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QMX+ dev-board

 

What is the usable height above the dev board once installed in the QMX+ standard enclosure? I plan to build a complete QMX+ and use the dev board to install:
- a set of four LiFePo4 batteries (105x65x26mm);
- a DC-DC 12V 24V to 9V 4A 36W Converter DC Voltage Reduction and Stabilization Waterproof Voltage Reduction Module Suitable for Various 9V Equipment to generate a stabilized 9V voltage to power the QMX+. (https://www.amazon.com/Converter-Reduction-stabilization-Waterproof-Equipment/dp/B0C179FLV3/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.xqzM 2Hf03dOzy2nwqMax7Qf4sJEp_zLLnwUGQY-uK66l12Hz3NDHnJAtg5CKDuO1Gv6cJpWSPdPM--7-OKOI9LueaAjCLUhr_nMp32NVSTGR8H4bASlSvuoWmzrtD9MQnpgJuaW 9RiEoLtvPrcrjc3o4umJlOuxhySJ_seF1oQNPFv86sfw_SiUxu983cpfXdj5typRCWbYQXZzjHi4Md0Snoxj94pgdX4_LB6sVs_g.-juE80eVb5RbLMEfZu7Nk-jkFn7Fu tPixjGIfHq44EE&dib_tag=se&keywords=12v%2Bto%2B9v%2Bdc%2Bconverter&qid=1734408845&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1);
- an audio amp and speaker.
Connections would be made through additional connectors soldered to the dev board aft line and accessible through holes drilled in the rear face of the enclosure.
73 - Pierre - FK8IH
 

Pierre,
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Sounds like four 26650 cells, side by side.
Could work out well.
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I see slightly over 31mm above the dev board to the inside of the top cover, almost 32mm.
Mounting the LiFePO4's to the dev board should work fine.
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You might consider attaching the LiFePO4's to the top cover,
keeping weight off the main QMX board in case of a sudden shock.
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Could also mount stuff to a new board that slides into the top rails,?
just like the main board slides into the bottom rails.
Your LiFePO4's would fit, but perhaps touch the top of some toroids.
Would definitely fit if you cut holes in the new board that the LiFePO4's sink down into.
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Jerry, KE7ER
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On Wed, Mar 12, 2025 at 05:02 PM, Pierre - FK8IH wrote:

What is the usable height above the dev board once installed in the QMX+ standard enclosure? I plan to build a complete QMX+ and use the dev board to install:
- a set of four LiFePo4 batteries (105x65x26mm);
- a DC-DC 12V 24V to 9V 4A 36W Converter DC Voltage Reduction and Stabilization Waterproof Voltage Reduction Module Suitable for Various 9V Equipment to generate a stabilized 9V voltage to power the QMX+. (https://www.amazon.com/Converter-Reduction-stabilization-Waterproof-Equipment/dp/B0C179FLV3/ref=sr_1_1_sspa?dib=eyJ2IjoiMSJ9.xqzM 2Hf03dOzy2nwqMax7Qf4sJEp_zLLnwUGQY-uK66l12Hz3NDHnJAtg5CKDuO1Gv6cJpWSPdPM--7-OKOI9LueaAjCLUhr_nMp32NVSTGR8H4bASlSvuoWmzrtD9MQnpgJuaW 9RiEoLtvPrcrjc3o4umJlOuxhySJ_seF1oQNPFv86sfw_SiUxu983cpfXdj5typRCWbYQXZzjHi4Md0Snoxj94pgdX4_LB6sVs_g.-juE80eVb5RbLMEfZu7Nk-jkFn7Fu tPixjGIfHq44EE&dib_tag=se&keywords=12v%2Bto%2B9v%2Bdc%2Bconverter&qid=1734408845&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1);
- an audio amp and speaker.
Connections would be made through additional connectors soldered to the dev board aft line and accessible through holes drilled in the rear face of the enclosure.
73 - Pierre - FK8IH

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Reply
 

You can make the necessary connections directly to the dev board, by installing standard male and female connectors to the QMX+ board.? Hans put footprints on the QMX+ for audio, all voltage busses, etc.? Sardar used these for his ABS (ATU-Battery-Speaker) design that several of us built.
Stan
 

Pierre, as you probably know, you probably want to include a battery
management system?to balance cells and avoid over-discharging or over-charging.
LiFePO4 is not as forgiving of overcharging as some chemistries.
This means can't overcharge some cells in a string of four to restore balance
while the remaining cells not yet fully charged catch up.
Do a web search for "4S LiFePO4 BMS".
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Alternately, you could pop the four individual cells out of the battery pack
and put them into a commercial battery charger.
?
Jerry, KE7ER
 

