[Elecraft] Field Day experience with K3

[dave]

 > lot?).  So the load is 204w x2 x 0.30 = 122w which after an hour has
 > totally discharged the 110AH battery

This isn't right. The capacity of the battery in watts is 110x12 or 
about 1320WHr. If the load is 122w/hr the battery should be totally 
exhausted after about 11 hours.

Of course you should never intentionally fully discharge a battery so 
a reasonable time of operation on battery alone would be about 7 hours.

The solar panel, if in full sun and at max efficiency would generate 
~120w. This is barely enough to keep up with both transmitters. 
Nothing left over to recharge the batteries.


73 de dave
ab9ca/4





On 6/29/12 3:05 AM, Edward R. Cole wrote:
> Look at energy instead of power.  You have a 120AH solar panel to a
> 110AH battery.  What is your load?  Two 100w transmitters running 12v
> at 17a dc load (204w load to the battery for each radio).  Your Tx/Rx
> duty cycle is probably = 30% during FD (are you calling CQ FD CQ FD a
> lot?).  So the load is 204w x2 x 0.30 = 122w which after an hour has
> totally discharged the 110AH battery if were not being charged by the
> solar panel.  With solar charging at 120AH you still have a negative
> energy equation (so maybe it takes a couple hours operation to
> discharge the battery).
>
> It sounds as only one battery was used for two radios.  A better
> solution would be separate batteries very close to the radios.  Still
> the 120AH solar charging system is undersized to maintain the
> batteries very long.
>
> So lower RF power to 50w (as has been suggested) to lower dc
> load.  Also increase dc wiring size to lower ohmic losses.  Battery
> boosters will give a little more voltage at the end of battery life,
> but at the expense of battery current (no free lunch).
>
> I ran 20w psk-31 one FD using a single 60w solar panel and a 100AH
> diehard marine battery and was able to run about 6-hours.  Of course
> psk-31 is keydown in transmit.  The radio was a FT-847 so I do not
> know its efficiency running at 20w RF.  The Rx and digital ckts
> probably consumed 3-4 amps continuously, and transmitter probably 50w
> at 50% efficiency for another 4 amps.  So say it was 7 amps in
> transmit (7x12= 84w).  I did not call CQ extensively but instead
> searched and pounced so most of the time was Rx so Tx/Rx duty cycle
> was probably 10%.  Overall the load was probably 48w per hour so the
> 60w solar panel should hold the battery charge long-term.  Things
> rarely run exactly according to theory.
>
> In my former job I maintained two remote repeater sites that were run
> on solar-charged batteries in summer and on alkaline batteries in
> winter (system auto-switched when solar battery voltage dropped to
> 10.5v).  The solar system was two 60w solar panels feeding two 100AH
> deep-cycle batteries; winter was a 10,800 AH air-activated alkaline
> battery bank (90 1.5v cells in 10cell banks).  Each 1.5v battery was
> rated at 1200AH.  The site was operated in a stby status 99% of the
> time with only the UHF control radios activated full-time.  We got
> three years life between battery replacements (helicopter only
> access).  With new batteries the site had a 30-day operational
> status.  Repeaters were 30w and there were more than one at each site.
>
>
> 73, Ed - KL7UW, WD2XSH/45
> ======================================
> BP40IQ   500 KHz - 10-GHz   www.kl7uw.com
> EME: 50-1.1kw?, 144-1.4kw, 432-QRT, 1296-?, 3400-?
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