Battery sag too much on my new build

So I rebuild my battery using these terminal connectors:

uxcell 50Pairs 18650 Battery Negative to Positive Conversion Spring Contact Nickeling Plate 16.5mmx16mm

Using only the springs on all terminals, it’s a 12s6p pack with p42a cells, one side welded to 3mm copper plate:

2 Pcs 99.9%+ Pure Copper Sheet, 6" x 6", 28 Gauge(0.3mm) Thickness, No Scratches, Film Attached Copper Plates

The other side welded to 6awg coppe bus bars with 16awg tin copper wire as fuse wire.

My old pack would not sag more than 1v at full throttle. It was awesome. Sadly a single cell was faulty so had to remove it. Decided to make a 3d artery case so I could swap the cells out whenever they were faulty. And today I tested it out but the sag is insane. From 48v to 38v. Hell I can’t even charge it because it will go past 50v and the bms will shut it on and off charging 9a…

Idk what gives. Its as if the connections are made of mud and the resistance is up the roof. I intended to have low sag with the copper bus bars and 3mm copper plate. Is the copper plate too thin? Are the connector nickle plate not good? Are the springs in the terminals not enough to make a good connection?

It’s practically unusable I’ll have to scratch it off and start over but need to know what went wrong

On one of the photos there some p groups without springs but that’s an old photo, it’s been replaced with all springs cause the connection was not good

Judging from the photos, your soldering isn’t good enough. You want shiny pools that surround the wire, not crumbly bits that sit on top or splayed out ends like shown.

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This + wtf is this system?


this is ur problem


Whats the problem with using springs?

How much the cold welds affect it?

I’m trying to understand why this doesn’t work. Does nickel strip have less resistance than nickel springs? I thought it would be similar.

Those blue things are holding the battery together so I can put the bolts in. The design is inspired on the trampa fuse box but it’s a failure.

I’m Wondering if any of it is rescuable. The bms cable management is really nice on it. And the ability to swap cells. And the individually cell fused protection. But in the end it doesn’t even matter


these guys are heartless bastards about soldering,but listen to what they have to say. They mean well and know what they are talking about,they just get triggered and say the meanest most hurtfull things(im still crying in a dark room under a blanket about the bullying i got for using phillips head screws .)


As you should

We mean well, don’t take us too seriously.

We are a bit mean because poor soldering and all that shit makes for more battery fires which makes the public hate us more.

Poor technicians give eskate a bad name

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my sloted screws is rainbow titanium are on back order


Springs have insanely high resistance due to how thin they are, and by the fact they’re spring steel coated with nickel, not pure nickel. People have melted spring terminals on Nerf blasters with IMRs with far less current than what a board would need.


Fuck imrs. They’re the lazy way of making a flywheel blaster good.

4s brushless stryfe is the only answer.

On topic, your battery construction is to blame. Spring systems have always sucked. Look at the arcing problems with NESE.


Not even good, downright dangerous given how much current is required to start up the motors. Most AA sized IMRs get overdrawn even with stock motors.

Cold solder joints can cause a tiny little LED head lamp with at most a 12v battery (pretty sure it was a much lower voltage though. I think 5v) to not work at all. They can be still hold up to physical force even but then fail when it comes to current flow. (typically a cold joint would be weaker to physical force than a good solder job)

I still think they go a bit too hard against any phillips head use. If you just need a couple bolts and they don’t sell socket head or flush/ triangle head bolts with a hex bit on them at your local stores, then I think it is fine to use phillips head bolts. I have to use them with my back trucks since the hex bit versions in the length I need are NEVER sold in stores IRL and are expensive to get online. The few places that have decent prices per bolt make you buy way too many at once so I just use the phillips head versions. :person_shrugging: I’ve not had any stripping issues in the location they’re used and when being careful + using hand tools only.

There are places where you don’t want a phillips heads unless you enjoy removing stripped screws though. So I do agree with them saying they’re bad in general since a lot of our parts can result in stripping them way too easily. Plus, If someone only uses a drill on their build then phillips heads will 100% end up stripped super fast. Even if the phillips heads are used in locations where they would be safe and unlikely to strip with hand tools.

I’d keep my eyes peeled on the forum here to try and snag something like a used Malectrics spot welder. They come up occasionally for very reasonable prices. Spot welding is the only way to build safe, reliable packs with low resistance, at least imo. You clearly put a lot of effort into your build but it’s going to take a bit more perseverance. The custom bus bars are very nice. I killed two Flipsky 6.6 dual ESC’s last year which bummed me out so much I didn’t ride all summer. I’m still trying to get over it. Don’t let this stop you.

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Im just going to spot weld everything as before but atleast this battery casing can be removed and serviced later. Thanks for the insight and sorry to make anyone upset by my lack of knowledge

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My brush guards being attached with Phillips head screws will be the downfall of western civilization, no doubt

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I found the issue

These are not for PEV batteries, better for accessories like lights and USB charging


Seller said excellent conductivity so I was like why not, shoulda known better


All good, I should have read the entire thread before commenting anyways. Godspeed on your DIY adventures!

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A couple of other things to consider…

  • The spring is only clamped onto the contact, not welded or soldered to lower the resistance.
  • The spring wire itself is tiny, a very small gauge that increases its resistance even more.