iPad charging: can conditions make the "charging" status show but not actually charge the device?

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
This one has a lengthy intro, so bare with me:

I fly an aircraft that uses this device to provide power for an iPad.

https://www.aircraftit.com/Uploads/ContentPages/CMS/Documents/Clara/Tablet-EFB-Systems.pdf

The device states it is made for iPad, and carries the “made for” stamp on it.
However, we have noticed different behavior between different iPads when plugged into this module. Assuming equal charge, OS, same apps opened, some will produce a charge while others won’t.

More specifically:
  1. They show the lightning bolt “charging” notation; and
  2. Some (whether used or asleep) will show a verifiable increase in state of charge; or
  3. Some (whether used or asleep) will show a noticeable decrease in charge; or
  4. Some (whether used or asleep) will remain static at whatever battery level it had when attached.
  5. None of the iPads mentioned here had a problem with the OEM 12W block plugged into a standard 110 outlet.

I know the apple OEM adapters are power supplies that (at least for the iPhone) take two passes at making AC to low voltage DC—smoothing and regulating it.

I haven’t gotten a USB tester inline on it yet to see what the voltage is. I was looking at some inline USB testers on amazon, by X-dragon.

So:

  1. If the voltage tested isn’t 5.1 I can assume it’s not doing it’s job. I had a home outlet that couldn’t put out a steady 5 for my iPhone and it wouldn’t hold the charge icon—fluctuating.
  2. What if it tests 5.1VDC and isn’t smooth on that device? Can I even detect that?
  3. If it isn’t smooth—could that be enough to interfere?
  4. HOW MUCH voltage is required to produce the “charging” message on the iPad? Is it amps or voltage?

I know it's clumsy but that's all I have for the moment.

Any thoughts are appreciated.
 

Dodgydave

Joined Jun 22, 2012
9,910
This can happen with a faulty usb lead, the cable becomes high resistance to charging, . Try different leads on each socket.
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
So, I put my bench DC power supply through a USB meter, then on to my iPad.

One it was charging and showing about 5.2 V and around .9 amps I reduced the current and got it to stop charging.

Re-raising the values did not initiate charging again. I had to remove and re-insert the lightning cable into the iPad (without adjusting the bench supply) at which time the charging started back up.

So, it makes me think the internal charging logic in the tablet needs to zero out before it can begin again--when an error is detected.


Does that sound like a fair (albeit temporary) hypothesis? This makes me think the OT charging device I mentioned has some unstable voltage or current, causing the disconnect in charging.

And, we've found that turning off the charging device and re-powering it will fix the problem and begin charging.


thoughts?

trying to talk to Apple engineering to see if such logic is inside.
 
maybe this https://store.rossmanngroup.com/f4-nxp-610a3b.html explains it.

NXP 610A3B Tristar IC for: iPhone 7, 7+ as U4001. Also compatible with 6S, 6S+, SE, iPhone 5S, iPhone 5C. It will NOT work in an iPhone 5! This IC talks to the charger before allowing it to charge the phone, and often causes slow charging, no charging, or death after being plugged into a fake charger.

It does say iPhone and not iPad.

https://support.apple.com/en-us/HT201569
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
Yeah, there are several IC #'s for the different devices. The question is, do they have some sort of built-in protection that requires a "re-boot"?

(see post #4).

Because we've tested about 10 devices using the apple cords, they were all varying in "charging" or "not-charging" when plugged into this device: http://utcaerospacesystemsefb.com/images/uploads/documents/Tablet_Interface_Module_(TIM(R)).pdf

In each case, resetting the power (unplugging or turning off that module) would fix the issue.

So, I'm trying to determine if it's one of these:

1. the cables are doing their job, and fluctuations in power put it I that "you gotta re-boot" condition. In this case it means the power is dirty from that device (most likely).

2. the cables have been damaged--the IC's in them have been damaged--and as long as the power from that module isn't "excessive" you get the "charging" or "not-charging" at different times, but your device is not damaged.

I ran this up to engineering at Apple, and I'm waiting for a turn around response from them. Tech support was not familiar with this sort of thing.
 
Note, that you have two ports and they are DIFFERENT. There is a 0.5 A port and a 2.1A port.

