Fuse tap is confusing my car's computer.

[frnak]

I've had weird things happening in my car after tapping into a fuse for rear seat usb sockets. The dealership says they've seen this before when people pull power from fuses, and they suggested I pull power directly from the battery.

I have a Blackvue DR900X Plus 2CH setup with 2 x B124X+E batteries for parking mode.

Can you point me in the right direction of how to pull power for this setup that charges the batteries when the car is on, but runs off them when it's off?

The car is a 2021 Citroen e-C4.

 

[kamkar]

Welcome to the forum frnak.
It is true the smarts on many new cars can play havoc when you try to do something.
I cant say i recall any tricks posted on here regarding your year / model of car, you might be able to get more help in regard to this on a model / brand specific forum.
Having to go all the way to the battery it have been seen, and as i recall that can even be a problem too on some brands, but here my BMW alarm is going off.

I am not familiar with these Dashcam power packs, but quite a few people in here have them, so i am sure someone will be able to share some user experience.

 

[frnak]

Welcome to the forum frnak.
It is true the smarts on many new cars can play havoc when you try to do something.
I cant say i recall any tricks posted on here regarding your year / model of car, you might be able to get more help in regard to this on a model / brand specific forum.
Having to go all the way to the battery it have been seen, and as i recall that can even be a problem too on some brands, but here my BMW alarm is going off.

I am not familiar with these Dashcam power packs, but quite a few people in here have them, so i am sure someone will be able to share some user experience.

The car is kinda too new for there to be any active communities of users, so I'm hoping for a generic straight-to-car-battery-solution, rather than a model specifi one. I have hopes I can go directly to the battery since the dealership okayed it, I thought they'd go off on me about voiding warranty etc but they were actually helpful

 

[kamkar]

Well you guys up there are the last of the vikings, down here with us descendants of slaves and crackpots not worthy of joining the exodus i am sure there would have been all kind of problems from the dealer.

 

[Kremmen]

I've heard of modern car CANBUS systems protecting themselves in this way. The ECU knows the expected draw on each fuse and it it exceeds what's expected it shuts down that circuit.

Does the Citroen fusebox have any accessory ports like Honda do ?

CANBUS/Ecu v fuse tap is risky on new cars.

 

[rcg530]

I just published a review / testing video for a BlackboxMyCar PowerCell 8 dashcam battery pack. In the video, I have a section about how I would suggest hardwiring the dashcam battery pack into a vehicle using a relay and a fuse tap. I use this approach for any device that draws more than 7 or 8 amps to power / charge the device. In my opinion, fuse taps have their limits especially when it comes to higher amp draw devices. I also have a Cellink B dashcam battery pack in this same vehicle (helps with my dashcam reviews) using the same relay power setup (using a separate relay and wiring) and it's worked well for several years.

In the relay wiring approach, the fuse tap would supply the accessory/switched power from the fuse box to the control circuit of the relay. The control circuit of a relay draws very minimal power and it would be better suited for drawing power from a fuse tap. The power (load) circuit of the relay sources its power from the vehicle's battery with a wire connected terminal 30 of the relay (with an inline fuse). Terminal 87 of the relay is connected to the hardwiring cable's positive (red) wire to supply the charging power to the dashcam battery pack(s).

The included YouTube link has a time reference that jumps directly to the section where I discuss the two methods of hardwiring the dashcam - the fuse tap providing the charging power or the relay approach mentioned above.

I hope that helps!

 

[frnak]

In the relay wiring approach, the fuse tap would supply the accessory/switched power from the fuse box to the control circuit of the relay. The control circuit of a relay draws very minimal power and it would be better suited for drawing power from a fuse tap. The power (load) circuit of the relay sources its power from the vehicle's battery with a wire connected terminal 30 of the relay (with an inline fuse). Terminal 87 of the relay is connected to the hardwiring cable's positive (red) wire to supply the charging power to the dashcam battery pack(s).

Ahhhh this makes perfect sense! So the accessory fuse is only used to switch on the relay when the car is on, and then it can draw it's power directly from the 12v battery? The Blackvue battery packs in hardwire mode draw 9A.

 

[frnak]

In the relay wiring approach, the fuse tap would supply the accessory/switched power from the fuse box to the control circuit of the relay.

Can I use a Canbus/ECU fuse for the switching of the relay? Those are the ONLY switched fuses I can find in the car.

 

[rcg530]

Can I use a Canbus/ECU fuse for the switching of the relay? Those are the ONLY switched fuses I can find in the car.

In theory, yes. Although, I usually suggest not to use fuse box fuse sockets that send power to or receive power from modules in the vehicle. Circuits that are involved with computer modules in a vehicle can be hypersensitive to voltage fluctuations or amp draw variations.

The control circuit of a relay usually draws in the 150mA to 200mA range, so it's not a huge load for the circuit, but it all depends on the sensitivity of the circuit being tapped into by the fuse tap.

 

[frnak]

In theory, yes. Although, I usually suggest not to use fuse box fuse sockets that send power to or receive power from modules in the vehicle. Circuits that are involved with computer modules in a vehicle can be hypersensitive to voltage fluctuations or amp draw variations.

The control circuit of a relay usually draws in the 150mA to 200mA range, so it's not a huge load for the circuit, but it all depends on the sensitivity of the circuit being tapped into by the fuse tap.

Yeah if those weren't the only switched fuses I can find I wouldn't use them. The fuse I'm using supplies voltage to the rear seat usb sockets, so those 200ma, if I'm not using the usb sockets, does the car even know that whatever's happening isn't just coming from there? I have it all wired up now and working.

Also, thanks so much for the info, I didn't know what a relay was until last week and your video really helped me understand what I was doing!

 

[rcg530]

Yeah if those weren't the only switched fuses I can find I wouldn't use them. The fuse I'm using supplies voltage to the rear seat usb sockets, so those 200ma, if I'm not using the usb sockets, does the car even know that whatever's happening isn't just coming from there? I have it all wired up now and working.

Also, thanks so much for the info, I didn't know what a relay was until last week and your video really helped me understand what I was doing!

Since the fuse socket is powering USB sockets, it's not a "critical" system in the vehicle like the ECM, SRS module, etc. That's likely to be ok to use for the fuse tap for the relay. You'll have to monitor it for a little bit after setting it up that way just to make sure you don't see any hiccups in anything, but I would guess that it should be ok.

 

[frnak]

Since the fuse socket is powering USB sockets, it's not a "critical" system in the vehicle like the ECM, SRS module, etc. That's likely to be ok to use for the fuse tap for the relay. You'll have to monitor it for a little bit after setting it up that way just to make sure you don't see any hiccups in anything, but I would guess that it should be ok.

Thank you my man, glad to have this sorted and have the cam properly powered now!