Low thermal EMF binding posts - a quality warning.

[notfaded1]

If they are not brass, they are pot metal (low grade zinc alloy). Pot metal connectors appear to be used in that infamous 10V reference.

What's the infamous 10V reference?

Thanks,

Bill

[Gyro]

What's the infamous 10V reference?

https://www.eevblog.com/forum/metrology/precision-dc-votage-source/msg3601830/#msg3601830

[GWL]

I have built a 1% high resistance box, for internal insulation/megger testing, for which i had used a brass-gold plated multi-comp binding post (SPC15203 and SPC15208). They were pretty cheap USD 4 each. The values i recorded had a good repeatability. I had tested only till 1 gig ohms at 1000 volt. I was thinking of upgrading the box with 1 tera ohms resistors and binding post that can withstand 10kV. Not sure if i can use the same binding post and test 1 tera ohms at 10kV. The multi-comp datasheet does not have any technical details other than max 15Amps. Any leads for upgrade will be helpful.

[leighcorrigall]

I have built a 1% high resistance box, for internal insulation/megger testing, for which i had used a brass-gold plated multi-comp binding post (SPC15203 and SPC15208). They were pretty cheap USD 4 each. The values i recorded had a good repeatability. I had tested only till 1 gig ohms at 1000 volt. I was thinking of upgrading the box with 1 tera ohms resistors and binding post that can withstand 10kV. Not sure if i can use the same binding post and test 1 tera ohms at 10kV. The multi- (Attachment Link) comp datasheet does not have any technical details other than max 15Amps. Any leads for upgrade will be helpful.

Welcome GWL,

As I mentioned previously, JP Fine Chem designs and manufacturers ultra-high voltage resistance references:
https://www.eevblog.com/forum/metrology/low-thermal-emf-binding-posts-a-quality-warning/msg3592418/#msg3592418
https://www.eevblog.com/forum/metrology/low-thermal-emf-binding-posts-a-quality-warning/msg3604042/#msg3604042

JP Fine Chem (also known as E&C) uses custom-made Miyama binding posts. You might not be able to acquire these binding posts as a consumer, but you could ask anyways. I spoke to a representative at DMTL from the UK (https://www.dmtl.co.uk/) and they were very helpful in answering my questions.

The JP Fine company also makes high voltage measuring equipment:
https://www.jfine.co.jp/eng/e_c/voltage/index.html

By the way, what brand are your tera-ohm resistors? I would love to know your experience with them in the precision resistors general thread:
https://www.eevblog.com/forum/metrology/precision-resistors-general-thread/

[e61_phil]

I have built a 1% high resistance box, for internal insulation/megger testing, for which i had used a brass-gold plated multi-comp binding post (SPC15203 and SPC15208). They were pretty cheap USD 4 each. The values i recorded had a good repeatability. I had tested only till 1 gig ohms at 1000 volt. I was thinking of upgrading the box with 1 tera ohms resistors and binding post that can withstand 10kV. Not sure if i can use the same binding post and test 1 tera ohms at 10kV. The multi- (Attachment Link) comp datasheet does not have any technical details other than max 15Amps. Any leads for upgrade will be helpful.

Nice box!

I'm interested in your 10kV setup: Do you have 10kV with such low uncertainties that it make sense to measure with 10kV instead of 1kV?

I can generate 10kV with <10ppm uncertainty, but that is a lot of effort.

[martinr33]

Unpleasant discovery.

When installing copper binding posts - make sure that the front terminal nuts are loose, several turns or so.

Otherwise, when you tighten the rear nut, you will hear the snap of your post breaking at the wire holes. It doesn't take much, you can do it with a nut driver.

Low thermal copper is not as strong as brass.

[dietert1]

If you want something stronger, you can try EIZZ EZ-303. Those are speaker terminals made from CuTe (!) and they are about 15 € per piece. I got some at www.audiophonics.fr.
They look like having about twice as much copper than a Pomona 3770.

Regards, Dieter

[leighcorrigall]

If you want something stronger, you can try EIZZ EZ-303. Those are speaker terminals made from CuTe (!) and they are about 15 € per piece. I got some at www.audiophonics.fr.
They look like having about twice as much copper than a Pomona 3770.

Regards, Dieter

Nice find, Dieter.

It would be nice to know what insulating material they use if they have not already said so. If you can, see if there is a thin nickel coating or something else suspicious hiding under that 'gold' coating with a strong magnet. Sometimes they will gold coat iron.

I love how it is blatantly obvious that these posts came from China. When I get back from vacation I am going to see if my friend can identify the manufacturer so we can avoid the middle man. 

[dietert1]

Yes, when they arrived, the first thing i did was look at the inside, and it had a similar reddish shine like the Pomonas. Nothing silvery. The body doesn't react at all with a strong magnet, including the set screw. The gold plated decoration of the knob and the back nut show a minute, hardly detectable attraction.
I bought from France to save time, they had some stock.

Meanwhile we also have a second SR1010 with 100 Ohm steps and with copper binding posts while the first one with 1 KOhm steps has binding posts made of white, non-magnetic metal.

Regards, Dieter

[Vgkid]

If you want something stronger, you can try EIZZ EZ-303. Those are speaker terminals made from CuTe (!) and they are about 15 € per piece. I got some at www.audiophonics.fr.
They look like having about twice as much copper than a Pomona 3770.

Regards, Dieter

Nice find, Dieter.

It would be nice to know what insulating material they use if they have not already said so. If you can, see if there is a thin nickel coating or something else suspicious hiding under that 'gold' coating with a strong magnet. Sometimes they will gold coat iron.

I love how it is blatantly obvious that these posts came from China. When I get back from vacation I am going to see if my friend can identify the manufacturer so we can avoid the middle man. 

Here you go:
http://eizz.cn/en-us/x23.html

[martinr33]

They do look nice, and that is a good price.

However - the Aliexpress ones call out brass, but also mention no nickel plate, which I have only seen on copper terminals. No nickel plate is consistent with the lack of magnetic attraction.

We may need some filing to see.

https://www.aliexpress.com/item/32722111716.html

[dietert1]

I would not trust that aliexpress any more than the EIZZ web page.
As far as i understand they have them in brass and CuTe (different product IDs). If i buy from a french company selling it as CuTe, i can insist. As i wrote above, i did the filing as soon as they arrived and it looked like the CuTe of the Pomonas, and softer than brass.
Recently we got a FLIR camara, and one day i will buy one of those handheld X-Ray analyzers they use for metallurgy (garbage recycling). As far as i understand it discovers traces of Pb in RoHS products and many other metals, depending on the setup.
Or make a thermal EMF voltage setup to do a real measurement.

Regards, Dieter

[OscarM]

This seems as good as place as any (even if it is old) to post this picture.

I received these from Digi-key last week.

When is a 3770-0 not a 3770-0 ?

Its not obvious but they are still in the original packaging.
It isn't a trick of the lighting.

[sahko123]

one of those is the 3760 which is tin plated. So pomona must have screwed up the packaging