Re: alternative power sources

>  From: Dan Jacobson <[email protected]>
>Subject: alternative power sources: can't fool the R2
>
>>>>>> "Bob" == Bob Parnass, AJ9S writes:
>Bob> You will probably destroy the IC-R2 if you connect an AC transformer
>Bob> to the DC battery contacts.  DO NOT do it.
>
>young Dan (a/k/a me) proceeded to... <ZAP>... well the radio is OK
>still, but my conclusion is: one cannot fool the R2. It can tell real
>batteries from any fake baby pacifier you try to give it.

In the first place, Bob may have meant that you shouldn't connect a "wall 
wart" transformer with an AC *output* to the R2.  Yes, some have AC outputs. 
 All the ones you tried were DC output.

Second, there are two different types of DC-output wall warts, unregulated 
and regulated.  The unregulated type provides considerably more voltage than 
what is on the nameplate when there is little load on it, dropping to about 
rated voltage at full load.  There is also quite a lot of ripple on the 
output voltage at full load, which will likely produce "hum" in the audio.  
The regulated type, on the other hand, provides virtually constant voltage 
with no ripple from no load to full load.  Two very different behaviours.

I have connected my R2 to a bench DC power supply, where it worked 
perfectly.  I have no doubt that a *regulated* 3 VDC wall wart with 
sufficient power output would work as well.

>I did try a "1.5 VDC 300mA" "wall wart" that gave the same 2.2 VDC
>reading on my tinseltown multimeter as does a pair of NiMH.
>
>I recall beeps even before hitting the "on" button... and then refusal
>to turn on.  Not enough juice? OK, then:

Yeah, because it will drop to 1.5 V under load.

>I also tried "3 VDC 800mA" from a "automobile cigarette lighter wart".
>More beeps and flashing of LCD...

So what was the voltage with no load?  When you tried to turn on the R2?

>The R2 is no simple light bulb apparently.

As you may have noticed by now, it's an electronic device.  It requires a 
constant DC voltage, not a pulsating one.

>I've got fist sized 6VDC gel batteries as found in emergency lamps.
>Do I just add one resistor to make this a 3 V power source for the R2?

No.  If the R2 drew constant current, you could make this work, but (as the 
recent battery saver discussions have mentioned) the R2's current varies 
over a greater than 2:1 range.  Since the current varies from instant to 
instant, so would the necessary resistor value.

You need a voltage regulator that electronically provides constant voltage.  
The simplest way is with a 3-terminal series regulator like a LM317 and a 
handful of additional parts.  Unfortunately, this design wastes half of the 
battery power as heat in the regulator, and only half of the total power 
makes it to the radio.  In other words, 50% or lower efficiency.

A better approach is to use a switching regulator circuit to provide 3 V 
output.  This can be up to about 90% efficient, but it's a more complex 
circuit to design and build.

>How about a 12V car battery?  Question 11 (35 points): The Martians
>have attacked, stealing the world's supply of AA batteries, and
>kidnapping the battery bunny. Your mission is to monitor Martian
>communications and rescue the bunny in time for Easter.  However, all
>you have is a 12V car battery.  What circuit do you rig up to power
>the R2?

Either of the voltage regulator circuits mentioned above can be designed for 
12 V input, though the efficiency of the series regulator drops to 25%.

But what *I* would do is put some of my stock of NiMH AA's (the Martians 
can't steal everyone's batteries) into one of the fast chargers that operate 
from 12 VDC (e.g. Maha MH-C204F, Rayovac PS4, Radio Shack "pulse charger"), 
charge them up, and operate the radio from the AA cells.\

        Dave


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