Help from some electronics expert

[Master Chief]

Hi all.

I am in the proccess of rerouting and connecting some new gauges and elctronics.

The wiring is a mess, since during the years, each time something was connected, a diffrent place for a MINUS and Switched PLUS wire, was used.

I wanted to make a central, for all PLUS wires to be conected to it.

I was wondering about connecting some FUES's.

Would it be better to connect 1 FUES on the main line, before it splits in to the rest, or would it be better to use a FUES for each line that goes out from the main one ?

I need quite a lot of wires, connected to a PLUS source - 5 gauges + boost controler + wide band.....
I gues using a fues on each one, would be a bit of an over kill.

I was thinking meaby grouping all the gouges togheter, using 1 fues - and the rest using a fues of there own.

What i need to know, is how to calculate the Amper of the fues i need.

Like, if i have two gauges, each needing a 3A fues - if i connect them togheter, do i need a 6A fues, or a 3A fues would be ok?

Thanks,
Dany.

[cotbu]

I would run a fuse before the split and a fuse for each gauge or device i want to protect.
If your gauges can be daisy chained, that will cut down on fuses. Don't just tie them together. It works, but it's not ideal. You will mostly burnout a gauge or wire if there's a short.

[Master Chief]

Thanks.

Any idea what fuse should i use, where all the wires join, if each gauge needs a 3A fuse ???

[g6civcx]

Would it be better to connect 1 FUES on the main line, before it splits in to the rest, or would it be better to use a FUES for each line that goes out from the main one ?

Oy, this topic is indeed a mess.

Theoretically, you can calculate the maximum electrical load on the circuit by adding the resistance in series (which I highly DO NOT recommend), or by adding the inverse of the resistance in parallen (which I recommend). Check physics textbook for this info.


In real life, what you should be concerned with when using fuses are: 1) protecting the component, and 2) protecting the wire itself.

Each wire is rated to a maximum current based on size, temperature, and voltage. Search American Wire Gauge (AWG) for discussions on this topic.

Imagine that you have really really thin wires, and you use those thin wires to connect a component to a really big fuse. If the wire shorted to ground, the current coming through the wire will not be enough to blow the fuse. You want the fuse to blow so you don't get heat, but the small wire will continue to draw a small amount of current, not enough to blow the fuse but enough to start a fire.

Even during normal operation, using a really small wire for the normal current the component is pulling will overheat the wire = smoke + fire.


What you want to do is match the wire to the expected load of the component. Then you want to throw a fuse in front of the wire so that if the wire and/or the component starts pulling too much current to the point of overheating the wire and/or the component, you want that fuse to blow and disconnect power to the faulty circuit.



As far as using one master fuse or using smaller individual fuses, it's really up to how you design the circuit.

On one extreme, you have a single 600A fuse for all the wires in your car. Obviously this will not work because the wires will fry at much less than 600A, and the fuse would never blow = fire.

On the other extreme, you run every single component/wire to a fuse. This is overkill, but it's safer to err towards this side than the other extreme.

I personally use one fuse for each component. The only component I daisy chain to a single fuse is the lights, but I make sure to use a 15A fuse and 16AWG wiring in case a bulb draws too much or a wire shorts to ground. Using 22+ AWG wiring in this case would not work because you can see up to 15A on the wire = fire.

The other component I don't use an individual fuse is the hot wire lead for relays. These pins pull maybe a few mA at most, and fuses don't come that small so it's not worth worrying about. I still use at least 16-18AWG wiring though just in case, and of course there is a single fuse for all of the relays.


What i need to know, is how to calculate the Amper of the fues i need.

Contact the vendor/manufacturer to find out the max allowable current draw for each component.


Like, if i have two gauges, each needing a 3A fues - if i connect them togheter, do i need a 6A fues, or a 3A fues would be ok?


It depends on how you connect them together. I personally would put 3A fuse - Y to gauge 1 and gauge 2.

This reduces the max Amperage to each component slightly, but it's guarantee to blow if any component pulls close to 3A = safer than sorry.


Good luck.