Radio Shack Mobil Paging Alarm

Cabin Alarm— An Answer

I noticed your Q&A reply on page 108 of issue #49. You suggested that a reader could construct for under $100, a remote alarm for his cabin that would operate on 12 Volts.

I have used a similar solution that used to be available off-the-shelf from Radio Shack for $100, ready to use. However, this year the only model offered is 49-722 for $200. This alarm has more useless features than the old $100 version, but is the only one left with a pocket pager remote that beeps when the alarm is activated. With a non-directional 108" CB whip we used the pager over 2 miles away. A3 to 5 element CB beam antenna would do even better. It can be activated by door switches and other sensors, or contains its own vibration sensor that would be more useful on a vehicle than for a cabin alarm. This is a good working system available off-the-shelf.

Medical Alarm—Friends of ours have linked one of these paging alarms with a wireless doorbell (rectify the audio output to pull small relay to start alarm transmitter) to make a health call alarm for their aging mother, who lives nearby in her own house. She wears the doorbell transmitter as a pendent which signals the doorbell chime which is linked to the auto alarm and pager. Thus they can be alerted to a medical emergency while still being free to move about and do errands within a few miles of home. The wireless doorbell costs about $20.00-30.00.

Or if you have a phone line available, instead of the wireless doorbell, you can use a real med-alert dialer (#61-2659 for $100, has alarm output to relay trip alarm), that dials a phone number for help, and can also be linked to the auto alarm pager for wireless coverage.

Steve Willey, Backwoods Solar Electric Systems, 8530 Rapid Lightning Creek Rd, Sandpoint, ID 83864, 208263-4290

Thanks for the solution, Steve. Richard PV Performance

While reading the article on PV panel; performance (HP#49, page 28), a thought kept flashing through my mind. What are the chances of these panels performing better after five years of service? To the best of my knowledge, this is not even possible. (I thought the best one can hope for is no degradation.)

Since the changes are only a small percentage, (about 1% or so), I finally dismissed it, but I thought you might want to address it in the magazine. Others may not have scrutinized it as I did. Folks should realize that while PVs can perform better depending on conditions, one cannot expect improved performance over time.

Keep the great alternative energy news coming! Kelly Larson, Reno, NV

Well, Kelly, we wondered the same thing. Why did this round of testing show slightly increased performance from all the modules? All we can figure out is that we changed the test jig from four Fluke 87 DMMs (and a chipboard for data logging) to a Remote Measurement Systems ADC-1 analog to digital converter which logs directly into a computer. We electrically calibrated the ADC-1 using the Flukes. The old manual test jig had about a 10% margin for error. We estimate that the new A/D jig has an error factor of around 5%. The A/D gives us over 400 data points per module, while the old manual jig gave us about 60 data points per module. Also, the Li-Cor pyranometer has a rated error factor of 5%. Bottom line is that the small performance increases we reported are within our window of experimental error.

If any of these PV modules have degraded over time, then the amount is so small as to be unmeasurable by our equipment. I think that the latest round of testing is more accurate than any of the previous tests. It will be interesting to make the same measurements, using the same test jig and modules, next summer. Richard Perez

Inverter Rating & Efficiency?

1. If the continuous power demand comes real close to a continuous power draw rating of an inverter is it then advisable to move up a step to a bigger inverter? Example: Exeltech 500 being operated at 480-490 Watts continuously.

2. How is efficiency affected near full load vs. 1/2 load? Harry Melts, Why, AZ

Hi, Harry. The answer to your question depends on the brand and model of inverter and your ambient temperatures. Some inverters are still time derated, others are rated at a continuous figure. All are derated at high (over 120°F) operating temperatures. The Exeltech you mentioned is a good example of realistic, solid rating. When Exeltech says 500 Watts, they mean 500 Watts continuous at room temperature (less than 95°F). We have been running three fullblown Macintosh publishing systems on a 1,000 Watt Exeltech. Their consumption is constantly between 900 and 1,000 Watts. The Exeltech has never shut down.

In the case of the Exeltechs, half load efficiency is about 85% while full load efficiency is about 82%o. This is a very small difference. Other inverters will have different characteristics, so check the maker's specifications for the particular model you are considering. Richard Perez


December 1995/January 1996


Very complimentarily, we have been told that our controllers are the Hum-Vee of PV charge controllers.

Do you remember when the last issue of Home Power reported using our 120 Amp, CC-120E at 142 Amps with a heat sink?

Heliotrope General doesn't require designers to "watch out" and de-rate our power ratings. We rate our controllers with a safety factor built-in.

Our new PV charging power center, the Solpan™, incorporates the Hum-Vee ruggedness. The Solpan™ is the new power center that was designed to answer the requests of system installers:

• Abundant Wiring Space

• Fuse Pull-Outs Disconnect Everything

• Amps and Voltage (both) Readouts

• Temp Compensation is Standard

• Correct Fusing for PV Output

• SOC Voltage is Set with DIP Switches

With the name means "reliability" motto, should Hum-Vee be part of our ads?

Our products are available through leading AE Distributors and Dealers worldwide.

The name means reliability. Heliotrope General 3733 Kenora Dr. Spring Valley, CA 91977

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