Saturday, July 18, 2015

Monolith Developments

If you follow my nerf stuff you will know I build these cylindrical high current lithium-ion packs. Here are the latest experiments.

First of all I am giving this Samsung INR18650-25R cell a shot.

Just a clarification on what I talked about earlier:

The Samsung 20R and 25R are not quite "the same cell with increased capacity". The 25R sags slightly more under heavy continuous loads. The cell that compares on IR and 20-30A performance to the Sonys I have used in the past is the 2000mAh 20R. This one trades off punch for capacity to some extent.

There is a 2500mAh cell that doesn't trade off anything, and that is the Sony VTC5, which is extremely expensive as cells go but is what I would use if someone wanted the best 18650 cylindrical pack available.

I went with the 25 this time because I want to test it. If it can perform great on a RS build and have 2500mAh at this cell cost, it has an application. And it certainly should perform great. This is all hair splitting and this cell still has major guts.

This is what the welded blank looks like for a Tacmod type, 2 cell stick. As usual - double thickness with 8x0.15mm nickel tab stock, split ends, 8 welds per tab end with the redneck 1 farad cap/SCR spot welder.

I want to upgrade that welder with another capacitor so I can increase the electrode tip size and make a bigger weld. However it does fine and I have never had a weld problem or a tab ever come off a cell. I even accidentally shot through 2 layers of tab at once during this build and it welded them to the cell just fine.

This is what it looks like wired. 14AWG discharge leads and 20AWG balance taps, silicone insulated fine strand.

Above pack shrinkwrapped and terminated.

As usual in end-to-end packs there is an insulating mica board piece under that center tab on the positive side.

This is something new I am trying; W.S. Deans micro connectors as balance taps.

Typically I have used industry standard JST-XH connectors for balance taps and I buy prewired pigtails. I have tried as hard as I could to be standard, but I have had too many problems with JST-XH. In my opinion it is just not durable enough to be used repeatedly and constantly for charging.

It is also difficult to terminate in the field. It is a common type of production connector with separate contacts designed to be crimped to the wire and then inserted into the plastic housing. The pigtails (buying and working with) are a bit of a pain and I don't like the quality of the wire I get with them.

In general I don't like connectors in which the pin is removable. I have had these JSTs spit out pins when plugged in. This is obviously bad, as you could have live metal floating around inside a gun.
2 cell packs have 3 wire tap cables. 3 cell packs have 4. 1S packs don't have or need balance taps. Those are the majority of nerf applications and this type connector covers them. The 4 pin Deans micro is usually red and the 3 pin always black, a convenient color code.

At least for internal charge systems, I will be switching my batteries to this style connector.

Size comparison. The Deans 3 pin is actually smaller and more streamlined than the JST.

The mating connector. These are polarized of course. One pin is offset. I wire the offset pin to the positive end of the pack.

Isn't that neat?

Mega and micro comparison to this pack.

That ought to give an idea of where these can be fit. Primarily these sticks are a stock or buffer tube battery.

With a bunch of other assorted packs. Red cells are Sanyo UR18650SAX, green cells are Sony US18650VTC3, black pack is a 4S Sanyo SAX for a Stampede.


  1. Are you looking to use these batteries to prototype the Draugr blaster? Or would something like this be more for personal uses?

    1. The plan for the Draugr is to use NiMH. Lithium-ion or LiPo coming stock has too many safety and durability issues with improper use.

      I do plan to sell these at some point.