No lithium batteries, No supercapacitors: No problem

[nhamilto]

This is a properly installed fuse tap that can not overload supply wiring even if both circuits are simultaneously loaded to maximum capacity. Their source wiring that supplies the +14v to the kick panel fuse box is protected by a larger fuse typically located in the engine compartment.

Typically: auto battery positive terminal +14v -> fusible link -> engine compartment fuse box -> large fuse -> kick panel fuse box -> smaller fuse -> load -> body ground -> auto battery negative terminal

 

[Nigel]

Typically: auto battery positive terminal +14v -> fusible link -> engine compartment fuse box -> large fuse -> kick panel fuse box -> smaller fuse -> load -> body ground -> auto battery negative terminal

That is not how my fuse box is connected, the passenger compartment fuse box is not a distribution panel!

 

[Kip]

The fuses in my cars glove compartment are wired directly to the ECU, overloading any one of them could fry it. A very expensive 4-figure repair job that would be. I'd always take the safest option.

 

[nhamilto]

Nigel: There must be a fuse/fusible link between the positive terminal and the fuse panel. If there is not any short due to insulation failure between the battery and the fuse panel will quite literally result in the supply wire becoming molten copper. This is why autos have electrical fuses in the first place.

Kip: The one of the fuses installed in your cabin panel supplies the ECU. If any circuit on that panel being overloaded could "fry your ECU" your car's wiring is defective beyond belief. For example you could "fry your ECU" by plugging a defective cigarette lighter power adapter into your car's socket and blowing its supply fuse.

 

[Nigel]

Kip: The one of the fuses installed in your cabin panel supplies the ECU. If any circuit on that panel being overloaded could "fry your ECU" your car's wiring is defective beyond belief. For example you could "fry your ECU" by plugging a defective cigarette lighter power adapter into your car's socket and blowing its supply fuse.

If your car's accessory socket is rated at 10A then it will be protected by a 10A fuse in the passenger compartment fuse box, plugging a 20A load into it will blow the fuse and not damage anything but the fuse. If you add a fuse tap and a second 10A fuse in parallel as you suggest then you can now draw 20A from the supply without blowing a fuse.

The supply to the accessory socket fuse does not come straight from the battery via a 10A fusible link, it probably has a 150A fusible link, maybe also a 60A fusible link, but it also needs to be switched. On older cars it would be switched by the ignition switch, position 1 and 2 being on and position 0 and 3 off. On newer cars it is switched by a relay in the engine compartment, on current cars it may be switched by a 10A relay soldered on the ECU - put 20A through that 10A relay and you need a new ECU and then need to pay a dealer to reprogram the security system to accept the new ECU - very expensive.

The numbers I've used may not be accurate and adding a 1A camera is unlikely to destroy anything, but why take the risk when you can put the fuse tap the correct way around and keep everything properly protected?

 

[Kip]

Kip: The one of the fuses installed in your cabin panel supplies the ECU. If any circuit on that panel being overloaded could "fry your ECU" your car's wiring is defective beyond belief. For example you could "fry your ECU" by plugging a defective cigarette lighter power adapter into your car's socket and blowing its supply fuse.

Perhaps I didn't make it clear enough. It is basically as Nigel said above this post. If I draw more than 30A through my 12v cig. socket it will blow the fuse, breaking the circuit and protecting my ECU. If I wire in a fuse tap incorrectly and draw 30A through my 12v cig socket then a further 5A through the incorrectly wired fuse tap plugged into the cig. socket fuse, then I would be drawing 35A through the ECU wiring/components only designed for 30A, without any fuses blowing. That could cause problems.

I don't understand too much in this area but do have a Haynes manual with many wiring diagrams. The ECU itself in my car is fused via a 40A engine compartment fuse, however, this isn't sufficient to supply all the glove box fuses, which totals 270A worth of fuses. Those 270A must be coming direct from the battery, however, literally everything is switched via the ECU, except front fog lights. It's complicated, which is why when using a fuse tap, always plug it in, in the safest way possible.

 

[Hombré]

Stay away from any ECU/PCM power and run some decent AWG wire straight to the battery with a fuse or two if need be.

 

[Rajagra]

The problem is that nhamilto's diagram shows the ideal or correct way to wire things up if you are designing an entire system from scratch.
But we aren't, we are modifying an existing system not designed to work that way. Unless we check the nature of that +14V feed, we don't know if that's safe.

Nigel's way is safer. I don't feel it's right to call it the "correct" way, because to any circuit designer's eyes it's as ugly as sin and screams "wrong." But in the absence of the information you need it is definitely the safer way.

Basically there is no right or wrong orientation, they are both flawed in different ways.

The only truly correct orientation is the one shown by nhamilto but only after checking the input feed rating.

 

[nhamilto]

To be clear installing a fuse tap on the ECU supply fuse is a bad idea but this is not because it is electrically unsafe. It is a bad idea only because the construction quality standards of the fuse tap are most likely lower than the car's factory fuse box. If the fuse tap failed the ECU would lose power and you would be stuck on the side of the road. This is no different than your if your car's battery had failed while you are driving.

As for Nigel's argument about adding a 1A load to a 30A supply causing electrical Ragnarök I call BS but this is really not the point of this thread. This thread is about using your automotive power system instead of lithium/super caps.

 

[RecycledElectrons]

1. A 5V regulator will get hot as it burns off (14-5)/14 = 9/14 of the power. A DC/DC converter is much better. They are $1-$3 on Ebay.

2. The battery gives the dash cam time to save the file when power is cut. Modern video CODECs do not create readable files if power is suddenly cut. They require the dashcam to write out an end of file. Because the last seconds before your battery is thrown out of your totaled car are important, the dash cam needs a small battery or capacity.

3. Adding in a capacitor with no fancy charging circuit would cause it to charge very quickly (70A + ?) when your car first give it power, which would blow your fuse. Therefore super-capacitors need a fancy charging circuit. In addition, you don't want to miss the first minute of driving (when you back out and might hit something) so you want the camera to start recording before the super-capacitor is fully charged.

 

[Lola]

The additional fuse in a properly installed fuse tap is in parallel. There is no before or after. The hazard light fuse and the dashcam fuse are completely independent. A blown hazard fuse has no effect on the dashcam circuit.

Camera fuse is purple and the hazard fuse is blue in the pic.

View attachment 23586

Can someone supply a annotated picture showing Nigel and SawMaster's viewpoints?

I thought I understood things from several previous discussions on wiring a fuse box correctly with a Add a Circuit, however the picture supplied by nhamilto seems completely opposite from what was shown in the other discussions like the pictures shown by Rajagra

This is a subject that has been talked about quite often and is getting very confusing. Can't it be discussed by the people in the know with Pictures until it is known to be the correct way. Then LOCK the thread and keep it under the Batteries and Capacitors heading.
I seriously doubt I am the only one confused, as people sometimes don't want to confess that they don't know or understand something.