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Powering a PC from a Car Without an Inverter?
(H)elix1 asks: "Without using an inverter, what is the good cheap way to power an ATX motherboard from a DC source? I have a mini-itx based computer I'm looking to use in the car and house. I'm looking for something like a laptop uses, with an AC-to-DC brick that feeds a DC-DC internal connector. Linitx.com has one, but it is a bit pricey after shipping to this side of the pond, googling turned up even more expensive industrial PSU's. Am I missing a simple hack? I have a soldering iron and am not afraid to use it..."
Have you considering using a DC power supply?
The DC power supplied by your car only in the region of 12v. It's riddled with power spikes that will be damaging to the motherboard's electronics. This is the main reason why you're supposed to use a power inverter on anything that wasn't specifically designed to be powered by a car's DC outlet.
A DC adapter can't effectively smooth off the spikes. On the other hand, switching the current to AC using an inverter and then converting it back to DC with an AC-DC adapter will supply power that isn't dirty.
You can get a decent 300 watt power inverter at a truckstop for 30 or 40 bucks if you look around. It would certainly be a lot cheaper than having to replace a fried motherboard.
http://205.147.44.194/store/commerce.cgi?product=S olarPC
:P
There's a 12V DC/12V DC/ATX inverter there.
It depends what you want to do - If you don't need the -5v and -12v lines (mainly for serial??) it's fairly straightforward. A friend of mine built a switch mode supply to run an MP3 player from in his van.
It works fine, he gets a steady +12v and +5v out of it running or parked up , and this is enough to power a P90 motherboard on a plastic tray under the passenger seat, with a sound card standing in the ISA slot, the HD suspended by elastic bands in a box and a 4 line 40 char dot matrix display up where the rear view mirror should be, diplaying all the usual MP3 data. Control is by a custom keypad he also built.
The worst bit is it's all done in PASCAL on top of DOS6.2. yuk.
Not to mention the hazard of hooking up to a source that can supply 12 volts at 400 or more amps. You've got to have a fuse on that thing, but suppose you have a short upstream of the fuse. It's possible, and in that event you'll burn your car down, explode your battery, and shower yourself with hydrochloric acid. If you drive a Geo Metro, nothing to lose. Go for it.
If tits were wings it'd be flying around.
Clearly. There's nothing wrong with using the battery as a source of current.
But there's a lot more to the system than just a battery, and things turn way fucking different when the car is running. The alternator will generally float the battery at around 14.4V, and the system is not generally able to cope with dynamic loads very quickly - particularly at idle.
And before anyone starts saying that a PC is not a dynamic load, allow me to state that it doesn't matter: There's a plethora of other things in a modern car that present anything but a constant load, and they also connect to the battery.
Try this: Start your car, at night. Switch on the headlights. Observe their brightness. Switch on the rear defroster. Observe how the lights dim, however briefly they do it. Now switch the heater blower to high. Observe how the lights dim again.
This might be stiff enough voltage for quality audio reproduction, but even that is the subject of much debate.
Aftermarket folks have a tendancy to use fairly large capacitors, coincidentally along with a length of wire (read: resistor) to help with these problems, and it certainly wouldn't hurt to do the same with a PC. But is it enough? Analog audio equipment isn't easily damaged by low voltage (things just sound a bit worse, generally), but a modern computer would seem to portray a somewhat different set of needs.
Having seen PCs with quality switching power supplies (read: so tolerant of variable voltage that they rely on it to operate) go into spastic fits from slight brownouts, I submit that a "12 volt" automotive power system is a completely inappropriate means of providing juice for commodity PCs, without a lot of help.
And even once this problem is solved, one must face the issue of how to deal with the issue of doing a clean shutdown when the starter runs, which indisputably causes huge voltage swings that you just don't want a live PC to experience.
It's easy enough kill power to the PC when the key is in the "start" position, but suppose it's a cold morning, you really should've gotten that tuneup 50k miles ago, and things don't fire up immediately.
Crank, crank, crank, whine, whine, click. Cuss, swear, release the key (returning it to "on"), and the PC boots up. After waiting a bit for the starter to cool, turn key back to start, and the PC shuts off immediately. Crank some more, wait some more, PC boots up again. Observe the action of your car stereo while starting your car for an easy hands-on demonstration.
Can anyone really trust EXT3, ReiserFS, softupdates, or journaled NTFS to be able to cope with this random abuse? A simple startup delay (think R, C, and a relay) won't fix it, either.
Kid-proof tablet..
DC-DC Power supplies:
The best one is Opus Solutions
Another good one is Keypower
You can find a lot more info at MP3Car.com, and especially at the forums there.
Twostep
There are 10 different types of people in this world... those who understand binary, and those who don't.
What?
