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Alternative Power Source Proof of Concept

Discussion in 'General Technical Questions and Answers' started by W4EGE, May 16, 2018.

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  1. W4EGE

    W4EGE Ham Member QRZ Page

    I don't feel like I'm the first to have thought of this...but wouldn't 18V Li-Po tool batteries make a great power source?

    I feel like the answer is: probably...if well managed.

    The thought experiment turned into a real experiment. I looked into down regulating an 18V source to 13.8v with a few methods. Ultimately I went with Drok Constant Current Constant Voltage Buck Converter. Test set up is: [​IMG][/URL]

    T0 power the rig in HF mode (100w nominal) about 7.3 amps will be needed. The single battery is good for receive only. I estimate efficiency at about 75%. This single battery should provide about 2.5 hours of power as is. The first test confirmed this calculation.

    Adding a second battery should provide 4 hours with a 25% transmit duty cycle. Perhaps not the best solution in the world...but...these batteries do charge in under an hour!

    Now i just need to build a better test rig than what I have. The only issue that might arise is what happens with batteries that have different charges on them. I like that i can hotswap them in RX mode...but im not sure if the batteries will try to charge themselves...hmmmm.
    W1TRY likes this.
  2. K3UJ

    K3UJ Ham Member QRZ Page

    Listed current consumption for a Yaesu FT-100 is 22A not 7.3.
    NH7RO and W4EGE like this.
  3. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    True, but that's for FM or RTTY.

    For SSB, it's about 7.3A average (22A peak) and for CW about 8.8A average (also 22A peak).

    For calculating discharge, we usually use the average current.

    But even those numbers assume transmitting 100% of the time, which nobody does except W1AW.:p

    I also have four Ryobi charge stations and four 18V battery packs (4.5A version) for my drills, leaf blower, etc. and never really thought about how good they are and how useful they might be for amateur radio work.

    I'd probably just buy one of these DC:DC 200W converters for $88. It can handle 18Vdc input to 12Vdc output at 16.7A with 90% efficiency, so only 20W lost under full load. Worth an experiment:

    W4EGE, thanks for the idea! I'll risk $88 to give it a try and let you know what happens.
    2E0TZX and W4EGE like this.
  4. W4EGE

    W4EGE Ham Member QRZ Page

    That is a decent unit at 16.7A. The converter im working with is capped at 12A. I transmitted @ 50W on VHF from the one 4AH battery and there was a struggle. The output voltage dropped A LOT so I know i need to add a few more batteries in parallel.
    The unit you shared seems to be a better 6 times the cost of the converter I got from amazon.
    It would likely do a better job in the long run.
  5. W4EGE

    W4EGE Ham Member QRZ Page

    You are correct. That is the listed consumption. At this stage I'm not too worried about peak transmit power as this was just a POC test. I suppose when I get to that point I could use two converters in parallel drawing from 4 batteries that would provide 24A current. Should that Could be a worthy power supply solution for under 30 bucks plus wire (and under 1 pound). Most of us have tool batteries already...why not use them?
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I agree about the converter...but don't know how well paralleling batteries will work: If they are absolutely identical and at the same SOC, should work but probably not quite double the capacity.

    Let us know!
  7. W4EGE

    W4EGE Ham Member QRZ Page

    Actually...i just had an idea that would work for sure. Way back when, when i cared about car audio, we would use huge capacitors to flatten out demand to keep the strain of the alternator. Something on the order of 1 Farad was enough to handle peak loading of at least 500w. So...i jut remembered...I could add a single 1/2 farad capacitor to a single 2 battery system which could easily handle a 22A (~300w @ 13.8v) peak load.
    KI7QVR likes this.
  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Be careful attaching that.

    The peak charging current when first connected (or if already connected, when powered "on") may trip any overcurrent protection the power converter has (depends on ESR of the capacitor).
  9. W4EGE

    W4EGE Ham Member QRZ Page

    That's a smart thought!!! Perhaps I need to use an isolation circuit and "jump" it with a car battery before connecting it to the converter circuit.
  10. KF5FEI

    KF5FEI Ham Member QRZ Page

    Whew. I thought this was going to be one of those over unity, perpetual energy threads.

    I'd go with a good LiFePo battery and leave the drill batteries in the tool shed.
    NH7RO and KA9JLM like this.

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