So, I'll tell my story. I have an ancient Motorola phone and a lot of chargers wont works at all. There is a special data cable that can enable faster charging rates.

The phone could use a new USB port and some chargers fit loosely. The battery contacts are not the most stable in the world either.

One device I bought could plug into 120 VAC or a lighter socket. The ports aren;t labeled but there was a mention of the capacity. They are labeled now. The 2.1A port will charge a Garmin UPS, but not the phone.

So, which port is used matters. That might be your "no charging" condition.

The phone will occaisionally develop a "no boot" condition when doing the "charging dance". I must pop the battery to boot. "charging dance" is plugging in etc. This is likely due to the loose connections. Just yesterday, I increased the size of the battery by 0.01" with two layers of Kapton tape.

I found that a "right angle" pigtail tends to work a little better.

So, I have 3 chargers: one in the bedroom, one in the living room and one in the car. The car versions give me the most trouble. They break.

1) cables - stress.
2) Power fluctuations. Typically Chinese. One charger died after the car was jump started.

I also have a "stand alone" charger where I can take the battery out of the phone and charge it. yesterday, mom had an AM radio on and I plugged in the charger. There is lots of EMI. It was bought from Aliexpress. I did not find another problem until after the "warranty" was up. It's a different type of "loose connection" problem. The 120 plug doesn;t meet specs. It's too thin.

I do like the "battery specific" cases. But this charger has some display, but it's impossible to see, it's like a plug-in wall wart and eye visible outlets are few and far between. The frictional nature of the charger makes it easy to loose contact when re-positioning.

The ancient phone uses the micro USB connector which has the OTG capability or "charger only" capability. That side has 5 pins and the USB connector has 4. Pull-ups to the data line set the max charging current.
These are basically in the cable itself.

One of my older phones supported 0.1 A, 0.5 A and 1 A. So, you get 0.1A if the resistors in the cable are not in place to support the higher rates. I think the phone schematic didn;t really enable the 1A rate, I think that was an older Motorola phone.

Other issues, with yet another phone. The Motorola V3 and V9. These phones had the older micro USB connectors and didn;t support automatic two-way master/slave selection. That said, I could use the phone in data mode forever without incident. it would continue to charge.

The Backflip which is the "ancient smart phone" doesn't seem to charge from the Laptop and do data at the same time. It always runs out of juice. I even tried an isolated USB adapter where I powered the phone from the car side and not the USB port. So, it just dies.

Even though we are talking literally about Apples and Oranges, my experiences seem to mimic yours;

If there is nothing to tell the phone that higher power is available, it tries to charge at the lowest 0.1A rate.

Look at a description of OTG: https://en.wikipedia.org/wiki/USB_On-The-Go

I don't think the issues are surprising.

I asked for help from Apple once and I've never bought an Apple product since because of their additude.
The warranty was just about up on my iBook clambshell and i did cause our department to exclusively switch to Apple. (Windows 3.1 vs Mac OS 9) The software I needed was labView and it was transitioning to multi-platform. It was developed for the MAC initially, probably because of the graphics. The flat memory model for the MAC and the long filenames vs 8.3 for the PC, it was an easy choice. The rest of the office needed the MAC for desktop publishing for scientific journals.

I had modem issues and I could make the modem disconnect at will just by sending an email containing ATH$ over a PPP modem connection. I could not get past the gatekeeper at Apple.

The command it was supposed to respond to was <silence>ATH$<silence>. I had to suffer got 6 months until Apple released new firmware for the modem that fixed the problem.

There was a software company that was hesitant with issues we had with their software on a Mac Centris. They sent us a special "debug version" of their software and they found the bug.
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
Good info. That’s a lot.

No I checked the ports. I’ve never mistaken them.

And getting the “no charge” can be fixed by cycling the power in the module. No cable tugging or shifting required.

Cycling the power fixes this.

I keep circling back to bad power from this module and a touchy-feels IC on the lightning USB cord causing be to restart the module each time.

I’ll put a usb meter on the module on Tuesday to see if it fluxes at all while being used.

I have been searching for Tristar U2 info on what are it’s features. That’s proving to be difficult.
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
*update*

I got a hold of a more expensive USB-meter, but the results were telling.

