Edited 3/28/2020 to add measured power data for both battery charging and tethered shooting.

Olympus, to their credit, has finally been replacing their old proprietary USB camera cable interfaces with USB-C on more-recent OM-D camera bodies. But until the E-M1X was released in early 2019, this just provided a data interface — for things like firmware updates, and file transfers.

With the E-M1X, Olympus began to use USB-C as a power interface as well — for battery recharging, and for tethered power supply to the camera. Olympus took a middle ground with the E-M5III, using USB for data and battery charging (but not tethered power, and even then using an old-school micro-USB connector). More-recently, the E-M1III followed the E-M1X‘s example in using USB-C for data, battery charging, and tethered power supply.

I’ve recently seen confused exchanges online about the uses and limitations of USB-C with the E-M1III — so as a card-carrying geek, I thought I should attempt to clear things up a bit. But first, you’ll need some background — so find yourself a comfortable seat and a warm beverage, this won’t be a fast read.

A quick tangent about units

We’re all familiar (at least to some degree) with the concept of voltage in electricity — it expresses the electrical potential of something, roughly analogous to pressure in a water line. Current, measured in Amps (A) or miliAmps (mA, 1/1000 A), measures the flow of electricity, like gallons/minute or liters/second or whatever for water. Electrical power, measured in Watts (W), is just voltage multiplied by current — so, 1 W = 1V * 1A. Electrical energy is power multiplied by time.

Unfortunately, vendors tend to use these simple units inconsistently in their advertising text, making it even harder to decide if their gadget will answer your needs. But more on that later…

USB: first a universal connector, then a universe of connectors

The first version of the USB specification (USB 1.0) was released by a consortium of seven technology companies in 1996, in an attempt to simplify the host of interfaces and cables (many of them proprietary) used at the time for low-speed computer peripherals. USB 1.0 (and later 1.1) allowed for just two data speeds for connected devices — 1.5 Mbits/sec and 12 Mbits/sec — over 4 wires in a “dumb” (no circuitry) cable. Everything connected to a computer with a 4-pin USB Type A plug, no provision was available for providing significant power over USB 1.x cabling, and that was all OK since USB 1.x was primarily used for computer mice and keyboards and such.

The USB 2.0 spec was released in 2000, and introduced a third data rate (480 Mbits/sec) and additional connector designs, which now allowed for provision of limited power over the interface. The release of USB 3.0 in 2011 brought more wires, more connector pins, the potential for smart cables (with circuitry built into their plugs), and much higher speeds — first 5 GBits/sec, then 10 (with USB 3.1 in 2014), then 20 (with USB 3.2 in 2017), and now USB 4.0 gives us up to 40 GB/sec.

Somewhat in parallel with the increases in data speeds, a separate spec was developed by the USB Implementer’s Forum — known in shorthand as USB PD (for power delivery) — and released in 2014. Where USB 2.x and 3.x only allowed for power supply at 5V, USB PD allowed peripherals to negotiate with their power sources for higher voltages (9V, 15V, and 20V). And yet another connector was introduced — the USB-C — intended to be the only USB connector going forward.

So basically, two desires have pulled USB in different directions — one, to higher data rates and a wider set of uses, the other to converge again on a single USB connector in order to simplify the mess of USB cables people currently need for all their devices.

USB-C, and the mess we’re in

In many ways, the USB-C connector, USB 3.x / USB 4.0, and USB PD are all good things when taken separately. The USB-C connector supports all kinds of uses — power delivery, high-speed data, old low-speed device support, etc. — and doesn’t require the user to align it just so to insert it in a port. The USB 3.x and 4.0 specs allow the interface to handle a variety of data types, even high-rate video. USB PD allows the USB interface to provide useful levels of power (currently up to 100W) to power and charge peripherals of many types.

The first place where this all gets tangled is in the cabling (pun intended). Most USB-C cables can’t support both high data rates and USB PD levels of power. Since vendors are pushing toward universal use of the USB-C connector, different connectors can’t be used to distinguish data-optimized vs. power-optimized cables. Meanwhile, there is no standard (at least that I can find) requiring or even encouraging labeling of cables w.r.t. their capabilities. So in the near future, people will likely have a drawer full of USB-C cables, some of which can only do some jobs, others of which can only do other jobs, and there’s no way for the owner to tell which is which (without cable test equipment).

The second thing that trips people up is understanding the power supplies (either AC adapters or power banks) they want to / have purchased. I suspect in part this is because the people writing advertising (and Amazon listing) text aren’t engineers so don’t fully understand the technology. The tendency to pull out big words to make your company’s product sound better is also likely at play. The end result is customers buying things that don’t work for them.

TLDR: Devices can draw low amounts of power over USB using non-PD power sources and cabling, and higher levels of power over USB PD. PD cables all use USB-C connectors on both ends, but any given USB-C cable may / may not support PD levels of power (and it won’t be marked to indicate whether it’s a PD cable, or if so, how much power it will transfer). Power sources (either AC adapters or power banks) with a rectangular USB-A socket don’t support USB PD, but do provide lower levels of power; power sources with a USB-C socket may or may not provide USB PD (but the socket will be marked PD if it does). Cables are currently just a big bag of hurt.

