PSTT Inverter

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Overcurrent Overvoltage Spikes Overtemperature High Battery Low Battery Reverse Polarity

* Efficiency up to 95%

* Surge Power to 7000 Watts

* Standby Battery Power under 0.5 Watts

* Unique patented design starts and runs any load

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Stocking Distributors AZ-CA: Photocomm 602-948-8003 CA: Energy Depot 415-499-1333 HI: Inter-Island Solar 808-523-0711

Amateur Radio for Home Power People

Windy Dankoff KE5HV & Brian Green N6HWY

Recent issues of Home Power have mentioned ham radio and its practicality for independently-powered folks. When I was in high school in the late 60's, you couldn't keep me away from radios. I got my ham license and was thrilled to discover how easily I could talk with people all over the world. Then, just as I was shifting interest to environmental concerns and independent living, I happened to tune into the New Directions Roundtable (NDR). NDR was a nationwide network of hams with information to share about energy systems, self-reliance, economics and environment.

In the late 70s, the West Coast NDR was active enough to be a practical forum for useful info exchange among about 30 active members. We had an established frequency at which we would meet three evenings per week, like friends at the corner bar. A typical session would include about 10 people with various guests and family members chiming in. One person would moderate the discussion to keep it on track and see that no one was left out while we would concentrate on specific, pre-scheduled topics of discussion. Occasionally a guest speaker was brought in to address a special subject, which might be anything from alternators to zucchini recipes. I gave several talks on wind power, batteries etc., and obtained answers to countless questions of my own from the pool of expertise available. I also made some lasting friendships.

Some of the members of the old NDR have formed the West Coast HOME POWER NET, and we are proposing a schedule of frequencies to help other nets from around the country. Not all these nets are established, so if you are able and willing to participate, please HELP START THEM by calling "CQ HOME POWER" at these times and frequencies: 7.230 to 7.250 MHz at 16:30 Local on Sundays 3.900 MHz at 19:30, 20:30, 21:30, & 22:30 Local on Tues, Thurs, & Sun

7.240 MHz at 18:30, 20:00, & 21:00 Central Time on Fri & Sun 14.290 MHz at 17:00, 19:00, & 20:30 Local on Sat & Sun 7.110 MHz (Novice CW) at 22:00 Local on Weds & Sat. Listen for CQHP from KE5MI

If you don't get any action, please keep trying! Future issues will re-list schedules as Home Power Nets crystallize. If you DO get a regular schedule established, let us know so we can publish it! If you are NOT a ham radio operator, you might contact one who has the equipment to operate on these frequencies. Look for wires in the air, or a tower in your neighborhood with an antenna that looks like a TV or CB antenna on steroids. It might be a ham who can help you communicate with us! Remember hams provide a service, and do it for fun. Most will be happy to involve a friend or neighbor. We encourage Home Power people to become licensed amateur radio operators. See hP#5 for inspiration. Licensing involves learning morse code, some radio theory and laws, and passing an exam. Used equipment can be had for under $500 that will put you in touch with our net AND with other hams worldwide! The transistorized 12 Volt equipment uses no more power than a car stereo (10 Watts or less) to receive. While transmitting, it's typically about 100 Watts average. Not much electric power for the potential you can tap!

Windy Dankoff

Home Power Net News

On 19 June 1988, home power hams got together on 40 meters. It was like old home week, most of us had been active on the New Directions Roundtable (NDR). NDR was a local version of the international net started by Copethorne MacDonald of Mother Earth News. We all agree that the time is right for renewable energy (RE) to grow; there have been many changes since the nDr was running.

I received an informative letter from Gary Peterson of Breckenridge, CO. As a SWL, he passed signal reports for everyone on the net's first session. Gary just passed his Novice exam and is waiting for his ticket. Gary's station and homestead is powered up with PVs and microHydro. We're looking forward to hearing Gary on the air.

I have it on good authority that Ann Taylor Jones N7LFM has been reading "The How To Do It!" manual by Mary Duffield WA6KFA. Ann and 149 senior citizen's club members built a trailer park for retired seniors near Yuma, AZ. Knowing the importance of emergency communications, Ann started studying the ARRL novice exam material (see Home Power #5). On 22 March 1988, she passed her Novice exam. On 16 April 1988 she passed her Technician exam, on 14 May 1988 she passed the General exam. The icing on the cake is that on 18 June 1988 Ann passed her Advanced Amateur exam. That's four grades of license in 4 months! Outstanding! Ah, you folks that have been putting off upgrading your license take note.

