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Old 24th May 2024, 3:32 pm   #1
WaveyDipole
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Default Bourns potentiometer

The story here is that some time ago I replaced the two main channel voltage adjusters on a power supply I use for secondary purposes such as Arduino projects and the like. I did this in order to give me better selectivity of the voltage value. I replaced the original standard 10k 1/4W pots for Bournes 2W wirewound 10 turn pots. This allowed me to select voltage to the 0.01V instead of to a random value of approximately 0.5V or so.

A month or so ago I noticed that one channel had failed and was producing no output. To cut a long story short, the problem turned out to be an open pot, one of those i had replaced. Since the pot was over-rated, I was not expecting this. A replacement pot was purchased and installed, problem solved.

But why did the pot fail? I thought Bournes were a quality brand, and although the pot was purchased off eBay it still cost well over £6. It should definitely not have burned out. Curious about this, I decided to take the old one apart and examine it.

It came apart quite easily and the interior is as shown in the photos. The good news was that there was no scorching that would indicate a catastrophic event. The pot basically contains a long wire-wound section, which is itself wound in a coil inside the barrel. There appears to be no mechanism that would move the wiper up and down through the depth of the coil. It simply slides up and down the shaft, so it is presumably driven by the rotating action and engaging in the grove between coil layers.

The wire-wound coil was lubricated with grease so the wiper should have been able to travel easily along it. However, I did also find some debris inside including a couple of loose segments of restive wire and a hair, so I guess assembly is not done in the cleanest of environments. I could not see any obvious sign of damage, not even under the lens of a magnifier lamp, but I was able to establish approximately where the break was by probing and then zoom in to that area with the microscope and so locate the damage. Taking a photo was a somewhat frustrating matter with the phone constantly changing cameras and the macro function kicking in automatically even when turned off, but eventually I managed it. The resistive wire does appear disturbed this particular point and although out of focus in the photo, there does appear to be a random piece of loose wire dangling just below. The wiper edges do not appear to have been smoothed or curved in any way to allow them to better fit between the layers of wound wire, so it is not exactly a surprise that it has evidently snagged on and/or cut though the resistive wire, causing the pot to become open.

What worries me is that is the likelihood of this happening again. I always though Bournes is a quality brand and I was in safe hands. I purchased these off eBay - so are these a knock off, or has the brand been purchased by the Chinese who are not trading on its name?

I guess I could replace these with Vishay branded pot. They are significantly more expensive however. I guess I now understand why.
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Last edited by Cobaltblue; 24th May 2024 at 11:23 pm. Reason: title spelling corrected
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Old 24th May 2024, 4:04 pm   #2
Craig Sawyers
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Default Re: Bournes potentiometer

The RS price for exactly this pot seems to be £17.90 vat inc plus delivery.

The Bourns spec sheet says rotational life with no electrical load 1,000,000 shaft revolutions.

https://docs.rs-online.com/061b/0900766b81420853.pdf

If it cost significantly less than that and failed early - well if the price is too good to be true....

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Old 24th May 2024, 4:35 pm   #3
G6Tanuki
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Default Re: Bournes potentiometer

Was the one you bought sold as Bourns or Bournes??

If the latter I would put money on it being a fake.

(Bourns is a reputable company but that makes them all the more profitable to fake)
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Old 24th May 2024, 6:53 pm   #4
Trigon.
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Default Re: Bournes potentiometer

Tags on a genuine Bourns pot:-
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Tags on one of the many cheap eBay 'Bourns' pots:-
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Possibly reflects a change in production values, but I'd be surprised if Bourns turned out something like that...

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Old 24th May 2024, 6:58 pm   #5
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Default Re: Bournes potentiometer

I think I have some Chinese pots marked 'Burens'.
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Old 24th May 2024, 9:08 pm   #6
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Default Re: Bournes potentiometer

Sorry, that was my spelling error. The first photo below shows the back markings on the pot, and it is written as BOURNS not 'Bournes' as in my post. I have also attached a further two photos of the failed and now dis-assembled pot as well as its replacement for comparison of the tags.

