poe - Jiri Brejcha

How to power any 802.3bt Wi-Fi access point using standard USB-C battery pack

I’ve been on a mission to fully power my Wi-Fi demo kit using a standard USB-C battery pack. That way I don’t need to worry about power sockets and power cables with the right plugs. I can temporarily install the AP at the exact location where I want it, power up my AP anywhere, and get work done while I am travelling.

With battery pack detached from the power injector, I can replace the battery back in case I need longer battery life. And when the battery pack loses capacity in few years, I can just swap the battery pack out. If I spot an AC 230 V socket nearby, I can just use a USB-C GaN charger instead and use the battery to fast-charge my phone or laptop.

“So what are your requirements?” you might ask. The solution should power a high-end access point using UPOE, 802.3bt, PoE++, PoE+++ (pick your favourite name) and allow it to negotiate up to 10 Gbps multigigabit Ethernet on its uplink. And I will take 4 hours of battery life, please.

Let me share the solution with you first. If you are interested in the (rather long, expensive and painful) journey, scroll all the way down.

It works! Here is how I use it.

Yes, yay, hurrah, sláva! It works great and does exactly what I wanted it to do! I guess you can feel my level of excitement 😊

I’ve been testing several outdoor point-to-point links. While I can power the infrastructure side AP by a PoE capable switch, I can now easily use a USB-C battery to power the remote C9124AXD AP.

Battery-powered C9124AXD outdoor access point

Let’s enable site survey mode on this large public venue CW9179F access point for a couple of colleagues. Shout-out to you, Olu and Pete. I put a quick guide together on how to enable site survey mode. Make sure that your site survey AP is only used temporarily by a trained engineer and clearly labelled as site survey equipment. It can’t be used in production by any clients. From compliance perspective, the 6 GHz LPI AP can’t be battery-powered.

USB-C battery pack delivering UPOE power to Cisco CW9179F AP

When I was measuring difference between dipole and directional patch antennas connected to CW9163E, this allowed me to easily mount the AP wherever I needed it. No strings attached. Yes, I did use a longer cable and a tripod.

The CW9176I happily ran for about 3.5 hours. No reliance on 230 V sockets. Keep in mind that LPI restrictions apply, 6 GHz capable LPI AP can’t be powered by a battery.

Mobile Wi-Fi 7 CW9176I AP running in full power mode

Now, how do you join an AP to Dashboard and perform few quick configurations? You plug it in your switch, right? But what if that switch doesn’t support PoE (yes, those still exist)? I only had a small battery pack in my bag, but it still worked like a charm and gave me 1 hour of battery life.

CW9179F powered by 802.3bt using smaller USB-C battery pack

But how? Where did you buy this thing?

I tested many power injectors. Scroll all the way down if you are interested in the journey. This is the best solution that I could find for me.

Let me introduce you to Phihong POE90D-1BTP-R power injector. It takes 20-55 Volts DC on the 3-pin terminal block input and provides 802.3bt 90 W on its PoE output.

Phihong POE90D-1BTP-R 802.3bt 90W 2.5 GbE power injector

The battery packs I use are Anker A1336 (20,000 mAh). Potentially Anker 533 A1256 (5,000 mAh), but it has significantly lower capacity, and you would be pushing it to its limits with regards to power.

Always make sure that the battery pack can comfortably provide more power than the AP requires! They important part is that your battery must support 20 V on the USB-C output. Not all of them do. Check the data sheet.

Anker A1336 battery pack powering Phihong injector

Negotiation of 20 V with the battery pack is job for a USB Power Delivery (PD) trigger cable. It has a built-in chip inside the USB-C connector which tells the battery pack to supply 20 Volts.

20 cm USB PD trigger cable programmed to request 20 V

Wi-Fi is a discipline of engineering and art. So, here comes the art part! Let’s trim the trigger cable to the right length. We will keep the part with USB-C connector and keep the barrel jack with a bit of cable for another project.