For comparison / summary, here’s a quick table from the USB PD spec showing the limits of USB power over various interfaces (remember, power = voltage * current):

Back to the E-M1III

The E-M1III is a bit of an odd duck when it comes to its use of power over USB. Both battery charging and tethered power supply occur with a USB cable using a USB C connector at the camera, but they work differently and have different constraints. For instance, the USB cable that comes with the camera can be used for data transfer or battery charging, but not for tethered power. It doesn’t help that for no apparent reason, the manual for the E-M1III requires you to look in two widely separated places to learn how it handles power from USB.

Battery charging in the E-M1III is old-school (see p. 22 in the English language manual, original 2020 release), analogous to how the E-M5III works. Regardless of whether your power source has a USB 3 or USB-C socket, the E-M1III appears to draw no more than 6 W while charging (my measurements show charging from USB C to draw 9V @ 0.65 A for 5.6W, and from USB 3 to draw 5V @ 1.2 A for 5.9W, although the numbers fluctuate during charging). In either case, charging via USB won’t be as fast as in the camera’s stock (external) charger — but honestly, a lot of 3rd party USB-based battery chargers only draw 5V @ 0.6 A or 0.8 A, so in-camera charging is still faster than that. Note that the battery will only charge via USB when…

1. The camera is powered off — and that means really off, so you can’t be doing any of its fancy “Power Off Standby” Wi-Fi tricks (see manual p. 249) at the time.
2. The battery temperature is between 0 and 40 C — although I don’t know if this range is actually enforced by the camera (the temperature limits could just be usage “guidelines”).
3. Only the battery internal to the camera body is charged. If you have an HLD-9 grip / battery holder attached to the camera, the HLD-9‘s battery is out of luck.

Many USB power supplies (those rated at 1A or better) and USB A-to-C cables will handle this task, so you’ll likely not need to upgrade what you already have on-hand if this is all you want to do.

Tethered power for the E-M1III (see manual p. 278) is new to most folks, and (as I’ve pointed out previously) handled differently than is battery charging. You’ll need a cable and power supply built for the USB PD standard, plus they need to provide one of 3 power types:

1. 9 V at 3 A
2. 15 V at 2 A
3. 15 V at 3 A

There are also (of course) constraints:

1. Tethered power supply only works if the camera’s internal battery is charged to at least 10%.
2. Tethered power supply is disabled if the HLD-9 grip / battery holder is attached to the camera, regardless of whether or not it’s holding a battery (the USB PD option is grayed out on the camera’s normal USB mode screen).

Using my RAVPower power bank, my E-M1III only draws 9V @ 0.46 A for 4.12 W while recording video — presumably some other mode draws enough power to drive the 3 A requirement, but I haven’t found it yet.

So what do I need to buy?

For in-camera battery charging, nearly any USB AC adapter / power brick / cable will do. Use the USB A-to-C cable that comes with the camera, and an AC adapter or power bank that can provide at least 1A (most smartphones need at least this charge current nowadays).

To support tethered power, though, you’ll need to read device listings / documentation very carefully. For power banks, the battery capacity is usually given pride of place — but that’s of more concern to people powering laptops than cameras. What we really care about is 1) whether the power source supports USB PD, and 2) the voltage / current output capacity of the device. Note that another trick manufacturers use (for multi-port devices) is to advertise the gadget’s total output power — when again, what you really need is the individual ports’ specs.

As an example, let’s look at a power bank that I purchased for my E-M1III — a RAVPower 20000 mAh unit with two ports — one with a USB A socket, one with a USB C socket. RAVPower does an unhelpful thing in their Amazon listing, though — by promoting it as a 60 W Power Delivery device.

Fortunately, they redeem themselves by including per-port power in a separate image.

So the USB PD port can source 45 W of power, while the USB 3 port can source 15 W. Ideally, the item listing would spell out the voltage / current combinations their device can output via the PD port — and some device listings do — but at least with this one, we can take what we know about the USB PD standard (supports 5 V, 9 V, 15 V, and 20 V) and fairly safely assume that the 45 W output spec for the port means either 9 V at 5 A or 15 V at 3 A (either is plenty for the E-M1III).

Summary and recommendations

Remember the list of power types the E-M1III will accept for tethering? Lets turn them into power levels:

1. 9 V at 3 A -> 27 W
2. 15 V at 2 A -> 30 W
3. 15 V at 3 A -> 45 W

So I think it’s safe to say that if a power bank outputs at least 30 Watts from its USB PD port, and the cable you’re using is rated for 30 Watts PD, your E-M1III will be happy running from it. A 45 Watt PD source gives you some margin, though, so I’d recommend it.

As for USB-C cables, I’ve taken to labeling them myself — just as soon as they come out of their packaging — with their power and / or data capabilities (which ever is known). Most of the USB-C PD cables I’ve come across only handle USB 2.0 data rates (480 MB/s) rather than the high rates that non-PD cables can provide — so it’s good to keep PD cables separate from the ones you need for high-speed transfer. Note that Thunderbolt 3 cables can provide both high data rates and PD, but they’re stiff, short, relatively expensive, and vary widely in their power capabilities (read their specs carefully).

By the way, if you prefer learning this sort of material via video rather than in text, Rob Trek has a good one on YouTube (make sure to read the comments).

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