Surface Pro - External DC charging questions

Thread Starter

deanfourie

Joined Nov 6, 2022
4
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

339ecaaf2ebfdc0048dbc56184fa6799056432d3.jpeg

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Ya’akov

Joined Jan 27, 2019
6,853
Welcome to AAC.

Which port are you connecting the power to on the Surface? If it is a USB port you will probably have to provide some termination to the data lines to tell the Surface it is a charger.

The simplest is just shorting D+/D-. This should indicate to the Surface’s charge controller that the power supply offers unspecified current but that it is a charger. You could measure between D+ and D- on a working charger. There will either be a resistance (short or some other) or voltages relative to V-. The voltages are less likely because that is Apple’s strategy for determining the nature of the charger and it is quite outdated at this point.

In any case you may find that you have to provide some clue to the Surface that the connected device is a charger before it will decide to sink current from it.
 

Thread Starter

deanfourie

Joined Nov 6, 2022
4
Welcome to AAC.

Which port are you connecting the power to on the Surface? If it is a USB port you will probably have to provide some termination to the data lines to tell the Surface it is a charger.

The simplest is just shorting D+/D-. This should indicate to the Surface’s charge controller that the power supply offers unspecified current but that it is a charger. You could measure between D+ and D- on a working charger. There will either be a resistance (short or some other) or voltages relative to V-. The voltages are less likely because that is Apple’s strategy for determining the nature of the charger and it is quite outdated at this point.

In any case you may find that you have to provide some clue to the Surface that the connected device is a charger before it will decide to sink current from it.
I think this is it! It has to be!

I just don't know "what" clue to give it :p

I will check power between data pair tomorrow, and possibly try shorting them if I feel it is safe and report back.

Thanks for the quick reply.
 

Ya’akov

Joined Jan 27, 2019
6,853
I think this is it! It has to be!

I just don't know "what" clue to give it :p

I will check power between data pair tomorrow, and possibly try shorting them if I feel it is safe and report back.

Thanks for the quick reply.
It is perfectly safe to short the data lines. It may or may not solve your problem, though. It is the very simplest indicator of a charger and used by cheap chargers regularly. If this fails, something like this product that specifically supports charging protocols is probably an answer. It only outputs up to 3A, but that’s a substantial current for a charger and the Surface probably can’t use more.

I hope the reply was helpful as well as quick. Glad to assist (if it turns out I did).
 

Thread Starter

deanfourie

Joined Nov 6, 2022
4
It is perfectly safe to short the data lines. It may or may not solve your problem, though. It is the very simplest indicator of a charger and used by cheap chargers regularly. If this fails, something like this product that specifically supports charging protocols is probably an answer. It only outputs up to 3A, but that’s a substantial current for a charger and the Surface probably can’t use more.

I hope the reply was helpful as well as quick. Glad to assist (if it turns out I did).
Thanks again. I did try this exact one, same issue.
12V to 5V converter FREE FREIGHT | Trade Me Motors

I just jumped up and did some testing! The device must have been charging @ 500mA as it has now powered on.
I guess its possible that it has some smarts built in, as I've gradually noticed the charge rate increase over time.
So here is my guess so far.

When the battery is dead, it reduces the charge rate to a trickle charge to safely bring the battery back up, this literally started at 500mA, then when there was enough juice, it has booted and is now charging at 2.5A while running.

I'm not sure if it will continue this behavior though, I will leave it for the night and see what happens tomorrow.

I basicity just want the thing to stay @ 100% plugged in 24/7, maybe with some cycles to keep the battery from swelling.

I'm really not sure what else it could be.

Thanks again, ill let you know how things pan out.
 

Ya’akov

Joined Jan 27, 2019
6,853
I hope you sort it easily, but just an observation: although the device you linked does look like the device I showed you, nowhere does it say that it supports any charging protocols, and since it has only 5V out, it is not likely to do so.

I have an older Surface, but it uses a dedicated charger. What kind of port are you plugging into? Is it USB-C?
 

Thread Starter

deanfourie

Joined Nov 6, 2022
4
I hope you sort it easily, but just an observation: although the device you linked does look like the device I showed you, nowhere does it say that it supports any charging protocols, and since it has only 5V out, it is not likely to do so.

I have an older Surface, but it uses a dedicated charger. What kind of port are you plugging into? Is it USB-C?
Yea, I noticed that.

Having said that, this thing is so old, I think its before the days of Fast Charging standards.

I'm plugging into a MicroUSB port. It's a Surface 3, not a Pro. I think it was one of the first generation surface deives to hit the market that came out with MicroUSB.

Surface 3 - Wikipedia

For a charger Surface 3 uses a standard Micro-USB, giving users a wider variety of charging options, including charging the device with a mobile phone charger.
 

Ya’akov

Joined Jan 27, 2019
6,853
Yea, I noticed that.

Having said that, this thing is so old, I think its before the days of Fast Charging standards.

I'm plugging into a MicroUSB port. It's a Surface 3, not a Pro. I think it was one of the first generation surface deives to hit the market that came out with MicroUSB.

Surface 3 - Wikipedia
QC2.0 is quite old as well. But in any case it may still need some indication that charging from the supply is OK. I don’t quite understand which thing is working right now. Is it your DC-DC converter?

It would probably be good to use a USB tester to see what is actually happening. A good one is not cheap, though.
 
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