DIY Kelvin Test Lead Kit (added source info)
Due to some precision measurements that I need to run, I needed to acquire a kelvin adapters. We have all seen the dirt cheap Kelvin clips on eBay, the ones where there is barely any actual metal in the leads and they use the same cheap clips. These clips tend to use a cardboard, fiber board or plastic insert to keep the spring from shorting out the clip. This was unacceptable to me, if I am going to pay money it will be for something that lasts. So I decided to contact a supplier I know in HK and really trust. Previously, he had been selling Kelvin clip kits but they didn't quite meet what I needed. He had a new version that looked dramatically better. After some waffling I decided to try his most recent iteration of this kit and I must say I am thoroughly impressed.
Contents of the kit:
I opted for the stackable banana plugs, though in hindsight I should have gone with the standard shrouded like he originally offered. The stackable are great for individual cables but make no sense here.
The kelvin clips are made by ETA (Electronic Test Accesories) Taiwan and appear to be the same ones used by GWInstek for their LCR leads. These clips feel VERY nice, they are very solid and have a solid spring to hold them together. They grip the DUT nice and tight, without any problem of slipping. The wire connect can easily detach from the body by the removal of a single screw. This makes it VERY easy to solder a very reliable connection without damaging the plastic body of the clip. The quality of the everything feels very good and everything comes together very tightly when fully assembled.
Cutting the wire to length; each color was cut to two wires of 60 cm length and the small amount of excess (~6-7cm) was discarded. The cable has a nice soft silicone shell and is VERY flexible.
Stripping off 5mm of the outer silicone jacket, I was really surprised at the number of strands in this wire. This high number of strands, combined with the soft silicone shell mean this is a very flexible wire which is easy to work with. Another thing to note, unlike most discount Chinese wire there is a solid amount of metal in the wire.
I dissolved a small spare portion of the wire in concentrated sulfuric acid, so far only the outer tinning has dissolved. That being said, the wire is very clearly tinned copper, as you can see in the image above. After the tin was removed, the copper is very obvious.
Stripping 5mm is basically perfect for inserting into the banana plugs.
Stripping 2-3mm off of the other end is perfect to fit into the wire connector for the Kelvin clip. The 14AWG wire is absolutely a perfect fit for these connectors. The silicone is a nice fit in the barrel, while the wire is the perfect size to fit in the solder cup. Sorry for the blurry photo, unfortunately, I didn't realize it was blurry until I started typing. Since everything is soldered, I can't go back and retake the picture.
A quick comparison of cheap solder (red) versus Kester 44 (black). Both are supposedly 63/37 solder but it is clear they aren't even close to the same quality. I ended up removing the solder from the cheap one and applying fresh Kester 44.
Cutting a bit of heatshrink to cover the connector. I really like this heatshrink. This heatshrink really shrinks down, much more than most of the cheap heatshrink I have encountered. Additionally, when it shrinks down it gets a lot more firm, to the point it serves as a kind of strain relief. It has a feeling somewhere between a thermoset plastic and a hard rubber.
Trimming the heatshrink back to the camfered edge to allow it to properly fit into kelvin adapter.
Putting it all together, large screws attach the connector to the kelvin clip.
The screw covers are a very nice touch. There is one for High Force, High Sense, Low Force and Low Sense.
Now the most important part, how does it work?! Very well, my meter fluctuates between 0.1 and 0.4 mOhm when shorted. Additionally, a precision 294K resistor reads exactly 294.000K. I have NO clue why the images look so compressed, a recent update to my phone really messed up the digital camera it seems.
As I said before, I am REALLY damn happy with these. Especially when you consider the price! The whole kit was cheaper than just the clips on eBay. Also, shipping from Hong Kong only took one week, three days of which the package was sitting in New York waiting to be shipped to my region.
Sellers Contact Info
Because I have received almost a dozen messages requesting his info, it was serving nobodies benefit for me to be obtuse. Here it is for everyone:
Name: Franky Tong
Website: www.franky.com (this links to his ebay store 99centhobbies)
Email: franky @ 99centHobbies . com
EEVBlog Username: iloveelectronics (you can message him on there as well)
Due to some precision measurements that I need to run, I needed to acquire a kelvin adapters. We have all seen the dirt cheap Kelvin clips on eBay, the ones where there is barely any actual metal in the leads and they use the same cheap clips. These clips tend to use a cardboard, fiber board or plastic insert to keep the spring from shorting out the clip. This was unacceptable to me, if I am going to pay money it will be for something that lasts. So I decided to contact a supplier I know in HK and really trust. Previously, he had been selling Kelvin clip kits but they didn't quite meet what I needed. He had a new version that looked dramatically better. After some waffling I decided to try his most recent iteration of this kit and I must say I am thoroughly impressed.
