BONENS (BOCHEN also works here) counterfit bourns trimpot analysis

[ftransform]

I figured this would merit a new thread because the difference is fairly significant.
So I have two 100k 20 turn trimpots. One of them is a genuine bourns trimpot sourced from digikey. The other is a ebay. The digikey one cost 2 or 3 dollars, while on ebay I think I got 20 for 10$ or so.

Both trimpots were adjusted to form a ~50k voltage divider. Then both trimpots were put inside of a stryofoam shipping box with 4 alligator clip leads inside of it. One half of the trimpot was hooked up in a 4 wire kelvin configuration.

The genuine trimpot jumped around by a few ohms right after it was adjusted and it quickly settled down and after about 2 minutes alone in the box with my typing disturbing the table it is on it fluctuates by about +- 0.1 ohms. I have read that these trimpots may take up to 30+ minutes to properly settle down, but this result is in my opinion good.

The results from the BONENS trimpot do not match by an order of magnitude. The experiment was arranged the same way and the reading would not stabilize, the variation was about +- 30 ohms. This corresponds to a 0.06 percent variation.

The box it is in has a thermometer and a halogen lightbulb so as time goes on I will update this thread with a resistance temperature measurement comparison of both trimpots.

The BONENS time to settle experiment is currently underway. I will take note of how jumpy the pot is in 10 minute intervals.

 

It is possible that the strain from the alligator clips can be effecting the chinese trimpot more then the genuine brand one and that better performance is possible soldered in a PCB. I might try with veroboard.

[Jay_Diddy_B]

Interesting 

I would be interested to know if the Bonens pots are microphonic. Do you have something with a noisy fan in and look at the output on a scope?

A teardown would be interesting too. They don't say on the eBay listings if the pots are carbon or cermet.

Regards,

Jay_Diddy_B

[c4757p]

I would be interested to know if the Bonens pots are microphonic.

I have some of what I believe to be the same pots, and yeah, they are, severely.

[ftransform]

7:16 pm
-2 minutes into experiment -drifing alot, I would say +- 500 ohms)

7:21 pm
- 48.8 jumping around at least 0.2 kohm, slowly falling.

7:23 pm
48.5 kohm still fluctating and dropping

7:27 pm
48.2 kohm, fluctating and still dropping

7:31pm
48.2 kohm, fluctating by about 0.05 kohm

7:36 pm
48.15 ohms, dropping

The experiment will be ended because its apparant that this trimpot is a bunch of bullshit.
The whole point of a multi turn trimpot is easy settability. It is apparant that this is not
settable at all, considering it jumps around 500 ohms right after messing with it.
I suppose you can randomly spin it and come back in 3 hours to see what it settled to.

I will attempt to conduct a temperature coefficent experiment but considering how jumpy it is
it will be useless. This experiment is conducted in hopes that the trimpot will become a
super conductor at higher temperatures due to my suspicions that it has a infinite negative TCR.
Maybe it will form the worlds most stable resistor because its shitty tempco will match up with
its shitty temperature irrelevant drift.

Start Temperature 69F.
Start Resistance: 48.28 +- 0.05  (7:40 pm)

the tcr on this thing is ridiculous. I had readings of 55 which then dropped to 53 kohms over the course of 69 to 114F
I'm not even going to bother trying to calculate a TCR for this thing. It would probobly requre a 10th order polynomial and many data points.

Do you guys think I am being harsh on this trimpot by calling it bullshit?
I don't really see the merits of such a jumpy multi turn pot.

[c4757p]

This experiment is conducted in hopes that the trimpot will become a
super conductor at higher temperatures due to my suspicions that it has a infinite negative TCR.

 

Do you guys think I am being harsh on this trimpot by calling it bullshit?
I don't really see the merits of such a jumpy multi turn pot.

Mine went straight in the shame bin (that's where I put my "why the hell did you think you could get away with that low price" items) right next to some alligator clip leads that had such high resistance you could "paint color stripes on them", as I think I recall saying. They are bullshit.

[ftransform]

I don't know how difficult it is to set a 1 turn pot to 1 kohm divisions so maybe having a few of these around has its merits. I might be being too hard on this thing. But I don't think its useful to set it past 1 kohm precision.

I am playing with it now by setting my meter to only display one decimal place. After some fiddling I managed to get it to 75k. After 1 minute this dropped to 74.9k.

