5v step up to 120v?

[Eric Qian]

Hi everyone,

I'm trying to build a hand crank/solar generator, and I'm just using a geared dc motor and a piece of 5v 500ma solar cell to generate electicity. And it is working at around 5v, so is there any way to step up from 5v to 120v?

-------- Parts I'm using---------

The Geared DC motor: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=331033819771

The 5v 500ma solar cell: http://www.ebay.com/itm/200933878177

The handle on the geared dc motor: http://www.ebay.com/itm/76955-Dorman-Help-Window-Handle-/161317848540

capacitor for stability: http://www.ebay.com/itm/250852005544

5v regulator: http://www.ebay.com/itm/10-x-LM7805-L7805-7805-Voltage-Regulator-IC-5V-1-5A-USA-SELLER-Free-Shipping-/321411683138

[David Hough]

The electronics is simple in principle, but if you're only generating
2.5W then you're only going to get about 2W at 120V (DC, not AC, that's
a whole load more pain). Better to ask the question of why you need 120V
- if it's to power something that just converts it back down to a lower
voltage then you might be better using electronics that takes your
generated input and converts directly to what you need at the end. Even
if you only wanted 5V, you might do better with a switching regulator
instead of the linear 7805 regulator.

If you want to research a bit more, look for references to a switching
boost converter.

Dave

[Chris Albertson]

I'm trying to figure out how you might have combined the solar cell and generator.   I assume you have a switch to allow use of one or the other?

That 7805 wastes a LOT of power.  It is very inefficient and not needed at all if the goal is 120 volts.  You could go from what you have to 120V in just one step using a switching regulator.    But either way you are not going to be getting much power.

On Sun, Jun 1, 2014 at 11:39 AM, Eric Qian <q11...@gmail.com> wrote:

Hi everyone,

I'm trying to build a hand crank/solar generator, and I'm just using a geared dc motor and a piece of 5v 500ma solar cell to generate electicity. And it is working at around 5v, so is there any way to step up from 5v to 120v?

--

Chris Albertson
Redondo Beach, California

[Eric Qian]

Hi David, thank you for the prompt reply. But I can't seems to find any switching regulator that steps up from 5v to 120v. can you give me an item link address for reference? Thank you.

--
You received this message because you are subscribed to the Google Groups "HomeBrew Robotics Club" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hbrobotics+...@googlegroups.com.
To post to this group, send email to hbrob...@googlegroups.com.
Visit this group at http://groups.google.com/group/hbrobotics.
For more options, visit https://groups.google.com/d/optout.

[Peter N. Glaskowsky]

Eric,

What you need isn't a "switching regulator," it's what's traditionally known as an "AC inverter." These are widely available to work with a 12V input:

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=AC+inverter

But I'm pretty sure you won't find any such thing intended to produce useful amounts of AC power from 5V. As input voltage declines, the current goes up and efficiency goes down.

What you should really do is reconfigure or replace your generator and solar cells in order to charge a 12V battery, such as a basic 12V/7AH gel-cell battery (also known as sealed lead-acid or SLA) such as the ones commonly used in UPSs. Then you can use one of those commodity AC inverters to produce AC power.

Best,

.                  png

[Chris Albertson]

On Sun, Jun 1, 2014 at 7:01 PM, Eric Qian <q11...@gmail.com> wrote:

Hi David, thank you for the prompt reply. But I can't seems to find any switching regulator that steps up from 5v to 120v. 

I doubt you would find an IC marked "5v to 120v".    In short what you do is "chop" your low DC voltage into a square wave and then send it to a 5:120 transformer.  Now you have 120V AC, rectify that.   Compare it to a 120V reference.  The difference or "error" is used to control the duty cycle of the chopped low voltage.  That is a very simple switched mode power supply.    Doing such a design right is not easy and required some computer simulation and iterations.    There are simpler designs using a coil and "flyback" to make the higher voltage but they might be harder to design.  The other method is a "voltage multiplier" using a bunch of capacitors and diodes.  But this has loses in the diodes.   The transformer might be best.

This might not even work as there is so little current.  What are you trying to power?

[Peter N. Glaskowsky]

Actually, just out of curiosity, I poked around online and found that there is an entire market niche for package-integrated 5V to AC inverters-- they power the CCFL backlights used in LCDs.

Here's one that goes from 5V to 120V.

http://uk.farnell.com/pacel/p5ehp-r/inverter-el-lcd-backlight/dp/1180993

This one happens to be out of production, but that's okay, since it's useless here anyway-- this device, like all CCFL inverters, operates at a relatively high frequency, 1.82 kHz or higher. And it's limited to 3/8ths of a watt of input power, probably producing much less output power.

But at least there is such a thing.

.               png

[Eric Qian]

Peter, thanks for your reply, but most of then are available at 300W or so. Is it possible to power a inverter that is designed for 300W with only 12v 1A?

[Peter N. Glaskowsky]

Eric,

There are two aspects to the amount of 12V power an inverter will require.

The inverter itself needs some power to run. This is usually only a few watts, so you'll usually be able to turn on the inverter (with no AC-powered devices plugged into it) even if your 12V supply can only provide 1A of current. (A really big inverter may have a larger start-up surge current than that, though.)

Then, on top of that, your AC-powered devices require additional power when plugged into the inverter and turned on.

You may have AC-powered devices that need only a very small amount of power, like an alarm clock or a cellphone charger. These might run fine from a good inverter connected to your 12V, 1A supply. Or you may want to run a microwave oven, which will obviously need a lot more power than your supply can provide.

This is why I suggested using your generator and solar cells to charge a battery, because the battery will be able to provide larger amounts of power for short periods of time. The low-cost 12V, 7AH gel-cell battery I mentioned before can provide roughly 7A or 90W of output power for about half an hour-- plus or minus, depending on condition-- even if you can only charge it at 1A.

Now, 90W isn't enough to run a microwave, but it would be enough to run a small TV or a laptop charger for a while, so you may find that useful. Adding a battery and a battery charger circuit will add cost, size, and weight, but greatly increases the functionality of the solution. So it's your call.

Best,

.                  png