Q regarding 12V DC-DC adapters

**jaytyn** · 10-12-2005, 06:29 AM

Hi

I am using the power supply below:

This power supply will work OK when connected to the internal car ciggy lighter,

But I also have a cig lighter output in the boot that I wired directly to the battery (+ terminal) and the negative to ground. (Fused of course). When plugged into the boot cig lighter, the adapter power light comes on, but will not power the laptop. It eventually blew the adapters fuse.
here are the specs of the adapter:

Vibration Input Voltage Range
DC11V-16V

Input Rated Current 7AMP

Input Min. Current 100mA
Input Power 88W

Efficiency
>88%(TYP)

Output voltage:16V/18V/19V/20V(-0.4/+0.5V@4A LOAD)

Output current:
DC16V-20V 4AMP(max)

Why would it work OK on the car cig lighter, but not work and blow fuses from the boot cig lighter?

THanks
Jayt

**Bugbyte** · 10-13-2005, 01:12 AM

There is a voltage drop that can be an issue with longer wires. What gauge wire did you run to the back and what is the total wattage you are drawing on your system?

**jaytyn** · 10-13-2005, 04:01 AM

Thanks for your reply...

I was starting to get suspicion it may be due to current/voltage loss from the cable length.

I am not entirely sure on the gauge of the wire. Its medium grade automotive figure-8 cable.

The voltage with engine OFF is 12.52 V
With the engine OFF it is 14.45 V

I am not really draining much current, the laptop adaptor only draws a MAX of 7A, and has a 5A fuse in it...

**Bugbyte** · 10-13-2005, 06:32 PM

Are you certain that you haven't reversed thepolarity of your wire? Check it again with a multimeter to confirm that it is the same as the lighter in the front.

Otherwise, I'd think it was due to voltage loss.

BTW, you meant that your voltage with the engine ON was 14.45, right?

Have you tried booting the laptop with the engine on?