Nigel
Well-Known Member
- Joined
- Jul 7, 2014
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- Location
- Wales
- Country
- United Kingdom
- Dash Cam
- Gitup F1+G3ꞈꞈꞈꞈꞈ Viofo A229ꞈꞈꞈꞈꞈ Blueskysea B4K
As an example, in my car, a nice fuse to tap into for powering a dashcam is the electric windows fuse. It has the advantage that if I turn the engine off while waiting at a red light, the electric windows keep working, they only turn off when I open the door to get out. The power for this fuse comes from a relay which is controlled by the car's main computer, which is also watching the doors for turning on interior lights and triggering the alarm, and of course it doesn't use a huge 40 amp relay when a 20 amp one will do, and since the relay is smaller there is no point wasting copper on huge wiring which would make the car more expensive and hurt performance by adding weight, the wiring loom is the third heaviest component in the car after the engine! If I took an extra 9 amps from that fuse for charging a battery, it would probably work fine, until one day I tried to open the window while the battery was charging and the window was stuck due to ice, then depending on which way around the fuse tap was installed, it would either blow the fuse leaving me unable to open my windows, or it would melt the relay and maybe start a fire.For example, if the device uses 3 amps, then the fuse might be 5 amps and the feed wire would be 7 amps. I'm trying to see if anyone knows this is true or not, or if car manufacturers set all feed wires to say 40 amps.
In some cars, the power may go through the fuse before going to the relay, but in mine it goes through the relay first, mainly because they could then fit separate fuses for left and right windows while only needing one relay, and relays are more expensive than fuses.
Unless you know how your car is wired, it is not safe to take a large amount of power from a fuse tap, and 9 amps is a lot of power, 110 watts.