Precison Potentiometer - Page 1
Forum section: electronics / beginners

author: SgtRock
author_rank: Unknown
timestamp: July 15, 2011, 06:21:01 am
content: Greetings EEVbees:--Foolishly I replaced the 10K Ohm Linear Potentiometer in my Heathkit Tri-Power Supply with a Hong Kong Cheepy "Precision 10K Ohm Linear 10 Turn Pot, which I bought on eBay.--To my chagrin I discovered that the original Heathkit Pot. with 310 degrees of travel was capable of adjusting the voltage much more precisely than the Hong Kong Cheepy with 3600 degrees of travel.--By holding my mouth just right I was able to get 12.00 VDC +- 0.01 with the Heathkit Pot., but could do no better than +- 0.15 with the Cheepy.--When I left negative feedback, I got an immediate response, offering a full refund if I would give them 5 stars. I responded that I was not interested in a refund, but would give them 5 stars if they promised to immediately stop selling their extremely imprecise "Precision 10 Turn Potentiometer". So far, "Answer came there none".--Fool though I be, I think I am beginning to see why a precision 10 turn potentiometer costs more than 6 dollars. Has anyone had a similar experience, and does anyone have a recommendation at to what I should get.Nuff Sed, Clear Ether

author: saturation
author_rank: Super Contributor
timestamp: July 15, 2011, 11:20:55 am
content: If you buy a part that has no brand name or from an unauthorized dealer, you have to be very skeptical about its capabilities. Even if it has a brand name but it comes from an unauthorized distributor, you have to be very careful its not counterfeit, and you pay unnecessarily extra for the fake part.A true good part can be traced to the manufacturer directly, no matter how many hands it changes through on the way from factory to warehouse, to distributor x, y, z and finally retail ... what's called the supply chain. All parts have good documentation as to its specs, and it lives up to those specs.If you need quality or true precision part, pay extra for it and get it from an authorized distributor.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 15, 2011, 12:10:23 pm
content: Quote from: saturation on July 15, 2011, 11:20:55 ami dont mind paying extra for the part. but if the shipping cost/method and availability for these "authorized distributors" is like chinese/cheapo distributors, then it will much easier.

author: Rufus
author_rank: Super Contributor
timestamp: July 15, 2011, 12:13:07 pm
content: Quote from: SgtRock on July 15, 2011, 06:21:01 amNot sure you should be complaining about this, it isn't that simple. Single turn pots are wipers on carbon or cermet tracks and resolution depends on how precisely you can position the wiper.10 turn pots are usually a wire resistive element wound in a tight coil then wound in a spiral around the pot. The wiper bears on the coil and winds up and down the spiral as it rotates.The resolution of such a pot is nominally one turn of wire on the tight coil. The devil is in the detail of the wiper contact and I don't have any real knowledge or experience of that detail.Basically I would not expect a 10 turn wire wound pot to have better resolution that a single turn composite pot and I would not necessarily expect an expensive 10 turn pot to be better than a cheap one in this area.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 15, 2011, 12:42:42 pm
content: Quote from: Rufus on July 15, 2011, 12:13:07 pmmaybe we should look for larger diameter carbon trimpot with 1:10 gear ratio inside? only if there's such thing. wire wound is not good for high frequency as well.

author: saturation
author_rank: Super Contributor
timestamp: July 15, 2011, 02:21:15 pm
content: Yes, mecha, that's one reason there is a market that isn't from authorized distributors:the authoriszed folks won't ship to certain countries, ask for too much paperwork, cost so much more once you add shipping. If you do the eBay route to make it easy and fast, then you take the risk. There are of course, many good eBay vendors, I collect them, I buy a small item from them and see how truthful their posts are about the part, and try a purchase. If they are good, I'll add them to my favorite vendors. In the future, if I need a good part from eBay I'll buy from them first before I try someone unknown.Quote from: Mechatrommer on July 15, 2011, 12:10:23 pm

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 15, 2011, 02:37:45 pm
content: Quote from: saturation on July 15, 2011, 02:21:15 pmmind to share or pm?its better if the seller is closer to eastern side here.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 15, 2011, 03:05:53 pm
content: The solution to the problem " Precision Potentiometer " called BOURNS or CONTELEC.Either manufacturers makes top end materials.At about 30$ per pot, you do get quality.Not to say that you can find on Ebay (if you know the part code that you are looking) old stock, at half price.

author: qno
author_rank: Frequent Contributor
timestamp: July 15, 2011, 03:53:03 pm
content: I think it is not the 10 pot-meters fault.Resolution is limited by the resistance of one single turn of the coiled up resistor element.Manufacturers of precision power supplies used to have a coarse and fine adjustment pot on the front.You can do the same if you want to precisely tune your power supply.

author: saturation
author_rank: Super Contributor
timestamp: July 15, 2011, 04:23:45 pm
content: Hi mecha,I don't know if they'll ship to Malaysia, but here are my guesses of those who might from my parts suppliers, the % is their eBay rating. I normally buy precision passives because many cost less than tolerances of >=5%! Many overstock, bankruptcy, closed manufacturing or lab inventory and finally salvage, some brand names, some none :j-barkley99.9%rf.nut100%thesequoiagroup99.9%eBay Store: The Sequoia Grouptlccomp100%eBay Store: tlccompmckean200299.9%eBay Store: McKEAN MACHINERY SALESledwholesalers_inc99.2%eBay Store: LEDwholesalers_Incgedeon-qc99.8%eBay Store: HoneyCompsTo find their wares, click below search by seller, then pm them if they'll ship out to your country and what costs:http://shop.ebay.com/ebayadvsearch/?rt=ncQuote from: Mechatrommer on July 15, 2011, 02:37:45 pm

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 15, 2011, 04:49:05 pm
content: thanx saturation. i'll keep that in view. none of the seller i dealt with before.Quote from: Kiriakos-GR on July 15, 2011, 03:05:53 pmwell maybe i can work around 10 cheapo trimpots if that is the cost in USD or same rated currency. or maybe i'll get it if there is really good business for it.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 16, 2011, 03:44:47 am
content: Quote from: Mechatrommer on July 15, 2011, 04:49:05 pmWhen ever you will become an owners of one precision PSU, you will become also a big spender about such pots.The spare wheel of an Ferrari its costly too, blame Ferrari.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 16, 2011, 02:16:04 pm
content: Quote from: Kiriakos-GR on July 16, 2011, 03:44:47 amdont blame ferrari. but blame economy and the bankers!

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 16, 2011, 08:14:46 pm
content: I got lucky, and got two 10 turn BOURNS before the bankers do their damage.But with out those pots my KenWood PSU would be as handicap.The positive part of the crisis are that the pricing of products will drop too,the question is : How soon.

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 16, 2011, 09:09:11 pm
content: Quote from: Kiriakos-GR on July 16, 2011, 08:14:46 pmnever will! everything will go up, except "breast",

author: Lawsen
author_rank: Frequent Contributor
timestamp: July 17, 2011, 10:02:11 pm
content: I have worked on tension tester machine that needed to sense displacement. My instructor installed a Bourns Potentiometer, a very good brand.Surf here:http://www.bourns.com/ProductFamily.aspx?name=potentiometershttp://www.bourns.com/AboutBourns.aspxLawsen Lew