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Korad KA3005P improve efficiency

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The Korad KA3005P has an lineair power supply with 50 Hz transformer and power electronics to reduce the voltage (and dissipate heat). I think the Korad KA3005P can be much more efficient. Below are some measurement with different power outputs and different gridvoltages:

Gridvoltage   Power in   Vout   Iout   Power out   Power loss   Efficiency
230 V   111 W   9,22 V   3 A   28 W   83 W   25%
160 V   75 W   9,22 V   3 A   28 W   47 W   37%
230 V   207 W   15,41 V   5 A   77 W   130 W   37%
160 V   138 W   15,41 V   5 A   77 W   61 W   56%

The Korad KA3005P has multiple taps on the transformer that are switched with relays. The tapsetting is only depended on the actual output voltage. It does not take the gridvoltage in account.

I want the tapsettings to be more efficient. The powerloss is pretty high now. How can i change this tapsettings without rewinding the transformer ;D For longer high power loads i am using an autotransformer to reduce the gridvoltage to 160V...

To gain what in the end ?   more design complexity ?  lower temp losses  etc ...

It is designed like this,  it is normal in a sense you have thermal losses etc ...  LINEAR says it all,   even having tons of supply taps,  you have the load variations,  if the supply get a little bit low on the input power section  you may loose efficiency and stability ...

This is a pretty basic psu ... and lucky you you have xformer taps in it, other dont  loll 

Not my 52 pourd   Lambda 80vdc - 8 amp psu,  when i push it to the max,  i have an 864w heater  loll

Get a switchmode ??   or some  psu  like Kikusui, they are in some models  pseudo phase controlled with a mix of buck and linear mode,  they dont heat at all

If not,   get some sorensen or other psu based on phase controlled ac main inputs  ...  they get bulkier because of the big coil input they have, since they almost work lik buck converters

my 2 cents


I understand the principle of a lineair power supply. But the heatloss is unnecessary high.

An switchmode was better. But I already bought this one a few years ago. Can I fix or improve this bug  8)

It seems my device is designed for 160 Volt, but in my country I have at least 207 Volt.

The supply needs some reserves for different effects. One is a possible drop in mains (e.g. 220 instead of nominal 230). Another is the ripple in the filter capacitor, that can be larger when the current is high. A 3rd point is a reserve for the short interruption of the power when switching the relay. The relay is on the AC side an apon switching on may just miss much the a half cycle. So for this transition the ripple may be about twice the normal size.

Because of the stress to the relay contacts is would be problematic to make the filter capacitor much larger.

A few more voltage taps could allow for a slightly higher efficiency, but with more effort.
One could take the current (at least the current limit setting) into account and in some case allow for a slightly lower voltage for tap switching. Still this in a relatively large effort for an often small gain.
A rather crazy idea could be synchronizing the relay switching with the mains phase and this way reduce the dopt due to the break before make time a little.

A much better efficiency would need a more drastic change, like a switched mode preregulation or may be electronic cross over between 2 supply levels possibly in addition to the relay switching.

any switchmode reputable brand should do at least minimum 85-100vac  up to 240vac,  if not search for goodbrands,  not china crap stuff

you main losse is  before the main power stage and after it is versus the consumed current as you may guess,  not necesarly on the primary xformer

for the xformer you choose an toroid one, better efficeiency, less thermal loss for a start

if the main rectified filtered voltage is 40 volts, and after the pass transistors, you ask 20 volts, you have 20v of loss multiplied by the consumed current, 1 amp is already 20 watts of loss ...

you have to find better design psu if it is a real consern to you

scr controlled bridge rectifiers  etc ....

in the end you redesign almost everything  loll and you have no garantie it will work reliably with and without load ...


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