Receiverd from PhotoGuy:

Hey,
I began making a MOT spot welder to rebuild battery packs for my cameras. I have spent too much time and money to drop it and build a CD welder now so I want to keep pushing until I get this thing going...
I built a timer with a 555chip but am having some interference feeding back from the large relay that is tripping my primary coil on my MOT. Can you refer me to a schematic of the circuit you used for your MOT spot welder? I'm powering the 555 timer with a small wall wart transformer and the timer work perfectly when the MOT isn't plugged in. When I plug in the MOT, the 555 timer begins getting erroneous signals and trips itself even without my hitting the trigger switch.
Any help on a circuit would be much appreciated.

Grace,
Guy Lyons

Also, any recommendations on the amount of pressure needed on the electrodes? I'm getting about 3.5V and am using .005 nickel strips. I'm having a problem with arcing that blows my metal away on the ends of my batteries and it is too expensive to experiment with them.

Unfortunately, PhotoGuy has PM turned off, so I could not reply directly. Here is my response:

I think this would make a really good thread in the Projects Forum. Please post it there. You will get much more and better advice than I can supply alone.

John

 

Here is a response to the vicarious OP:

My MOT welder was very similar to the one described by 5bears: www.5bears.com/welder.htm

The transformer was scavended from a 1000 or 1200 W microwave. The secondary and control windings were removed in the usual way. A new secondary was wound using 6-1/2 wraps of #4 welding cable. Welding cable was used for flexibility. O.C.V. was 6V with 120V input. Nylon ties were used to keep everything in place and tight. Copper welding crimp fittings were used for termination.

A 555-based one-shot timer was used at 5V.

I could vary the timing as needed. Most experiments were done with 170 mS for the pulse.

The solid state relay was a Continental S505-OSJ410-000 and was scavenged from a refrigeration unit. The Crouzet equivalent is 84134000. The data sheet is a bit hard to find, so here is a link to it. The relay is zero crossing.

If you will post the schematic for what you have done, we might be able to find where the problem is.

John

 

Hi John,
Thanks for responding to me. Sorry about the PM thing, I'm new to the forum and didn't know about the settings. It's funny that I found your response not by coming back to AAC but through a Google search!
In the mean time since I sent you my note, I've found a compromise and now at least know the source of my problem even though I didn't "defeat" it completely.
I was using a standard relay to close the circuit on the primary wind on my MOT and somehow the "jolt" during the release of the relay re-triggered my 555 timer circuit. My circuit is basically the same as the one you posted but with a few differences in the component values. I put a 1M Pot on my RC timing circuit so I could vary the time from about .1s-1s.
I'm pretty sure if I had used a solid state relay as you mentioned it would have isolated the MOT to relay circuit from my 555 timer circuit. One of my last attempts to overcome this problem was to power my 555 circuit with a 9v battery and that did the trick.
An EE friend of mine has been "counseling" me over the phone at after church about my timer and found a nice timer that ranges from .1 - 100hours but is broken down into decimal grouping so the first range is .1- 1s and is made for HVAC systems and runs @24v. I'll probably use this and scrounge a solid state relay once I become proficient at actually welding my battery packs. For now I can just replace my 9v batts as needed.
My next project will be a CD welder like the guy in the UK made.

I can't thank you enough for taking the time to write me back. I've looked at your work on here and am really impressed and want to say thank you for being so thorough and helpful to this community. And, sorry for being a newbie about the PM settings and all.

Grace,
Guy

 

Are you using a diode so the reverse emf from the relay doesn't trip the 555? It may be as simple as a few cent diode to fix what you want. You want to be SURE the thing doesn't fire when you dont want it to.

 

RM,
Yes I do have a diode as well as a small capacitor. I've finally determined that I just need to get a solid state relay that will handle the load. Until then, I'll keep powering the timer with the 9v batt.
At this point I have it working but am in the learning curve of finding the right combination of electrode pressure, tip size/shape and weld duration. Not to mention that batteries seem to have different thicknesses on either end and come have difference coatings on the steel cans that add more variables into the equation! It's getting frustrating but I hope to have it figured out soon.

Grace,
Guy

 

Yes, batteries do change quite a bit from company to company. The art of the tab weld is a difficult one to master. And it is an art.

Are you scuffing the cells with a bit of 220+ grit sand paper? That should help with odd coatings and cleaning.

Time between welds and space between welds change by cell and tab material. You will find what works best for you. The most important thing is repeatability and staying consistent. If the welder changes output randomly, you will never master the task.

 

Hey,
I hadn't thought to pass on any of the links and resources I'd looked over in my pursuit of beating "the man's" high priced batteries...

Here they are:

http://www.philpem.me.uk/elec/welder/

http://www.ledhacks.com/power/battery_tab_welder.htm

(this one is my dream welder...)
http://frikkieg.blogspot.com/
http://www.youtube.com/watch?v=yabesdeGKJo

Just found these:

http://99mpg.com/blog/makingacapacitordi/

http://diyspotwelder.blogspot.com/