Regulated automotive PSU (6-15v -> 12v 5A, 5v, etc)

[sparx]

Just a quick question - I want to (at some point!) - install a PC into my car to take over music, sat nav, etc.  I had a crude install in my previous car of a windows xp based tablet running from a 5v 5A regulated buck converter, but it suffered drop out at engine turn-over.

I have found some buck/boost converters (eBaycapable of 2A supply, with 6-33v input, however was wondering if there is another, better way, to get regulated 12V from 6-15v. Could I put 2-3 of these in parallel? What if one failed? This supply would run a computer system of some description and also an lcd screen.

Once I can get this one supply sorted, the rest of the system can be sorted with regards to switching on with ignition/timing out after ignition is off to prevent drainage, etc.

Cheers!

[urlkrueger]

Starting a car requires a lot of current from the battery which, due to internal resistance in the battery, causes the voltage to drop too low resulting in the computer shutting down.  The answer to your problem is to keep the voltage up at the computer. 

One way to do this would be to power the computer from an additional small 12V rechargeable battery.  Perhaps a UPS unit could come into play here.  Then with a battery isolator, essentially a large diode, you could connect this up to your automotive system in order to keep the small battery charged.
     

[UnaClocker]

Automotive ECM's run at 5v (well, most, they may have finally come out with some at 3.3v). It's not an insurmountable task to get 5v while cranking. Were you using something like a 7805? There's a low dropout version which has been used with great success in automotive applications. If you're using a switchmode power supply, just read the datasheets on the chips to determine how low it can go. You want down to at least 7.5v, 6.5 is even better. Seems like the mc34151 is good down to 6v if I remember right.