Surface Pro - External DC charging questions

[deanfourie1]

So, I'm out of ideas on this one! And really do need some help! There is NO information online.

I have a Surface Pro 3 that I'm trying to power externally, this tablet will be used as a wall mounted tablet for Home Assistant. The issue I have is with getting it to charge. If I plug it into a standard wall USB charger, it charges just fine, but when trying to use a DC to DC buck converter, 12v to 5v 10A, it doesn't seem to want to charge.

When flat, I've measured the draw given to the tablet. When dead flat and plugged in, its proving 5v @ 0.5A. I'm guessing this is not a limitation from the buck converter but rather what its demanding.

I've tried powering the buck from a 7AH 12v battery, and now a 12v 3.8A AC wall adapter.

When fully charged, it detects that something is plugged in to the charger port, but does not charge. The battery continues to decrease.

I don't think there are any smarts in the charger as I said it charges off any AC to USB 3A fast charge adapter just fine .

Any ideas? This tablet is worth nothing but perfect for a wall mount touch display for Home Assistant and would be a shame to let it go to waste.

Thanks

 

[John Canon]

Does the notebook charge when using the proper charger? If not then you have blown the mosfets on the motherboard. Been there, done that. I accidentally connected a different charger backwards for 1 second ... boom, $200 repair.

In your picture the cable going to the notebook seems to have a center conductor and a copper shield. Most low voltage charging cables use the shield for negative and the center conductor for positive. No matter what color it is.

Check the label on the notebook for plus/minus configuration. See paragraph 1 for solutions.