Author Topic: Microwave owen transformer spot welder?  (Read 13588 times)

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #50 on: January 06, 2016, 08:02:49 AM »
Thank you very much. I heard good stuff on Sigilent stuff, but one person warned me stay clear of http://www.siglent.eu/ site. He had trouble with that and does not show on sigilent page either.

Those handheld seems "perfect" but price is least doble on what I am prepared to spend at this point.

Some have recommended USB scopes like this:
http://www.ebay.com/itm/Hantek-6022BE-PC-Based-USB-Digital-Storage-Oscilloscope-20MHz-Bandwidth-48MSa-s-/331245851756?hash=item4d1fca946c:g:kaAAAOSwGiRTrT9N

But they will need a laptop, not sure if measurement is isolated from the laptop and where they are grounded or nulled.

Pretty ideal would be two channell benctop, simple triggering and with 1:10 attennuated probes I should be able to measure all threepahse stuff. It just looks like just might get that about 200, but really should shell out least 100 more to actually get the spec and usability.

I tried long time ago some of the first handheld scopes and they were damn too difficult to use and so limited that you actually had to know the wafeform and fiddle trough all menus and then you had to figure from few dot's on the screen that yup, subber is duff.....

Is there simple and easy to use benchtop type on very low end price range, or am I better off with USB cacadoodles and when I throw one trough window out of frustration I'll just swallow and prepare to spend 300 on something that is nearly enough.

Pekka

Offline PK

  • Full Member
  • ***
  • Posts: 240
  • Country: au
Re: Microwave owen transformer spot welder?
« Reply #51 on: January 06, 2016, 08:34:48 AM »
We have a couple of PC based test tools. The purist in me says they are an elegant and cost effective solution. I mean why pay for a screen on every single instrument when you can just use a laptop? In practice I find myself preferring the stand alone gear..  Go figure!

So these are very good value for money http://www.emona.com.au/products/electronic-test-measure/oscilloscopes/ds1054z.html#.Vo0XjxV95hE, big screen 12 million points capture buffer (trust me, this is an important spec) and peanut cost.

They get even better when you unlock the 100MHz bandwidth with a simple hack http://hackaday.com/2014/11/12/how-to-get-50-more-zed-from-your-rigol-ds1054z

PK

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #52 on: January 07, 2016, 02:23:09 PM »
After lengthy negotiations with her royal highness I have legitimate fund for a new toy....but nowhee close to anything like 500 or any other that type of figure.

Rigol DS1052E starts to look like possible canditate, but where to get it in Europe?

Is it allways same or are there different versions floating?

Found these:
http://www.batronix.com/shop/oscilloscopes/Rigol-DS1052E.html
http://www.rigol.eu/products/digital-oscilloscopes/ds1000e/ds1052e/
http://www.rigol-uk.co.uk/Rigol-DS1052E-Digital-Oscilloscope-p/ds1052e.htm#.Vo6sGVl8dzk

Anything else I should know before.

Pekka

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #53 on: January 09, 2016, 06:11:30 PM »
Got one old UK-made 10MHz scope for free and nearly fried it today....

Got some measurements done. Have to dig up and connect my isolation transformer somewhere.

Have to get some probes and acessories.

Any good tutorial on AC power circuitry measurement. Figured I'm a bit rusty. Too long time from studies.

Pekka

Offline PK

  • Full Member
  • ***
  • Posts: 240
  • Country: au
Re: Microwave owen transformer spot welder?
« Reply #54 on: January 09, 2016, 06:50:14 PM »
Like I said, hand held, isolated scopes are nice things in some applications.

All you really need to keep burned into your consciousness is that the little croc clip on the scope probe is connected to the earth and neutral wires in the plug.
If you can get your head around that then everything else becomes obvious.

