Let's talk about fuses

#1

I have about a month before I head back to Mid Ohio so I figured now is a good time to hack the crap out of my car’s electrical system some more.

One thing I need to do is run some dedicated electrical lines for all of my electronics. I’m working on some basic code that will function as a lap timer and I’ll eventually be expanding it into a full DAQ system (baby steps).

Anyways, I’m going to need power for the LCD screen and Arduino as well as a few redundant gauges and the associated lighting. Does it make the most sense to just run a positive and ground line from the battery to the front of the car and into a fusebox? What amperage fuses should I use?

#2

Don’t put too many things on the same fuse or when the thing goes it will not only take everything with it, but it will also be much harder to ID the culprit.

#3

So why did you choose 10 amp fuses for most of the wires?

#4

[quote=“Ranger” post=67219]Don’t put too many things on the same fuse or when the thing goes it will not only take everything with it, but it will also be much harder to ID the culprit.

[/quote]

Cut the orange wire! :unsure:

Depends whether you want it to be hot or switched. Don’t forget that you need to take positive power from after the killswitch in case you haven’t installed it yet. If you’re willing to unwrap your body harness a bit you can get switched power from under the dash at the splice of green wires. The easy way is to get positive from the power distribution block in the engine bay. I just installed a fuse box like rangers on top of my trans tunnel behind my switch panel for my helmet blower and a few other things.

You’ll have to figure out the fuse amps, but you may need to use glass fuses. I don’t think you can find auto fuses under 7.5 in the regular bmw size.

#5

The power distribution block isn’t switched, is it? I’m hesitant to wire a bunch of crap up to the same wire that the window buttons are on since I can see myself burning out all of the time.

Maybe it would make sense to use the green wire to switch a relay which would then power the fuse block from the power distribution block.

#6

FWIW ATC blade fuses (standard BMW fusebox) are available down to 1A. If you’re already “hacking the crap” out of the existing harness, won’t you end up with some fused sources that you’re no longer using? A lot of fused circuits could already be considered “over-fused”. That is the engineer designing the wiring chooses the next highest fuse rating and wire size for the load he is trying to fuse. I wouldn’t think the Arduino and LCD would represent much of a load. Accessory circuits (cigarette lighters) are also usually a good source of fused power. Resistance heating is ridiculously inefficient and requires a lot of current.

#7

[quote=“MrDomino” post=67223]So why did you choose 10 amp fuses for most of the wires?[/quote] Putting in more fuse than is necessary is kind of at odds with the purpose of the fuse. I want the things to blow if something goes wrong.

The fuse box in the pic is switched. I have unswitched power going separately going to the Traqmate power switch via it’s own fuse.

#8

Stereo or obc would be good circuits to get switched power from assuming you’ve removed them. Fuses are generally double the maximum amperage draw. I believe some or all arduinos have a 500ma breaker built in.

#9

Yeah but at some point you decided to use a 10 amp fuse instead of a 5 amp or a 7.5 amp or a 20 amp or a 30 amp. Did you get out your multimeter and measure current draw?

What is the fuse box switched off of? Does it come straight from the relay or is it from something like the window motor power wire?