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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 31st Jul 2018, 3:04 pm   #21
broadgage
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Default Re: Battery tag spot welder.

I presume that that the reference was to single core flexible cable with a cross sectional area of ten square millimetres.
The "tri rated" bit means that it conforms to the national standards for 3 different countries, Canada, the USA and the UK. (and is indirectly accepted for use in many other nations that accept one of those three standards)

Primarily intended to simplify the production of equipment for export, but has become the de facto choice for many applications that need a good quality single core flexible.

Pretty the same thing as panel wire, apart from the international approvals, and available in larger sizes, up to at least 50mm.
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Old 1st Aug 2018, 2:16 pm   #22
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Default Re: Battery tag spot welder.

Quote:
Originally Posted by rambo1152 View Post
Thus guy is seen removing the "I" laminations, the lifting off the entire HT bobbin with relative ease.

https://www.youtube.com/watch?v=DRVlqwsIl6M

<edit>
Actually after watching it properly he safely removes the primary and filament windings and leaves the bit we want to know for another episode.

Looking at one of mine, the weld is quite superficial. More so in real life than this picture suggests, and I think a small grinder might be more suitable than a hacksaw.
Do not see the point of cutting the laminations removing secondary and heater windings and then re welding when you can cut the secondary winding with a hack saw and drill out the rest bit fiddly I Know and you have to be careful not to damage primary winding, If you are good at tig welding not a problem welding the laminations back. I went for the easy option cutting and drilling the heater and secondary windings.
John
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Old 1st Aug 2018, 3:22 pm   #23
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Default Re: Battery tag spot welder.

Nice project. I've been planning on building one myself for the same application (welding battery terminals) for a while now and got as far as sourcing and modifying the transformer. Like you I removed the secondary with a hacksaw and hammer. I also removed the shunts, and re-wound with two turns of 10mm2 copper. Your project is encouraging me to get on with finishing my own version.
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Old 1st Aug 2018, 4:47 pm   #24
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Default Re: Battery tag spot welder.

I would double up the 10mm2 and then run the windings in parallel this will give more current, if you trigger it with sold state relay and use a timer it will give a good account of it self.

John
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Old 1st Aug 2018, 4:58 pm   #25
PSValves
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Default Re: Battery tag spot welder.

Cheers - that's useful to know. Admittedly I was just guessing when I rigged it up.

Is a solid-state relay essential? I have a couple of large 10A mechanical relays in my parts box...
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Old 1st Aug 2018, 7:18 pm   #26
broadgage
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Default Re: Battery tag spot welder.

A heavy duty mechanical relay should be fine if generously sized, but may not give such accurate time control, as neither the pull in nor the release times are accurately known/repeatable.

To guard against the relay contacts welding or sticking I would prefer to use two relays with the power circuit contacts in series. Preferably with some form of monitoring to warn of stuck or welded contacts on either relay.
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Old 1st Aug 2018, 11:36 pm   #27
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Default Re: Battery tag spot welder.

Quote:
Originally Posted by PSValves View Post
Cheers - that's useful to know. Admittedly I was just guessing when I rigged it up.

Is a solid-state relay essential? I have a couple of large 10A mechanical relays in my parts box...
I found with a mechanical relay I was unable to get accurate timing, and found sometimes when contacts were releasing there was a lot of arching, back emf from the transformer, causing contacts to stick which is what you don't want as it will vaporise the nickel contact strip and could blow a hole in the lithium battery, I purchased one of these, https://www.ebay.co.uk/itm/Solid-Sta...DJ2WGnRq4laSUQ and swiched it via a 12 volt power supply via a cheap timer one of these.https://www.ebay.co.uk/itm/5V-30V-US...IAAOSwFGNWRacN. and wired in an external momentary switch and external potentiometer to adjust the timing I also fitted an external led near momentary switch. I found this to be very reliable and have not had any issues.
john

Last edited by jonnybear; 1st Aug 2018 at 11:56 pm.
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Old 2nd Aug 2018, 10:09 pm   #28
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Default Re: Battery tag spot welder.

I am still waiting for my timer from China, but in the meantime here are some pix of my transformer.

I cut off the HV windings with a hacksaw and pushed out the remaining copper with a cold chisel, and also removed the two magnetic shunts. This gave me lots of room to wind on a couple of turns of welding cable, which is very flexible.

As you can see I did not have to touch the lams.
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Old 3rd Aug 2018, 10:46 pm   #29
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Default Re: Battery tag spot welder.

I think you should be on a winner there once you have the timer, I would also use a solid state relay, see thread #27 for reasons.
John
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Old 5th Aug 2018, 6:56 am   #30
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Default Re: Battery tag spot welder.

One of these in kit form came up on the EEVblog tother day see - https://www.youtube.com/watch?v=e4lIkonz7Rw @ 45:10 The kit used a whizz bang battery.

In the past I've soldered battery tags with a very hot iron, ok if you keep the dwell time to a minimum.

Andy.
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Old 6th Aug 2018, 3:14 pm   #31
PSValves
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Default Re: Battery tag spot welder.

Quote:
Originally Posted by jonnybear View Post
I found with a mechanical relay I was unable to get accurate timing, and found sometimes when contacts were releasing there was a lot of arching, back emf from the transformer, causing contacts to stick which is what you don't want as it will vaporise the nickel contact strip and could blow a hole in the lithium battery
Thanks - you've confirmed my worst fears here. Electronic switching it is
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Old 7th Aug 2018, 6:47 am   #32
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Default Re: Battery tag spot welder.

This is a great DIY project. A great job!

I repaired MWO's for about 20 years. The transformers are great for projects like this.

Of note: Some put the primary on the outside and the secondary on the inside of the windings. Makes it a pain , and best to find another tx.

If you manage to find an original, old commercial Raytheon MWO transformer- its worth its weight in gold. they are huge and put out mass current. (Also make a great PS transformer for a hi power CW rig.).

If you get one that has welded laminations, a grinder is the way to go. Sometimes I'd luck out and get ones with just bolted laminations. The cats pajamas to disassemble!

The newest ones use an SMPS and are good for little but a few parts. Just heft the oven to tell if its got real iron in it or not.


I might consider using a car starter solenoid or relay, since I have a box of them, but a solid state one is likely the best way to go, as you did.
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