25th February 2018 24th February 2018 By Bzzz In basic building blocks 10 turn potadjustable resistoraudiobournscomparisonfakeinternal constructionmountingpotpotentiometerproduct piracyvishaywasherwiper

3590S-2-103L 10K Ohm Rotary Wirewound Precision Potentiometer Pot 10 Turn vs genuine Bourns and Vishay pots (WHL #36)

Visiting the dark side of China today – product piracy.

First things first, I actually bought this item twice from two different sellers on AliExpress. One back in September for 1.07€ and now two more for 0.95€ each in early January, just to be able to kill one during inspection. The seller may be the same (I’ve seen that recently from BME280 sensors, review to come), but the shop name is different. It is intended as replacement for the current adjustment knob on my electronic load, as I am an idiot and during build I set the voltage over the pot not to the two end pins, but to one pin and the wiper. Well, 15 volts and some current capability do not do good when shorted via a teeny tiny wiper. End of story: Not repairable due to the resistance wire not taking solder – buy a new one and try again. Classic D’oh moment.

So I did. As I said, these Wan Hung Lo 10 turn pots are dirt cheap. The Vishay pot that I destroyed was already around 7€ at Reichelt, and the Bourns pots are usually more in the 10 to 15 Euro range. That’s a lot for a small plastic housing, some nicely wound resistance wire, a wiper and some knob on the front. Well, they may have great temperature coefficients, perfect linearity and self cleaning contacts…but it’s still only a pot that I need to fiddle with when adjusting something. It’s not rocket science, and it’s also not used for rocket science. So cheapos may actually be a valid choice.

Unless it’s fake, obviously. Here’s the unit straight from the shitty plastic bag:

The two star washers aren’t really great quality, but for front plate mounting, they’ll do. Back and front:

When compared to each other, every pot has a different label (and a different tint of blue):

That’s not some problem with your eyes, those are shitty labels. The worst one is really hard to read in person, it comes out much better on the photos than it actually is. I’m not even sure how to make these – they are not lasered, maybe this is an extremely worn or dirty injection mould? It’s not hand written with a tuned down iron, but especially the right one with the really bad print looks like there’s no black ink inside the letters, but it’s just darkened from burnt plastic. Very strange. And therefore suspicious. Remember – if this would be a genuine part, one would shell out 10 to 15 bucks for it. For that money, I’d expect clear labelling, no THAT shit.

3590S-2-103L is actually a Bourns part number of exactly that pot. Both Chinese sellers do not use “Bourns” at all in their product description or anywhere else, one of them has pictures with the back side stating “Bourns” on the pot, one doesn’t. Both use pictures from the manufacturers, and so do I – please have a look and compare yourself:

Clear labelling and blue potting compound around the fixed terminals. Aside from those two things, I cannot really spot a difference. They have a golden pin for the wiper terminal as well, there are two terminal styles – and these use the correct one, Bourns includes star washers as well (although only one per unit and probably of better quality), and the housing is sort-of glued together, although there are snap-in parts in the top and bottom parts that hold to the central part really well on their own. There’s also a flat head slot on the top of the knob (that sounds strange?), which looks a bit better on the genuine one of course.

So, let’s have a look on the inside. I only do this because I already broke the Vishay one, and that one jumps in your face when you open it. The fake Bourns one doesn’t. At least when you take out the bottom only. Good design, you bastards. I also removed the retaining ring, but that’s just there for alignment. To further underline that I’m an idiot, I also tried doing that on the Vishay pot. ZING, I broke my best pair of pliers when trying to weaken the ring, as it does not want to come off. At all. Meh. I’m really pissed

The outer shell actually looks quite similar. They have the same basic design, with 10ish windings of coarse wire, which is wound with another tiny wire. Given that I can feel the stuff but not really take a picture of the individual windings, they could be in the low two-digit micrometer range. You can see the color variations along the coarse wire (especially on the fake Bourns one below), but I cannot make the individual wires more visible. I’d need more macro capabilities to do that, or a microscope.

I can offer a bit of audio here, as fake Bourns and Vishay have a different wiping sound. I’d say the Vishay one is a bit harder on the wire, making it a little less durable, but ultimately I like the sound a bit better. But I’m not selecting/preferring pots for their sound

Vishay:

 
Wan Hung Lo:

The other parts are a bit different due to having different segment sizes. From a functional point of view, they just do the same. The Bourns pot still has the wiper attached to the stem, which is highly delicate. For both pots, it is basically impossible to get this wiper ring back in place without breaking something. Maybe that’s the reason why these things are so expensive? Nude virgins sitting around in moon light, trying to get this thing to work and breaking tens of units in the process?

There’s not much else to say, these fake pots do what they should, they are absolutely linear beyond my capabilities of measurement, they do have the 10kΩ that is promised on the package (9.9, 10.2 and 10.2k respectively – that’s alright and inside the 5% spec of the original part as well), and their zero-resistance is around 0.6Ω to 0.7Ω on both ends of the pot. The genuine Bourns part allows 1Ω or 0.1% for that – whatever is larger.

But – as this is clearly a fake, I tried reporting that to AliExpress. I would be fine with these things if there was no mentioning of a reputable company on it, but this way, I just have to. AE does not accept that reason for disputes, but you can report individual items without even buying them. So I did, for both offers. We’ll see if (and how) AE reacts to that.

I accept genuine Bourns pots for a future comparison! Cheers!