• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 753 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Lipo Battery help

Dennis Starbird
Prodigy 115 points
Other Parts Discussed in Thread: LM25116

I using 4 Lipo pouch type batteries that charge to 4.20 and provide 20 amps, so at full charge that will produce 4.20 X 4 = 16.80 volts @ 20 amps. I want to use this battery pack to power my Ham Radio. The specs on the radio indicates the radios input voltage is 13.8 +- 15% = voltage range is 15.87 to 11.37.  The Radio requires 20 amps to TX at 100 watts.  So here is my problem how to I bring down the voltage from the Batteries and still use full power? I'm sure that some of the battery voltage is surface charge and will bleed off quickly, but I still don't want to risk powering my radio with the 16.80 volts.

The big issue is not finding a IC voltage regulator to drop the voltage that's easy my problem is the current I want to draw from the batteries during TX operations. I have found some very high end voltage buck regulators that cost around $200 that will to allow me to operate at 100 watts. I sure like to get some feed back before I move that direction.

Thanks

Dennis 

  • 0
    TI__Guru**** 191445 points

    You would not have a problem to convert 16.8 V down to 13.8 V using a buck converter.  You should be able to get efficiency greater than 90 % (maybe not that high at full load).  You state you need 100 W for TX, but 13.8 V at 100 W is only 7.25 A.  Can you clarify?

  • 0 in reply to JohnTucker
    Prodigy 115 points

    John,

    Hey thanks for your feed back - like you said using a buck is not the issue but finding one that will work with 20 amps and have a LDO spec. is becoming a real problem. I'm getting the 20 amps from the radio data sheet, I understand you did the math for 100watts with 13.8 volts and came up with a little over 7 amps. But I have to use the radio specifications sheet and it state 20 amps so Im building to 25 amps at 12 volts. 

    Thanks 

    Dennis

  • 0 in reply to Dennis Starbird
    TI__Guru**** 191445 points

    assuming 95% efficiency, and 16.8 V @ 20 A input, you can get 16.8 * 20 / 13.8 = 23.1 A maximum output current.  I would look at LM25116 as a possible solution.    You can use Webench on line tool to help you design your circuit:

    www.ti.com/.../power.page