The battery game

[safe]

I prefer the solderless because when you ride there is a lot of boucing around. Solder is inevitably going to come loose and that means you will have a potential loss of conductivity at some point. With Solderless tubes the spring ensures that no matter how nasty the bumps get that when the bouncing stops the cells will be pressed together.

SubC's are pretty close to the same size as C cells... smaller than D cells, but much larger than the AA cells.

SubC's also have the reputation for being the "leading edge" as far as chemistry is concerned. You can get cheap high discharge rate (10C) SubC cells, but try to find that in D cells and they don't exist. It's very rare to find anything in the 10C range for any chemistry... so when I saw that you can also buy NiCad SubC's for about a buck each ($1.25) that's what I bought. If a cell goes bad it's no big deal, I just pull it out and throw it away. With the solderless pack design you just accept bad cells and live with it. (you assume that things break and you are prepared to deal with it)

 

[Fuzzo]

I like the way you're thinking there in terms of replacement - it's a major gripe of electric car enthusiasts, trying to find and remove bad cells. I take it your springs are pretty heavy duty? If they were soft then bumping would cause micro gaps, and your current would be all over the place? But I notice your batteries are closer to horizontal than vertical, which probably reduces that effect, since most bumping/vibration will be in the vertical plane.

 

[safe]

The springs are pretty stiff.

It doesn't take all that much pressure... and before I started doing this I researched RC airplane folks who were doing the same thing and their experiments found that direct metal to metal contact delivers about the same conductivity as a soldered connection. The reason is that solder has some resistance itself, so in the end it all ends up about the same.

For those into perfection you can buy silver conductive paste that when inserted between the cells achieves the highest conductivity they were able to find.

The scale goes from more resistance to less:

Solderless (no paste)
Soldered
Solderless (with paste)

...but the difference is very minor across all three.

 

[Fuzzo]

Does make you wonder why more battery packs aren't made that way. RC packs seem to always be welded or soldered together rather than just squeezed. But I guess they want to sell you the whole pack. Spring loaded battery packs are very cheap items from stores, unsurprising given how simple they are. Are they up to handling high wattages? I doubt it. But ones that were up to it would hardly cost much more.

 

[safe]

Steel is a poor conductor compared to copper.

Those cheap battery pack spring loaded units just flow the electrical current through the steel spring itself.

You CANNOT do that if you want good performance.

The proper way is to use copper contacts and then place the spring behind them just to supply the pressure. I use pre 1982 copper pennies for mine and then solder the 10 AWG stranded copper wire I use for my wiring directly to the penny.

So the answer is that the cheap ones at the store are improperly designed.

MEC used to sell the tubes (and the people that used them seemed to give them rave reviews) but for whatever reason (the economy) they went out of business.

http://wantitnow.ebay.com/Solderless-Power-Tubes-for-A123-RC-batteries_W0QQadidZ110371104904

 

[duivendyk]

Wattage per se means little,it's the current that matters and the contact resistance& actual contact area, many integral batteries use spot welds.If you have 20 or so batteries in series, one bad contact or battery can louse up the entire string.

 

[machiasmort]

Speaking of pre-'82 pennies, I'm a big advocate of saving them! They'll become what silver coins were to our Grandparents in a few years!

Thanks for the u-tube clip, Seems as tho if your soldering NiMH you want solder w/lead!