The normal procedure is to plug the DUT (in your case your spot welder) into an isolation transformer. This lets it float with respect to ground and means that you have to touch two points on it to die instead of one.
Catch is, an isolation transformer that can handle the power your welder should draw are big and expensive. (maybe you could get two more MOT's and wire them back to back??)

So what you would probably do is plug the scope into an isolation transformer and float it WRT ground.  NB, this is QUITE A LOT MORE DANGEROUS because the case of the scope including  the front panel (do the knobs on the front have metal grub screws in them that your fingers may touch when you adjust the settings?) will sit at whatever voltage you connect the earth clip to....

Having said that, there's no reason not to do this, just plan ahead and write a short note bequeathing all your tools to me in the event of your death.

I have a bit of a process I like to follow when I work on high voltage stuff I'm not confident with.  I take a digital multimeter set to AC volts and hold one lead. Then I poke the other lead onto whatever bit of metal I'm thinking about touching. If I see more than 20VAC on the meter then I know I've just avoided electrocution. It's not a fool proof process, but I'm still here..

Oh, and RCD's are a MUST HAVE for this kind of work..


Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5081
  • Country: gb
  • East Sussex, UK
Re: Microwave owen transformer spot welder?
« Reply #55 on: January 10, 2016, 03:33:04 AM »
To think that for years and years I carried a Textronix 465 in the car as a standard computer servicing tool that had the mains earth lead disconnected and poking out of the plug so that it was obvious to all.

But Health and Safety hadn't been invented then, nor had RCDs so it was OK  :lol:

But on the other hand Common Sense hadn't been banned then, so that probably saved us  :ddb:
Andrew Mawson
East Sussex

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #56 on: January 10, 2016, 04:30:07 AM »
Yesh...that was all normal when I was a student and lab tehnicias hovering among us to prevent us from sme of the most dangerous stuff.

My problem here was a senior moment....I'm aware of the problem and in order to avoid it I had all figured and checked out, but then I put the plug wrong way in.... I actually have two poplarized Shucko plugs, but no power strip that is polarized.

We used flot sopes, but the scope had long plastic extensions for the knobs...for the reason mentioned before. We were wondering why the front panel was metal and plastic knobs had metal parts....maybe it's just cruelty to apprendices?

I had a look on current probes and isolated probes....good thing that I was sitting down. I must have sunk deeper in the couch. Least it felt that way.

Is there any economical floating probe/isolation amplifiers available for a) mains measuremet b) instrument level signals 24vdc, +/- 10V?

Or am I better of cobbling on a plastic enclosure double insulated system, that has it's own isolated PSU, then DIY voltage divider/differential amplifier and a EL-cheapo digital scope with very limited bandwidth but cheap price tag? Sort of bangood scope mentioned here?

Pekka

Offline PK

  • Full Member
  • ***
  • Posts: 240
  • Country: au
Re: Microwave owen transformer spot welder?
« Reply #57 on: January 10, 2016, 05:09:47 AM »
Re all of the above, if you slow down and think it through then the risk is zero. The cautionary language is for the young'uns reading this who aren't going to take that approach.

On the topic of isolation..
We have a few DIY isolation transformer boxes here at work that are nothing more than two mains to 24 transformers wired back to back. We're still alive.

It sounds a bit excessive, but the cheapest option for you might be to get two more oven transformers and wire them together. This will give you an isolation transformer of some significant capacity...

I'm not sure I understand the requirement to isolate both the scope supply and the signal of interest?

Re options:
A battery powered handheld scope isn't the same thing as an isolated scope (look for cat II or cat III specs). Sadly the manufacturers of these devices understand this and charge commensurately.

All handheld scopes are complete crap compared to the same dollars in a bench scope, mostly because they have tiny, low res screens, also mostly because they have tiny capture buffers and finally mostly because they have slow processors which makes the menus slow to pop up and hard to use.

So my vote is for the bench scope and isolation....