It actually appears to be more stable depending on what it is set to. At 75k it seems to be ALOT better then it was a 50k.
It also has this nasty trait where it jumps up and down while you are spinning it. I guess this is referred to as poor linearity? It will be like 70k, 72k, 71k , 72k, 73k ..

It seems that now when I brought it back to 50k its behaving better then it was previously.

Maybe the trick is to move it around some so the wiper can scratch off some imperfections?
I think that may be the case. Maybe you need to sweep through its entire range 3-4 times in order smooth things out.

at 9:05 pm it is 54.18 kohm. from an initial setting of 54.24
"grinding" the wiper does not seem to help stability that much. I think its a bit better.

OK it seems that I can set a single turn 150 ohm trimpot to a better equivalent resolution then this 100k bonens shit.

In short these chinese multi turn trimpots are fucking useless. All they will do is make you turn things 10 times more lol!

**i got lost in the edits because of multiple tabs so some stuff got deleted

[ftransform]

An ebay brand panasonic trimpot, at 80kohms, only drifted 100 ohms over 5 hours when it was set to ~27K.

If you need cheap ass trimpots I'd recommend getting the 1 turn panasonics over the 20 turn bochens. They are a little more difficult to set but 100ohm drift is alot better then 500-800 ohm drift, if you catch my drift.

[amyk]

I was expecting a teardown to see what's causing it. Loose wiper or some other manufacturing defect? Could lubrication help?

Also did you try the others you bought, as testing one possibly defective part isn't conclusive.

[Mechatrommer]

i have those "BONENS" brand bought in lot from ebay. 1Kohm 10 turns used for ±2.3V divider for voltage offset, hardly move from and accurate for ±1mV range worst case after few minutes (i cant see any visible movement even at ±500uV range), like 30 minutes or so, even with moderate wind or mouth blow, on naked pcb. did some slight pcb banging on the desk made little to no change. so its 0.04348% deviation or error worst case, for my 1Kohm its around ±0.2ohm tolerance, for your 100Kohm it should be ±20ohm, fair as you reported, but it works to my circuit spec, ie acceptable.

blowing the Bonens trimpot with 100degC hot air, sure the voltage offset moved further down, but blowing the zeners that form the voltage range for it, moved the offset up, so i accidentally accomplished the "tempco cancellation" engineering achievement on my circuit, no worries the trimpot that i observed has taken significant abuses from me, ie few times solder desolder, all leads decapitated. burn marks due to soldering iron accidentally hit it from the side.

i agree, teardown comparison side by side will be a good idea, lets see what they are made of. i dont have original Bourns to compare with. and you havent explain your measurement setup, what meter did you use?

[ftransform]

i have those "BONENS" brand bought in lot from ebay. 1Kohm 10 turns used for ±2.3V divider for voltage offset, hardly move from and accurate for ±1mV range worst case after few minutes (i cant see any visible movement even at ±500uV range), like 30 minutes or so, even with moderate wind or mouth blow, on naked pcb. did some slight pcb banging on the desk made little to no change. so its 0.04348% deviation or error worst case, for my 1Kohm its around ±0.2ohm tolerance, for your 100Kohm it should be ±20ohm, fair as you reported, but it works to my circuit spec, ie acceptable.

blowing the Bonens trimpot with 100degC hot air, sure the voltage offset moved further down, but blowing the zeners that form the voltage range for it, moved the offset up, so i accidentally accomplished the "tempco cancellation" engineering achievement on my circuit, no worries the trimpot that i observed has taken significant abuses from me, ie few times solder desolder, all leads decapitated. burn marks due to soldering iron accidentally hit it from the side.

i agree, teardown comparison side by side will be a good idea, lets see what they are made of. i dont have original Bourns to compare with. and you havent explain your measurement setup, what meter did you use?

I used an agilent 34401. I described the setup, 4 wires go into a styrofoam box and get connected to the trimpot via alligator clips. The pot is then turned and the lid is then put on and the measurement (well to the nearest kiloohm lol!) is made with the 4 wire ohm measurement.

And I'm not tearing down my 2$ trimpot to compare to that trash. No way.
I also don't have the tools to do it right, I would need some kind of dremel, when I tried crushing it with pliers I ended up destroying it too much to take meaningful pictures. I might be able to cut it half with a hot wire but I don't think i'm going to bother.

BTW remember that this experiment was conducted on a 100kohm pot. Your pot is 10 times smaller, so it might be easier to deposit the material uniformly.
I would assume that smaller values are more stable and easier to make then large value trimpots.
I will conduct an experiment with a smaller value bonens trimpot next.