Contents of the kit:
- 4x Banana plugs - 2x red, 2x black.
- 1.2m of red 14AWG silicone wire
- 1.2m of black 14AWG silicone wire
- 2x updated Kelvin clips
- Red and Black high quality heat shrink
I opted for the stackable banana plugs, though in hindsight I should have gone with the standard shrouded like he originally offered. The stackable are great for individual cables but make no sense here.
The kelvin clips are made by ETA (Electronic Test Accesories) Taiwan and appear to be the same ones used by GWInstek for their LCR leads. These clips feel VERY nice, they are very solid and have a solid spring to hold them together. They grip the DUT nice and tight, without any problem of slipping. The wire connect can easily detach from the body by the removal of a single screw. This makes it VERY easy to solder a very reliable connection without damaging the plastic body of the clip. The quality of the everything feels very good and everything comes together very tightly when fully assembled.
Cutting the wire to length; each color was cut to two wires of 60 cm length and the small amount of excess (~6-7cm) was discarded. The cable has a nice soft silicone shell and is VERY flexible.
Stripping off 5mm of the outer silicone jacket, I was really surprised at the number of strands in this wire. This high number of strands, combined with the soft silicone shell mean this is a very flexible wire which is easy to work with. Another thing to note, unlike most discount Chinese wire there is a solid amount of metal in the wire.
I dissolved a small spare portion of the wire in concentrated sulfuric acid, so far only the outer tinning has dissolved. That being said, the wire is very clearly tinned copper, as you can see in the image above. After the tin was removed, the copper is very obvious.
Stripping 5mm is basically perfect for inserting into the banana plugs.
Stripping 2-3mm off of the other end is perfect to fit into the wire connector for the Kelvin clip. The 14AWG wire is absolutely a perfect fit for these connectors. The silicone is a nice fit in the barrel, while the wire is the perfect size to fit in the solder cup. Sorry for the blurry photo, unfortunately, I didn't realize it was blurry until I started typing. Since everything is soldered, I can't go back and retake the picture.
A quick comparison of cheap solder (red) versus Kester 44 (black). Both are supposedly 63/37 solder but it is clear they aren't even close to the same quality. I ended up removing the solder from the cheap one and applying fresh Kester 44.
Cutting a bit of heatshrink to cover the connector. I really like this heatshrink. This heatshrink really shrinks down, much more than most of the cheap heatshrink I have encountered. Additionally, when it shrinks down it gets a lot more firm, to the point it serves as a kind of strain relief. It has a feeling somewhere between a thermoset plastic and a hard rubber.
Trimming the heatshrink back to the camfered edge to allow it to properly fit into kelvin adapter.
Putting it all together, large screws attach the connector to the kelvin clip.
The screw covers are a very nice touch. There is one for High Force, High Sense, Low Force and Low Sense.
Now the most important part, how does it work?! Very well, my meter fluctuates between 0.1 and 0.4 mOhm when shorted. Additionally, a precision 294K resistor reads exactly 294.000K. I have NO clue why the images look so compressed, a recent update to my phone really messed up the digital camera it seems.
As I said before, I am REALLY damn happy with these. Especially when you consider the price! The whole kit was cheaper than just the clips on eBay. Also, shipping from Hong Kong only took one week, three days of which the package was sitting in New York waiting to be shipped to my region.
Sellers Contact Info
Because I have received almost a dozen messages requesting his info, it was serving nobodies benefit for me to be obtuse. Here it is for everyone:
Name: Franky Tong
Website: www.franky.com (this links to his ebay store 99centhobbies)
Email: franky @ 99centHobbies . com
EEVBlog Username: iloveelectronics (you can message him on there as well)
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Looks good.
Where did the green wire leads come from?
I didn't see mention of them in your write up.
Also, my great camera doesn't work so well either
after the last apple upgrade to my iphone. 🙁
Just so I understand,
one pair goes to the high pair on the meter
one pair goes to the low pair on the meter.
Would you be kind enough to show us how?
Nice little tutorial.
Oh, one more thought. I take it the H2SO4
piece was just for testing? Sorry I might
have missed it. I thought you dipped the
ends to removed the tin so the copper only
wire would perform better? not?
What is the concentration? Percent or molariity?
Where did the green wire leads come from?
I didn't see mention of them in your write up.
Also, my great camera doesn't work so well either
after the last apple upgrade to my iphone. 🙁
Just so I understand,
one pair goes to the high pair on the meter
one pair goes to the low pair on the meter.
Would you be kind enough to show us how?
Nice little tutorial.
