Making external storage work on iPhones with iOS 13

- or, why do I get "too much power" error with my drive and how do I fix it? -

Apple's official Lightning to USB Camera Adapter

With iOS 13, native support of USB external storage was introduced to iPhones. Files stored externally can be accessed from the Files app included in the OS. Other apps can do it as well if it can connect to this Files app. Sadly, modern iPhones' external port of choice is Lightning, which means you either buy a storage device with a Lightning port or get an adapter to connect a USB device. This is where things get complicated.

I bought a Lexar MicroSD to Lightning Reader (part # LRWMLBNL) more than three years ago. It connects directly to the Lightning port and I can open files using a dedicated app. Apple MFI certified storage can supposedly work with the iOS 13's Files app, but that wasn't the case here despite the certification. Adding insult to injury, its app had not been updated in more than two years - the screen resolution and the file sharing functions were outdated. I needed a different solution.

Apple sells many types of USB adapters, one of which is the Lightning to USB Camera Adapter you see above (US$29). It can be connected to a camera for transferring photos and videos, hence the name. Other devices could be plugged in as long as the OS recognizes it, like keyboard, MIDI equipment, or Ethernet adapter. iOS 13 expands this to general storage and mouse.

Plugging in a USB flash drive directly do the adapter results in a "Cannot Use Accessory: This accessory requires too much power" error

So I bought this adapter expecting that any low-power storage devices like USB flash drives and memory card reader could be plugged in directly for my file management uses. Boy was I so wrong. Of the multitudes of flash drives and card readers I own, all of them, save for one, caused the "too much power" error you see here. This was bizarre because they shouldn't consume enough power for this to appear. There had to be a reason and a way around this, so I decided to dig in.

Plugging the USB flash memory into a USB hub first was a good workaround

Someone suggested on the Internet that the error could be avoided if the drive went through a USB hub. While this would actually consume more power, all of the various hubs I owned did enable the drive to be usable on my iPhone. Functionally, the hub-reader combo (the top one on the photo above) would be most useful because I wouldn't need to carry a separate reader. But since this one was too large for my phone case I looked for a more compact version.

Netmate's 4-port USB hub NM-BY226 (left) and the USB-C 2-in-1 multi-hub NM-MCR01 (right)

I found the Netmate NM-MCR01 to fit the bill. It has two USB ports (one 2.0, one 3.0) and separate slots for SD and MicroSD cards in a package the size of an ultra-compact 4-port USB hub. One downside was that it has a USB-C connector instead of the USB-A that the camera adapter uses, so I bought a tiny adapter (COMS ID028) to bridge the two. There's a similar hub from Cosy that uses a USB-A connector (UH3151CR), but for some reason this produced the "too much power" error on both iPhones and Macs that I owned, and thus unusable for me.

The multi-hub lets me open files from a MicroSD card (left), and also use a USB flash drive at the same time (right)

With this hub attached to the camera adapter, I could easily connect memory cards (SD and MicroSD), USB flash drives, and other USB peripherals - individually or simultaneously - for use on my iPhones. It was like using a computer - something Android OS phones could do since early on. The catching up was long overdue.

Kingston Digital Multi-Kit/Mobility Kit - the look of the packaging (left) and how the card reader plugs into the camera adapter (right)

Meanwhile, there was a claim on the Internet that a certain memory card reader was compatible with the camera adapter and no hub was necessary. The device in question was Kingston FCR-MRG2, a thin and tiny MicroSD card reader barely twice the length and thickness of the card it works with. At the time of the writing, it was cheaper to buy it in a bundle - part # MBLY10G2/16GB had the card reader, a Class 10 MicroSD 16GB memory card, and a MicroSD to SD adapter all for US$4.99. After waiting about two weeks for it to arrive, I plugged the reader into the camera adapter and found it indeed working quite well without any errors. MicroSD cards of various makers and sizes all worked, including a Samsung EVO Plus 256GB card shown earlier.

A USB hub reports that 100mA is required for use (left), while a USB flash drive that causes the error wants 200mA (right)

With "what" to use solved, I wanted to know "why" this was happening. The camera adapter is said to be able to provide up to 100mA current on its USB port. When I checked the status of the USB devices on my iMac, I discovered that all the USB hubs reported its required current as 100mA. The one flash drive that worked with the adapter reported 100mA, while the Kingston card reader reported 98mA. So all the natively working devices were at or under the maximum value.

On the other hand, most of the other USB flash drives and memory card readers reported its requirement to be at least 200mA, and some were as high as 500mA. This is not necessarily how much current that the device is actually pulling, but iOS is apparently checking this "current required" value and preemptively disabling the device instead of checking its actual power usage. Interestingly, iOS doesn't seem to check this value beyond the device it interfaces with first. Therefore the devices attached to a hub has its current requirements effectively hidden. You can see on the picture above that the hub's requirement remains at 100mA despite connecting a drive with 200mA requirement on one of its ports. This is "why" the hub workaround worked.

Since you can't manually modify a device's current requirement value, your best bet for connecting an external storage to an iPhone via the camera adapter is to use a USB hub in between. The facts that you can connect multiple devices with it, or add additional power source (if the hub supports it) are also plusses. If you want a much more compact solution, then you should get that Kingston card reader or find a reader / drive with low (100mA or less) current requirement by yourself.
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