Modding my Sunkko 709A

so a while back i got tired of the manual acrobatics required to weld large packs on my Sunkko 788H.

I bought a 709A thinking that since it had wands it would be the ultimate solution to my problem. This is the unit in question, though not from this seller:

I was wrong. It is weak as hell and barely tacked my balance tabs on. Nevermind the the regular sized nickel i use. So it was back to the 788H which is still tacking my packs like a boss however inconveniently.

I started poking around and found another guy somewhere else in the world using this as a spot welder:

This thing is powered by either a car battery or a 3S lipo. Obviously i bought it immediately and then went over to hobbey king and got an 8Ah Zippy 3S 30C lipo pack, and i’m now hunting down a tiny 3S BMS and charger.

My plan is to crack open the 709 and remove all of its guts, the replace them with this arduino unit and the Zippy and BMS. That should result in a highly portable rechargable battery pack spot welder that will tack the fuck out of anything.

We’ll see when it comes together. IT will probably be a couple of weeks before the parts all get here.


Actually it is powered by both… The 3s battery runs the aurdino and the ca battery supplies the current for welding.


That specific spot welder works by shorting the battery - you should not be doing that with a Lipo. A car battery is pretty forgiving for this type of thing but Lipos not so much. There is another kit available on the forum that can be used with a Lipo apparently (not sure what the different mechanism is actually). I think @The_Dude had one version where he combined a car hifi capacitor with that spot welder - so the capacitor is shorted and not a battery. That could fit inside your housing.


I’ve got the 788H as well. I was wondering if it is possible to swap out the two metal welding pens with a “wnad config”. I have not tried it yet though. It might get too weak because of too much resistance though, I dont know.

Is it just the wand that gives you trouble, or does the machine produce the same welds from the onboard contacts?

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i’m getting the same crappy welds on the 709A using either the wand or the front mounted leads.

yeah i just realized that. Blargh. So maybe it won’t be quite so portable.

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Hey, Check this out for a super portable and cheap spot welder.

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it runs off just the lipo in the v3 model anyway

maybe i’ll just use my rage vision to weld the tabs from now on.


Just sayin’

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You may have to rub it in my face a few more times before i learn. Maybe call me a bad boy. A bad, bad boy. Then point to that welder a few more times until i figure it out.

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Hehe :smiley: :yum:

whats the thickness of the nickel on that one?

0.15mm :thumbsup:

i may be selling both of my welders soon. Even if i go into autozone and buy brand new everything its still under $150 for everything here, and i will not have to do that. Damn.

I bought the arduino kit and love it. It can do 0.25 and thicker if needed. I get free used batteries from work all the time so it was a no brainer

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I’m loving it, 3000 welds in :stuck_out_tongue_closed_eyes:

Kinda what I did with my Sunkko. Got rid of it and went compact and off grid. I spent more than I actually needed but one of the units is for soldering and the other for spot welding and its still strong. Working the welder with 4s lipos and solder with 6s1p 18650s

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More details please, that looks pretty slick

I think it could be done, but you’d have to use some very heavy gauge cable to keep the resistance down. Maybe 2/0 flexible welding cable?