All the power in the world and not enough battery!

Discussion in 'Amateur Radio News' started by VK6FLAB, Mar 2, 2019.

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  1. WA6VVC

    WA6VVC Ham Member QRZ Page

    I was thinking the same thing with the diodes. Add a switch across the diodes when your down to the end and you'er on reserve power time. Seems to me it would provide a little more voltage headroom for some of those sensitive less that 12 volt rigs. NO???
     
  2. K3KIC

    K3KIC Ham Member QRZ Page

    That's not how you calculate efficiency. You need to calculate the total energy used and deduct the amount lost in the diodes.
     
  3. KD6VXI

    KD6VXI Ham Member QRZ Page

    The rig pulls 22 amps.

    At 1.2 volts drop, that's 24ish watts.

    For a rig that pulls 22 amps at the given 16 volts we are looking at 352 watts of input power from the batteries, give or take.

    My simplistic formula was still pretty damn close, and he's still in the 90s.

    Being pedantic doesn't make you right.

    Even if you wanted rig input power alculate the power used that's 22x13.8= 304 watts. And the 22 watts wasted by the diodes still puts him in the upper 80s this way.

    And you still don't have the problems with a DC to DC cheap chicom switcher.

    If you have a problem with the math, show where it's wrong so people can learn. Please don't just sideswipe with a fairly useless comment.
    --Shane
    KD6VXI
     
    AG5DB likes this.
  4. K3KIC

    K3KIC Ham Member QRZ Page

    You need to calculate Watt hours or similar units to determine which approach is more efficient as both battery voltage and current draw is dynamic during discharge.
    Your response included the comment that math was easy for some of use and then you proceeded in using the wrong analysis.
    The numbers you provide above are an instantaneous calculation of losses at the start. Not across the full discharge cycle.
    KF5LJW stated that 15% of the total power would be lost using the diode approach. Without running the numbers my educated guess is that he is right. I just would have presented that thought differently. (I've done many battery discharge tests for projects at work.)
     
    Last edited: Mar 7, 2019
  5. KD6VXI

    KD6VXI Ham Member QRZ Page

    I us

    I used an apples to apples analysis.

    I was comparing the efficiency of the DC to DC converter vs his diode drop. I also stated that it was being simplified by thinking constant carrier.

    I didn't touch on the dynamic draw, duty cycle, battery VDrop over time, etc.

    His DC to DC converter didn't take any of that into account, either.

    Please don't try to change my intent of the post to fit an argument.

    --Shane
    KD6VXI
     
  6. K3KIC

    K3KIC Ham Member QRZ Page

    KL5LJW referenced battery capacity. Neither of your calculations related to capacity. I think knowledgeable readers of the thread would have noticed this as did I.
    I merely pointed it out because of your quirky comment.
    As someone who operates remotely I wouldn't throw capacity away when I'm on a mountaintop and worked hard to haul that weight up the hill. So I wouldn't use diodes to drop the voltage.
    I just hook up the battery with the understanding that it's a tad over the voltage spec for a while.
     
  7. 4Z1UG

    4Z1UG Platinum Subscriber Platinum Subscriber QRZ Page

    Could you use one of the Chinese buck converters that keep the output voltage constant as the battery voltage starts above the 13.8 then falls below it?
     
  8. N7KO

    N7KO Ham Member QRZ Page

    Thank you, Very good information, and well written. You shed some light in that Rabbit Hole.
     
  9. NN6EE

    NN6EE Premium Subscriber QRZ Page

    I got tired of keeping an eye on the earlier flooded marine batteries (12vdc+) because during warmer spring and summer months you'd have to make sure that the electrolyte in the cells was always TOPPED-OFF!!! So we changed to "AGMs" instead, and those have been serving us VERY WELL FOR 6yrs so far!!!

    PS, We use ours for a very modest "Solar-panel" arrangement!!! It's very gratifying to some times "Thumb your nose" @ the local ULTILITY COMPANY!!! :)
     
  10. WA4KFZ

    WA4KFZ Ham Member QRZ Page

    The power lost in passive diode configurations can be reduced dramatically by using active diode configurations. A simple control IC operates a power MOSFET switch. The voltage drop across the device is reduced from volts to a few millivolts. Power dissipation drops accordingly.
    https://en.wikipedia.org/wiki/Active_rectification
     

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