A perliminary experiment ( I don't feel like getting the box right now) is setting a 5k trimpot to 2221 ohms at 11:44 am in the open in a 69ish F room.
I will report back with drift in 20 minutes.

[ftransform]

Over the course of 25 minutes the drift of this 5kohm bonens trimpot has been from 2221.3 ohms to 2222.8 ohms.

This trimpot seems better , but it still cannot be relied on for ohm precision. It is up to you to decide if 1.5 ohm drift over 30 minutes is acceptable.

After about 2 hours (in room, which may have warmed up slightly, lets say 72 degrees) the pot drifted to 2226.7 ohms. This has now turned into a 5 ohm drift.

I think it's pretty bad for a 20 turn pot, but this is within 0.1% of the full scale.

[ftransform]

The value of the 10k ohm bonens trimpot was still 2226 ohms after 24 hours in open air in a room.

5 ohm drift is not too terrible I suppose?

[Mechatrommer]

it will depend on your circuit requirement. we get what we pay. and sometime even Bourns will not met the spec, we need to sort to $K trimpot. the conclusion resulted when you compare $3 with 50c trimpot. thats what china brand are for, to give cheaper alternative, but with weaknesses of course. btw thanks for this report, i now know how stable the original is, maybe will be my next buy. cheers

[akis]

I know this is an old post but I have bought bagfuls of these off ebay before I noticed this thread. Had I read it I wouldn't have. However I ran my own test just now just to see just how bad these are. (so many justs in there).

So I took a 500R one, connected two crocodile clips on it, let it hang off the desk and adjusted it to 250R. While adjusting it I did not notice any "jumps", it was perfectly linear. I let it "settle" for a few minutes and when I came back it was still at 250R as you'd expect (actually there are 4 digits, so it was 0.2502 K). I then took the hairdryer and blew hot air at it, to the point that it became impossible to hold by hand. The digital meter measured 50C but my fingers "read" at least 65C. In any case it was quite hot. The temperature read 0.2480 K). So we lost around 2R over a 500 R range, that is the equivalent of 0.4%. Not bad for the price.

[dannyf]

Do you guys think I am being harsh on this trimpot by calling it bullshit?

Unrealistic expectation. If the variation is indeed 0.06%, I would say that it is good for 99% of the jobs out there.

[linux-works]

I bought a bunch of trimmers from ebay, they were all listed as 'bourns' but only some of them were real. ;(

the names are actually funny to me, though...

[wraper]

Have also seen TBIMER, BARONS, BOATER, King.

[free_electron]

who uses trimpots anymore. serially  controlled dacs are cheaper than a trimpot these days ...

[linux-works]

running audio thru a digital pot is not such a great idea.  we still use trimmers to set bias, dc offset and gain.  zero reason to use a digipot for things like that.

I like using digipots, but only when they make sense.

[David Hess]

It is usually a bad idea to rely on stable wiper resistance in a potentiometer when used in precision applications.  When wired as a voltage divider, the variation in wiper resistance is divided by the input impedance of the following circuit.  This also allowed temperature tracking between separate sections of the divided resistance element.

[calexanian]

who uses trimpots anymore. serially  controlled dacs are cheaper than a trimpot these days ...

We were having that conversation just the other day on one of our new designs. Its one of these bridge mems sensors and we were having a 0 offset issue. So we just broke down and threw a trim one of these bourns pots in question across the bridge reffed to the ground side. Also since we had that we just used the same part as a span control. Double the qty, lower the price. Its a product we can afford an extra $2 in though. Industrial application where they like zero and span control. Much easier to explain over the phone than guide them through menus on the control panel to calibrate. We also wrote a self calibrating scheme, but decided to go with a manual cal to rule out any firmware derived calibration errors not caught before deployment. Most people have screwdrivers. Not to many have pickits in the middle of a field. Yes... We are a Microchump, I mean Microchip house.   

[amyk]

the names are actually funny to me, though...

I wouldn't be surprised at all if some other Chinese company decides to name theirs BONERS...

[calexanian]

the names are actually funny to me, though...

I wouldn't be surprised at all if some other Chinese company decides to name theirs BONERS...

Sales may be enhanced by drunk people cruising the Internet drunk impulse buying! I just bought a tube of 50 boners! Hahahahaha very popular in Japan for some reason..