I do not rule out the possibility that these may be replicas that may also be mis-representing their country of origin.
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Old 24th May 2024, 10:33 pm   #7
radiomobile
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Default Re: Bournes potentiometer

I bought a number of "Bourns" 10-turn pots off eBay and had similar problems with several of them, clearly they are fake. Ironically the Chinese alternatives of a different design have proved to be ok.
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Old 25th May 2024, 8:04 am   #8
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Default Re: Bourns potentiometer

This type of pot can fail if you get the tags too hot, you have to be quick with the iron.

Andy.
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Old 25th May 2024, 11:08 am   #9
WaveyDipole
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Default Re: Bourns potentiometer

Quote:
Originally Posted by radiomobile View Post
I bought a number of "Bourns" 10-turn pots off eBay and had similar problems with several of them, clearly they are fake. Ironically the Chinese alternatives of a different design have proved to be ok.
I have to agree that would seem to be the conclusion here. I didn't expect that the more obvious alternatives to actually be better, although at least in their case at least there is no pretense of being something they are not. Maybe I should have gone with the obvious cheap alternatives instead.

Quote:
Originally Posted by Diabolical Artificer View Post
This type of pot can fail if you get the tags too hot, you have to be quick with the iron.
I did wonder about that. There is no mechanical connection between tag and wire-wound element, such as being crimped on. There is just a small solder blob connecting the two. It is not difficult to imagine that if the tag gets too hot, the blob could melt and disconnect.

For now, I will leave the replacement as is and see how it goes, but should another failure occur then I will definitely consider replacing both with something better from one of the reputable vendors. I see that Vishay make something similar so there are options.
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Old 25th May 2024, 12:18 pm   #10
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Default Re: Bourns potentiometer

I've used a fair number of Bourns ten-turn pots back before there were any fakes around.

Having values and type numbers moulded in is suspicious. The real ones I've seen have text printed on. They use those same plastic parts on a very wide range of values and variants. Doing a mould for each would be crazy. The fakers would cherry pick those in demand. Bourns have to be able to make every type in their catalogue and some variants sold only in small numbers. Printed on text is easier to change.

David
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Old 25th May 2024, 4:26 pm   #11
G6Tanuki
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Default Re: Bourns potentiometer

Yes the little square blue Bourns multiple turn Trimpots I use a lot of also have the details printed on the side, not moulded into the plastic.
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Old 25th May 2024, 5:45 pm   #12
kalee20
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Default Re: Bourns potentiometer

It does seem strange - even for a fake, it's surely cheaper (and more realistic!) to have a plain moulding and print the value on the side?

(I do like Bourns potentiometers, never had a problem with them, the 3386P square trimpot is my go-to type of choice).
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Old 26th May 2024, 7:21 pm   #13
factory
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Default Re: Bourns potentiometer

Here is one bought from RS in 2011 at £15.13, it also has the text moulded in, anything new being sold at low prices on other online shopping sites must be fake.
https://uk.rs-online.com/web/p/potentiometers/6928538

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David

Last edited by factory; 26th May 2024 at 7:28 pm.
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Old 26th May 2024, 8:06 pm   #14
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Default Re: Bourns potentiometer

I think that's laser written. The round blue pot in the earlier post has shiny bottom to the markings which looks like moulding, while yours has the granular surface of exposed filler material in its markings.

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Old 27th May 2024, 12:03 am   #15
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Default Re: Bourns potentiometer

Bourns are pretty much the most faked potentiometer brand out there. I speak from experience of them being fitted to new equipment.

Bours, Bourne, Bures and Bearns are common misspellings but that's the honest ones. The worst ones spell it right
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Old 27th May 2024, 11:45 am   #16
kalee20
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Default Re: Bourns potentiometer

Good to know that! I'll be sure to get mine from authorised sources.

They really are good - the multi-contact wipers of the trimpots, the precision-moulded, sealed, enclosures, the ceramic substrate that the resistive element is formed on, all adds to a stable, very-long-life product.

The only case where I look elsewhere is for 10-turn panel-mount knob-adjustable potentiometers, where I go for Spectrol. But that's purely out of force of habit.
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Old 27th May 2024, 7:23 pm   #17
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Default Re: Bourns potentiometer

Reading this makes me appreciate that most of my Bourns pots have been in my stock maybe 15 - 20 years or more.
But, is that a reliable guide to assume not fakes?
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