Making Thundersky Packs

4 02 2010

Ack, no updates in a long time.  There’s actually been a bunch of stuff going on too!

In the middle of January, i received my batteries from Thundersky and EVComponents.  Woo!  Here are a couple of iPhone pics of the batteries.

The box of Thundersky batteries with a 6 pack pulled out.

Another view of the batteries

Unfortunately, when i ordered the batteries, i didn’t know what the configuration was going to be.  I now know i need 3 packs of 6 batteries, and 6 packs of 3 batteries.  The batteries as shipped from thundersky and evc are 6 packs of 6 batteries.  That means that I have to dismantle three of the packs and make them packs of 3 batteries.

I had to work with Travis from EVC to get 3 more sets of end plates, and then figure out how to modify the straps that they sent (the straps look like they’re for packs of 5 batteries).

Why does this need to be done?  Well, Lithium batteries have a habit of swelling under load (either charging or discharging), especially when they’re pushed hard.  To combat this, the batteries come shipped with end plates that are strapped together.  There isn’t much compression placed by the strap/plate combo, but they prevent swelling not allowing expansion.

Dismantling the packs of 6 batteries and making them packs of 3 batteries means that the straps need to be shortened, or a different method of strapping must be done.

To make matters more difficult, the straps are made of stainless steel, so since i don’t have a drill press, i wasn’t able to drill through the straps.  I toyed with other methods like using worm drive hose clamps.  They worked great, but i need an 8″ clamp for packs of 3 batteries.  8″ hose clamps are hard to come by, but 4″ hose clamps are not.  I could use two 4″ clamps to make one strap.  These work great, however it costs about $1.15/clamp.  There are 8 straps per pack, and 6 packs, makes for 48 clamps.  Way too expensive.

I asked on, and some folks mentioned things like tack welding and using stapping tools (

I found a sheet metal punch on amazon (, that i figured i’d try.  I wasn’t sure it’d work with stainless of the thickness of the straps, but what the heck.

Turns out, the punch works great.  Now i can modify the straps. Woo!

Below is a set of pics of me making one strap.

6 down…only 42 more to go…aieeeee!




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