Powerbot Qi charger baseI wrote a while back on how I’d converted my HTC One M8 into a Qi wireless charging animal and some of the reasons behind doing that. This article is just on how to find a receiving coil, what to look for in a wireless Qi charge solution, and what to avoid.

As I haven’t tried all the coils out there (I’ll be trying three more next week but shipping’s slow), and I’m still on two types of bases (more coming), these are just some general things to look at.

There are three components to a Qi charging solution. These are the power adapter, the base, and the Qi receiver coil. The base unit seems to more often than not to not come with a power adapter, although your product may vary.

Power adapter

Wall adapterThis is the wall plug unit you’ve been probably using the charge your phone. It seems to be a given that people get these and never consider that perhaps the adapter their phone shipped with wasn’t the highest performing quality.

A whole lot of Qi charging bases do not ship with an adapter. They leave that side up to you.

In short, you’re looking for an mA rating on your power adapter. If you want to wirelessly charge at 1000mA you’re going to want something the next step up, probably 1500mA due to conversion loss.

It’s pretty important to remember that your 1amp wall charger probably only has an efficiency of 60-80%, so you’re already not seeing what your charger claims to deliver. I’m just mentioning this because you’re probably going to be looking at charge rates very closely after you start wirelessly charging.

Charging base

While they’re generally referred to as charging pads, from what I gathered at CES this year they’ll be in the shape of buckets, shoeboxes, tabletops, and spoons pretty soon.

You’re looking for an mA output rating and an efficiency rating if they have it. 1000mA=1A, so sometimes on a charger you’ll see something like Output 5V/1A. That is what to pay attention to. It’s always going to be 5V or it’s not a Qi spec charger.

Most charging base have a 90-95% charging efficiency – this means if they get 1000mA in, they transmit 900-950mA out. If you run across one with a rating substantially lower than that, avoid. You’ll turn your wireless charging station into a slow charge event.

Receiver coil

Receiver Coil

The aftermarket receiver coil is generally housed in a square tag that affixes to the back of a unit or just hangs out in a case. You’re looking for three things on this: charging output, connector style, and efficiency. You generally won’t find receiver efficiency listed, it should be ~90% and most coils deliver that no problem.

Many people buying bargain receiver coils find they have a 450-500mA unit and have gone from charging their phone in to to three hours to it taking up to nine hours to charge a completely dead phone. As far as I can determine, the price difference between a crappy receiver coil that does 450mA and a 1000mA universal is $1.

The connector style is absurdly important to note. Unfortunately in the phone ecosphere they put charge ports everywhere on devices. Bottom, left, right, in Des Moine, etc. What’s worse though is they also change the orientation of the ports where what is up on one is down on the other. You can see the different styles of connectors, along with a unit I’m trying, here.

I’ve noticed that some places have it listed as Type A and Type B connectors, but I’m not sure there’s a standard as the two I was looking at that had those definitions used different definitions (one involved cable orientation, the other involved Apple connectors).

If your tag ships with an absurdly long flat USB cable, you’ll want to fold it under the tag (away from the receiving side).

A chain is only as good as its weakest link

Whatever the lowest number you have on any equipment is the highest charge speed you’re going to get. 2000mA charger, 2000mA base, 500mA receiver coil = 500mA charging.

500mA charger, 2000mA base, 1000mA receiver coil = 500mA charging.

You see where this is going.

There’s no 100% efficiency

You can read over on the Wireless Power Consortium page a lot about charge rates and loss. From what I can tell from the wall to the phone the difference between wired and wireless is between 10 and 30%. With my current setup I’m seeing a loss of about 13% which results in an increased full charge time of about 20 minutes.

I’ll be switching receiver coils shortly from a 750 to 1000 and see what that gets me.

Wasting all that electricity for a gimmick

We’ll assume we’re wasting 30% juice to charge wirelessly. That’s the high end of loss as far as I can tell.

Going by Lifehacker’s guide (since I’ve misplaced my Kall-a-watt), they say an iPhone 5 uses 3.5kWh per year and a Galaxy S III about 5kWh. Their estimation of the latter is $0.53 spent on electricity per year.

So let’s assume something crazy and say it’s a dollar a year to charge your phone normally. The wireless charging would cost you $0.30 a year. You also wouldn’t risk breaking a USB port, or have to keep replacing worn-out USB cables (I go through them about three a year at the moment).

Wasting all that money for the equipment

Based on the lowest entry prices for decent receiver and base it’s going to set you back $20-30, and you’re going to probably want to have more than one base if you plan to never remove the receiver coil.

Last I checked it was $50 for most places to look at a cell phone, more to repair damage if it wasn’t covered under your warranty (which USB port damage generally is not). So your call on whether that’s a deal or terrible.

In the end

If you want it, go for it. I had my phone plugged in today due to leaving a receiver coil at work (had unplugged it due to needing wired adb for this piece). My baby took managed to turn off an outlet strip and nearly dropped a lamp when she grabbed my phone from the bedside and decided to leave. For me, it’s a damage-reducing toddler defence. Your experience and needs will vary.