¿ªÔÆÌåÓý
a current limiting PSU should be the second item in your toolbox after a multimeter.
There are plenty of designs around and can be made quite cheaply.
I would recommend a linear PSU (NOT DIGITAL)
I have had mine over 40 years and has served me well over that time.
The PSU in itself is not enough, you have to know how to use it. (not as obvious as it may seem!)
The PSU should only be connected AFTER the basic checks are done using a multimeter.
When the PSU is connected for the first time the current limit should be set at its lowest, the voltage should be set at the design voltage for the equipment you are testing.
When the PSU is connected, you will notice that the voltage drops to a very low value, this is because the current limit set is below what the circuit requires,
You now gradually increase the current limit ( you should know roughly what current your device is expected to draw i.e? receiver current usually less than 100ma)
as you increase the current limit the voltage should start to rise towards the set value e.g 9v, 12v etc.
IF it does not, then you have a problem that needs investigating.
If it DOES rise it should stabilize at the set voltage and the current will also stabilize at or about the design value e.g 80ma
some devices do not like their voltages gradually rising but now you know there are no serious problems on the power side, the PSU can be disconnected and reconnected and everything should be ok.
You can now set the current limit somewhat higher and everything should be ok, obviously on transmit you will need a much higher current setting.
My recommendations for the PSU are as follows:-
Use a LINEAR PSU that has current and voltage limiting variable resistors and voltage and current meters so you can see what is happening.
it should be capable of delivering up to 30v (use a 15-0-15 0r 18-0-18 volt transformer) at a current of 1 to 2 amps - larger if you must but this is adequate to test most things before powering with a higher current PSU).
It never ceases to amaze me that people build these kits from QRP Labs and others without even the basic tools or knowledge for that matter,
bearing in mind we are all supposed to be radio hams.
From: [email protected] <[email protected]> on behalf of Sandy <mac3iii@...>
Sent: Sunday, January 14, 2024 6:23 PM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] current-limited power supply. ?
Hi John - I bought a cheap 6-36 volt 5A adjustable buck boost from Amazon for $25. It has adjustable voltage and amp limiting that has saved my QMX on at least one occasion from shorts during construction. I've used it daily since June 2023. The only issue is that sometimes
(rarely) the display shows 0 amps out when I know it has 90mA - but turning it off and on usually fixes that. - Sandy On 1/14/24 20:46, John KY4WW via groups.io wrote:
Ready to start my QMX high band kit build. |
