Laptop DC Extension lead

[steaky1212]

Hi,

I was wondering if anyone could help me.
I've got a project where I need to monitor the current consumption of a laptop, but I dont want to cut the laptop wire.
I've looked at non-contact methods, but they leave a lot to be desired when my dynamic range is 0-3A, but I also need mA resolution.
I've built a circuit up using the same op-amp (MAX4238) Dave uses in the uCurrent and my circuit works like a dream - only I have to bodge the connections to the jack and laptop.

Does anyone know of a DC extension lead that I can cut for my circuit? The laptop is a new HP Probook with the 3 conenctions on the DC jack (power, ground and a data connection for identifying the charger).

Thanks in advanced,

Steaky

[G7PSK]

You can get cheap power supplies from ebay that you could cut up. A power supply is cheaper than the replacement socket and I do not know where to get the plug. The socket is around the £24-00 mark and a power supply around £6-00.

[peter.mitchell]

A few things;

A laptop will charge its battery when the charger is plugged in, so you will probably have top wait until the battery is full, however, even then i think they do some weird balancing between battery and AC adapter. You could try with the battery out, but some laptops don't power on without it.

[sacherjj]

I know that Dell has one for their travel adapters.  It allows the small portable adapter to stretch further.  You can also pick up one of the generic laptop power adapters that should be pretty easy to cut into, as the ends are changeable.  You might be able to just solder to the correct tip.

I have to follow along the comments of the others about AC power and charging.  However, you will get close if you power the laptop by ONLY is AC adapter.  i.e. remove the battery.  This will still be higher drain than the drain from the battery, as the AC adapter is a bit higher voltage than the battery and you will have charge and voltage drop regulation (that may or may not be very efficient as it is on the AC side.)  Usually it is 12V or more for the adapter and 9-10V for the laptop battery.