With all the power outages being caused by Hurricane Irene, I thought it might be useful to have an inverter that I could charge my cell phone with. Plug in battery power on one end, cell phone on the other. I've poked around a bit and found this schematic:


So a few questions...

First, would this work? Second, would this damage my phone or whatever device I charged with it (a 3DS for example)? Third, how fast would this drain say, a 9V battery? Is it even feasible to do this?

EDIT: I've just been notified it sounds like I'm trying to build a charger. This is not the case, I'm shooting for a power source that I can plug chargers into. Also, I just realized, is this outputting 120V or 120V RMS?

And I'm sure it's obvious, but just in case, I'll be building this thing myself..because well..I like building things!

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    \$\begingroup\$ With the 9V Battery are you referring to a PP3? \$\endgroup\$ – Dean Aug 29 '11 at 21:02
  • \$\begingroup\$ The mintyboost ladyada.net/make/mintyboost goes from batteries to 5V for charging in one stage, with some significant thought put into the design, and you can even assemble it yourself if you want. \$\endgroup\$ – Jay Kominek Aug 29 '11 at 21:22
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    \$\begingroup\$ @MGZero, you can increase efficiency by going to the DC voltage your phone needs. \$\endgroup\$ – Kortuk Aug 29 '11 at 21:25
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    \$\begingroup\$ It seemed to me, and I may be wrong, that he was looking for the ability to use existing chargers, which may be for LiIon one cell (eg many cellphone), LiIon 2 cell (eg DSLR cameras), NimH (various) and cells with magic handshakes to let you charge them (eg some Dell). Being able to just plug chargers into a device would avoid reinventing a number of versions of the charger wheel. Instead he is reinventing thje DC/AC inverter wheel :-). \$\endgroup\$ – Russell McMahon Aug 30 '11 at 13:22
  • \$\begingroup\$ @Russel McMahon Yea, basically haha. Really for me though, these little projects I do are to just see if I can do it and also to see what I can learn from it. But that post you put seriously is packed with information and is probably going to be a great resource in itself! \$\endgroup\$ – MGZero Aug 30 '11 at 13:45

More comment if useful:

This is the circuit diagram that you referred to. They have copied it from elsewhere and some of the original information is missing. Building this from that much detail would be "difficult" without more input from others.

enter image description here

  • Something as simple as this is still capable of killing you. There are safer things to play with.

  • The circuit would work "after a fashion" but there are too many variables and it is a very old design. There are many better designs available.

  • The output voltage is not well defined (depends on battery voltage and transformer used and some more.

  • The transformer is not driven as well as it could be (half bridge and AC coupling = interesting result.)

  • If by 9V battery you mean a typical transistor radio battery, then ANY circuit that powers or charges cell phones or similar would flatten it (use it up) very quickly.

  • You need a higher energy input source and one with a relatively stable voltage.

  • Ideally output voltage should not depend on input voltage as much as this one does.

  • DC to AC is good for charging.

This is an interesting project BUT you can but commercial units that do what you want better and probably cost less to buy than this costs to build (unless you can get parts for free).

There are many useful and interesting things that you could build. Others are less dangerous and easier to make work well.


Look at these and understand how they work. Discuss if still interested.

Old design and simple but with 12V lead acid battery and parts discussed would work OK.

enter image description here

A potentially good design despite the appearances with circuit diagram here - parts are on PCB and most of the electronics is inside an IC so not quite as complex as it looks.

Commercial designs from $US30 - you can get much cheaper.

And more commercial designs

Commercial from $20

Instructable - Suspect - but useful things to learn from the circuit

Things to learn - shows 230VAC but can be 110 VAC.

Things to learn:

enter image description here

$20! 100 Watt continuous

enter image description here

Things to learn

enter image description here



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  • \$\begingroup\$ Great post, +1! Just out of curiosity now, if I wanted to make one just for learning purposes, I'd imagine that building one that outputs a much lower voltage (say the same as the input is, or just a few volts higher) would make this a lot safer. Am I right in thinking this? \$\endgroup\$ – MGZero Aug 30 '11 at 13:15
  • \$\begingroup\$ @MGZero - yes - it's largely the output voltage that is hazardous. By using a transformer with eg 2:1 stepup or less you can still get something that is useful. eg 12V -> 19VDC (which is just AC rectified) would give you a PC battery charger in many cases. While safety is ceryainly a concern, I'd also have doubts about the first circuit proposed. And you need to understand energy from batteries and how much energy you need. A 12V (or just maybe 6V) lead acide battery or a multicell LiIon battery would be a better starting point. \$\endgroup\$ – Russell McMahon Aug 30 '11 at 13:25
  1. If you think you should be building an inverter, you don't know enough to do this safely.
  2. Most chargers are DC, you want a DC to DC converter (but probably at a different voltage).
  3. It would drain a 9V battery quickly; those don't have much current.
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  • \$\begingroup\$ 1. Could you elaborate a bit? 2. Well true, but if I'm using the inverter as the power source as opposed to the wall, why would I want DC to DC? \$\endgroup\$ – MGZero Aug 29 '11 at 20:29
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    \$\begingroup\$ It would be far more efficient to take the 9V and convert it down to the 5V or whatever the device needs. Taking the 9V up to 120V and then back down to 5V is needlessly wasteful. \$\endgroup\$ – Majenko Aug 29 '11 at 20:52
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    \$\begingroup\$ @MGZero - What me means by 1. is this: You do not need an inverter for this application. If you are not familiar with electronics enough to realize that you do not need an inverter for this application, you do not have the skills needed to safely troubleshoot a 120/240V inverter. These are high voltages, and require a fair amount of experience to troubleshoot without potentially injuring/ killing yourself. \$\endgroup\$ – Connor Wolf Aug 30 '11 at 1:57

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