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[aprssig] Solar Powered Digi's.

Mark Earle wa2mct at mearle.com
Tue Dec 4 19:44:19 UTC 2007


John Ronan wrote:
> 
> On 4 Dec 2007, at 18:53, Phillip B. Pacier wrote:
> 
>> I had a solar powered digi up for five years (W7RBV-2).  I have since 
>> transferred ownership of the digi and it is no longer solar powered, 
>> but what what information are you looking for?
>>
> Typical "Rules of thumb" I guess for battery/panel sizing.
> 
> I was thinking of a OT2 and maybe a FT-1500 or some other dedicated 2m 
> Radio.  The OT2 will also broadcast battery voltage as telemetry for me.
> 
> Its not something we've done before.. so avoiding any 'gotchas' would help.
> Apparently, the 'average' Sun hours per day over here is about 3.75.  So 
> I was going to go for a rough figure of TX'ing 20% of the time, and try 
> and size the battery so that it never gets discharged below 80% on that 
> figure.  And then I guess, size the panel so that it could recharge the 
> battery from roughly 80% discharge on a 3.5 hour day of sun.  Does that 
> sound reasonable?
> 
> Regards
> 
> John
Those are reasonable numbers, but no synthesized radio.

They are not optimized for stand by.

Let's say you transmit 20% of the time. That's 288 minutes of 
transmitter time, or, say at 2a 288 x 2a = 576 amp-minutes or 9.6 
amp-hours.

Now then. 100 ma (0.1 amp) of stand-by for 1152 minutes
1152 x .1 = 115.2 amp-minutes, or 1.92 amp-hours.

Oops. The 1500 shows .3 amp squelched. More while receiving.

So 1152 x .3 = 345.6 amp-minutes or 5.76 amp-hours.

Of course, there will be receiving time and the current there is 0.6a 
for that radio.

So you are looking at a power budget of 7.68 or so amp-hours/day.

Notice that the standby time is a significant part of your power budget. 
You would want to find a transceiver which can draw much less current.

Use a crystal radio, and remove or disable / disconnect the audio 
portion of the receiver - you just need to buffer discriminator audio. 
You could get the standby requirement down to on the order of 0.05 a vs 
0.30 a. Save you a lot of energy.

Just some thoughts.


-- 
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