[ARC5] Prelim comments on a DC - DC B+ converter.

[Bob kb8tq]

Hi

Check the capacitors on the board. They (obviously) have a voltage rating. They also 
these days have a current rating. In high frequency switcher duty, current in the caps
can be a fairly big deal …. finding that information may not be easy at all. In the case 
of voltage, I’d be a lot happier at 80% of the marked numbers than I would be at a 
higher level. 

Bob

> On Apr 18, 2018, at 4:24 AM, Leslie Smith <vk2bcu at operamail.com> wrote:
> 
> 
>    Testing a DC-DC step-up converter.
> 
>    My unit appears to be the same as the DC-DC converter described here by David Stinson recently.
>    The converter is sold on eBay for a little less than $10.  See photo.
> 
>    Mr. Stinson's tests were directed to estimating the RF noise generated by the converter.  My tests were directed to the more basic performance of the converter. For the moment the results are quite incomplete.  This was because I chose to test the unit wit a PSU with over-current fold-back voltage limiting.  With even a modest load the immediate inrush current at the moment I turned the power on cut the PSU source voltage well below the converter's lowest operating voltage.  I estimate that to be around 10V DC - although the unit is advertised to work at 8V.    So at some low source voltages the converter failed to start (expected) and the result was invalid (because my PSU was under-rated).  This applied even when the expected power to the load was well within the static capability of the Marconi Instruments power supply.  
> 
> When the source voltage was lower (eg 14V DC and the current delivery of my M.I. PSU was 2A) the converter started more reliably than at a higher voltage (eg 28V DC with the current limited to a mere 1A).   So the experiment failed because I need a PSU with more "grunt".  
> 
> Generally, once the output voltage on the converter has been set, the regulation appears to be good.   At 250V, and using a resistive load of 4k ohms the converter delivered 16 Watts (as expected) from a 14V supply.  I could get this by setting the output voltage low, connecting power and then winding up the output voltage.  If I left the voltage setting untouched and simply turned on the PSU it protested (fold-back) and the converter failed to start correctly.  So - again - I need to drag out a PSU with more grunt.
> 
> I'll do that and complete a table of observations, including ripple current (and so on).  The supply is rated at 40W; I want to see if the unit can deliver this for any length of time.  The efficiency appears to be in the order of 0.85 to 0.90.  Delivering 16W the heat-sink is only modestly warm.
> 
> My initial impression of these power supplies is that they seem to good value for money.  Further testing will show if the impression is reliable.
> 
> All the best!
> 
> Les Smith
> <DC-DC step-up converter (oblique x6).jpg>______________________________________________________________
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