Any Electrical People Out There?

juice_1080

juice_1080

Member
I am trying to figure out how I can hard wire an external hard drive into my car so that it will turn on when I turn the key. I am going to have it hooked into my stereo system with all of my music stored on it.
Maybe I am wrong but from my understanding the hard drive is a DC powered device and so is the car. The hard drive has a power converter on it that changes the wall's 110V AC to 5V and 12V DC @ 2A. I am wondering if I can just bypass the weird idea of going from the car's DC source to an inverter (AC) and then back to DC again.
I have a pretty good grasp on electronics and have taken intro classes to AC/DC but that was quite a while ago and I don't recall a lot of it. I have my electronics kit from classes (breadboards, tools, multimeter, etc.) and I am wondering if I can put together a small circuit to modify the battery power to properly control the hard drive.
Does anybody know how to do this or am I missing something and should be going the power inverter route?
 
scsinet

scsinet

Active Member
Believe it or not, the 12V is the tricky one.
5V is easy to get from a car's power supply. The best thing to use is a 3 terminal regulator. The 7805 regulator is the easiest to use, but it can sink 1a, maybe 1.5a at the most. Instead, the regulator I'd use is an LM338, which is an adjustable 5A regulator. I'm pretty sure that National Semiconductor makes it. You should be able to find a datasheet on it online which will show you an application circuit that will work for you. Then you just use a small trimpot to adjust the voltage and dial it into 5V.
The 12v is tricky because a car does not produce exactly 12V, it produces 13.8 nominal, but that can vary wildly, and a hard drive requires regulated 12V power. Even 12.1V could damage the drive.
The trouble is that most regulator ICs require a certain amount of input voltage over the operating output, (I'm working from memory here... but).. usually about 3v for stable operation. That means that you have no trouble with the 5v side because the car's power is always going to be well more than 8v, but 13.8V is not 3 or more volts over 12. What will likely happen is the output voltage with a (rounded) 14v supply voltage will top out at around 11v.
So to accomplish this you will need to step up the 12v supply to a higher voltage, then regulate it back down, essentially building a switching power supply. Or, you can use a DC/DC converter module of sufficient current handling, which will be pricey.
If you want to try the circuit, go for it, it's not complicated. Be sure to use hefty filter caps on your input from the vehicle end (2200mfd@25v or so) to filter out engine noise. Then build 2 identical adjustable regulator circuits, and dial one into 5v and the other into as close to 12 as possible, and see if your drive works.
Or, stick with the inverter. I dont' think DIYing a solution around a DC-DC converter is cost effective.
OR, use a 2.5" laptop hard drive. They don't require 12V and will run off a 5V supply only.
 
salty blues

salty blues

Active Member
Or you could simply use a 12vdc to 120vac inverter(available at wally mart and other fine stores)to power the hard drive as it would be normally.
 
scsinet

scsinet

Active Member
Originally Posted by salty blues
http:///forum/post/2596164
Or you could simply use a 12vdc to 120vac inverter(available at wally mart and other fine stores)to power the hard drive as it would be normally.
That's what he had been doing.
Problem is, it's incredibly inefficient and not a very elegant solution. Still, it may be the best for him.
 
salty blues

salty blues

Active Member
Originally Posted by SCSInet
http:///forum/post/2596268
That's what he had been doing.
Problem is, it's incredibly inefficient and not a very elegant solution. Still, it may be the best for him.
Sorry, if he stated that in his original post, I am missing it. I can understand the inefficiency angle if you are say, trying to run your entire house from your car's 12v system, but he is just trying to run a hard drive.
Also, it seems more elegant, as you stated, than what was proposed. However, each to his own.
 
stdreb27

stdreb27

Active Member
Originally Posted by salty blues
http:///forum/post/2596353
Sorry, if he stated that in his original post, I am missing it. I can understand the inefficiency angle if you are say, trying to run your entire house from your car's 12v system, but he is just trying to run a hard drive.
Also, it seems more elegant, as you stated, than what was proposed. However, each to his own.
It isn't a problem with amperage, but conistant voltage. Cars alternators do not produce a consistant current. After it is transformed through the regulator, it doesn't produce a consistant 12 volts it swings from 14 and on (depending on the car) down to 11 or so. Your vehicles electronics has more tolerance than say a computer hard drive. The biggest issue is ensuring a consistant 12 volts to diy power inverter so it can produce a consistant 5 v for your hard drive. (I think that is what the voltage was) And that will probably be harder and more expensive than just buying a out of the package inverter.
Voltage has nothing to do with the amount of items it can power. Think of it as a water pump, you need the right sized pipe to

[hr]
into the water pump (voltage). and the amount of water the overflow provides the pump is the amperage. If it doesn't have enough water flow (amperage) then the water pump will run dry and burn up. To much is ok. Because it only draws what it needs.
 
