. If you try to push too many people through, they'll end up bumping into each other and slowing down. The best way is to reduce the number of people, or make the hallway bigger.

There are charts that will tell you how much current certain wire gauges can support. You can easily find them with google.com.

3) You may use whatever relay that turns on with the ignition switch and piggy-back the fans onto it provided you keep in mind #1 and #2 mentioned above. Figure out how much current the fans will be drawing under maximum load and see if the circuit can hold it.

[jt1583]

its a s14 if that helps at all. is there anyway to combine and of the fuses or relays in the above picture while still being able to operate fans individually on high/low, maybe combinining the portion the is activated by the ignition.