 Vchat20Landing is the REAL challengePremium
join:2003-09-16
Columbus, OH | Powering 12V device with own regulator directly off car? Although this little 'side project' of mine is a long ways off I was looking closer at my donor hardware today and wanted to figure something out.
I have an Iomage iConnect NAS here which I have blown away the stock OS on it and have open to do with as I wish. Eventually I want to dump it in a corner of my car for data/wifi logging and possibly more.
It has a normal barrel connector on the back and asks for a 12V/2A power source. Now I know this means jack squat and to look deeper you really need a closer look at what chips are doing the power conversion for the more sensitive electronics running the device.
So far I see these two chips nearest the barrel connector:
»www.fairchildsemi.com/ds/FD/FDS6986AS.pdf
»www.marvelldirect.com/assets/fil···8101.pdf
Can't clearly tell which one is first in line but I am wild guessing here it is the latter. Seems like a standard wide range regulator and the first takes the regulated power and splits it to different voltages (3.3,5,etc).
Given this and the input voltage range shown, would it be within a margin of error in a car environment to power it directly off vehicle power with no external regulation? Granted I could probably scare up a 12V regulator that can do 2A pretty easily and cheaply and would potentially save the internal regulator should something go awry but this is piquing my curiosity.
--
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz |
|
|
|
 shdesignsPowered By Infinite Improbabilty DrivePremium
join:2000-12-01
Stone Mountain, GA | Measure the voltage on the stock power supply. If it is unregulated, you can probably get away with a direct connection. |
|
 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:8
 ·SONIC.NET
1 recommendation | reply to Vchat20
The first chip contains the two mos-fets for the second chip (step-down voltage regulator). It is really only one voltage regulation circuit.
Given that your device has an internal voltage regulator you will probably be fine with the wildly varying car battery voltage. However there are hidden dangers when connecting I/O cables to devices designed for isolated power supply (which almost every device with AC power adapter is). The input voltage ground may or may not be the same as the signal ground on the I/O connectors! Once again you should be fine as long as you only use the ethernet connector (since ethernet is an isolated interface). I would however stay away from using any serial (including USB) interfaces that the NAS may have.
--
Got some spare cpu cycles ? Join Team Helix or Team Starfire! |
|
TheMGPremium
join:2007-09-04
Canada
kudos:2 | reply to Vchat20
Typical hard drives require both 12V and 5V.
More than likely the on-board regulator provides the 5V, while the 12V comes direct from the external regulated power supply. This is a fairly typical arrangement for NAS and external hard drive enclosures.
I'm not sure the hard drive(s) would be too happy with the direct unregulated 12V from the car, which can soar close to 15V when you put your foot on the gas and can have significant amount of ripple from the alternator.
Sounds like a job for a very low dropout regulator/limiter! |
|
lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to Vchat20
said by Vchat20:Given this and the input voltage range shown, would it be within a margin of error in a car environment to power it directly off vehicle power with no external regulation? I posted a table showing all kinds of transients that happen on the 12V bus of a car in this thread: »Most cars still have 12V lead-acid and lighter port ?
The built-in regulator inside 12V computer devices are not really designed to handle such wild transients. Good quality car accessories incorporate more robust surge protection. The "surge stopper" devices from Linear Tech are considered the very best. |
|
| reply to Vchat20
Most 2.5" HDD and all SSDs run only off of 5V and don't need 12V. |
|
lutful... of ideasPremium
join:2005-06-16
Ottawa, ON Reviews:
·TekSavvy DSL
| reply to Vchat20
The output from the NAS power supply is 5V. The motor driver definitely uses only 5V. There would be one or more 5V to 3.3V/2.5V/ 1.8V regulator(s) on the board to supply various chips.
The Fairchild dual MOSFET IC can tolerate up to +30V and ground can go down to -16V. The Marvell PWM chip tolerates up to 16V. Both chips have excellent specs for computer peripherals. However, the transient voltages in a car do occasionally fall outside those specs.