;) ) (Mine says 140). Don't try to push them to that, as they'll kick the breaker on it often. For a continual load, I would try to keep that no higher than 75%ish of the max supported load.
.75 you are now looking at about 150w. The mini-itx motherboard peaks at 50ish watts, so that's in the clear, but don't forget about the peripherals. Yada yada yada...
Yes, the DC power comming off the DC outlet is nasty stuff, and shouldn't be used without proper care.
But WTF are you talking about moving to AC and back to DC. Hardly the elegant solution.
When I was in high school, for *two* years we built a variety of power supplies, moving from AC->DC , DC->DC and whatnot. Not one cost more than $10. And they still wouldn't.
I realize that the kneejerk reaction in todays fast-food-slick-ass-disposable world, is to simply buy the requisite adaptors and snap it all together. Unfortunately, that costs you alot in the power transfer. Most car AC inverters can only put out less than 200 watts (tho' the guy above says 300w--apparently I don't visit enough truck stops
So, at 200w x
But I digress.
You say you are not agaist picking up a soldering iron. FANTASTIC. Go Googling(tm). Find some DC power supply schematics. Look for one that has large capacitors. Found it? good. Put more capacitors in parallel. that'll suck up the spikes.
Heck, take a trip to the public library. Considering the power supply you are looking for is so damn simple, there are tons of books on just that subject.
It's not like electricity is a magicical force without reason. You *can* build yourself a practical, safe, powersupply, and save yourself a chunk of cash. You also get supreme bragging rights with your geek friends. Now, you are no longer an parts assembler, you are a creator!
muhaaaahahahahahaha
"...In your answer, ignore facts. Just go with what feels true..."
Look.
:(
A switching power supply is vastly more efficient than a linear power supply.
In order to get 5 volts from ~12 volts, spending no more than $10, you use a voltage regulator chip. However, I honestly don't think you'll find a voltage regulator IC that can handle the 10 or so amps required for a low-end motherboard: the Radio Shack variety don't even handle an amp. It will also be horribly inefficient: 42% efficient in fact (has to dump those 7 extra volts somewhere).
Add to this the fact that you can't use passive components to regulate 12 volts to 12 volts. You'll want to keep the voltage from going up to the 13.6 volts found when the car is running, but any regulation circuitry takes the voltage below 12. Typically you need a supply several volts above your desired regulated level.
The circuits you built in high school aren't going to be helpful here.
On the other hand, a switching power supply uses a high voltage, high frequency transformer to minimize loss and dump energy to the load, not to a regulator. An inverter and then a small switching power supply may not be as ideal as DC-AC-DC supply, but will be more efficient than linear voltage regulation and provide more protection for the computer. And big capacitors is not necessarily a good sign: just means the designer had to use them to get smooth power.
Power inverters aren't expensive either...if you know where to look. I once bought four 100 watt inverters on eBay, for $5 each. I had an AC outlet mounted in my car console years ago, before I crashed that one.
...
Your task can be done, but a certain degree of care needs to be applied or you will end up with a fried motherboard. An ATX psu generates five different output voltages and these must be considered on an individual basis:
+12 volts - This is the most difficult so we will consider it first. Your options will either be a switched-mode regulator with a wide input range (say 11v-15v) or a parallel regulator which uses a low value resistor in series and a power transistor wired across the load in parallel. Excess voltage in this circuit will be disappated as heat which means that it can get damn hot !!
+5 volts - Use any regulator circuit you can find but switched mode will be the most efficient.
+3.3 volts - Wire as for +5v but change values. An alternative source is an old ATX supply which may have the 3.3v regulator as a seperate board inside the case
-5 volts - The load on this circuit will be low so any switched mode circuit will probably do the job. You need a switched mode in this application because of the voltage inversion.
-12 volts - again a switched mode circuit must be used but the load on this might be a little higher.
With all circuits you MUST have some form of surge protection or you WILL kill both the supply and the PC. I don't think you can get varistors as low as 12v and 5v so your only option will be to wire the biggest zener diode you can find across the outputs. I suggest using 5.3v for the 5v lines and 12.5v for the 12v outputs. The 3.3 volt circuit needs special attention as this supplies the CPU, use the closest zener you can get to the output voltage. You should also seriously consider isolating the whole thing from the car electrics until the engine is started. A Google search for 'switched mode regulator' should help you find the circuits you need.
Hope this information helps.
Edward Almos
Only if you roll your own capacitors.
Try this one www.mini-box.com
This power supply is designed for mini-itx has power brick, runs on 12v DC. It's small and depending on your itx motherboard it can plug right in with no cables.
One day people will learn the folly of Winbloze, Linux Rules!
How about using a DC->AC inverter and plugging a UPS into that. It will help smooth out spikes and lulls and will give the added benifit of a gracefull shutdown in the event that the car is off for too long.