Batterypack for Mrf101

[Randal Warren]

I was thinking of building a 12s1p lipo battery that would range from 39.6v-50.4v or possibly use my 60v dewalt flex battery. What are the tolerances of the DC input voltage of the MRF101?

Will a wide range of voltage from a HV lipo pack cause any issues? Would it be better to just use a boost controller?

Just thinking about ideas on how I could power this while portable.

Randal

VE7NHW

[jcve...@gmail.com]

The absolute maximum rating on the 50V to 12V DC-DC converter on the amp board is 60V. The MRF101 can take 133V but remember the RF voltage is swinging 2X the DC rail so to 60V that's 120V on the MOSFET which doesn't leave a lot of room for high SWR.

I'd say for continuous operation 52-54V is about as high as you want to go, it'll take 60 for short periods of time and expect damage to occur any where above 60V.

73,

Jim WA2EUJ

[Randal Warren]

I have a bunch of 6s RC batteries, I was thinking of running 2 of them in series. The voltage would vary from 40v-50v depending on charge, Sounds like the amp will still operate at 40v just probably less output I would presume. 

My idea is to have an external 50v meanwell PS for home use and when portable I could use my 2x 6s RC batteries in series.

Randal

VE7NHW

[jcve...@gmail.com]

Yes the amp will operate at lower voltages and have a lower output power. The theoretical equation for an amp with a 1:4 output transformer is Po = Vdd^2 / 25.

So 40V will make about 65W.

73,

Jim WA2EUJ

[Carl “Nate” Howard]

Jim,

For the equation you used above, why did you use a 25 ohms impedance?  With a 50 ohms load and a 1:4 impedance ratio, wouldn't the load on the FET be 12.5 ohms? I'm just trying to understand the theory behind it a little better...thanks!

73,

Nate W9AXU

[jcve...@gmail.com]

Hi Nate,

The short answer is Vdd is the peak voltage and we calculate power based on the  RMS voltage.

For DC we use P=E^2/R but in the case of a sinusoidal voltage we would use the RMS voltage (DC equivalent) voltage in the power equation and the load impedance that the amplifier 'sees'. 

In an RF amplifier the peak voltage is Vdd so the RMS voltage would be Vdd divided by the square root of 2. Squaring this you get Vdd^2/2 so the final equation is Vdd^2/(2*Zo).

I hope that makes sense.

73,

Jim WA2EUJ

[Carl “Nate” Howard]

Thanks Jim!  My brain was stuck in DC.  This makes perfect sense now.

73,

Nate W9AXU