I'm planning out a car pc build, and I want to something a bit different than most of the people on the forum...
I'd like to run the car PC to be always on, even when the ignition is off. I haven't seen anyone do this, so I am curious as to why not? I think the big technical reason that people aren't doing it is because of the power drain - if your PC takes up 15 watts at idle, then running for one day takes 15*24=360 watt hours, which is 30 amp hours on a 12v battery - or about the total energy capacity of a small car battery. Now of course, I don't want my PC to just sit there and idle, I'd like it to run a few web cameras, and save the video off to an SSD. I am guessing my power draw will be around 25 watts while the car is off. I won't need GPS when the car is off, won't need to run the stereo, won't need to run the screen, won't need wifi, etc. All that would be running would be an accelerometer, maybe some parking sensors, and the web cameras. 25 watts is just a wild *** guess, by the way.
I'd like to rig it up to GPS (or just a manual switch!) so that when I turn the car off when it is in the garage it will fully power down, so my running time while the car is off will be about 12 hours (a typical day at work) - maybe stretching up to 16 hours on occasion. 25*16 = 400wH / ~35Ah@12v, so I think a 50 amp hour deep cycle battery should do the trick, and then plug in the car every night to top it off.
Has anyone done anything like this? Any tips? Any 'gotchas' that I should consider? Thanks!
CyberBill, What your asking, you either will have to pay a lot of money for, or write a lot of software to do yourself.
That seems like with a little modification and an extra small PC, it will do what you need. The only caveat would be that you might need a solar cell to keep your battery topped off while the computer is running, just to offset the constant power usage. Then you have the PC pay attention to your location when you turn off the car, and if it's at home, you turn off the camera power. If it's not at home, you keep the camera power on. Once again, it's likely going to require some programming, but a manual switch would be much easier.
The Rupel iVox is a great recommendation - it is on my list for sure. Although, I have some concerns with that device because it's so new. For example, I'm not sure how the quality of recording both cameras at the same time holds up, also I don't know how many MB per minute is required for recording, so I don't know how much time 16GB will buy me. I'm not sure if I can manually force it to start recording, or if the accelerometer is the only way to trigger it. Yada yada yada, you get the idea. It also limits me to only recording two cameras and doesn't give me the capability to automatically upload the videos or to notify me with a text message that the accelerometer triggered an event. But still, it's on the short list! Honestly, if I got it, I wouldn't even need the car pc, so it would save me a crap load of money.
The solar panel recommendation is something I've considered, too. I'm putting this in a Honda CR-Z, and it has a big window in the back. I've got about 85 tabbed 3x6 solar cells left over from a project I was working on, and that would fill up the area pretty well and give me probably around 100 watts, more than enough power to keep the battery topped off.
CR-Z is a hybrid right? Wonder if you could tap into the battery for the electric assist side...
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100W is a bit overkill, but it dosen't hurt to overkill :P. Those are the half volt 3x6's? 42 of them would give you a 27W 16V panel, plenty enough to keep your batteries topped off on that thing I'm sure. The only question would be, on a really cloudy day, would your battery be big enough.
On a side note, I'd hate to even think about soldering together 85 of those panels :/. Makes my hands cramp just thinking about it.
That said, I would never attempt to touch the hybrid pack! Too much voltage, too many amps, too dangerous for me. Besides, I can toss in a deep cycle 12v AGM battery with the same (or more) capacity for like $150, and then not have to worry about blowing out the super expensive hybrid pack.
Sounds like an interesting project.
I know a few users have done always on computers for things like remote start and other simple taks like that. For these they used things like beagle boards that draw far far lower amounts when on. Maybe you could look at how well they could store video etc?
If you are running off a dual battery system I can't see too many issues, make sure it isolates so it doesn't flatten the starter.. Have it setup to shutdown if the battery gets too low (what happens if you have to leave the car overnight.. or want to power IR leds for night vision)
As long as you are happy with it only being always on in "typical" situations that you planned for and happy for it to shutdown in extreme cases then what you have planned should be fine. If you truly want it to be always on then I think you need to look for a much lower power consumption than normal. Even an atom or an AMD E350 will suck down the juice quite quickly.
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