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Reply With Quotetrial and error will be the best way to find out ... it depends on the strength of your battery, as well as the draw of your car's systems during crank ... just give it a try.
Hey guys I am very new to this carputing stuff and I was wondering this.... I am going to get a VIA EPIA Nehemiah 10000 with a DVD-R and a PW-70A. I was reading on here with all of you talking about this "crank survival" and I am wondering if I will have a problem with that. I have an Optima yellow top battery, deep cycle, I don't know if that helps or anything. What does it come down to as far as... do I have to start the engine every so often to let the battery charge or can I sit in a parking lot with the engine off for a long time using the computer? Let me know what you guys think! Thanks alot!
trial and error will be the best way to find out ... it depends on the strength of your battery, as well as the draw of your car's systems during crank ... just give it a try.
My JeepPC Install
"there are no stupid questions, just stupid people."
"it's been agreed the whole world stinks so no one's taking showers anymore"
Ok let's say I need something to survive the crank. What would I need? How would I make it survive the crank? Thanks!Originally Posted by shakes
do a search for 'tank circuit' ... ignore all references to a capacitor based circuit as it's crazy talk.
in short you need a small battery (12v 7ah lead acid works well), and a diode (MBR6045 i think is the part number) ... it is also good to have another diode and a current limiting power resistor to control the spare battery recharge. there's schematics for this posted on here somewhere.
My JeepPC Install
"there are no stupid questions, just stupid people."
"it's been agreed the whole world stinks so no one's taking showers anymore"
Get an Opus.
And you do not know what you are talking about. They do work, it's just that nothing can dig you out of the hole that the ITPS regulator puts you in. Pair it up with an efficient switched-mode regulator based DC-DC PSU and then see.
oh ... ok ... thanks for clearing that up for me ... i thought this degree i have sitting here (BS in EET) suggested i knew a little something about electronics ... but thanks for informing me otherwise so i don't make a fool of myself.
so you're telling me ... (based on this thread and others i've read from you) ... that a 2200uf cap (or two) will "smooth" the voltage out enough to allow a computer requiring 12v to survive a crank that pulls the system voltage down to 8v for about 3 or 4 seconds???
the ITPS, while inefficient, doesn't put you in much of a hole ... especially if you don't have any 12v components in your system.
the fact is ... i *know* battery based tanks work (i've done it, and people have posted here with similar results) both with and without an ITPS involved. however ... the calculations and basics in electrical theory suggest a capacitor based circuit won't do jack to help your 12v system runn off 8v for 3-4 seconds ... and while a lot of people (like you) keep saying how it works ... no one's come accross with proof.
william ... you can also look into the opus as oppsed to the pw-70a as 'none' suggests. a lot of people use this and i hear it survives a crank (although i've never used one so i don't know) ... i think they're about $150+ so if you've got the money to spend go for it. however many people opt for the ITPS / PW-70a / lead acid battery option as that whole setup will run about $100. i favor the pw series supplies because they take up less room.
My JeepPC Install
"there are no stupid questions, just stupid people."
"it's been agreed the whole world stinks so no one's taking showers anymore"
Shake, that is exactly my point. Going into a car (or truck in this case) you want to take up as little room as possible and I just don't see that happening with a Opus. I was actually going to do that deal that they have on ituner.com that is for cars... it comes with a Nehemiah board with the PW-70a and a ITPS for $249. My other 2 questions are this... if you run the lead acid battery with the ITPS will the alternator charge the LAB also? #2 If I run on the optima yellow top and the backup LAB how long would it last if I sat in a parking lot with the truck off running normal computer functions such as CDROM/DVD-R, etc.? and #3 About how big are the LAB's that you are referencing to? Thanks for you guys' help!
Just to clear things up with those who dont really understand the basic law of physics...heres a graph :
The first one is the discharge rate of lead acid battery. The second is that of a capacitor. Notice the disharge rate of the capacitor is exponential which make it unsuitable for keeping the voltage level. The lead acid battery or a very good battery such as NIHM or LIONS as used in laptop have a very flat curve on the first few hours of disharge. The voltage is kept at 12V lets says and then drop suddenly.
Now you can laugh at the capacitor performance
Come over to my house and see the proof.
If your car's electrical system is dropping to 8v you have problems - and if it is staying there for 3 or 4 seconds you have huge problems. Perhaps a mechanic is your first stop to avoid tanking.
The tank circuit is not there to supply a full 12v to the computer for the whole crank. It only needs to lessen the falloff of that first dip - after that a proper DC-DC power supply won't have a problem. PW60/70/120 is a poor design that isn't efficient enough to cope.
A backup battery is fine and will get the job done, but a capacitor based tank circuit has worked for others here in the past, there are just long gone since they move on when done with a project. Saying that nobody has come forward to prove is ridiculous. I certainly don't plan on visiting this board for the rest of my life - once my system is perfected I'll never be back most likely.
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