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Author Topic: Question about power consumption  (Read 4685 times)

Posts: 1

« on: February 02, 2001, 09:55:05 AM »

   I have a DJ-580T and occasionally I will use a 12V 6AH Power Pack for day events - and I was wondering the power consumption of a 5 Watt transmission.  How much is being drawn from a battery in - let's say a 2 minute transmission @ 5 Watts.  I find that the NiCads that came with the HT are not sufficient for such an event - and go through 2, 12V 1200mAH packs while I also feel this 6AH battery is overkill since I could use it again without recharging it.

   Could someone with some technical knowledge of this give me an idea of the power consumption of a 5Watt  transmission.  And a way to guage this so that I don't have to lug this pack around with me - maybe I'll be able to build a smaller pack for myself for the future.   
   Sorry if this vague in any way - I have no idea how to put this.

Thanks in advance

Posts: 145

« Reply #1 on: February 02, 2001, 01:27:00 PM »

The answer is not so simple.  
To accurately calculate the expected battery life you need to know the current draw on transmit.  Unfortunately, the owner's manual doesn't give this information.

We can make a guess though.  The current draw will be 5W /12V x efficiency.  We don't know the efficiency but let's assume 50%.  That is, your radio will draw twice as much power from the battery as goes out the antenna.

So:   I = 5W/12V x 2 = .833 A (or 833 mA)

If you transmit for 2 minutes, that's 1/30th of an hour.  
So your power consumption would be 833 mA x 1/30H = 27.8 mAH

Your battery pack is rated at 1200 mAH so:

       1200mAH/27.8mA =  43 two minute transmissions (or 1.4 Hours continuous)

Experience tells me that no HT is going to put out 5W   for 1 1/2 hours on one battery, so I assume that my guess for efficiency is way off.

Now, when I estimated 50%, I was only figuring the power consumption of the final amplifier.  The battery also has to run the frequency synthesizer and driver stages.

Do you really need 5W?  A local event in a park or some other situation where the radius of communications is less than 1 mile, could probably be covered with 1W or less.  Also, a 2 minute transmission seems very long.  Perhaps your answer is a modification in your operating habits.

I hope this helps.

73, Jerry

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