1000 A current probe for spot welder measurement - Page 1
Forum section: electronics / testgear

author: Martinn
author_rank: Frequent Contributor
timestamp: August 30, 2023, 05:07:40 pm
content: Hi all,I purchased a CP01 spot welderhttps://www.aliexpress.com/item/1005005334325622.htmlwhich, somewhat unexpectedly, works surprisingly well (I did some quick tests on AA cells).Of course I am wondering what current this unit provides, I have seen it advertised at "1000A", currently the Ali description says ">650A". As I don't own a current probe in this range (I have a Tek A6302) I am looking for other options. As I am not going to specialize in spot welder development, there's no point investing in a high grade unit. I thought about poking needles through the cable insulation, doing a four-wire resistance measurement and use the cable then as shunt for a current measurement.Checking Mouser parametric search for matching sensors comes up with thishttps://www.mouser.ch/ProductDetail/Tamura/L06P800S05?qs=DDWeUbTzG0fyBrNwDestkQ%3D%3D800 A Tamura sensor, which looks perfect and is quite cheap at Fr. 20.Any other suggestions?

author: nctnico
author_rank: Super Contributor
timestamp: August 30, 2023, 05:22:02 pm
content: Rogowski coil

author: Martinn
author_rank: Frequent Contributor
timestamp: August 30, 2023, 05:28:07 pm
content: Quote from: nctnico on August 30, 2023, 05:22:02 pmAren't those AC only? Expected waveform is a 20 ms 500-1000A single (DC) pulse.

author: Stray Electron
author_rank: Super Contributor
timestamp: August 30, 2023, 05:39:39 pm
content: I've seen people make current shunts from various sizes of steel drill rod. IIRC there is a Youtube video of someone testing lithium jump starter battery using a drill rob current shunt.Link:https://www.metalsupermarkets.com/what-is-drill-rod/Hmm. I looked and there are a few commercially-made 1000 Amp current shunts for sale on Ebay.

author: nctnico
author_rank: Super Contributor
timestamp: August 30, 2023, 05:52:35 pm
content: Quote from: Martinn on August 30, 2023, 05:28:07 pmThese work excellent for spot welding. Been there, done that (up to tens of kA).

author: MadTux
author_rank: Frequent Contributor
timestamp: August 30, 2023, 06:17:38 pm
content: LEM ultrastab, if cheap, on ebay ;-D

author: Martinn
author_rank: Frequent Contributor
timestamp: August 30, 2023, 08:00:11 pm
content: Quote from: nctnico on August 30, 2023, 05:52:35 pmIt seems the integrator is the key part for this. Not sure what current rise/fall times these spot welders achieve, probably in the microsecond range in order not to vaporize the switching FETs, which would mean you'd need quite some bandwidth.What would you recommend? Official ones (PEM) are likely too expensive, Chinese ones are affordable with questionable or unknown specs.

author: nctnico
author_rank: Super Contributor
timestamp: August 30, 2023, 08:11:11 pm
content: Quote from: Martinn on August 30, 2023, 08:00:11 pmThe spot welders I worked with are also in the milli-second range where it comes to the pulses. For the application I worked on, the goal was to measure the amount of Coulombs (integrated current over time) that went into the weld.But I see now you are looking for a temporary solution... Another option could be to use a current transformer. It won't produce a perfect pulse but good enough to asses the ballpark current. But the (supposedly HAL effect) sensor you found is pretty cheap.

author: srb1954
author_rank: Super Contributor
timestamp: August 30, 2023, 10:30:55 pm
content: Quote from: Martinn on August 30, 2023, 05:07:40 pmSince you have already got a Tek A6302 it might be worth considering looking for a Tek CT-5 current transformer to go with it giving the benefit of a wide frequency range (0.5Hz to 15MHz), high pulse handling capability (50kA) and the wide sensitivity range (5000:1) of the A6302.You might be able to pick a second-hand CT-5 up for not much more than a reasonable quality commercial Rogowski coil.

author: thm_w
author_rank: Super Contributor
timestamp: August 30, 2023, 11:24:20 pm
content: Looks like this guy got 900A but using a different setup:Would be interesting to know.BTW I have a similar spot welder, worked well, until the battery drained and now its no longer working. Tried some regular packs and they can't weld at all. So be careful to keep the battery charged at ~60%.Not sure if something failed or if the battery it came with is just very optimized for high current draw.

author: tautech
author_rank: Super Contributor
timestamp: August 30, 2023, 11:34:32 pm
content: There is much about battery spot welding in this thread:https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/

author: John+audio
author_rank: Newbie
timestamp: August 31, 2023, 03:22:34 pm
content: Shahriar of The Signal Path does a good tear down of a spot welder - including current measurements:He also checks - and improves the safety of his unit......

author: Marco
author_rank: Super Contributor
timestamp: August 31, 2023, 05:23:06 pm
content: Put some kelvin taps on your welding wire and measure the inductance and resistance, then calculate the current from the voltage waveform using some differential math. It's going to be a little off due to temperature, but you don't need high accuracy.

