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May the POWER be with us!

Discussion in 'QRP Corner' started by KK4NSF, Dec 25, 2015.

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  1. KK4NSF

    KK4NSF Ham Member QRZ Page

    Right now I'm using a 9 amp hour gel cell battery, and I think it's overkill for my uses. I can operate it all day on SSB, and it never breaks a sweat. I like the fact that it charges up perfectly from a car cigarette lighter, but it's simply too heavy for my new, scaled down set-up.

    My operating criteria are simple: small enough to be easily back-packable, but have enough capacity to to run all day. Just for sake of discussion we'll say 10 hrs at 25% duty cycle w 5 watt load. I can use 9 to 15vdc. So to keep things simple, we'll use 10v. So lets see 10v @ 5w equals .5amps times .25 duty cycle= .125 amp hr per hour.... so for 10 hrs I'll need a minimum battery capacity of 1.25 amp hours. To account for battery life, power drain while recieving, effiency of the transmit circuits and so forth, we'll double that to 2.5 amp hours @10v.... which still might be overkill, but at least I'll know it'll do the job.

    So... what are my options?

    1. smaller gel cell- 2.5 amp hours would still last all day, and have the "ease of charging" factor but might be heavier than I want to lug around.

    2. AA batteries in a holder- cheap to set up, and light to lug around.... but then I have to keep buying batteries

    3. rechargable NiCads....

    4. Lithium Ion.... a lot more expensive and a special charger is required.... but very small and light to carry around

    5. 10w solar panel and a battery

    What do you use? and how many amp hours do you carry?

  2. AI6KX

    AI6KX Ham Member QRZ Page

    These work great, and weigh next to nothing. You can go bigger capacity too. The full-charge voltage is 12.4 but drops to 11.2 after a short time, then holds that until pretty much full discharge. It comes with a charger. I have cut the blue tape and rearranged the leads. I carry one and a charged spare, never needed more on a day outing.
    I noticed someone is selling the identical item "For Yaesu 817 and 857" for about $60. Nice work if you can get it.

    Steve in Okinawa
  3. W7CJD

    W7CJD Ham Member QRZ Page

    LiPo battery is not LiIon battery.

    The power rating is the same: 3,000 mAh.

    They also have a different discharge rate, and "fall off" at the end.

    The FT817 and FT817ND tolerates low voltage input.

    It is nice to not have it suddenly drop out.

    However, I have never got to the end of the battery in a day or two portable, perhaps because I am doing other things.

    It looks like a great value, to carry along with my LiIon-powered YouKit TJ2B that is designed to be "happy" with it's own LiIon internal battery.

    It just stops.

    I like that, for that transceiver.
  4. RN3ANT

    RN3ANT Ham Member QRZ Page

    For my multi-day cycling trips I have refused all kinds of lead batteries in favor of a much lighter lithium batteries. The lightest of them — lithium polymer (Li-Po), lithium-ion (Li-Ion) is slightly heavier. But they both have explosive dangerous, poorly maintained negative temperature and have a relatively small number of charge-discharge cycles. So my choice is a lithium-iron-phosphate (LiFePO4) batteries, which are devoid of these shortcomings, though there are the most heavy and most sized Li-Ion batteries.

    I use two 12 volt home assembled (4 x 38120 elements) batteries with nominal capacity 10 Ah (actually measured capacitance is 11.4 Ah). Each battery weighs ~1.4 kg, and can be recharged from any power source of suitable voltage and power. For example, I charge it at home by a special two-stage charger for LiFePO4 by current of 10 A, a fully discharged battery will charged for 1 hour and 15 minutes. From power supply of a transceiver it can be charged by current of 25 A during of 30 minutes.

    In the trip it is possible to charge it from car battery also for 30 minutes (not from the cigarette lighter, but directly from the battery terminals with the engine running).

    Undressed battery


    Comparing to leads 14 Ah battery of 6.5 kg

    Two-stage 10 A charger for LiFePO4

    Some wires

    For a short outing for just one day, I take the only battery without any gear for recharging. Its capacity is enough for QRP during a day and night quite active work and, in addition, it is possible to increase the power of my K2 to its maximum of 15 watts, if necessary, without whatsoever impact on remaining battery power. If I use 100 watt amplifier, I can actively CQ with one battery up to 4 hours at full power.

    In addition, I can recharge the photo camera, smartphone, GPS-navigator, the battery of bicycle front light, VHF-handy radio using the DC-DC converter, and even feed the LED-lighting in a tent at night.

    For coming summer I plan to assemble folding 18 volts up to 6 amps solar panel ~ 900 g in order to be completely autonomous during multi-day trips.

    73! Vit, RN3ANT
    Outdoor QRP Activity Group
    Last edited: Jan 16, 2016

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