12v circuit design

[banginbishop]

ladies & gentlemen I need some help on a simple circuit!

I'm running a 12v device off the cigar lighter in the car but I want to have power still running to it once I've turned the ignition off. I don't want to hard wire it but just have a charge to last for 3-5 minutes at most.

I'm thinking of a capacitor to hold the charge and a resistor to slowly release the held charge instead of dumping the charge too quickly.

All ive got at the moment is a +/- wires going into the device & into the cigar lighter.

[Hansoon]

Re: 12v circuit design

A typical job for a piggyback rechargeable battery connected through a diode I would say.

Hans

[NeoMatrix]

Re: 12v circuit design

Some methods

1. A 555 timer IC with a small bread board resister for current limiting, and a VR/pot to set the timer cycle.

2. A 2000uF cap with a 10meg resistor for a ramp up charge time of say 2 or 3 mins before the forward voltage triggers a BC 534 trans to shut off.

3. Getting more advanced you could use digital timer chips or burn your own EEprom I guess

Wheres all those uni-students with EWB software when you need them...

Come on fellas knock the guy up a quick simple circuit and/or PC board artwork.

[subaro]

Re: 12v circuit design

you will have to take into consideration the amperage rating of the device, cause if you have the volts and not the specific current for the device it will not work or work erratic. As to the circuit, youtube could help you there. If your car in new, and something happens, your warranty will not cover it, just something to think about.

[Tonerbomb]

Re: 12v circuit design

subaro is right about the current requirements, as that will change the circuit for the amount of on time. And Neo what a blast from the past, a 555 timer,, that sure dates us both................ but really would it take that long to pinch a hot wire after the fuse block??? most newer cars have a hot accessory plug in them now days................

[banginbishop]

[NeoMatrix]

Re: 12v circuit design

The red wire from the camera must go on a constant uninterrupted power source or to the car battery.
The black wire must go to vehicle ground.
The yellow wire goes to an interrupted ignition wire or lighter socket.

Otherwise keep you current configuration :.

Try a 3,6,12volt AAA NiCad battery pack in parallel with the power lead.
The system should power down when the NiCads run low.
The older more warn out the battery pack the faster it will discharge and power down the system.

[slimslob]

Re: 12v circuit design

Since the car is only 8 months old, check to see if it has a power outlet that is constantly "ON". Usually look like a cigarette lighter socket but with a flip open cover instead of a lighter. I have even had cars where at least one lighter plug is constantly powered. If you have a charger device for your mobile device that plugs into the lighter socket that has an indicator to show it is getting power, use that to test the socket.

[blackcat4866]

Re: 12v circuit design

Another approach is to power you dashcam off the 12vdc unswitched power to the radio/clock. Almost all cars provide a continuous 12v to run the clock and remember your radio stations. Otherwise you would lose your time and radio stations every time the car turned off. Like, for example when your battery went dead.

It shouldn't be a big deal to pull out the radio far enough to tap into the continuous 12vdc. Don't know which wire? Turn off the car and meter each wire to frame ground. The wire you want will stay hot at 12vdc. =^..^=

[theengel]

Re: 12v circuit design

Seems like those newer radios, which are often just little computers, are a lot more complicated than the old ones. Messing with anything from the radio could screw up a warranty. I'd stick with the cig lighter or make sure you don't have a cell phone outlet.

[subaro]

Re: 12v circuit design

Here are two videos on dash cam . one is an excellent description on all the features and what to look for and the other is to tap into the fuse box [inside the car] for a direct 12volt . He aslo explains why a capacitor would solve your problem.

1. General description and infomation

2. how to tap into fusebox for 12v continous with ignition off. [just do the opposite of what he is describing to get the 12v continually with key out of ignition]. this is very simple, but make sure your assembly is sound and no loose wires ect.

3. to avoid the original problem, buy a decent dash cam and not the cheapies, as they don't last that long and cause headaches.

[banginbishop]

[banginbishop]

Re: 12v circuit design

I've ordered some cheap circuit boards and intend to add a capacitor/s with resistors to drop the voltage down to protect the device and regulate the flow. Once I've worked out the details i can go from there - I'll probably fry the bleeding thing anyway!

[NeoMatrix]

Re: 12v circuit design

I've ordered some cheap circuit boards and intend to add a capacitor/s with resistors to drop the voltage down to protect the device and regulate the flow. Once I've worked out the details i can go from there - I'll probably fry the bleeding thing anyway!

Drop a current probe inline or external and give us the current require to power the device under load.If your thinking about a voltage devider resistor circuit you may not drop the voltage enough to get the current to power the device.You may need something like an LM 317 with a TO transistor case an heat sink???

[qbert69]

Re: 12v circuit design

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