Posts Tagged ‘USB


My Old Power Bank

I was given a power bank quite some time ago that I’ve used sporadically when I’m away from home to charge my devices. Recently when I went to charge it I found that the connector was intermittant and about to fail. So I decided to take it appart and see if it is repairable.

Taking it appart was fairly easy, I just peeled off the upper label, removed 4 screws and it came appart. Here’s a photo of the board.



The board is of a fairly simple design, but there are some notable deficiencies. Firstly you’ll notice the lack of any bulk storage capacitors, but just a few small surface mount ones. The main inductor is the only component on the other side of board, and it is pretty small. So I suspected that this power bank might have severe problems with ripple on the output. I decided to investigate, so I got out my oscilloscope.

Ready to measure

Ready to measure

Basically I hooked up a load to the power bank, my phone and my tablet in turn, and used my oscilloscope to measure the waveform on the output pins of the power bank. Here’s a screen grab from the scope showing the waveform with my phone on charge.

Yikes! The ripple is really quite bad and appears to contain higher and lower frequency components. The most disturbing thing is the range of the voltage. 5.84V is greater than the usually 10% tollerance accepted, which could damage the charging circuit of a phone. This is likely because the board lacks any bulk storage capacitors.

Charging my tablet which imposes a larger load only seems to make things much worse with the ripple magnitude and frequency increasing. The voltage peaks at 6.4V which is way to high, understandably I’ve taken this power bank out of service because of how bad this is. I was going to repair the charging problem which turned out to be a faulty input socket, but I guess that’s no longer necessary.

I wondered how the unit would go with some bulk capacitance added, I noted that the Arduino that I have has exactly such capacitance on it’s input circuitry, so I tried connecting it and measuring the ripple. I didn’t get a screen capture, but the ripple became almost flat and settled at a peak of 5.13V. If they had added the bulk capacitance needed, I’m sure the ripple would have been reduced to usable levels.

I’m certainly no expert when it comes to electronics, but I can tell when something is not good. If you’re more interested in power banks I’d suggest you look into reviews and tests of them on Gough Lui’s blog/website. He performs much more detailed tests and has tested a number of power banks over time.


Solar Panel USB Charger

One of the panels

One of the panels

During the mayhem of last weeks storm and aftermath I had one problem that I hadn’t prepared for. Charging my phone and Android tablet. Whilst I was out and about I visited my not-so-local Jaycar to see if I could get something that would help. They had a 5W solar panel made by Powertech that provides both USB charging and charging for 12V batteries. It was expensive compared to other solutions at about $70 AUD, but I wasn’t sure when I’d get my power back on and I wouldn’t have to wait to get it from an Ebay seller. Some people were without power for almost a week, I wanted to be prepared so I bought it.

At first I wasn’t terribly impressed, but there are some nice features to this unit. For a start the charge regulator is separate to the panels, and the wire from the panels is sturdy with a solid connector on the end. This means you can use the panels elsewhere if the regulator were to fail. A similar connector is used for the 12V output which terminates with a cigarette lighter socket. This is hardly useful for me, so I might have to wire up something else so I could trickle charge a SLA battery.

Charge Regulator

Charge Regulator

The regulator has a port for connecting other panels/regulators of the same type. It comes with a cable that allows you to connect three panels together for a total of 15W. There are better ways to get that much power, so I don’t recommend using these panels for this feature.

The unit doesn’t include a Lithium-ion battery bank, which in my view is a positive thing. Although you may disagree, I’d rather not have my panels tied to a battery that will eventually fail. Also I’ve noted that power banks with solar panels generally speaking will not charge very quickly from the sun. This is because they have panels that are too small to produce any meaningful amount of power. With this unit you can always attach an external battery bank for charging if you want, but aren’t stuck with the battery when it wears out.

So, how well does it charge a phone/tablet? There isn’t really a simple answer because it depends on many things. When I first tried it to charge my phone I wasn’t impressed because it didn’t seem to charge it much, but there were a few things I did wrong. I found it best to turn off the phone or at least all wireless and bluetooth to save power. During times the solar panels are not outputting much power, the phone will still think it’s connected to a charger and turn on extra features such as these, sometimes using more power than the panel provides and actually discharging your device instead. So you can get some charge on a cloudy day, but you absolutely must turn off your device or charge something passive like a battery bank.

On a day with much better sun it charges quite well and is more than capable of fully charging my phone from about 50%. I have a fairly small phone which charges very quickly (a Samsung Galaxy Y) but with full sun it will even put some charge into my tablet which consumes quite a bit more energy. Like any other solar panels you get peak charging rates in the middle of the day whilst the sun is at it’s peak, and properly pointing your panels increases the amount of energy they collect.

In my window

In my window

I hung my panels in my window using some suction cups I got from Woolworths, so the positioning of the panels wasn’t really ideal. That window gets the best sun, but gets shade in the late afternoon. This is where I did most of my testing, so you may get better performance by positioning your panels in a brighter locale at the correct angle.

I think for practical use you probably want to also have a power bank or 12V battery to charge. Most people would be carrying their phones about with them during the day, and a battery bank will likely continue to charge under worse light conditions, so may gather more charge. I haven’t tried charging a 12V battery with it yet, but I suspect it will work fine provided the battery isn’t too large.

Now that I’ve had more time to try it out in better conditions and with different devices and circumstances, I’m much happier with this Solar charging kit. It’s capable enough that given an situation without mains power, I’ll be able to charge a device like my phone given enough time and sun.

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