Jerry, my LiFePo4 cells have already a battery management system. About the voltage, I guess I will power the QMX+ with 9V since the 4xLiFePo4 give between 14.2V fully charged and 12V discharged, 9V would be nice. Thanks for the idea to find the connections inside the box and attache the cells to the enclosure.
73 - Pierre - FK8IH
 

Stan,
Thanks for your comment.
Looking at the rev3 Assembly Manual and Schematics it seems that I can send the +9V and Gnd from the 12-24 to 9V converter to JP101 on the mainboard. In which case I can glue with araldite the DC socket upside down and use it to plug in the charging DC current from the wall charger and solder to its two lugs now visible on its top the two wires from the LiFePO4 batteries. This would make a very easy modification to the QMX+ however I have one question: the schematics show JP101 as a 8 pins socket (pin 3 V_IN and pin 2 GND) and the assembly manual shows this JP101 as a 4 holes only footprints! I don't know what are the GND and V_IN holes on the mainboard footprints! Obviously I would use sockets and pinholders for these connections in order to keep the dev-board removable.
About the amp-speaker, I think the easiest way is to plug a 3.5 wire amp-speaker with inside batteries.
All in all there would be no visible modification to the QMX+ and make it an easy to transport outside xcvr with an EFHW antenna or my PAC&é vertical antenna.
Any comment about JP101 or any other suitable points where to connect the GND and +9V from the converter to the mainboard will be appreciated.
73 - Pierre - FK8IH
 

It seems that JP105 is a nice place to sold a socket and pin holder and get in the dev-board the GND and +9V points. There are soldering places both on the mainboard and on the dev-board for JP105.
There remains to find a way to sold a pin holder and socket near the DC input I will use to connect tha wall charger for the batteries.
73 - Pierre - FK8IH
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Yes, the Vin signal is there, and is what we used for our battery.? There is also a similar JP right behind the audio connector with the audio signal.? So you don't need external connections except perhaps for the charger power.? However, note that a 9V QMX+ works fine in receive mode at 12V.? You just need to avoid transmit.? ?So if you set the protection Vmax to 10V, and set the protection method to inhibit TX, you could use the original power-in jack for charging.? These settings prevent tx during charging.? Just use a 2 amp diode on the output of your 9V converter to protect it from the back-voltage during charging.? ?And of course,? you are in receive-only operation (or powered off) during charging.? ?And no external connections or holes in the back panel required.? The design we used did add a switch on the battery output, which we extended through the back panel.? This was done mostly for protection-since the internal battery/converter output to Vin via JP105 is present on the power jack, and we wanted to remove that when not in use, or when powering from an external supply.?
Stan
 

Thank you Stan for your nice explanations, everything is by far clearer in my mind now.
I understand that I can connect the batteries and the 12-24V to 9V converter to JP105 (GND of both to GND of JP105 and +WIRE of both to a bidirectional switch "CHARGE or OPERATION" added on the aft panel with its common +output soldered to JP105 V_IN).
I found in the operation manual "5.17 Protection menu" and will set "Protection voltage" to "Prevent Tx", "Min Voltage" to 7 and "Max voltage" to 10.
I guess I can solder the DC socket as written in the manual and plug into it the LiFePO4 batteries charger when needed but as my charger output is 14.75V when unloaded I should never sxitch ON the QMX+ when these 14.?? voltage is entering the DC socket. Am I right to think that if the QMX+ is unpowered there is no danger to have these 14.?? V entering the DC socket?
Obviously as there are 7 holes available for spacers and screws to mount the dev board on the mainboard, I will use all these 7 holes in order to mount the batteries on the dev board.
73 - Pierre - FK8IH
 

I think the easiest way for me would be to add two components to the aft enclosure and a few wires:
- one DC socket directly connected to the LiFePO4 batteries bank to plug in the 14.75V charger;
- one switch in the output +line of the 12-24V to 9V converter in order to switch ON or OFF the internal batteries themselves connected to JP105 GND and V_IN.
The normal DC socket would then still be usable in the shack to supply DC current to the QMX+ from a 120-250V AC to 9V DC wall power supply and my QMX+ would have two kinds of DC supply: shack AC supply and SOTA/POTA internal batteries DC supply. The QMX+ could even be in charge in the shack while being operated from the AC current.
73 - Pierre - FK8IH

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