Let’s terminate it onto the 3-pin terminal block of the injector. Take a deep breath. Double-check polarity to avoid any magic smoke escape moments.

USB PD trigger cable connected to injector

Finally, why don’t we make the connection aesthetically pleasing and permanent using about half sachet of black Sugru.

Cable connected to terminal block and protected by Sugru

That’s it.

All I need to power any 802.3bt access point by a USB-C battery pack

Tested access points

I am using about 2 meters of twisted pair CAT6 cable in total.

Outdoor C9124AXD and CW9163E APs worked absolutely fine.

To test backwards compatibility, Catalyst C9105AXI worked great too and used its 1 Gbps uplink.

The only valid reason for powering Wi-Fi 7 LPI APs is for site survey purposes as I mentioned above:

Cisco’s CW9176I access point as well as CW9179F large venue AP both negotiate 10 Gbps Ethernet connection. If you need a significantly longer twisted pair cable, you might want to test it first, since this injector is officially certified for 2.5 Gbps Ethernet.
Powering CW9172H wall plate access point was no problem at all. Ethernet port ran at 2.5 Gbps and the PoE Out port of the access point happily powered my WLAN Pi M4+.
Likewise, CW9172I access point negotiated at 2.5 Gbps and CW9174I ran at 5 Gbps.

If you tested any other models and vendors, share them with us in the comments below.

Incompatibility with Meraki MS220 switch

Depending on your use case, you will likely never run into this and your injector “DATA IN” uplink port will have no cable connected in it.

When I connected the 802.3bt injector uplink to MS220 switch, many of the APs switched to 802.3at “Medium Power” mode. I suspect there is something going on with LLDP negotiation between the switch and the AP. The AP doesn’t figure out that it’s actually powered by an injector and it ends up defaulting to Medium Power 802.at mode.

Most APs fall back to 802.3at mode when connected to MS220

When I connected the injector uplink to a different switch like C9200CX, the access points drew full 802.3bt power from the injector.

Fully powered by injector, injector uplink connected to C9200CX

AC vs DC power injector

Here is side-by-side comparison of Cisco’s official 802.3bt 60 W power injector CW-INJ-8 with AC input to my 802.3bt 90 W battery-powered DC injector. Power socket not shown in the photo 🔌 There wasn’t any socket where I took this photo! 🤷🏻‍♂️

AC power injector CW-INJ-8 vs Phihong battery-powered injector

There are purpose-built site survey PoE battery packs available from the great people at AccelTex and Ventev.

Use whatever works best for you or your customer.

The journey

This is one of the very few projects when I’ve nearly given up. I purchased and tested all of these injectors hoping that the first, second, third, will hopefully work and I kept fast-failing again and again.

“Success is not final, failure is not fatal: it is the courage to continue that counts.” Attributed to Winston Churchill.

Few hundred pounds later, I thought I was done. Nothing seemed to work the way I wanted it to.

The industrial Procet injector on the left only provided 802.3at power although it was supposed to support 802.3bt. Their documentation was also extremely poor with conflicting information about input DC power range, they were heavy and not necessarily of the best form factor.

Few weeks later I ordered the Planet industrial injector but it only provided 802.3bt power to high-end CW9176 and CW9179F access points and failed to power CW9172I and CW912H APs completely.

I found this Phihong injector data sheet online but it was out of stock in the UK. I just couldn’t win! It was about time to get out of this rabbit hole and see what was the best way to deal with all of this. I contacted the manufacturer, who kindly helped me find a nice local distributor Heading Power Limited who had one in stock and the rest of the story you’ve just read above. I just had to figure out how to power it and connect everything as nearly as possible. Happy days!!!

To paint the full picture, the 2 injectors on the right were my shot in the dark into the 802.3at (the 30-Watt standard) world. I love the right-most PoE Texas 802.3at injector so much that it found its place in my every day bag. If you are looking for a light and compact injector and don’t mind 802.3at, read more about it here (I will add link as soon as I publish it).

