Thread: Help with DC-DC Power Connector

[QUOTE=zeppelin]Folks,

I'm a newb here, so be kind. I'm installing a carputer comprising a laptop to a motorised 7" VGA touchscreen mounted in a DIN slot in the dash. Most of the install is done, and I'm presently hooking up the power supply to the laptop. This is where I'm having problems. BTW, my knowledge of electronics is rather minimal - just enough to be dangerous.

I have a 12vDC-12vDC car power supply that I bought for the laptop. I cut the cig lighter fitting off, and connected two bayonet fittings in it's place. In doing this, I assumed the inner core was (+) and the outer winding was (-).

Querie #1: Is my assumption correct?

Yes

I then tapped into an auxillary power source in the back (whick looks like it's for a CD stacker), and ran a separate line to ground. I connected the (+) to the aux power line and (-) to ground.

I booted up the laptop, turned on accessories power, and plugged in the adapter. The power light on the adapter then proceeded to cycle every couple of seconds between green and red, associated with an audible click from the adapter each time it went to red. The laptop screen also flickered with each click. Power management showed that the laptop wasn't charging. A mulitmeter showed the adapter outputing 17v. Specs on the back of the adapter are:

DC Input: 12v
Fuse: 13A 250v
DC Output: 18v - 20v 90W (max)
17 Volts is low.. the Outpu spec is dodgy, are u able to fix it at 19V? Also the input for a Auto DC-DC converter is in a range..e.g. 9v-22v or so.

The laptop spec is:

Input: 19v 3.16A

Querie #2: What am I doing wrong here?

try running your motor, the 17V output ur getting is typical of a DC-DC converter wanting more power and the lappy isn't getting it. It is a lot of fun but you want to throw it all away at times... keep trying..

Cheers
Peter

zeppelin,

Your DC-DC converter probably cannot survive below +12V at the input. Check the DC-DC input voltage with, and without your engine running. You may find that everything works OK with the eingine ON since the voltage into your DC-DC will be 13.8V from your alternator. When the engine is off this voltage will drop to whatever your battery can provide. If your battery has some age on it, you will most likely be below +12V pretty quickly after the engine stops.

Good luck.

I agree with the other posts. Try it with the engine running.

When I first installed my carputer, it wouldn't boot with the engine off. I went nuts trying to figure it out. It finally occurred to me to try it with the engine on and it worked.