China BPR56 ceramic 5W power resistors

Dear fellow DIYers,

I like to show you the inside of a cracked open 5W power resistor I bought on Aliexpress.
Those resistors are sold as "BPR56" 5W non-inductive power resistors and cost roughly 0.30€ p.p. including shipping so I was hoping they could be somewhat well made.
Needless to say I accidentally destroyed one of them during measurements and cracked it open to see what is inside.

What I found inside looks rather disappointing:
Lots of cement filler and the actual resistor looks like it can handle 1W maximum.
Also, the resistor is wire wound, thus not low inductance.

Here is the picture:

What do you think?


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The half-watt inside a "2 Watt" brick is an old-old story.

For 1/3rd of a buck, I think you got everything you paid for.

Yes wire-wound (shocked) and low-Ohm but it takes a LOT more turns than that to matter inside or above the audio band. Look at an output transformer's 8r winding: 30-100 turns on an iron core.

The naked element may be one-watt but embedded in masonry can handle a lot more. Bad embedding (porous plaster) could reduce the rating but good clay and porcelain can raise it by increasing the effective surface substantially (and cheaply) without raising thermal resistance as much.

Old-name resistor makers can be found at OEM-grade distributors like Digikey. (They may still be made the same, but A-B and Ohmite and others used to have someone paid to test and think.)
Prior to buying those I didn't find much useful information about the quality. This thread may help future potential buyers to decide whether such parts are worth their money or not.
For me, they are even useful as pitch compatible drop-in replacement for 0.6W metal film resistors that fuse too easily, but I find that they are a bit too expensive for the actual quality and performance.

I agree that the cement fill together with the huge package may help to dissipate more power than the naked resistor element alone. I plan to test actual power dissipation capabilities in order to find out.

Looking at the datasheet of the original KOA Speer parts instantly reveals that the Chinese parts must be fake because the KOA resistors are available up to 1 Ohm only, while the Chinese fakes shown here have 10 Ohm resistance. Also, the KOA parts do have a planar resistor element with trombone pattern instead of a cylindrical resistor inside.

I also ordered 1 Ohm resistors from the same vendor and plan to crack one open as well.
Terrible and only reaffirms it's barely worth buying anything from over there.

@Lee Knatta If still possible, hope you can leave a feedback on Aliexpress, I have also seen several feedback's where the customer have written an additional 2nd feedback message attached to the first one in addendum, but not sure if any pictures can be added, worth checking out.
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According to feedback that other buyers left, those resistors are excellent. :D
I bought them last year in April, so it might be a little late for feedback.
But I'm waiting for 1R and 0.1R resistors from the same "brand" and the same vendor to arrive.

I would not generalize that everything from there is junk, but chances are there is some junk among the offers.
At least once a month somebody opens a thread complaining about such junk, just like I did. This may help to warn prospective buyers.
So far I successfully procured tools, screws, radiators, chassis, ferrites, inductors, connectors and countless other things. And I saved a lot of money. Most of the items are good, some are not. Those that are not good may still be partially useful like the resistors. Some items are just a waste of precious resources for manufacturing and shipping and are best recycled.

Greed is all along the chain: Manufacturers, vendors and buyers. Sometimes you win, sometimes you lose...
Very interesting i just bought some resistors from TME, SR passives a brand i never heard of, they were supposed to be metal plate non inductive. When I got them i saw they were marked BPR56 but this series of resistors is called MPR in the data sheet, and then i saw this thread....


Oh no! did I just buy junk?

I bought 10 resistors but only planned to use 8, but it was cheaper to buy 10 so i have 2 spares. So I decided to crack one open.


Seems legit, looks like they cloned KOA Speer BPR58 with a snake like resistive element, these resistors cost 0.31€ from TME if you buy 10 so the same price as the dodgy Aliexpress ones but no free shipping from TME.
Short update:

Meanwhile I tested one of the 10R resistors for power rating and I'm surprised that the resistor was actually able to dissipate 5W.

I don't have a well equipped lab, thus no adjustable DC power supply, but used the output of my amplifier instead. Test frequency was 1kHz.

The test lasted roughly 10 minutes. The first 5 minutes was a slow ramp up of the power until 5W with occasional temperature sensing by finger.
At ~3W, the resistor became too hot to touch.
Then I left the resistor at 5W for another five minutes.
The resistor survived and did not show any unwelcome effects like smell or (dis-) coloration.

While the 10R resistors are clearly fake (KOA Speer does not even offer resistors with that value), they deliver what they promise. I guess that surge power rating of the rather thin wire is not very good, but overall I'm satisfied with what I got.

The 1R and 0R1 resistors have arrived and they look different outside: Both the print and physical dimensions are different. I'm curious how they look like inside. Do they have the snake shaped metal plate like the original parts or do they have a wire wound resistor like the 10R resistors as well? I will find out another day.
I put the 1R0 resistor into the same test setup like the 10R resistor.
At a voltage that should result in 5W dissipation, it burned my (Chinese) anti-static soldering mat:

I must have done something wrong because the 10R did not burn a hole into the mat. I guess that the (Chinese) multi-meter reading was wrong.
Even the resistor ceramic slightly changed color due to overload:

The resistor inside looks similar to the one inside the 10R resistor, just has thicker wire and if you look closely, you can see the overstressed wire changed color:
I did not test the 0R1 resistor, but cracked it open right away. This is how it looks inside:

Totally different design. This is how I expect such a resistor should look like inside.
I was kind of expecting this since the bottom view hints that the opening is too narrow for a cylindrical resistor element.
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Very interesting thread !! Had purchased many resistors , BPR56 , from same mentioned ali*** , and never had big problems with them . Purchased low values like 0,1 ohm and 0,2 ohm as i can remember now , have some unused ,some desoldered ,so probably i will disassemble one to check what's inside and post photo. Used them in amplifier ,and in electronic load ,had some oscillation issues , which had resolved. But what if that was caused by these resistors fake parameter (non inductive)...
since the bottom view hints that the opening is too narrow for a cylindrical resistor element

Excellent point!
Lee, what is the thickness of your 3 different resistors shown in #10?

I wonder what the filling is made of, it looks like cheap plaster, do you find it easy to penetrate and break up with a sharp tool like a screwdriver etc.? One thing to take into consideration here is that the plaster may not be particularly well fit for handling power cycling where heating and cooling down causes physical expansion and contraction leading to the filling becoming ruined and losing contact with the resistive element, and hence losing thermal conductivity, just a speculation.

@ximikas Thank you too for reporting your findings!
Actually resistors can be made non inductive, or at least less inductive with one simple solution. When a wire is wound on ceramic tube , in the middle winding direction needs to be changed to opposite. From one end clockwise till middle , then counterclockwise till other end. You get two partially coupled inductors , connected end-to-end, and inductance would decrease.
Probably the need to put small resistor inside fake resistors caused by higher resistance nominal (10 ohms), which hardly can be made by other methods.