juice_1080

juice_1080

Member
Originally Posted by SCSInet
http:///forum/post/2596025
Believe it or not, the 12V is the tricky one.
5V is easy to get from a car's power supply. The best thing to use is a 3 terminal regulator. The 7805 regulator is the easiest to use, but it can sink 1a, maybe 1.5a at the most. Instead, the regulator I'd use is an LM338, which is an adjustable 5A regulator. I'm pretty sure that National Semiconductor makes it. You should be able to find a datasheet on it online which will show you an application circuit that will work for you. Then you just use a small trimpot to adjust the voltage and dial it into 5V.
The 12v is tricky because a car does not produce exactly 12V, it produces 13.8 nominal, but that can vary wildly, and a hard drive requires regulated 12V power. Even 12.1V could damage the drive.
The trouble is that most regulator ICs require a certain amount of input voltage over the operating output, (I'm working from memory here... but).. usually about 3v for stable operation. That means that you have no trouble with the 5v side because the car's power is always going to be well more than 8v, but 13.8V is not 3 or more volts over 12. What will likely happen is the output voltage with a (rounded) 14v supply voltage will top out at around 11v.
So to accomplish this you will need to step up the 12v supply to a higher voltage, then regulate it back down, essentially building a switching power supply. Or, you can use a DC/DC converter module of sufficient current handling, which will be pricey.
If you want to try the circuit, go for it, it's not complicated. Be sure to use hefty filter caps on your input from the vehicle end (2200mfd@25v or so) to filter out engine noise. Then build 2 identical adjustable regulator circuits, and dial one into 5v and the other into as close to 12 as possible, and see if your drive works.
Or, stick with the inverter. I dont' think DIYing a solution around a DC-DC converter is cost effective.
OR, use a 2.5" laptop hard drive. They don't require 12V and will run off a 5V supply only.
Thanks alot for the help. I didn't think about a laptop hard drive. I actually don't have the hard drive yet I was just going off what my current one I use to back up my PC uses. That seems pretty straight forward.
So what you are saying is run from: Key -> Filter -> LM338 -> Potentiometer -> Hard Drive ?
That engine squeal drives me insane my last car did that with just an aftermarket CD player. I think I have capacitors and potentiometers laying in my electronics case. I know for a fact that I have hundreds of different resistors in it. Any particular requirements on the Pot that I am looking for?
I know there are some Hard Drives like the WD Passport that run entirely off the USB drive (including power) but I am not sure if that CD player would have enough power to run it. Otherwise that would be the best bet.
I think the hardest thing is going to be hard wiring this to turn on and off with the key. Cars are generally fun to work with around the steering column area.

As of now I am still waiting on my reply from Pioneer to see whether or not the CD player is going to be capable of reading 20,000+ songs since most say the have a max reading capacity of around 255-1000 files. The plus side is that it says it will accept up to a 250GB drive.
 
juice_1080

juice_1080

Member
I really want to avoid trying to find a place to permanently hide a power inverter. It's bad enough that I need to find a place to stash the HD where I can easily remove it to re-sync new music as I get it. The last inverter I saw was too big to fit under my seat, but then again that was 1995ish, who knows maybe they fit in the pocket now. The other problem with that is that it would consume my only cigar lighter plug in my car. Not to mention its power consumption along with that of my amplifier in the back I think my alternator/battery would have some problems keeping up.
 
renogaw

renogaw

Active Member
why don't you just go buy a radio that can play mp3's and put them on disks, or a radio that an iPod plugs into?
 
juice_1080

juice_1080

Member
Originally Posted by renogaw
http:///forum/post/2597167
why don't you just go buy a radio that can play mp3's and put them on disks, or a radio that an iPod plugs into?
This one does both, I just want to have my entire music collection available when I want it. I have way to many CD's to even think about keeping them all in my car. This is just an idea that I am thinking of doing. The only real thing I am worried about is winter. I think I will have to take it out of the car in winter.
 
scsinet

scsinet

Active Member
Originally Posted by juice_1080
http:///forum/post/2597140
So what you are saying is run from: Key -> Filter -> LM338 -> Potentiometer -> Hard Drive ?
Not exactly. There are considerations at play here as well...
The potentiometer is part of the LM338 circuit. It is employed to adjust the regulator's output. What you need to do is look up the datasheet for the LM338. It should be available on National Semiconductor's web site, just google. The datasheet will have an application note that you can gank and use to design your regulator.
All the parts you need should be available from DigiKey, but Parts Express, MCM Electronics, or Jameco may have them and they are far less intimidating.
The second issue is current. If you find a wire underneath the dash that is ignition controlled, there is no telling whether it can handle the current you need. The best way to build the circuit would be to include a relay, so that your ignition wire switches the relay, and the relay turns on and off a constant battery feed that supplies the main power. I assume you can figure this out. Needless to say, any power wires that are not ground from the car should be fused appropriately.
That engine squeal drives me insane my last car did that with just an aftermarket CD player. I think I have capacitors and potentiometers laying in my electronics case. I know for a fact that I have hundreds of different resistors in it. Any particular requirements on the Pot that I am looking for?
See datasheet and application circuit.
I know there are some Hard Drives like the WD Passport that run entirely off the USB drive (including power) but I am not sure if that CD player would have enough power to run it.
You are almost certainly correct. However, it's easy to get around.
First, you can often find a 2.5" enclosure that can optionally be run off an external power supply. If so, just hack off the power plug on it and swap in your regulator circuit in it's place, of course being careful to observe polarity, etc.
If you can't find one, the USB bus consists of four wires (+5, Ground, and 2 data lines).
All you need to do is take a USB cable tha fits your drive, and shave off the outside insulation. You'll need a pinout diagram of USB (available online) and a meter to identify each wire. Then you'll want to cut the 5V wire and divert it to your regulator, and splice into (but do not cut) the ground wire and run that over as well. I attached a professional looking diagram to illustrate. That will allow your circuit to power the drive.
 
