Author Topic: 1000 A current probe for spot welder measurement  (Read 3198 times)

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Offline MartinnTopic starter

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1000 A current probe for spot welder measurement
« on: August 30, 2023, 05:07:40 pm »
Hi all,
I purchased a CP01 spot welder https://www.aliexpress.com/item/1005005334325622.html which, 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 this https://www.mouser.ch/ProductDetail/Tamura/L06P800S05?qs=DDWeUbTzG0fyBrNwDestkQ%3D%3D 800 A Tamura sensor, which looks perfect and is quite cheap at Fr. 20.
Any other suggestions?
 

Offline nctnico

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Re: 1000 A current probe for spot welder measurement
« Reply #1 on: August 30, 2023, 05:22:02 pm »
Rogowski coil
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #2 on: August 30, 2023, 05:28:07 pm »
Rogowski coil
Aren't those AC only? Expected waveform is a 20 ms 500-1000A single (DC) pulse.
 

Online Stray Electron

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Re: 1000 A current probe for spot welder measurement
« Reply #3 on: August 30, 2023, 05:39:39 pm »
  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. 
 

Offline nctnico

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Re: 1000 A current probe for spot welder measurement
« Reply #4 on: August 30, 2023, 05:52:35 pm »
Rogowski coil
Aren't those AC only? Expected waveform is a 20 ms 500-1000A single (DC) pulse.
These work excellent for spot welding. Been there, done that (up to tens of kA).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline MadTux

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Re: 1000 A current probe for spot welder measurement
« Reply #5 on: August 30, 2023, 06:17:38 pm »
LEM ultrastab, if cheap, on ebay ;-D
 

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #6 on: August 30, 2023, 08:00:11 pm »
These work excellent for spot welding. Been there, done that (up to tens of kA).
It 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.
 

Offline nctnico

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Re: 1000 A current probe for spot welder measurement
« Reply #7 on: August 30, 2023, 08:11:11 pm »
These work excellent for spot welding. Been there, done that (up to tens of kA).
It 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.
The 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.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline srb1954

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Re: 1000 A current probe for spot welder measurement
« Reply #8 on: August 30, 2023, 10:30:55 pm »
Hi all,
I purchased a CP01 spot welder https://www.aliexpress.com/item/1005005334325622.html which, 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.
Since 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.
 

Offline thm_w

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Re: 1000 A current probe for spot welder measurement
« Reply #9 on: August 30, 2023, 11:24:20 pm »
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.
Profile -> Modify profile -> Look and Layout ->  Don't show users' signatures
 

Offline tautech

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Re: 1000 A current probe for spot welder measurement
« Reply #10 on: August 30, 2023, 11:34:32 pm »
There is much about battery spot welding in this thread:
https://www.eevblog.com/forum/projects/guesses-on-what-i-am-attempting-here/
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Offline John+audio

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Re: 1000 A current probe for spot welder measurement
« Reply #11 on: August 31, 2023, 03:22:34 pm »
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......
 
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Offline Marco

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Re: 1000 A current probe for spot welder measurement
« Reply #12 on: August 31, 2023, 05:23:06 pm »
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.
 

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #13 on: August 31, 2023, 05:29:01 pm »
I have seen this video. However I don't see how I could nondestructively add the bypass wire.
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%.
Thanks for the warning! I'll try to keep it in mind!
 

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #14 on: August 31, 2023, 05:32:31 pm »
Since 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.
Didn'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!
 

Offline tautech

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Re: 1000 A current probe for spot welder measurement
« Reply #15 on: August 31, 2023, 07:31:53 pm »
Since 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.
Didn'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!
Typically under 100A but DC.
Shunts would be the simplest however add some HF Start/Run and it's not so simple.
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Offline DaneLaw

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Re: 1000 A current probe for spot welder measurement
« Reply #16 on: August 31, 2023, 09:09:04 pm »
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 meter https://docs.rs-online.com/8278/0900766b8095f724.pdf
 

Overall 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/36rpsd2r with a around 40C rating
4S 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 & CC65

55ms  HT208D


20ms


If 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.
« Last Edit: August 31, 2023, 10:33:27 pm by DaneLaw »
 

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #17 on: October 14, 2023, 01:19:18 pm »
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.
« Last Edit: October 14, 2023, 01:22:46 pm by Martinn »
 
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Offline mk_

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Re: 1000 A current probe for spot welder measurement
« Reply #18 on: October 15, 2023, 03:00:04 pm »
Since 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.
Didn't know that these exist! There is even one nearby (<1000 km) for quite a decent price.
at.

Thanks, 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.
 

Offline TizianoHV

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Re: 1000 A current probe for spot welder measurement
« Reply #19 on: October 16, 2023, 05:21:45 pm »
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!

Offline MartinnTopic starter

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Re: 1000 A current probe for spot welder measurement
« Reply #20 on: October 16, 2023, 06:20:38 pm »
Would be interesting a small review / test of this current transformer. Seems good for the price.
What's the smallest current it can measure?...
Not 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.pdf
Anyway 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).
« Last Edit: October 16, 2023, 06:24:01 pm by Martinn »
 

Offline TizianoHV

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Re: 1000 A current probe for spot welder measurement
« Reply #21 on: October 16, 2023, 07:01:50 pm »
wops, yes, I was interested in your Tamura CT. Thankyou for the tests.


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