author: Martinn
author_rank: Frequent Contributor
timestamp: August 31, 2023, 05:29:01 pm
content: I have seen this video. However I don't see how I could nondestructively add the bypass wire.Quote from: thm_w on August 30, 2023, 11:24:20 pmThanks for the warning! I'll try to keep it in mind!

author: Martinn
author_rank: Frequent Contributor
timestamp: August 31, 2023, 05:32:31 pm
content: Quote from: srb1954 on August 30, 2023, 10:30:55 pmDidn't know that these exist! There is even one nearby (<1000 km) for quite a decent price.However as my storage space is limited I am reluctant to buy stuff I probably need once in a decade. Also if I purchase some kA measurement equipment it should at least be able to measure my TIG welder current (not that it would need measuring...) and a non-DC transformer would not be ideal for that.Anyway thanks for pointing out!

author: tautech
author_rank: Super Contributor
timestamp: August 31, 2023, 07:31:53 pm
content: Quote from: Martinn on August 31, 2023, 05:32:31 pmTypically under 100A but DC.Shunts would be the simplest however add some HF Start/Run and it's not so simple.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: August 31, 2023, 09:09:04 pm
content: Tried with an inrush clamp meter and with two sub 50 bucks AC/DC current clamps for low amps for scope, to see what they could pick up on short current pulses with a spot welder.Hantek CC-65 (20K) & ETCR007 (100k), and tried with a 1000A AC/DC clamp meter Habotest HT208D. with its inrush.... but I don't have the tools to validate if those inrush values are somewhat accurate, but HT208D was able to pick up very brief current pulse down to like 10ms.How accurate inrush <DC values are on a sub 40buck 1000A clamp meter like below..it certainly aint a Fluke PQ345 as exampled above, very impressive clamp meterhttps://docs.rs-online.com/8278/0900766b8095f724.pdfOverall pleasantly surprised about how it performed even at thicker or stacked nickel strips. for me it was critical that I could separate the batteries from the spot welder when dealing with bottom of the barrel from China, as 10 buck delivered is chancing it.was using old 4S lipo cells from this old CP stingray clone..https://tinyurl.com/36rpsd2rwith a around 40C rating4S is higher than its rated 12v but it's the first old rev. that seems to have better circuitry, not sure if later revisions will tolerate 16v.With the price in mind, impressed, does the job very well for the few times I had a use for it, it got a display where you can toggle from 1 to 99ms (1to99E) & two welding modes "aut-time delayed or manual for fx foot pedal.-ETCR07 & CC6555ms HT208D20msIf these quite cheap 1000A current clamp meters like the HT208D, with inrush peak, are able to deliver somewhat accurate numbers in DC, then it would be pretty straightforward as a tool to measure current draw on fast pulses under 100ms.

author: Martinn
author_rank: Frequent Contributor
timestamp: October 14, 2023, 01:19:18 pm
content: Quick update: Got an 800 A sensor from Tamura (link in first post).Welded a nickel strip onto some junk AA cell. Pulse is 416 A, 85 ms.Works! Quick, easy, inexpensive, does its job.

author: mk_
author_rank: Regular Contributor
timestamp: October 15, 2023, 03:00:04 pm
content: Quote from: Martinn on August 31, 2023, 05:32:31 pmThanks, this one from nearby is on its way to my lab... going to measure slow hv-pulses (with high current) the CT-4 isn`t able to handle anymore.

author: TizianoHV
author_rank: Regular Contributor
timestamp: October 16, 2023, 05:21:45 pm
content: Would be interesting a small review / test of this current transformer. Seems good for the price.What's the smallest current it can measure?...Thankyou!

author: Martinn
author_rank: Frequent Contributor
timestamp: October 16, 2023, 06:20:38 pm
content: Quote from: TizianoHV on October 16, 2023, 05:21:45 pmNot sure if you are replying to my or to mk_s post.Regarding the Tamura sensor: The datasheet is pretty specific:https://www.tamuracorp.com/clientuploads/pdfs/engineeringdocs/L06PXXXS05.pdfAnyway I have not remotely high enough current capable calibration sources. Maybe I could check what the noise in my flying probe setup would be. Sensitivity is 1.5V/800A = 1.875 mV/A.Did a quick check: Sensor on 1:10 passive probe on scope 20 MHz BW limit gives about 1 mV RMS noise. So 5 A would be easily resolvable. However DC offset is 2.5 V, so minimum DC current level your scope can show depends on the offset capabilities of your scope frontend (unless you go to AC coupling of course).With an AM502 set to 100x gain and DC-10 kHz bandwidth, 200 mA are about the minimum you can see in a single ended connection (did not have differential cabling at hand). The AM502 also can (in the 100x attenuation setting) remove the DC offset (in a DC coupled measurement).

author: TizianoHV
author_rank: Regular Contributor
timestamp: October 16, 2023, 07:01:50 pm
content: wops, yes, I was interested in your Tamura CT. Thankyou for the tests.