TL;DR - hit me with your best tips for soldering QS8 connectors to batteries

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New Jersey
Arrma RC's
  1. BigRock 4x4
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I have a weller 40w iron I’m using for this job. It’s the biggest one I’ve got. I soldered two 4s batteries last night from EC5 to QS8. Tinning battery wires was not bad, but did take longer than expected to heat up and accept solder.

Now getting the cup to accept solder was a real bear. It took forever for the cup to heat up and even when it was hot it felt like it cooled down as soon as I introduced more solder. I do have the male/female connection to manage the heat, but it still seemed like an eternity to get things flowing.

Flux was added to one cup to see what happened, but I ended up burning a little bit of it into the cup because again, it took forever to heat up and accept solder. That said, when I introduced the cold wire to the cup the solder instantly cooled, securing the wire kind of wonky. I heat up the joint by pressing down on the wire and waiting for it to seat a bit better. Adding more solder to the cup was another challenge because I didn’t have enough hands to hold everything.

I’m going to try another set tonight use what I learned to try and have a smoother processor and better connections. I did notice that when I heat the cup from the back and work forward I can lay down a more even pool of solder for the wire to sit in.

Kudos to those who have this down pat, because it’s f’kin hard to do/learn. I wish more people shared more detail about how they did when they first learned this. I’ve got iron, solder, vice grips holding the connector, other pliers to hold the wire if need be, wet sponge, battery, battery wires all to Be mindful of. My head was spinning 😵‍💫

Also bonus, I created an arc last night when I tried to use pliers to seat the anti spark sleeve. Good thing the pliers had rubber grips because I saw lightening in front Of my eyes and really almost 💩 a 🧱

So any tips you have from working with these connectors is appreciated.
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What is the gauge battery wire? 12AWG? 10AWG? What solder are you using? Rosin core solder is a must. Rosin core specific to electronics is even better.

Are you tinning the wire and connector prior to trying to make the connection? Tinning each aids in heat transfer.

My workshop sues a Hakko 940 soldering station, and it is hard pressed to do 10AWG the one time I tried it. 12AWG at highest temp setting is its practical limit. Throwing this in just in case you're shopping about for an upgrade to your 40w iron. Be sure to get one that will do higher gauge (e.g., lower number) wire now becoming prevalent in builds.

True, the longer the soldering device dwells on the connector, the better the chance of heat transfer melting the connector. Procedure in use for me is to plug in an unused or 'dummy' connector to the one getting the solder. This helps maintain the integrity of the connector under [prolonged] heat and wicks away excess heat.

Perhaps the QS8 connector takes a specific technique? Am aware of them but have not tried soldering one. Can't help there. Check out YouTube for soldering vids. Watch half a dozen or so and then practice, practice, practice. You'll get it soon right soon enough. Hope this helps. Good luck. 'AC'
So any tips you have from working with these connectors is appreciated.
TIP #1

Grab a butane torch, 1 pair of vise grips and your solder.

Put the bullet in the vise grip on a flat non burning surface holding the bullet flush lightly, don't crush the bullet.

Tin the wire with your iron.

Heat the bullet with the torch, add in solder filling the cup 3/4 the way.

Bring in your tinned wire. Add heat to the bullet pool while introducing the tinned wire to the bullet pool.

Put your wire in the bullet pool straight and centered. Remove heat. Hold there till it solidifies.

Heat in soldering is your friend, heat ensures solder gets sucked up in the wire avoiding a cold solder joint. Just be sure to add in enough solder to the bullet pool before dropping in your wire and you will be GTG.
Yeah, that 40w iron isn’t enough for a QS8. The torch method works great, just be careful not to melt the housing. I use a 70w soldering station, and I’d still use the torch method.
So yeah you need a 80W min iron for good soldering on a QS8 100W recommendation.

You can not butane torch them as the plug are in the plastic connector and you will damage there fit if you remove them.

Connect the male and female ends of the QS8 before soldering using a unused QS8 This will help ensure that when soldering you don't melt them out of position and give a better thermal sink to again keep from melting the plastic. Your real problem is an under watt iron. I know that the miller 80W soldering stations at home depot can do the job as a cheap option to get. Used one the other day was not sure it would work but was out and mine was at home and it did the job better then I expected. Its your heating time that is the problem you should shove the iron in the bullet push some solder and watch it flow. If its taking much longer then this you are pushing unneeded heat in the plastic. Or even up the silicone wire sheath melting the inside of it to your wires.
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Update because why not.

I successfully converted eight 4s batteries from EC5 to QS8.

With shakey hands I started with my least expensive battery and boy am I glad I did. My technique was to snip off the EC5 connectors one at a time to avoid blowing myself up. I can say I mostly achieved that. More on this later. I’d snip the black, strip, tin, prep cup with monstrous amounts of solder, then shove tinned wire into cup, set, cool repeat. Well the step I left out on the first battery and another one down the line was to put the damn spark preventer thing ON THE WIRE AS SOON AS YOU CUT IT. I’d be feeling amazing looking at a beautiful solder joint only to realize I forgot the f’ing plastic piece.

on my first battery I actually created a spark AFTER the solder job was done. I had the male and female adapters together for heat management, but did not cover the exposed copper cups on the other side. I went to use a pair of pliers to make sure the plastic thing was clipped on and touched or was too close to that exposed brass and saw lightening in front of my eyes. 😮
I went ahead and checked the cells, charged then discharged the battery and everything seems fine. My pliers have a burn mark on them though.

Something everyone probably already knows, but I learned along the way is to start introducing solder to the cup as soon as possible. After a few tries I was able to manage the heat of the cup much better than the first few.

Finally thanks everyone for reading and for the advice along the way. I’m a n00b, but feel pretty proud of this project. Hopefully they don’t blow when I run them. 😱

Lightening strike spot

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