scsinet

scsinet

Active Member
Here is the application circuit from the datasheet.
It should work fine for your application with a bit of modification.
I'd add another large filter cap on the input, fuses on your input wires, and that relay I was talking about to control the whole works.
Of course, the LM338 IC needs a hefty heat sink as well.
Ignore the "28V" on the input. It'll produce 5V off a 12V car electrical system just fine.
 
bionicarm

bionicarm

Active Member
Originally Posted by juice_1080
http:///forum/post/2595918
I am trying to figure out how I can hard wire an external hard drive into my car so that it will turn on when I turn the key. I am going to have it hooked into my stereo system with all of my music stored on it.
Maybe I am wrong but from my understanding the hard drive is a DC powered device and so is the car. The hard drive has a power converter on it that changes the wall's 110V AC to 5V and 12V DC @ 2A. I am wondering if I can just bypass the weird idea of going from the car's DC source to an inverter (AC) and then back to DC again.
I have a pretty good grasp on electronics and have taken intro classes to AC/DC but that was quite a while ago and I don't recall a lot of it. I have my electronics kit from classes (breadboards, tools, multimeter, etc.) and I am wondering if I can put together a small circuit to modify the battery power to properly control the hard drive.
Does anybody know how to do this or am I missing something and should be going the power inverter route?

Kind of curious why you want to design an electrical circuit for a hard drive, when the technology is already out there. They make power inverters now that plug into the 12v power outlets (also known as cigarette lighters) that are in most cars these days. The unit is only around 4 inches long, and has one or two AC plugs on the end of it. Do a search for Xantrex Technologies XPower Micro 175-Watt Inverter #851-0178. It's only $26.
As far as the hard drive, you can find all kinds of self-contained external hards drives that already have the 120v to 12v circuitry built into them. Costco, Wallyworld, Newegg all sell them. Here's a 320GB for $75 -
Kaser StorageVault 320GB USB 2.0 External Hard Drive (Black)
How are you connecting this hard drive to your car's stereo head unit? Unless you have some USB input into your car's head unit, you'd have to tear it open and mess with the circuitry. Cheaper just to buy an 32GB Ipod and an FM Transmitter unit.
If you want to get real fancy, do a search for CarPC. For around $700, they have complete PC's with small LCD screens that you can install into your car. They come with adapters to hook the system directly to your car's 12V system so that it turns on when you turn on your car. For another $75, you can get an InDashPC unit that is compatible with almost any make of car. This device allows you to hook a CarPC directly into your car's audio system so you don't have to buy and external amplifier.
 
scsinet

scsinet

Active Member
Did you even read the thread?
He's got a head unit that does accept USB (many modern head units do) and he already considered the power inverter and doesn't want to use it.
 
bionicarm

bionicarm

Active Member
Originally Posted by SCSInet
http:///forum/post/2598231
Did you even read the thread?
He's got a head unit that does accept USB (many modern head units do) and he already considered the power inverter and doesn't want to use it.
Is there a reason why you're taking an offense to my post? I'm glad you gave him the suggestion you did, but he was asking for alternatives. Are you insulted that current technology already has what he wants available, and he won't use your electrical design that you spent so much time putting together? You're wanting him to hack into a hard drive case to install this little circuit of yours, even "shaving into the USB cable to expose the wires"? The wire on a USB cable is very small. Unless you've done a lot of electrical soldering, all you're going to do is destroy a good cable, especially if you don't have the right soldering iron. And you want him to tweak the 5V with a pot? By the time he gets all the components, a good soldering iron, and a decent voltmeter, he could buy the plug-in inverter for half the price.
I never read anywhere where he stated his head unit had a USB port. Unless your car is only a couple years old, the factory unit doesn't come with one. He says he only has one power outlet. I just bought an inverter that plugs into a lighter that has one AC outlet, and then another 12V power outlet in the front. A hard drive in a case doesn't draw that much power. Your 12V system will have no problems handling the current draw. On long trips, I run two power inverters that drive two laptops, a DVD player, and a PS3.
 
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