1. The voltage at the charging port was 5V.
2. The amps pulled by the iPad were appropriate for the tablet's level of charge (closer to 100% = less and less draw)

Here's where the problem was:

1. among all the reports of problems no one ever indicated "when" they started charging. Some habitually plug right in, and others wait until it's needed.
2. When the aircraft power was switched from an outside power source to the internal power (engine on) there is a brief interruption to the charging port.
3. the logic ICs (two in the OEM cable and one in the tablet if I read correctly) no longer have the conditions they agreed upon to start charging.
4. the only way to get around it is to start the handshake over.
5. the only way to do that is pull out and re-insert the lightning cable.
6. then all is well again.

However,

1. when the iPad was using it's Apple adapter, plugged into a nearby 110 outlet (and not using the USB), and the power was switched from external power to internal power...nothing happened. It worked just fine throughout.

How is this for a suspicion?

The apple adapters use several steps to get from high AC to 5V DC...smoothly.
This power interruption I mentioned--it's probably less than 1 second.
Could the capacitors that are providing a constant smooth DC flow have enough in there to make that power interruption unnoticeable to the iPad?

Using the USB = power interruption fouls it up.
Using the AC = power interruption has no effect.

And, both that AC outlet and the AC source for the USB charging port come from the same AC buss in the electrical system.


????


As alway, many thanks.
 
Not bad for an investigation. The results are not surprising at all.

It's really all based on the reset threshold and without the datasheet on the charging IC, your lost. I just picked a chip out of the hat and not even the right manufacturer.

This http://www.ti.com/lit/ds/symlink/tps2540.pdf IC defines an Undervoltage Lockou UVLO of around 3.9-4.3V. Not a lot.

It also says:
Longer Detach Detection Time for a particular version (TPS2540A/41A) for support of more legacy devices.

It might be something you can address with Apple.

Cars, for instance, kill everything except the headlights when the starter is engaged. Accessory power turns off too. Lights are fed from a fuse or breaker direct. Who knows how the new fangled cars work.

So, the state of charge also matters.

So, let me propose a solution which the MFR of your FAA gizmo could implement. See http://www.analog.com/media/en/technical-documentation/data-sheets/610912fa.pdf#page=25 for a precision power on reset circuit.

It might even be possible to build it externally.

Look at this URL https://ipadpilotnews.com/2018/03/charging-your-ipad-what-you-need-to-know/ and the Stratus link: http://www.sportys.com/pilotshop/stratus-powertm.html?utm_source=ipadblog&utm_medium=referral (also FAA certified) may have figured out how to do it.

You also might want to look at the amount of time the aircraft DC bus drops to during the switchover.



®
Supporting
Additional
Legacy
Devices
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
Not bad for an investigation. The results are not surprising at all.

It's really all based on the reset threshold and without the datasheet on the charging IC, your lost. I just picked a chip out of the hat and not even the right manufacturer.

This http://www.ti.com/lit/ds/symlink/tps2540.pdf IC defines an Undervoltage Lockou UVLO of around 3.9-4.3V. Not a lot.

It also says:
Longer Detach Detection Time for a particular version (TPS2540A/41A) for support of more legacy devices.

It might be something you can address with Apple.

Cars, for instance, kill everything except the headlights when the starter is engaged. Accessory power turns off too. Lights are fed from a fuse or breaker direct. Who knows how the new fangled cars work.

So, the state of charge also matters.

So, let me propose a solution which the MFR of your FAA gizmo could implement. See http://www.analog.com/media/en/technical-documentation/data-sheets/610912fa.pdf#page=25 for a precision power on reset circuit.

It might even be possible to build it externally.

Look at this URL https://ipadpilotnews.com/2018/03/charging-your-ipad-what-you-need-to-know/ and the Stratus link: http://www.sportys.com/pilotshop/stratus-powertm.html?utm_source=ipadblog&utm_medium=referral (also FAA certified) may have figured out how to do it.

You also might want to look at the amount of time the aircraft DC bus drops to during the switchover.



®
Supporting
Additional
Legacy
Devices

Whoa thanks for all that.

I tried a different aircraft today and found that this one didn’t hit the threshold during power transfers. The iPad drew current throughout and didn’t require a reset.