*** If you use the NAS in a car, please plug it in ONLY AFTER starting the car and always unplug before turning on AC or turning off the car. That minimizes the risk of severe transients. |
|
Vchat20Landing is the REAL challengePremium
join:2003-09-16
Columbus, OH | reply to Vchat20
Thanks guys for the info. To clarify, there aren't actually any attached drives on this thing. It is more or less a Pogoplug on steroids. gigabit lan, mini-pci-e wlan and 4 usb ports. Designed just to attach your own USB storage and share it out. I think initially it'll just be a microSD reader and 16gig card attached. And if I ever need extra space it'll probably be an additional flash based stick to avoid any remotely possible spinning disk annoyances. So FWIW at most for power requirements internally it is 5V for keeping USB happy and 3.3V and below for the CPU and attached peripherals. I've attached a few pics of the board for reference. Apologies for the flash and lighting. Any other light source in the house tends to glare as bad if not worse or isn't bright enough if I try to avoid said glare.  Given that and some very brief reading elsewhere I may hold off a little longer til I can invest in something that can appropriately regulate the power supply from the car. At best if I do test in these conditions I will take the advice of only having it plugged in not when cranking or switching a major load. --
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz |
|
 Tursiops_GTechnoidPremium,MVM
join:2002-02-06
Norwalk, CT
1 edit
1 recommendation | You also might want to take a look at these Automotive TVSS devices:
»www.eetimes.com/document.asp?doc_id=1317365
»www.digikey.com/catalog/en/partg···es/29941
»www.digikey.com/catalog/en/partg···es/29949
Shouldn't be too difficult to place one across the power input traces on the bottom of the PCB... 
-Tursiops_G.
--
If You're Unsure, "RTFM"... If You're SURE, "RTFM" Anyway.  |
|
 PaoloMr. Wireless
join:2004-05-29
canada | the mofset is required |
|
| reply to Vchat20
I'd use a simple LC filter augmented with a couple of Zeners.
input - fuse - 18V Zener & 100 nF cap - choke - 15V Zener & 100 uF & 100 nF cap - output
I'd select a choke that drops between 0.5 - 1V at normal current draw.
--
Wacky Races 2012! |
|
| reply to Vchat20
Note that while the car "runs" on 12V the actual output of the cigarette lighter/accessory socket when the car is running (because of the alternator) is closet to 14.2v
When starting the car, or when you have a sub, the voltage can swing wildly.
Trust me when I say a simple voltage reg. IC is not enough, you will kill it in a few months, you need something like this which is designed for this purpose: »www.mini-box.com/M4-ATX?sc=8&category=981 |
|
Vchat20Landing is the REAL challengePremium
join:2003-09-16
Columbus, OH | reply to aurgathor
said by :Note that while the car "runs" on 12V the actual output of the cigarette lighter/accessory socket when the car is running (because of the alternator) is closet to 14.2v
When starting the car, or when you have a sub, the voltage can swing wildly.
Trust me when I say a simple voltage reg. IC is not enough, you will kill it in a few months, you need something like this which is designed for this purpose: »www.mini-box.com/M4-ATX?sc=8&category=981
I am going to take a guess (and please do correct me if I am wrong) the main point of your post is being a computerized device and being HIGLY strict about voltages, direct power off the car is going to be bad news. Normally I would be in complete agreement and go for a proper power supply such as the one linked. But as previously noted it does already have an internal regulator that does have a wide input range and seems to have over/under voltage precautions thrown in (but I will be honest that I do not know the extent of what these limits could reliably hold back especially in the over-volt direction) hence this thread and my curiosity.
I've actually dabbled and lurked heavily on other CarPC centric forums and am quite aware of power related topics. But am certainly not beyond taking advice where I may have gaps in my knowledge.
said by aurgathor:I'd use a simple LC filter augmented with a couple of Zeners.
input - fuse - 18V Zener & 100 nF cap - choke - 15V Zener & 100 uF & 100 nF cap - output
I'd select a choke that drops between 0.5 - 1V at normal current draw.
I think I may actually give that a go. I have been meaning to dust off my soldering skills and that shopping list is inexpensive enough combined with a breadboard to take a stab at it. Anything on the negative/ground side I should be worried about? Maybe just a diode in case of polarity reversal in the power system?
--
I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz |
|
