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Hello all,

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My QMX suddenly shuts off at around 10.5V. Is it normal ? I can't recreate it but last summer I think had it giving me high voltage warnings when in fact, voltage was low even if I didn't understand at the time that the radio was suddenly shutting down when voltage is low (/g/QRPLabs/topic/110264408#msg135921)... It is problematic for me as I use a nominal 12V drill battery that goes down to 10.5V relatively quick before stabilising there....?

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I've already fried the SMPS once so I have a new set bought in April 2024. I am not too sure how to investigate this further.

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73,

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Yannig - F4IUJ?

And to be crystal clear, it is a 12V QMX...

Yannig, what do you have your lower protection voltage parameter set at? (protection menu, min voltage)

It should probably be at 7V.? But this setting should not cause your QMX to "shut off" - just disable TX or flash a warning.

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It is not normal for a QMX to "shut off" at any voltage above about 6.5V.? It will not transmit below about 7V, but the receiver works below that.? So if yours is powering off at 10.5V, there may be some problem with your QMX.? Or maybe not.

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With your battery pack, you may be able to measure 10.5V terminal voltage, but it may have no capacity for current.? The QMX will need up to 200mA at 10.5V in receive mode, and 1A in TX.? So if the battery is near depleted, it may not be able to deliver that current at 10.5V, so the QMX will "shut off".?? The way to test this is to put a mA meter inline, to see the current.? Or when the battery is at a point when the QMX "turns off", take just the battery and do a simple load-test on it to see how much current it can deliver.

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Stan

Thank you Dan,

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I've removed the battery pack out of the equation and I use my lab linear power supply which can deliver 1A. I let the QMX in receive mode and I slowly decrease voltage and suddenly it shuts off at around 10.5V.

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With the battery it was more erratic and sometimes I got a high voltage warning whereas the voltage was definitely below 12V.

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In the menu I have min voltage : 7V, max voltage : 13V, supply voltage : prevent TX

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I think there is probably something wrong with my QMX but I am at loss at what it could be...

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73,

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Yannig - F4IUJ

Yes, definitely something is wrong.?

Perhaps if you bring up the terminal diagnostics page that shows the power supply parameters, then turn down the voltage to just above where it turns off, it may give a clue on what's happening internally.

Hello all,

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Finally got the time to attach the QMX to the computer and I found interesting stuff... :

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This is what it looks like TXing when the voltage is about 11V, nothing wrong apart from the supply voltage reading wrong by 0.2V

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When I get the Voltage down to 10.8V, this is what I get and "interesting" stuff happens, namely the supply voltage is wrong by 1V, the 5V SMPS voltage is too high and the transmitter voltage is too low :

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When I get down to 10.7V not TXing, even ,more surprising stuff happens, the supply voltage is completely wrong and on top of this the 5VSMPS gives us a very high reading which might well be true(ish) as the screen becomes darker :

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My instinct would be the 5V SMPS is shot and weirdness ensues but I am not sure of myself at all! May be the overvoltage protection kicks and switches off the QMX. For reference, I destroyed one of the SMPS last year and replaced the 2. In theory they should be good....

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Any help welcomed !

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73,

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Yannig - F4IUJ

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