making a big power shunt? - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: March 03, 2025, 09:33:30 am
content: So you can buy those big high power shunts that you bolt cables to. I think its a manganin or other ribbon with some supports.How could you go about making them? I modified one before, on a mill, but I screwed it up because it was 5% under after deburring (so if you do this ,to make a serpetine resistor, get it to like 10%, debur, and go slow manually towards the end)How are great ones built? Is it just brazed on with silver, to the terminals, or do they use more advanced techniques to improve the tempco? (like diffusion bonds), or is it some kind of crimp?I only ever used cheap ass ones, which look like its some kind of solder type stuff there, but I am wondering what the 'cutting edge' might look like

author: thm_w
author_rank: Super Contributor
timestamp: March 03, 2025, 10:08:02 pm
content: These just say they are soldered:https://shunts.com/blogs/shunt-blogs-articles/precision-shunts-overview-and-applicationsThis might be laser welded manganin to copper:https://www.koaspeer.com/products/resistors/current-sense-shunt-resistors-low-resistance/power-shunts/hs/https://www.eevblog.com/forum/metrology/manufacturing-custom-high-precision-low-tc-resistors/

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2025, 07:37:16 am
content: I wonder if that bond choice has a effect on temp-co.They all seem worse then wire resistors of a similar compositionI thought maybe its because the wire is small and the weld area is small but with these things you need a big bond?For a laser weld, there is a small HAZ. For a diffusion weld, I am not sure if 70% of melting point gets you into heat effected zone region. Or if it matters.I think there is maybe a difference between the materials, i.e. the need to anneal the weld, but also the need to properly heat treat the manganin.But knowing the amount of error that comes from the bond could help answer that question .This seems to be the lowest drift one on DK.https://www.digikey.com/en/products/detail/vishay-dale/WSBS8518L5000JT34/6709544Claims its welded, but I wonder how.is that a laser weld? It looks kinda ratty for a laser weld, but I am not sure if its going to look as nice for dissimilar metals. is that how copper/nichrome laser bonds look like? or could it be some other welding process? All the laser welds I saw looked much prettier.This is a copper/stainless laser weld, look how much better it looks then the resistor weldhttps://ars.els-cdn.com/content/image/1-s2.0-S0924013615000904-gr2.jpgI don't see like a stack of dimes, or the glassy smoothness in the resistor weld. it looks like rough . in the picture of the copper stainless weld you can see a stack of dimes and also more smoothness.

author: Poroit
author_rank: Frequent Contributor
timestamp: March 05, 2025, 08:43:42 pm
content: The shunt blades are made from Manganin and are soldered to the mounting blocks.When we manufactured large shunts, they were calibrated by removing or adding material to the blades.Depending if the calibration was high or low , you made small hacksaw cuts or added solder to the back of the blades.

author: coppercone2
author_rank: Super Contributor
timestamp: March 05, 2025, 09:25:21 pm
content: what tempco did you get +-20C from ambient with that method?

author: joeqsmith
author_rank: Super Contributor
timestamp: March 05, 2025, 10:14:05 pm
content: For my UNI-T UT61E, I tried TIG welding. Worked like you may expect. Ended up with silver solver (brazing).

author: Zero999
author_rank: Super Contributor
timestamp: March 05, 2025, 10:32:29 pm
content: Quote from: coppercone2 on March 03, 2025, 09:33:30 amMake it a little bit too big i.e. low resistance, then trim by filling.

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2025, 08:05:37 am
content: for that shunt I put a picture of, what are the L shapes in the copper for? I thought you trim the resistor. It is to ballast the sense from some... distributed resistance thing?or is it just to put wires through for mounting?But L - shape is a trim shape, but its in the copper. It seems strange because its before the sense, so it looks like extra losses.and their like countercorner ?Since its before the sense its making me think some weird shit about electrons flow problems or somethingfor the material gets messed up from the welding and trying to position the sense point via geometry stops working so they add a resistor there.. then it makes me think of like a non ideal current sourceThere has to be a good reason. Tempco of copper sucks and you don't want copper to get hot and change the total shunt resistance. so why the hell would you put a cut in the copper???Or is it just a thermal isolator to make welding easier? and counter corner for strain balance ? and its a non ideality electrically that has to be made for manufacturing reasons? like to control the warp to be manageable?

author: Zero999
author_rank: Super Contributor
timestamp: March 06, 2025, 09:49:37 am
content: Could the "L" shape just be a point to put the sense pins? Less copper makes it easier to solder.

author: Poroit
author_rank: Frequent Contributor
timestamp: March 07, 2025, 07:03:56 am
content: As per @ Zero999....they are the Measurement lead connections and are kept as close as possible to the shunt.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2025, 07:11:10 am
content: the pin is the connection why is there a L shaped cut. You could solder that pin to the actual shunt, and infact you can solder it on before you weld them together, without a cut.That cut looks like it hurts the thermal capacity of the shunt too. It can stay cooler if it sinks more heat into the copper. If you put a cut in there, its not going to stay as cold when it passes alot of current. The more heat sinking is on that resistive section, the more stable it is.It seems like alot of electrical performance downsides

author: Zero999
author_rank: Super Contributor
timestamp: March 07, 2025, 08:22:26 am
content: On the other hand a slot improves heat dissipation due to convection.Why don't you ask the manufacturer?

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2025, 08:24:46 am
content: Hmm perhaps, the hole might be big enough to flow some airI doubt the manufacturer will bother telling me anything unless I order qt 500.But I still think , carrying that heat through pure copper with a huge surface area is going to do more then a little hole that might have a little convection. Even if its decent, I suspect the difference is extremely marginal... but something in the back of my head tells me that it would be worse then sinking heat through copper, possibly into a fat bus bar, possibly twisted 90 degrees so it has some real air cooling with a really big tight bolt making a great thermal interface between the shunt and bus bar.Maybe that weld ends up being a little weak and its there to allow it to bend a little, like warp upon installation so it does not crack the weld, if attached to big bus bars?How do you define a dissimilar metal weld anyway? A good weld is stronger then the material its in. WTF is the material that its in, its two materials. lolThe ductility of copper and resistor steel are totally different, so it makes it hard to conceptually understand the definition that it should be as strong as the weaker material when its in a interface. when you bend it, there is like a cusp because the ductility is different. it must be like stretched on top, I mean for bending not tensile strenght. mind blown.