Philmore PS123 Power Supply (11): 4th Unit -- Fan on LM2596 fail

 I previously reported that the LM2596 regulator goes into thermal limiting after about a minute at 3 amps load.  I ordered some small fans to try to cool the device.  Upon experimentation this fan did not supply enough air to cool the device and prevent thermal limiting. 

There are a couple of youtube videos that show using a sink sink on one of these units to prevent thermal limiting. For example here.  I am going to try mounting to a heat sink to try to duplicate their results.  After that it will be a problem of where and how to mount the unit with heat sink.

Philmore PS123 Power Supply (10): 4th Unit - Initial testing with LM2596 board installed.

 The photo below shows the PC board for the LM2596 unit installed in the 4th PS123 power supply.  I added a 3300 uF 35V capacitor, on the bottom of the board. It filters the output of the diode bridge for voltage ripple suppression at the input to the regulator.   The regulator is installed in the center of the board next to a PCB mounted fuse.  The screw terminals are input voltage on the left and regulated 13.8 volts output on the right. 

 

The photo below shows the LM2596 regulator unit before installation on the board.

The photo below shows the test setup for the 0 to 3 amp current load test.

The test results are shown below.  I tested and compared the performance of three regulator schemes.  Load current is on the X axis, load voltage is on the Y axis.  The first unit, blue curve, is the LM2596 unit, Unit 4. This unit output voltage declines 0.36 volt (2.8%) from no load at 3 amps load.  The second curve in red, shows the performance of the 2N3055 regulator, Unit 1, which declines 0.88 volt (6.2%) at 3 amps load compared to no load.   Finally, Unit 3, and original Philmore PS123, with a PNP 2SB410 pass transistor, shows a 0.34 volt decline (2.4%).   Looks like the original design has better load regulations than either of the modified versions. 

The LM2596 version has definite thermal issues at full 3A load.   The voltage drops out after about a minute of running.  

Philmore PS123 Power Supply (9): 4th Unit - testing LM2596 regulator

 I received the LM2596 regulator units this evening.  I was able to adjust the output voltage to 13.8V when it was connected to my bench power supply. When connected to a 15 ohm resistor,  the module produced about 0.9 amps as expected. 

Tomorrow I will reinstall the diode bridge in the PS123 and test the how the LM2596 unit functions.