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Exploring the realm of 12V adapters

21 Apr 2016  | Michael Dunn

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Our new house is working its way into 100% LEDness, from LED "bulbs" in standard light fixtures, to custom LED lighting, to flexible LED light strips. It's the latter I'm having some problems with.


Some of the LEDs we're already using.


After some preliminary research, I decided that the only affordable sources for LED strips would be from among the numerous Shenzhen & Hong Kong mega-retailer Websites. There, you'll find standard 5m LED strips in the $4-$20 range, instead of the $50-$100 range typical of other sources.

Cost is very important, as I plan to install a lot of strips: Under the kitchen cabinets (1), in a long storage "nook" (2), over the tub (1 RGB), and in the basement (≥6).

Having had a range of experiences with these Chinese suppliers, I knew there might be issues with the strips, but given the low prices, I ordered a few to try. Sure enough, the specs (lumens, wattage...) tended towards wishful thinking more than reality, but I found some I was pretty happy with anyway, and proceeded to order more.


The "90W 11,000 lumen" strip I am using. Not quite.


I'll write about these strips another time, but I will mention that I discovered I couldn't just slap 12V at the end of a 5m strip and expect it to work well. The conductor resistance is too high, and what's 12V at one end, is maybe 10V at the other. As most of my applications will be using the whole length instead of cutting it up, it means I'll have to solder power into the strips at maybe three points along their length using pretty heavy wire – assuming I care about getting full brightness.

With the LEDs themselves taken care of, I turned to power sources. In the basement, I'll probably use some centralized high current 12V power supplies, but elsewhere I'm using 12V plug-in adapters. I ordered a couple of 12V 5A adapters. That's when the problems started.

While I'm willing to accept some creative LED specs, I do expect a 5A adapter to be a 5A adapter. Silly me. They turned out to be more like 2A, and to add insult to injury, the output cables appeared to be vastly undersized – perhaps AWG 24 or 26! Even with the cable cut down to a stub sticking out of the adapter (which did help with voltage drop), I was still short 3A!

Some back-and-forth with the Web store ensued, but in the end, I decided to look elsewhere. My first thought was to give in and get some real units, like these CUI adapters.

Instead, I decided to turn the process into a project, and write about it. I correctly surmised eBay and Amazon would have the goods. Speciality LED shoppes are another source – and one expects they would print accurate specs – but in the end, I limited myself to five units from various sellers on eBay & Amazon.


Gaggle of 12V adapters.


Since a table is worth a thousand words, here is a table comparing the five adapters, as well as the originals (yes, two different models were supplied under the same SKU).

Interesting sidebar: I plugged the XY1205A into my "Kill-a-Watt", and calculated a conversion efficiency of about 110% based on the wattage reading! (PF=0.52) This must be a Kill-a-Watt issue with more outrageous current waveforms.



Notes:

1. Canadian dollars. Multiply by ~0.75 to get USD – sad but true. All had free shipping.

2. Most had over-current shutdown and retry.

3. They would not print my honest review.

4. After at least 0.5h. Yes, totally subjective.

5. Foldback, no retry.

What's the moral of the story then? You tell me. But... I know where I'll head (and particularly, where I won't head) when I need more adapters...

And yes, some of these junkers deserve a teardown. Stay tuned.


About the author
Michael Dunn has been messing with electronics almost as long as he's been walking. He got his first scope around age 15, and things have been going downhill ever since. The scopes now vie with wine racks, harpsichords, calculators, and 19th century pianos for space. Over the years, he's designed for the automotive, medical, industrial, communications, and consumer industries, as both freelancer and employee, working with analogue, digital, micros, and software.




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