I agree with Windy KE5HV about getting local area nets started. We will print any time, frequencies and call signs that are sent us. This is a good way to hook up for local 2 meter work. Tomorrow its back to stacking pallets in the warehouses of Tri-Valley Growers with my good friend Jim

Cook, ole' number 4. 73s, Brian

The following are making the Home Power net happen:

Windy KE5HV, Santa Cruz, NM

Johnny K7JK, Grants Pass, OR

Len WA6 ZXZ, Tuscon, AZ

Richard KE5MI, Arlington, TX

Buffy W6PSC, San Juan Capistrano, CA

Jim NK6P, Monrovia, CA

Bill KG6IN, Escondido, CA

Mike WB6EER, San Simeon, CA

Mary WA6KFA, Santa Cruz, CA

Mike K8XF/MM

Len WB6ZLQ, Fresno, CA

Rick N7ANL, Sandpoint, ID

Pat K6CXA, Van Nuys, CA

Dave KF6HG, Yreka, CA Silent Key

Shunts: Using wire & a DMM to measure current

Richard Perez

Use the wire that's already in your system to make current measurements. All you need is a tape measure, a meter, and the information right here. It's easy and will answer the perennial question, "How much does it draw, anyway?"

In Theory

Ohm's law informs us that any electrical current flowing through a material (like a piece of wire) suffers a loss in voltage. This voltage drop across the material is due to its resistance and the movement of the electrons (current) through that material. The amount of current flowing through the material can be determined if we know two things. One, the voltage loss across the material, and Two, the resistance of the material. Or in algebraic terms using Ohm's Law:

I=E/R (Equation1)

where:

I= the amount of current in Amperes

E= the voltage drop in Volts

R= the material's resistance in Ohms

Well, every appliance, power converter, power source and whatever is wired into the system with copper wire. The wiring in necessary to move electrical current from place to place, from source to load, etc. If we consider these bits of wire as resistors, then we can use the amount of voltage loss across a wire to determine the amount of current flowing through the wire. Wire used in such a fashion is called a "shunt" in electronics jargon.

How it Works

All we need to perform current measurements on our PV panels, inverters, refrigerators, or any other device that consumes, stores, produces, or converts electricity is a Digital MultiMeter (DMM) and the already existing wire in our systems. And a little help from Ohm's Law.

The DMM is used to measure the voltage drop across a piece of wire carrying current. The DMM should be capable of making measurements in the millivolt DC range. For example, the Fluke 77 we use at Home Power can measure down to 000.1 millivolts (mV or thousandths of a Volt). Such resolution is necessary as this technique involves using lengths of wire with resistances from 0.1W to 0.0001 W. The resultant voltage drops across such small resistances will be very low, and we'll need a DMM that can make accurate measurements in the milliVolt range. At about $140, the Fluke is a good deal for a 0.03% accuracy, very rugged, DMM. Radio Shack also offers DMMs that will measure in the mV. range for around $60.

We also need to know, as accurately as possible, the resistance of the piece of copper wire we are using. To find this resistance first determine the wire's size or gauge. Most wire has its gauge number printed on its insulation. Or the wire's gauge can be determined by using a wire gauge measuring tool. Once the gauge number is known, then measure the length of the wire. Copper wire has its resistance, in Ohms per foot, specified by gauge number. Once we know the gauge, we can look up the resistance (W/ft) in the Copper Wire Table (See BasicElectric • Home Power #2). This value is multiplied by the number of feet of wire we are using to make the measurement. And the result is the resistance of that particular piece of copper wire or shunt.

This technique can be used on wire of any size, and of any length. There are certain resistance values for shunts that have distinct advantages. Consider the following resistances: 0.1 W, 0.01 W, 0.001 W, and 0.0001W. If these values are used for R in Equation 1, then we are performing division by a decimal fraction of 1. This means that the measurement taken by the DMM can be read directly and a calculator is not needed to perform the math. Only the decimal point of the reading of the DMM need be shifted to obtain the amperage measurement.

What follows below is a Copper Wire Table that is optimized to display the lengths of various gauges that have resistances from 0.1W to 0.0001W. Find the wire gauge size of the wire you are using, and the lengths necessary to produce the shunts are shown across the table. Measure the indicated length along your wire and you have a shunt with a resistance that is a decimal fraction of 1. Attach the leads of the DMM across this length and you're ready to make current measurements.

At the head of each shunt column on the table, there is a reminder to shift the decimal point on the mV. reading taken from the DMM. For example, let's consider a 12 VDC light hooked up with 12 gauge wire. From the shunt table, we see that 0.63 feet of this 12 gauge wire will give us a shunt of 0.001W. The heading of the column tells us that the milliVolt (mV.) reading on the meter will equal the amperes of current through the shunt. If we measure 4.2 mV. across this 0.001W shunt, then the current flowing the shunt (and the light) the light is 4.2 Amperes. If the shunt had a resistance of 0.01 W (as in 6.3 feet of 12 ga.), the the milliVolt reading on the DMM would be 42.0 mV. and would have to be divided by 10 to produce the correct amperage measurement of 4.2 Amperes. The schematic shown below shows the electrical setup for using copper wire shunts to measure current. The measurement can be taken in the positive or negative wire, it doesn't make any difference. The wire need not be cut at the ends of the shunt. Simply strip back the insulation and make the measurement. In places where you don't need to make measurements all the time, use needle probes on the DMM to pierce the insulation without stripping. A piece of string is useful to transfer length measurements from a tape to stiff

Copper Wire Shunt Table

DIY Battery Repair

DIY Battery Repair

You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.

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