Offline awemawson

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5081
  • Country: gb
  • East Sussex, UK
Re: Microwave owen transformer spot welder?
« Reply #58 on: January 10, 2016, 05:36:51 AM »
There are some excellent bargains on eBay for analogue Tektronix oscilloscopes. 200 buys you a professional instrument in good order complete with probes - just because everyone wants more recent digital 'scopes it doesn't mean the analogue ones no longer did what the always did !

My 465 may not get used every day (or even every month!) but I certainly wouldn't part with it.

Andrew Mawson
East Sussex

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #59 on: January 11, 2016, 02:45:42 PM »
OK. ordered one hal conraption that might get me somewhere on current measurements, this type, but different shop:
http://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B00BLD6FB8

It's on the mail...I have palyed with hal clamps and transducers before...not having utmost trust on that one, but it IS isolated!

More questions:

1) Anyone found source for reliable shunt resistors (kelvin type)? No point of buying bad one measuremet, this one will be used for accurate measuremets and verify other measuremets.

2) Found few reasonable circuits for isolated differential probe, one way too much overspeck, but not too expensive BUT circuitboard would be a problem.

Here board and expense is no problem, but I have no idea of performance/speck.
http://www.chip45.com/products/detail.php?pid=isoprobe-1-kit
**UPDATE:
Looks like AM1200 isolation amplifier has Small Signal Bandwidth 100 kHz:
http://www.ti.com/product/amc1200
maybe 50% of it is final total system bandwidth??? Looks like a one of these cheap oscilloscope kits (with isolated power supply) would offer all that (except reference to another channel):
http://madmodder.net/index.php/topic,11145.0.html
**

Could not find circuit diagram or spesification. I would be very fine pretty much buying or soldering, but small surface mounted componenets or making PCB...

baby steps

Pekka
« Last Edit: January 12, 2016, 05:46:27 AM by PekkaNF »

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #60 on: January 31, 2016, 03:48:05 PM »
OK. ordered one hal conraption that might get me somewhere on current measurements, this type, but different shop:
http://www.amazon.com/Hantek%C2%AE-Current-Clamp-kHz-20mA/dp/B00BLD6FB8

It's on the mail...I have palyed with hal clamps and transducers before...not having utmost trust on that one, but it IS isolated!...

Got it some time ago and it works! Pretty close on sine wave and it does shows if there are any triaks on the line.

I'm been reading and shifting some info on "floating" measuement and it still is as it used to be before: Needs very carefull concideration. Next measurement is going to be scope grounded, but DUT floating. Basically I'm grounding the DUT fairly close to return path anyway, therefore I should be able to to measure it without blowing anything up and measurement should be safe too. Now I can put my 100:1 probe on good use.

I actually might still try to build isolated differential amplifier, but there are some steps I'm not too confident with, like SMD and making circuit boards.

Pekka

Offline PekkaNF

  • Hero Member
  • *****
  • Posts: 1602
  • Country: fi
Re: Microwave owen transformer spot welder?
« Reply #61 on: February 02, 2016, 06:28:47 AM »
Put those probes into some use.

Probes were 1:100 passive probe and HAL current clamp.

My friend has a problem: He has a ceramic oven he plans to use for hardening and tempering. The thing is someone "rigged" it for sale: Heater resistors are 110V + big transformer 110/230VAC, broken temperature sensor and controller that does not belong to it.

Cunning plan is to use main contactor that feeds the tranny and then put SSR between tranny and resistor. Good thing that a little hysteris will not kill the main contactor, bad thing is that SSR needs twice the current rating on secondary.

But I need to test the concept. I had 15A zero crossing SSR that is too small for the job, but just fine for a quick and dirty test: isolation transformer, secondary on float. SSR between secondary and 200W load resistor. Secondary nulled where comfortable for voltage scope ref (ground) and current clamp allows current measurement at will.

1. even with zero crossing, there are 32v "spikes" over the SSR, nothing to worry.
2. current and voltage wave form is nice into resistive load
3. zero crossing switching ON!

Right