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Korad KA3005P power supply: UI changes

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ebastler:

--- Quote from: 5U4GB on February 03, 2024, 09:47:07 am ---In general though the heatsink layout is pretty strange both for the original and updated heatsink, instead of the air flowing across the fins the HS is mostly blocking the air flow, which I would imagine leads to both poor performance and a lot of unnecessary noise because there's a solid block of metal a few cm from the blades.  What were they thinking?

--- End quote ---

That less-than-ideal arrangement probably dates back to the first generation of KA3005s. Those did not have a proper heatsink with fins at all, but essentially a flat aluminium plate with some token "fingers" along the edges, made by cutting and bending the plate. Blast some air straight onto the plate, done.  ::)

Can be seen in Dave's original teardown video from 2013: https://youtu.be/g94mpom2Ahs

5U4GB:
Yeah, and you can't easily change it because they're replaced the fake Rubycons with a single giant cap that would get in the way of the transformer if you rotated it 90 degrees to allow flow down the vanes:



You'd also, because of the metal plate to force airflow across the transformer, get very poor airflow across the heatsink.

5U4GB:
Just posted a bunch of photos and comments of whatever version it is they're shipping now.

Pfriemler:
Well, as far as I remember there was a single main cap all the time, even in the first version Dave teared down.

I do think different to the fan behaviour: Unlike any PC stuff with monitoring hardware, a tacho signal from the fan is rather seldom in such hardware and even a PWM controlled (4 wire) fan is a kind of overkill to such a device. The Korad does not have to know about the speed of the fan, as long as there's a sufficent correlation between rotation speed and the supplied voltage - which is the case, normally.

And for the air flow design: If you place a fan this way directly above the heat sink, you have a powerful airflow through the cooler even in the direction of suction, as here. The cooling would be better if you change the air direction as suggested by some users, but I would never heat the components inside this unnecessary way.

Ramping speed may come from the fan regulation. Unlike the first versions with a load regulated fan speed the cooler follows the load with a load dependent delay, very normal. I remember my Voltcraft DPS2010, famous for a stupid fan regulation: the fan starts at about 42 °C and reaches may speed @ 50 °C, regulation far too steep, which results in an oscillating speed of the fan with middle loads. And, full fan speed with any current >40% of maximum. That's annoying!

As mentioned above, I have a new Welectron design model and got me another second hand, RND 320 KA3005P, answering "V5.5" on *IDN?. I have no idea how long this version is on market (and how old it is). Now I can compare both versions in behaviour and performance and do like the improvements a bit more. At a first glance, the fan speed at no load is significantly lower with the new version.

Next week I will make a "light teardown" of both to examine differences, before I go and fix the non lit OVP and OCP LEDs and the (sometimes) snarring fan.

Pfriemler:
Hard to believe: both OVP and OCP status LEDs were dead. Because I wanted to change C.V. and output LED, I got two spare LEDs and solder them to OCP and OVP. After that, the third LED was broken.
Btw. the LEDs are of a dedicate low current type. They need not more than 3 mA for full brightness.

The differences of both RND (Reichelt) KA3005P V5.5 and KORAD (Welectron) V5.8 are only a few:
- there was no metal sheet inside above the transformer
- the com board looks complete different
The red/green led board and the housing color are obvious.

To my very surprise, there's no difference in fan control. Both uses 120 Hz PWM, I got no differences with the scope. But the fan seems to be different in sound as well as in air flow. I even put both devices side by side and let them power the opposite's fan - the Welectron's one stays more quiet.
If I stress both versions with a 5 amps full short circuit, the semiconductors on power board heat up to ~110°C, sometimes with a 2-3 degrees difference, so there's no lack n cooling under load.
Also the sound measurements show a rather light difference under full load (49 vs 51 dBC) and idle (34 vs 38 dBC, ~1m distance, back side, yet no housings)


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