[Elecraft] Field Day experience with K3

[Phil Hystad]

Slight additional correction...

Energy is computed as the integral of power over time.  The power itself from a battery that is itself not under recharge is constantly changing over time even with fixed load.  Thus, the actual energy computed is slightly less then the value you get with power times hours since power is not constant.

PEH's iPad

On Jun 29, 2012, at 12:28 PM, dave <ho13dave at gmail.com> wrote:

> 
>> 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-?
>> DUBUS Magazine USA Rep dubususa at gmail.com
>> "Kits made by KL7UW" http://www.kl7uw.com/kits.htm
>> ======================================
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