The safety and regulatory part

You are all smart people but let’s get the safety warning out of the way first.

Since we are modifying electrical equipment and dealing with batteries, please note that you are performing everything described in this blog post at your own risk. None of the hardware manufacturers and other parties including myself can’t be held responsible in case of any damage or harm caused.

Use caution when it comes to 6 GHz. Lower Power Indoor (LPI) 6 GHz access points shall not be battery-powered. Refer to EN 303 687 and FCC KDB 987594.

Unboxing Cisco 802.3bt 60W PoE power injector CW-INJ-8

To enable full radio capability of some of the latest access points, 802.3bt power source is required. If you don’t or can’t have a 802.3bt capable switch, power injector might be the right choice for you.

For Cisco’s CW9179F, CW9178I, CW9172H, and other APs, the correct injector is CW-INJ-8. It takes AC power and injects 802.3bt Type 3 Class 6 (up to 60 Watts) into your twisted pair copper cable, and it is designed for up to 10 Gigabit Ethernet.

Apart from documentation, there is just the power injector in the box. If you don’t have one in your “box of cables” already, order an IEC C13 power cable separately. It is not included.

When is injector not the best choice?

Here is my rule of thumb. If you can, power your AP using a switch. Why? Power injectors in general introduce extra points of failure. Unlike switches, they can’t be remotely monitored or controlled.

Now, if there is no switch available, use a power injector. Site survey, assuming that AC power or battery pack with inverter is available, is another good use case. Or lab use – for when you don’t have a 802.3bt switch.

Hardware overview

There are no surprises on the top side. Note the LED on the top right.

Here is a quick look at the label.

The injector has RJ-45 input, RJ-45 output, and AC power connector which accepts standard IEC C13 cable.

Status LED

Solid green LED indicates that a valid IEEE 802.3bt or 802.3at AP is detected, and the AP consuming PoE power.

Very occasional flashing green indicates that AC power is provided to the injector itself. Don’t expect it to be solid green with no AP connected.

Let’s test it

Microchip makes this pocket-sized PoE tester. Let’s see what we get at the output of this power injector. As we expected, 802.3bt Type 3 Class 6 (up to 60 Watts) it is.

Official documentation

Always refer to the official documentation, please.

How to power Cisco Meraki MR access point by USB-C battery pack

Battery-powered access points are typically used for site surveys. The engineer uses a professional battery pack with 802.3at/802.3bt PoE output which delivers power to the AP via Ethernet. I do love professional battery packs. Accelerator and VenVolt are your friends. I haven’t had a chance to test either one, but I’ve seen them in very capable hands of others.

Now, when you don’t have a PoE battery pack by hand and want to achieve a similar outcome, this tip might help you.

Use case and requirements

I am building a compact pocket-sized package consisting of an AP, small battery pack and I want to achieve at least 2-3 hours of battery life.

What am I going to use it for? I need to temporary install (and hide) an AP which we will then locate during my presentation using WLAN Pi Go – a mobile Wi-Fi tool which snaps magnetically to iPhone.

In the coming weeks, I am going to use the same setup for point-to-point Wi-Fi testing. So, this will help us kill two birds with one … battery pack I guess 😊

Solution

Cisco Meraki APs do have 12V DC input via barrel jack 5.5 mm x 2.5 mm connector. I then researched USB-C battery packs with USB Power Delivery 12V output. This part is important! Not all USB-C packs support this output voltage.

Finally, I found a USB-C PD cable which negotiates 12V with the battery pack, and outputs 12V DC to the AP’s barrel jack input.

I run the APs in Site Survey mode. To enable this mode connect to this AP’s SSID in normal cloud-managed mode, and browse to the Local Status Page (LSP). It is powered by a web server running locally on the AP. Access LSP via http://10.128.128.126/ while associated to the AP. I do recommend MR32 or newer software release which has some great survey mode enhancements.

