Products > Test Equipment
Why so expensive? BK Precision 1743B Power Supply
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tooki:

--- Quote from: AVGresponding on December 27, 2022, 10:09:18 pm ---
--- Quote ---Nope, the KA3005P is purely linear. Just uses a fan across the heatsink, which is largely obscured, to keep cool under load. (Heatsink design has changed over the years.)

--- End quote ---
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It's a puny looking transformer for something that can allegedly output 150W. Also the description in the Amazon link is wrong, as it claims 1mV resolution with a 4-digit readout. Good luck with anything over 9.999V!

--- End quote ---
Yeah, the listing is wrong. It’s 10mV resolution, even under 10V. (That power supply is my primary bench supply at home, so I know it well.)

Haven’t had any reason to doubt its ability to deliver 150W. It’s never had any trouble delivering the promised power. The fans just ramp up at higher currents.
Kleinstein:
The BK power supply looks relatively expensive, even if you take into account that this is  the manufacturers suggested price compared to an amazon price.
There max still be a few customers who actually need the slightly higher voltage - if you need 33 V a 30 V supply is not enough.

The KA3005 is more like a bottom end low cost version, that can be that cheap because of the large quantety. Also take into account that it is quite a bit less powerfull: 30 instead of 35 V and actual performance not really up to the promissed specs (e.g. overheating at max current and unfavorable voltage, possible ripple at come voltages and high current). So to be be fair one would need more like 2 of the KA3005.
MrAl:
Just to note some power supplies have a switching front end and linear back end so you get the linear characteristics and the switching converter efficiency.
The switcher keeps the voltage into the linear section just above the min input requirement so the linear part does not have to dissipate too much power (heat) to keep the output regulated in a linear fashion.  Both of my big power supplies are like this.  The heat sinks can be much smaller than too.
This is also probably how the size of these power supplies has come down too over the past 10 years or so.
My slightly older models are about 2 times the size of the ones you can get today.
ebastler:

--- Quote from: tooki on December 28, 2022, 05:09:56 am ---Haven’t had any reason to doubt its [the KORAD KA3005P's] ability to deliver 150W. It’s never had any trouble delivering the promised power. The fans just ramp up at higher currents.

--- End quote ---

Yes, same here. It is also worth mentioning that, like in many linear lab supplies, the transformer has multiple secondary winding taps. The Korad switches to the nearest one (lowest adequate AC voltage) depending on the desired output voltage.

Hence if you set a low output voltage and draw a large current, the regulator/heatsink/fan do not have to deal with up to 150W of excess power, but only approx. 1/3 of that in the worst case.
AVGresponding:

--- Quote from: tooki on December 28, 2022, 05:09:56 am ---
--- Quote from: AVGresponding on December 27, 2022, 10:09:18 pm ---
--- Quote ---Nope, the KA3005P is purely linear. Just uses a fan across the heatsink, which is largely obscured, to keep cool under load. (Heatsink design has changed over the years.)

--- End quote ---
<removed annoying formatting tags>
It's a puny looking transformer for something that can allegedly output 150W. Also the description in the Amazon link is wrong, as it claims 1mV resolution with a 4-digit readout. Good luck with anything over 9.999V!

--- End quote ---
Yeah, the listing is wrong. It’s 10mV resolution, even under 10V. (That power supply is my primary bench supply at home, so I know it well.)

Haven’t had any reason to doubt its ability to deliver 150W. It’s never had any trouble delivering the promised power. The fans just ramp up at higher currents.

--- End quote ---

Could you make some ripple and noise measurements at full power for us?
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