Oh, one more thought. I take it the H2SO4
piece was just for testing? Sorry I might
have missed it. I thought you dipped the
ends to removed the tin so the copper only
wire would perform better? not?
What is the concentration? Percent or molariity?
I'm sorry, I don't see any green wire leads. So I am not sure what you are referring to. Can you point to which image you are talking about?
A kelvin connection is a means of measuring resistance with high precision. It basically runs a known precise current through a device under test and measures the voltage drop across the DUT. Using ohms law, you can then calculate the resistance of the DUT. This results in the necessity of four connections. High Force and Low Force are for the current source. High Sense and Low Sense are for the voltage measurement. The benefit of this is that a voltage measurement has a VERY high input impedance (in the megaohms usually) and as a result the resistance of the cables, connection, etc are essentially nulled out due to the high input impedance. This means that the voltage drop measured is strictly across the device under test. Which means the resistance calculated is strictly for the device under test.
The H2SO4 was strictly for testing the composition of the wire, nothing else. It was 100% undiluted reagent grade conc. H2SO4. Nothing fancy there, I am just a chemist and it was the easiest thing I could think of that I have on hand. The individual strands are too thin for me to be able to see what the core was looking at the cut face on, it just looked dark. This small of strands are a good thing because in test leads you WANT the flexibility that this kind of high strand number gives you. They obviously are more expensive (which is why you don't see them usually in the discount wire.
Thank you for the replay.
Here is the pic:
Where it looks like the red leads are in the center
and the green leads are to something off on the left?
I would like to see from a longer view connected up
to the meters. I think it would be helpful for me to
see, and your reply was very good about it too.
For some reason I kept missing the part about the
slight current....and just reading this the Ah ha moment.
Now, I understand the concept.
Green over here.............red here.
Here is the pic:
Where it looks like the red leads are in the center
and the green leads are to something off on the left?
I would like to see from a longer view connected up
to the meters. I think it would be helpful for me to
see, and your reply was very good about it too.
For some reason I kept missing the part about the
slight current....and just reading this the Ah ha moment.
Now, I understand the concept.
Green over here.............red here.
That is just the white balance messed up. The cable is actually black.Thank you for the replay.
Here is the pic:
Where it looks like the red leads are in the center
and the green leads are to something off on the left?
I would like to see from a longer view connected up
to the meters. I think it would be helpful for me to
see, and your reply was very good about it too.
For some reason I kept missing the part about the
slight current....and just reading this the Ah ha moment.
Now, I understand the concept.
Green over here.............red here.
The hook up is pretty straightforward. The sense on the left, force on the right. High side is red, low is black
Sent from my LG-ls990 using Tapatalk
well don't keep us hangin' how much did it cost see that last zero😀
surprisingly a relative zero button would give similar results in this case.
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Haha yeah, the resistor chosen isn't the best example but I don't have any precision low value resistors on hand.
The cost for everything was $23 shipped.
I just took a bit of the scrap and measured the diameter of the metal in the wire. It's pretty much spot on for 14AWG of metal. Diameter of 14AWG is 1.63mm.
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Thanks
seems to me that using 14 AWG is overkill for 4 wire leads? all the action is at the point of contact.
interesting, yer checking wire dia and if Cu material. does some silicon wire have quality issues that need such checks by the end user? seems you want to know before hand not after the fact. I guess your new low ohm clips will come in handy for these checks.
seems to me that using 14 AWG is overkill for 4 wire leads? all the action is at the point of contact.
interesting, yer checking wire dia and if Cu material. does some silicon wire have quality issues that need such checks by the end user? seems you want to know before hand not after the fact. I guess your new low ohm clips will come in handy for these checks.
Electrically, yes it is WAY overkill. As long as the force leads have enough metal to properly carry the current then it is enough. From a mechanical and tactile standpoint, these leads support and connect into the clips very nicely. The very tight match in size between the wire and the clips gives a high degree of tactile and mechanical stability to the clips.
From the bargain basement vendors in China, yes without a doubt. I have no doubts about my seller, he has been nothing but 100% honest with me and anyone I know that he has dealt with (he's an electronics hobbyist as well, so he actually knows what is quality and what isn't). I am mainly illustrating the quality, because there are a lot of Chinese sellers that are not so honest. It is not uncommon to quote guage size based on the outer diameter with the inner actual metal size dramatically smaller ie a 12 AWG wire is actually 18AWG or worse. Other times, they quote the inner diameter but it conveniently off a guage size (so 12AWG is actually 14AWG inside). Additionally, it is not uncommon for sellers to sell aluminum core wire or tinned steel as tinned copper, that's why I did the test.
