Tag: poe

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.

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.

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.

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.

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.

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.

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.

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.

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

That’s it.

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.

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

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! 🤷🏻‍♂️

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.