Now, it is time to test and see if we can break things. How long does the battery last for? We get 6+ hours of battery life.

Let’s appreciate that the battery pack is nearly 7x smaller in volume than the already compact access point.

Kit list

Cisco Meraki MR20, MR78, or other AP which accepts 12V barrel jack input. Newer Cisco Wireless APs do have a barrel jack connector but they require 54V input. This approach won’t work.

USB-C PD cable with 5.5 mm x 2.5 mm barrel jack connector

Anker 533 Power Bank PowerCore 30W or any other battery pack – just make sure it supports USB PD 12V output, not all do

It doesn’t stop there

Many other devices like routers, modems, home automation hubs use the same barrel jack connector and take 12V input. The main fact to keep in mind is that this Anker battery pack can output up to 12 Volts at 1.5 Amps on its USB-C port. We don’t want to overshoot these 18 Watts.

Incompatible power injector with Cisco Catalyst Wireless CW9166 Wi-Fi access point

Just a very quick reminder that if you power your CW AP using an incompatible 802.3at power injector, you will likely see the AP successfully boot up, but it disables its radios few seconds later. The result is no SSID put on the air.

What to look for in the logs?

If you console or SSH into the AP, you will see this error message. Followed by radio interfaces going down.

set_sys_cond_state: condition critical state 4

condition critical state 4 error message

That’s it. Use officially supported injectors, and save yourself from the trouble I ran into 😊

Portable Catalyst 9136 Wi-Fi 6E demo powered by Zyxel 802.3bt power injector

I am building a portable Wi-fi 6E demo in a box solution. What do I use for that?

PoE powered FriendlyElec’s NanoPi R5S runs iperf3 server. Here a quick iperf3 performance review of this little, 2.5 GbE, and mighty Linux box.

My Catalyst 9800-CL controller is hosted on a cloud, so I don’t need any hardware for that. Finally, my Catalyst 9136 Wi-Fi 6E AP is powered by a Catalyst 3560CX 10 Gigabit Ethernet multigigabit switch.

Catalyst 9136 is Cisco’s premium AP with all the bells and whistles including hexa-radio architecture and built-in environmental sensors for smart building use cases. It requires an 802.3bt/UPOE power source to enable 6 GHz radio in full performance 4×4 MIMO mode. The switch I use supports 802.3at/PoE+, which is great, but 6 GHz radio downshifts to 2×2. And that’s where an 802.3bt power injector comes to the rescue.

Zyxel 5G PoE++ Injector

Cisco’s 5 GbE 802.11bt power injector (AIR-PWRINJ7=) is now available, and that’s my go to option for production use.

Since the Cisco injector isn’t widely available yet, I decided to test this Zyxel one. It provides 802.3bt power and allows the AP to run in full power and full 4×4 6 GHz radio mode with no compromise.

Do I like power injectors in production?

Absolutely not! Ideally you should design for 802.3bt/UPOE switches to power all your new APs via PoE.

It allows you to:

easily, centrally and remotely monitor how much power the APs use
enable/disable power on a port to bounce an AP
leverage redundant Platinum-rated power supplies for the AC to DC power conversion
manage the solution with ease – just think how difficult it is to manage more than 1 power injector, the number of AC power sockets, and what happens when someone disconnects the injector?

I still use C3650 UPOE mGig switch in my lab. Catalysts 9300 and 9400 the best choice these days.

UPOE and mGig capable C3650 providing full power to the AP

Final look

Carrying a full-size switch is not really an option for me, because small form factor is my main goal. So a power injector works best for me. But if I could I would love to use a compact 802.3bt switch.

Are you wondering if the PoE splitter connected to my iperf3 server (the little black box with 3 Ethernet interfaces) actually negotiated 2.5 Gbps Full duplex with the switch? Yes, it did. But keep in mind that the PoE splitter is technically only rated for 1 GbE. So use as short patch cable as possible and ideally CAT6.