Hi Yuri. I think this is the best overall method of field powering the 50w PA that I¡¯ve seen. For all the reasons you gave like same battery pack and charger for all applications, no DC-DC converters, lowest cost, etc. It also means no noise and no conversion losses, so maximum performance. Very nice work. Thank you for sharing this with the group.?
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Hello, friends
Let me share my experience with powering QRPLabs PA50 20m band during field activity.
As you might know, PA50 requires about 20V for outputting around 50W. On 20 meters bends it voltage might be 22-24V for 50 Watt output.
The problem arise here, because 50V is not common voltage for amateur radio.
To solve this problem I came with following solutions:
- Use DC-DC converter from 12V to 20V.
- Use 5S or 6S LiIon battery for having 20-24V output.
- Create adapter for connecting two 3S LiIon battery in serial.
Let me explain each solution.
During key-down PA50 consumes about 5A for 24, thus it requires at least 150W DC-DC converter. This is also big item like my PA50 and purchasing it only for PA50 is not a good idea. Have to mention that some DC-DC converters produce noise and it might be time consuming to find one with clear output voltage.
Having dedicated battery for PA50 is not wise. I am trying to have universal connectors and batteries which can be shared or used by different transievers and other items. Also I don't have a charger to charge 5S or 6S LiIon batteries. At the current moment I use ISDT PD60 for charging my batteries and purchasing new charges is not a my way. Also this battery will be dedicated only for PA50. I could do battery with internal balance charger but don't want to go this way.
This solution I used recently. I already have 3S LiIon 18650 battery which I created I few years ago. What if I create second 3S LiIon 18650 battery and connect them in serial. This solves my issues related to previous points. Three 18650 3500mAh cells with max current 8A are cheap. It is easy to assemble or purchase 3S battery. And I have a charges to charge 3S batteries.
Thus I created adapter using XT60 connectors to connect two 3S batteries with 18650 in serial. Have to mention, that both batteries use the same 18650 cell from the same shop aliexpress.
Overall output voltage from six 18650 cell is a little high like 25V, but during keydown drops till 23V. This 23V allows PA50 to have output like 50W.
Also in case I don't use PA50 I have two 3S 18650 battery which I can use for different field transceivers (one as working and second as backup). This allows to have scenarios when one battery is under load and second battery is charging using e.g. solar panel.
Here are a few photos, may be someone find this usefull.
73 de SP2RM
Ronald Taylor