The reason I mentioned the cheap crap kelvin leads before, I remember a guy doing a teardown on a set he ordered from China and inside the thick silicone wire was something like 32 AWG copper wire. Now it is likely enough to carry the force current but it was striking how little copper was in there for such a thick wire. Now let me be clear, the problem isn't China per se, the problem is the dishonest sellers. China can make some quality stuff (so many high quality electronics and things are made there), but in this case the sellers requested the maker to make this quality of stuff.
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Now lets see how much skin he removed from you in cash?
2 Pcs Copper Gwinstek LCR Kelvin Test Clip Bridge Clip Microresistivity Clips | eBay
Less than the cost of those for the whole kit. Though I'm not sure of the point of the passive aggressive wording.
Sent from my LG-ls990 using Tapatalk
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You seem keeping of some sort of secrecy of how much you paid for your pair of clips.
Additionally, because your trusty seller he was aware that you do not have a price comparison of this new product, he could charge you as much he likes.
There are two scam bags over eBay asking 26$ for a pair, this is stealing.
These clips worth 1$ USD price retail with VAT in Asia.
Additionally, because your trusty seller he was aware that you do not have a price comparison of this new product, he could charge you as much he likes.
There are two scam bags over eBay asking 26$ for a pair, this is stealing.
These clips worth 1$ USD price retail with VAT in Asia.
Kirakos,
Our friend, Parakalo, do you know a seller that has these clips ready
made and at what price? What quality?
Efkharisto, in advance.
Sycn
Our friend, Parakalo, do you know a seller that has these clips ready
made and at what price? What quality?
Efkharisto, in advance.
Sycn
Here we go again with your anti-china insinuations. Please take your psuedo-racist crap elsewhere. We all know you hate anything that might even have a hint of Chinese/Asian origin. These clips are not worth $1 in Asia, that is a flat out exaggeration/lie. Yes, I checked the prices myself via several friends and former colleagues I have in the Shenzen and the HK areas, a month ago. Going price is around $5-10 depending on seller and quantity purchased. The construction is much better quality than the usual cheap clips from China. When you factor in the cost of the wire, the cost of the plugs, shipping via HK Post and the fact that my seller has to make a profit, then everything is damn reasonable.
As for the trustworthiness of my seller, he has been VERY trustworthy and has proven himself to be so over MANY MANY transactions both with myself and others. Everything I have purchased from him has been VERY good quality. Every item has been leaps and bounds ahead of the cheap crap I have received from some other sellers in China. As a hobbyist it is the exact quality I NEED and at a price I want.
As for me not mentioning the price, this is because he has sold out already and won't be able to get anymore back in stock until after x-mas. But as usual, you look for a conspiracy.
PINTEK in Taiwan selling those clips with cables, but over seas availability this is poor. Retail price seems to be close to 130$
http://www.pintek.com.tw/files/pintek/RP-91.pdf
GW Instek using such clips too, these are closer match to what our friend buy all ready.
Generally speaking Kelvin clips is a good reason to get scammed and pay a tremendous price premium for no reason.
My 30 minutes investigation payed out, if I was about making Kelvin cables I would buy a pair of this clips.
Gold Plated Alligator Crocodile Clip Positive and Negative Test LCR Gray Kelvin | eBay
Given that Electronic Test Accessories (ETA), the makers of the clips I purchased, is a Taiwanese company, I will lay you odds that these are the exact same clips as the ones being used by GW Instek.
Then seek elsewhere, I simply post interesting stuff that I find and use. I find it very insulting and very uncouth that you insinuate that I would be dishonest with people (without a shred of evidence, no less).
So my friend Kiriakos, what is your complaint?
Pedro does a little tutorial, seems to pay a fair price
of $25 USD and you are complaining because PINTEK
are 130 USD?
I don't think Pedro posted links to the seller and
was careful to not be a shameless promotion thread.
OK, my friend what gives?
You think we should pay $2 USD for cheap china clips?
With mold stamps that will cut our fingers.
Maybe there are some folks there in Greece that
could use your electrical knowledge and help with
providing heat and power for those coming to your
country for safety. You think?
As always, thanks for your thoughtless and non-helpful replys.
Please don't feed the trolls.
Pedro does a little tutorial, seems to pay a fair price
of $25 USD and you are complaining because PINTEK
are 130 USD?
I don't think Pedro posted links to the seller and
was careful to not be a shameless promotion thread.
OK, my friend what gives?
You think we should pay $2 USD for cheap china clips?
With mold stamps that will cut our fingers.
Maybe there are some folks there in Greece that
could use your electrical knowledge and help with
providing heat and power for those coming to your
country for safety. You think?
As always, thanks for your thoughtless and non-helpful replys.
Please don't feed the trolls.
You are free to feel insulted by any real or imaginary cause.
Now answer the one million dollars question.
What did you pay for them?
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