I noticed my fellow group members in the Yahoo Group RegenRX are often using a 9V battery to power their projects. This blog is a way to save them a lot of money if they use a lot of 9V batteries. First, the 9V pro’s and con’s, then the DC-DC converter pro’s and con’s.
For a source of 9V power, there is nothing cleaner than a 9V battery. It makes no RF interference (RFI), no electromagnetic interference (EMI), no hum and very little audio noise. The batteries are easy to obtain and found at most stores.
The 9V alkaline batteries are ridiculously expensive (however the 9V ‘heavy duty’ batteries are a dollar at the dollar store). I went past a display at the Target store and saw that two name brand alkaline 9Vs were eight dollars. For that much, I can buy 16 to forty AA cells, or sometimes more at Fry’s or online.
The DC-DC converter circuit is simple and easy to build. It uses parts that can be bought mostly at Radio Shack. It can use a single AA cell if the load is low power, but for 9V power at over 20 milliamps it would be better to use two AAs in series for 3V, and the cells will last longer.
For RF receivers, the converter has one drawback that can be a problem if the builder doesn’t do due diligence: it can cause RF interference. I have used a converter on an AM / FM pocket radio and found that the FM works okay but the AM band has a lot of interference. I changed to 470 uF electrolytics for the filter capacitors and that reduced the noise a lot, but what it takes is some RF chokes and the ferrite sleeves that are found on keyboard USB cables and VGA cables. A few well placed EMI sleeves on the cords and power leads should help a lot. Remember that if you’re doing moon-bounce or deep space reception this may not be suitable. But even if you decide that it can’t be used in your project, it’s capable of powering any other of your 9V toys, etc or projects, such as a crystal checker, transistor tester, etc.
My DC-DC converters are not like the cheaper circuits you might see. These are just a voltage boost circuit commonly known as a Joule Thief that uses one transistor and a coil to boost the 1.5V up to 3.2V to light a LED. Except the LED has been replaced by a Zener diode, often 5.1V, that just wastes all of the power as heat while it acts as a shunt regulator. The load taps off the Zener’s current and uses what it needs. But the converter draws a steady load from the battery at its maximum current, and there is no change as the load varies. Instead, my converter feeds back the output voltage to the converter, and when there is low or no load, the converter shuts down and reduces its drain on the 1.5V cell, so that the converter only supplies the load’s demands and the battery life is extended.
Here is a link to the DC-DC converter I built for my cheapo DMM. It’s designed for only 8 or so mA maximum so that the battery will last a long time. L I N K
Here is another link to a DC-DC converter that uses two transistors for the converter. The second schematic uses two transistors that switch in a square wave instead of a single transistor that sharply cuts off and makes a steep waveform with a lot of harmonics. This should reduce the amount of RF and electromagnetic interference. Also the ratio of the windings on the transformer determines the output voltage. The windings have just a dozen or so turns so they are not difficult to wind. L I N K
I have some schematics out there from my old watsonseblog that are accessible but I can’t changes or corrections or delete them. Some of the ones for DC-DC converters are in these links. L I N K
Hello Watson, I’m the Chemalloy guy, i.e. saltwater battery using zinc alloy welding rods and carbon rods used for plasma gouging. I’ve since found a better cathode material in the form of magnesium bar stock. It produces a much higher output, (1.5v and >1 amp short circuited. Anyway, they’re used in conjunction with my mini voltage converters, which are quite similar to your 2 transistor units. Mine are basically astable multivibrator circuits that drive small PS transformers salvaged from 12-15 volt wall worts that have a secondary center tap. I’ve refined them to the point that they’ll work down to .5 volts input with adequate output to drive small low power devices, i.e. transistor radio. I’m now getting .8v in > 6 volts out under load with the carb-mag batt. The freq. is low and doesn’t affect AM reception Good stuff! Keep it up!
It’s nice to hear from you and to know there’s someone else experimenting with this stuff. I went to Harbor Freight and bought some fire starters, which have a block of magnesium big enough to make a decent electrode. They go on sale occasionally, otherwise I think they’re 3 or 4 dollars US, which is still a lot cheaper than Big Five sporting goods. I used a piece of copper pipe for the other electrode, and a salt solution, better known as sweat, for the electrolyte. Here’s a link to it and to the Youtube Vid.
Actually, that’s what I’m using too! I took 4 of them (at 2 bucks ea), and connected them end to end with small gauge safety wire. I bundled 4 12″ carbon rods for the anode. They both fit nicely in a 1 ft length of 1.5″ PVC. The salt solution can be dilute as water from my swimming pool and still performs well! My mini converters now use the D5041 you recommended for JT use and work down to 0.4 volts and 30 ma to power a particular germanium transistor portable called a Wega “Bobby”. It just happens to work pretty well.. down to as low as 2 volts!
Great! I’ll have more free time during and after the holidays so I’ll be able to do some more experimenting with the batteries. I used a flat piece of copper and put the solution between them on a few thicknesses of paper towel. It works, but after awhile the current drops because the electrolyte in the paper towels dries or gets used up. So I think it would be better if the electrodes were suspended in a solution. Thanks.