This would explain why some folks have experienced issues off and on in a given month. The generator control units GCU could be different generations from different manufacturers depended on where the aircraft came from—all still approved though.

Gonna go read those links you put up.
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
Here is another curious bit:

During all those power interruption tests, when the voltage comes back to 5.xx, and the amps are showing down around .05, I noticed the iPad was still displaying "charging" with the lightning bolt icon.

The USB meter pulls about 20 milliamps to operate.

Q1. What triggers the "charging" icon? voltage pending or actual amps?
Q2. I know the iPad won't charge (certainly not with apps open) on .05, so is that an artifact or actual iPad pull?

I'm just trying to find a reliable way to describe the appearance of that "charging" message when the rest of the device isn't performing. It would be helpful to explain what actually triggers the indication at the top of the screen.
 

wayneh

Joined Sep 9, 2010
16,769
Q1. What triggers the "charging" icon? voltage pending or actual amps?
I believe the icon is similar to a “connected” indicator. I suspect it triggers on voltage but I’m not certain. It does NOT indicate a successful handshake to begin high-current charging. So it might indicate charging while current is actually limited to 100mA or less. I’ve seen my battery percentage (on my iPhone) drop while the indicator is showing.
 
This https://www.diodes.com/design/suppo...usb-charges-just-about-any-electronic-device/ I rhink offers something to the mystery in this statement.

For example, per BC1.2 the USB port will detect the PD only once—typically when the device is plugged in. What happens if the device remains plugged in but needs a fast charge some time after its initial charge? Beyond unplugging the PD (which is what most of us do), some smart chargers can mimic a re-plug by generating the Vbus +5V if the device so requests. This starts the enumeration procedure without having to disconnect the device.

Disconnecting devices during charging can potentially result in voltage spikes, shorts (frayed cables), and other transients that can affect the charge IC, the PD, the battery, or all of them. Some nice-to-haves in an intelligent charge controller include:
See reference.
 
This https://patentimages.storage.googleapis.com/0a/f0/3f/9ed3840932907a/US7631111.pdf patent, I think explains a lot of the nuances.

So, in reality, some IC's may work better than others. Forcing a reset may work. The workaround is likely re-plugable USB connector after an APU (Auxilary Power Unit) transfer in either direction.

You could get a couple of breakout boards and breadboard a switch on +5, so you just push it. It would be the same as plugging and unplugging, but with less connector wear.

I still think the force reset suggestion has merit.

Your getting a "false indication" of the state, which is bad. You have good reasons why that happens. The system may enumerate once and/or your not getting a sufficient reset. Unplugging and re-plugging the USB connector causes an enumeration.
 

Thread Starter

ThirtyWest

Joined Jul 15, 2017
140
USB lore is a rabbit hole to read!

So yes, the VBus 5 fluctuation kills enumeration and puts the iPad on suspend.

Right now I’m tasked with “why”. I like those ideas too.

One question I need to learn about is why that power transfer—which affects every electrical bus there—doesn’t affect the 115AC outlet that happens to be on the wall for things like cleaners to use a vacuum. I tested that outlet using the 12W iPad brick.

That gets the same flicker but it never hits the 3ms threshold.

Is that because the iPad brick has a enough charge due to capacitance (it’s whole complicated smoothing /flyback process)to last across those 3ms and essentially never show a VBus falling edge?
 
I'll throw this out. i(whatever) generally means small, so I'd agree with you to a degree that the power brick probably has more reserve. It's also possible that the 120 VAC is made by a motor generator and there is some inertia as well. The brock prabably also starts at 85 V. The low end of the input voltage is 85 Volts because 100-0.15*100 = 85. 100 VAC is used in some parts of Japan and typical tolerances are +-15%/
The brick could have larger capacitances.

It may actually put the blame on the interface module. The 24 VDC bus might not be able to make 5V from something smaller.
Relay switching times can also play a part.

The manufacturer might want to fix it properly given a set of conditions, but he probably doesn't actually have an aircraft and APU to test with.

Concurrent Measurements of Vbus and the 24 Vdc aircraft bus might help the manufacturer of the interface,

A friend had to replace a Tek scope and he bought this https://hackaday.com/2017/11/09/review-jye-tech-dso150-oscilloscope-kit/ single channel scope for peanuts. It is single channel, though,
 
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