Use 2 UPS's, and a standard ATX or MicroATX power supply! (no, I'm not the only one that came up with this).
I've seen a lot of posts asking this, and some posts saying things against it. A few have even tried to to some degree of success or failure. I don't want people to ***** about the negatives of this setup, it's just info, you can always make something work.
Granted, it would take up more space, but for people with ample room, would this solution work as a surge tank, shutdown controller, startup controller*, and give you 110 in your car? Probably! I've seen people with TOWERS in their SUV's (not my cup of tea, but still).
*startup control depends on your bios, if it's setup to "power on after power fail"
2X 300w 550VA tripplite UPS sinusoidal power supplies, that run on 12-13v DC - total ~$100
1X standard, or micro 300w+ ATX power supply ~$25
Misc cables, maybe a relay or two, ~$25
Total cost, < $150!
UPS's have 4 main parts:
Battery (12v, at least 6ah, sealed lead acid, takes up 60% of the room in the case)
Inverter (takes 12v and turns into PWM sinusoidal AC 110, 75% efficiency at half load)
Controller board + switch (USB, beeper, surge filtering, signal detection)
Bulky case and outlets.
Be careful taking one of these apart! Unplug it from the wall, turn the switch off so it doesn't beep, and immediately remove the battery before tearing it apart further.
The biggest and heaviest part of the UPS's is the battery. You would not need one of the batteries since your car already has a huge one. The UPS guts can be reduced down to a much smaller footprint, with just one or two outlets, or hardwired to the 2nd UPS. Remove the buzzer/beeper while you are at it. Keep the battery as a spare. Lick it, use it as an emergency jump device, I don't care.
It's all about customizing right? I went out and bought the UPS's, and have tested them for you before posting this. I personally use a laptop, and have no need for this setup. I had tried a couple other UPS's but they don't work as well as the tripplite's. A tripplite will see another tripplite UPS as a wall outlet, but cyberpower, or apc will not, probably something to do with the smoother PWM sinusoidal AC, compared to the square or rectangle wave coming out of the other two.
Why not use a power inverter instead of the UPS? The readily available and less than $50 ones are noisy, terribly inefficient, and have square AC waves. Not a clean source of power, and not always UL listed. The UPS already has a power inverter built into it, and it's a much higher quality and needs no fan (unless you max out the wattage used maybe). It's also fairly cheap! It's also SMART, it has a USB connection to the PC, that windows power management finds as a HID Battery device, with no additional drivers.
The UPS's would have two modes of operation, on AC, or on Battery. These two modes combined, give you all the features I talked about earlier.
First UPS is hooked to a ignition or accessory switched, fused, 12v power source (at least 25 amp, use a relay if your car doesn't have any auxillary fuses). So when the key is in, and turned to the first spot, this UPS comes to life, and spits out 110v. This UPS is gutted, and has no battery or beeper itself.
It puts out 110v AC to another UPS, that could be complete, or modded by you to take less room (pull the battery, and mount it remotely, install in a small aluminum enclosure if you wish). This UPS simply feeds the AC coming into it, straight to your ATX power supply. It monitors the condition of the first UPS, and feeds that info to itself, and to your PC via USB. Your PC turns on, if the bios is set correctly. No hacking wires, no jumpers, etc.
You crank your car, voltage drops down to 5-8 volts, with almost no amps available. The first UPS shuts off, and kills power to the 2nd. The 2nd UPS switches to internal battery power within 2-4ms, and continues operating. At this point, it tells windows, "hey, I'm on battery power!" Windows monitors this, and does stuff accordingly. If the PC is just booting, it doesn't care.
You stop cranking, everything resets back to normal. And your PC is still on. You drive around, do what ever, and finally shut the car off an hour later, listening to tunes, GPS, etc.
Again, the 2nd UPS takes over, with it's internal battery, again it tells windows, "Hey i'm on battery again *****, what'chu gonna do about it?" You set windows power managment to shut down gracefully when the battery reaches 50% or whatever you want. You could set it to 90%, and it will shut off within 30 seconds of you turning the car off. You could set it to 10%, and give yourself up to an hour of shutdown, or anywhere in between, like standby for 4 hours, then hibernate after that point. It doesn't matter, it's full configurable. You would have to adjust to your setup.
Once it sees no load (less than 10w), it shuts off automatically. It won't drain it's own battery. The first UPS is an igntion switched device, meaning, no key, no power usage. No drained car battery.
I feel this approach is better than a DC to DC power supply, for these reasons:
DC to DC ATX supplies don't supply over 200w in most cases.
They can cost a lot more.
They don't always survive crank, all the time, and in every car.
They aren't easily replaced for cheap, nor at any local computer store.
They MAY not be as reliable, or easy to diagnose.
If you need one to survive crank, you need a tank circuit, which adds bulk back to the system.
No USB connection for advanced power managment info/scripting.
No 110v socket for your car.
Could drain car battery if you didn't configure properly.
Disadvantages of the 2 UPS solution:
Modding of big bulky devices to make them smaller, safely. You are dealing with 110v at times!
No instruction manual (other than what I wrote above)
Takes up more room in your vehicle. An issue for a 2 seater, not so big a deal for a larger 4 door or SUV
Mounting/strapping the bigger, 2nd UPS out of the way.
Could be substantially less efficient in terms of power use, unless you got a good active PFC standard ATX, with 85% or higher efficiency under normal load. Remember, your "inverter" section is only about 75% efficient in the tripplite's. On average, you are looking at 55-60% efficiency in the power conversion, compared to a 80-90% efficiency for most of the DC DC solutions.
People are gonna call you ghetto, and say mean things about your car/setup/haircut on their keyboards. Everything is ghetto to some degree, unless you bought a car with NAV preinstalled, or are a professional installer, but that's not what this is about.
Good luck, have fun, tinker! It's how you learn.
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