Why so expensive? BK Precision 1743B Power Supply

[Omega Glory]

I recently acquired a used BK Precision 1743B Power Supply on Ebay for about $125. It's a 0-35V 0-6A single output power supply. After checking BK's website, I discovered that this unit is priced at $690 new, and includes a 2 year warranty. I was shocked to see this price, and I'm wondering why it happens to be so very expensive. For example, for about $145, one can get a KORAD KA3005P, which has similar voltage and current capabilities, and more sophisticated controls, (it also comes with a 2 year warranty).

So what's going on here? Are you paying an extra $545 for the name brand and build quality? Or perhaps its something more subtle, like voltage ripple.

Any thoughts?

Product Links:
BK Precision 1743B: https://www.bkprecision.com/products/power-supplies/1743B
KORAD KA3005P: https://www.amazon.com/KORAD-KA3005P-Programmable-Precision-Adjustable/dp/B0085QLNFM?th=1

[BeBuLamar]

I don't know. The unit doesn't look expensive. Since you have the unit where did BK make them? It doesn't look like a USA model.

[Wrenches of Death]

I bought mine new from Amazon back in September of 2019. Amazon was selling them at the time for $117.64 with free shipping. It's been a good power supply and I have zero complaints. A friend of mine bought one a couple of days later for a similar price.

One quick warning though. The "short" button for setting the current settings should NEVER be used if you are using the supply to charge batteries. Especially large ones. My friend melted some internal wiring and fried the short switch.

Use an external inline rectifier if you are using any adjustable "lab" type power supply to charge batteries.

WoD

[Omega Glory]

Hmm, all right. Even looking at Digikey or Mouser, I still see this thing selling for many hundreds. Maybe I'll do a teardown and see if I can spot anything expensive, lol. I'll post pictures if I do.

[BeBuLamar]

Can you tell me where BK Precision made the unit?

[Wrenches of Death]

Can you tell me where BK Precision made the unit?

Mine has a gold and black sticker in the middle of the underside that lists Taiwan, ROC.

WoD

[AVGresponding]

Is it particularly heavy? Hopefully, the physical size indicates it's a linear PSU, with a big-ass transformer. The Korad is a switcher. Linear PSUs are always more expensive watt for watt as they are less noisy on the outputs.

[2N3055]

Is it particularly heavy? Hopefully, the physical size indicates it's a linear PSU, with a big-ass transformer. The Korad is a switcher. Linear PSUs are always more expensive watt for watt as they are less noisy on the outputs.

KORAD KA3005P is not a switcher..

[MrAl]

I noticed that some sellers raise the price of some of their stuff arbitrarily maybe to try to catch people off guard who dont know the real value of the product.  I see this so much online on many different web sites.  It could be just that, a gouging where the real cost is much much less.
If you look better for the same product even on the same site sometimes you can often find a much lower price.  Is the quality any different?  Well, if it works for you it works for you.  If it doesnt send it back.

When i bought one of my 30v 10 amp switching power supplies with linear back end it was something like $150 and now i see similar products around $70  which is half the cost.  I got another unit the same make and model for $60 at a later date.  It works exactly the same as the original unit.

[mcinque]

it is nothing new that bk precision rebrands some products and simply sells them at a higher price. you can see this behavior on manson power supplies (very good value products) that are sold rebranded under different brands.

many brands do this. bk for some asks the manufacturer for a black case or changes some aspects, but the unit is the same.

it is not clear why i should buy their product at a higher price if the features are identical. I can theorise about better support, in case repairs or upgrades are needed, but this is not guaranteed by the price difference (see peaktech who doesn't have a single product that isn't rebranded and who doesn't offer much support as far as I could experience: I asked them if there were differences between their power supplies and manson's, in particular if theirs had the same crapxcon capacitors, but they took offence at the insinuation and closed the discussion without replying)

see my old thread https://www.eevblog.com/forum/testgear/bk-precision-peaktech-only-rebranded-objects

[BeBuLamar]

In this case I think BK just want to charge too much. The unit doesn't look better than the other units and has a lot less features.

[Mechatrommer]

Is it particularly heavy? Hopefully, the physical size indicates it's a linear PSU, with a big-ass transformer. The Korad is a switcher. Linear PSUs are always more expensive watt for watt as they are less noisy on the outputs.

KORAD KA3005P is not a switcher..

looks like it is... at least there must be smps pre-regulator in there... hinted by the lack of hefty heatsink usually seen on purely linear PSU... but the Korad's regulation <2mVrms (similar to BK) also hinted they've done some homework. the BK's look bigger from the outside but we cant be sure without teardown, probably pure linear, probably with smps pre-reg as well, noise floor for both is about same 1mVrms..



i cant find teardown for 1743, if it has the kind of heatsink and toroidal like in this video, then the higher price is justifiable, ymmv.

[BeBuLamar]

I don't know about the Korad but I bought this one April 2021 for $129. Amazon wants $199 for it now. But it's linear, has digital readout and counting wheel as well as an RS-232.
https://www.amazon.com/Programmable-Single-Channel-Supply-MPS-3605LP-MATRIX/dp/B07Y86LBRY

[tooki]

Is it particularly heavy? Hopefully, the physical size indicates it's a linear PSU, with a big-ass transformer. The Korad is a switcher. Linear PSUs are always more expensive watt for watt as they are less noisy on the outputs.

KORAD KA3005P is not a switcher..

looks like it is... at least there must be smps pre-regulator in there... hinted by the lack of hefty heatsink usually seen on purely linear PSU... but the Korad's regulation <2mVrms (similar to BK) also hinted they've done some homework. the BK's look bigger from the outside but we cant be sure without teardown, probably pure linear, probably with smps pre-reg as well, noise floor for both is about same 1mVrms..

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.)

[AVGresponding]

Is it particularly heavy? Hopefully, the physical size indicates it's a linear PSU, with a big-ass transformer. The Korad is a switcher. Linear PSUs are always more expensive watt for watt as they are less noisy on the outputs.

KORAD KA3005P is not a switcher..

looks like it is... at least there must be smps pre-regulator in there... hinted by the lack of hefty heatsink usually seen on purely linear PSU... but the Korad's regulation <2mVrms (similar to BK) also hinted they've done some homework. the BK's look bigger from the outside but we cant be sure without teardown, probably pure linear, probably with smps pre-reg as well, noise floor for both is about same 1mVrms..

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.)

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!

It'll be interesting too see inside the BK for comparison. My guess is it'll be beefier, and by implication, more likely to meet claimed specs and be reliable.

[tooki]

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.)

<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!

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]

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.

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]

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.)

<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!

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.

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

[ebastler]

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

Here's an older review with measurements and some modification suggestions. (The temperature-controllled fans are already standard in the more recent versions of the KA3005x.) http://afug-info.de/Testberichte/Korad-RND-3005P/

German only, unfortunately. Ripple is "Restwelligkeit". 2 mVpp is what they measured, apparently met over the full range of voltages and currents.

[bdunham7]

I recently acquired a used BK Precision 1743B Power Supply on Ebay for about $125. It's a 0-35V 0-6A single output power supply. After checking BK's website, I discovered that this unit is priced at $690 new, and includes a 2 year warranty. I was shocked to see this price, and I'm wondering why it happens to be so very expensive. For example, for about $145, one can get a KORAD KA3005P, which has similar voltage and current capabilities, and more sophisticated controls, (it also comes with a 2 year warranty).

So what's going on here? Are you paying an extra $545 for the name brand and build quality? Or perhaps its something more subtle, like voltage ripple.

Any thoughts?

Your first clue would be the weight.  The BK unit probably weighs 25-30 lbs, not sure for the other one but I'll bet it's nowhere near that.   The transformer will be 3X or more the size of the Korad unit.  But the most important difference is that the BK will have full overload  and reverse polarity protection and is suitable for battery charging.  You can connect a battery to it while it is powered off without damage.  And if you are careless, you can connect that battery backwards and still not damage it.  If I were  you I'd be very happy to have that unit at that price.

[jeffjmr]

I have two 1743s. They have been bulletproof.

I believe the A and B models added an internal shorting switch for setting current without having to short the leads.

One of mine is noisy, one quiet but neither as quiet as my Leader LPS-152.

Here’s the schematic for the 1743.

Jeff