What would you do with a small collection of 18650 lithium cells?

[Tweety]

There is a huge difference between the LiFePO4 battey that Tesla uses and a Li-Ion battery that you have there MetroMPG... The cell size may be the same, but nothing else is... I'd say the idea to put the good one's in the "right" battery pack is the best one...

The charging is completely different... Don't try to use them instead of the alternator... They will die very quickly...

[MPaulHolmes]

Electric bike pack!!!!! They are super light. You need a good way to parallel and series them without wrecking them, but I would LOVE to have a lithium bike pack. Sealed lead acid is really annoying on my bike.

[Christ]

Originally Posted by MPaulHolmes

Electric bike pack!!!!! They are super light. You need a good way to parallel and series them without wrecking them, but I would LOVE to have a lithium bike pack. Sealed lead acid is really annoying on my bike.

Parallel/Series - Altoids tins and rubber caps. The AA batteries fit like 6 wide in a tin, and the rubber caps serve to hold the positive sides of the batteries from contacting the tins, shorting them out.

You use the tin for the neg side of each battery and run a wire for the pos sides up under the caps. Soldering the wire into a ring shape before you put it on, then putting a small spring or something inside the cap will make sure the wire retains contact.

[rgathright]

My biggest fear with building battery packs like this is what happens when you pull to much power and burn off the connectors?

I have seen Group 31 Marine batteries get so hot cranking an engine that they form a layer of carbon on the lead contact posts.

What would happen if you pulled to much juice out of a set of Li-ion laptop batteries?

How in the world would you find the break?

[MetroMPG]

Originally Posted by NiHaoMike

I once put together a simple circuit to check the capacity of rechargeable AA batteries. I had a single transistor and two resistors as a voltage detector along with a switchable current sink (two transistors and two resistors) and a relay to connect a charger. I had the circuit connected to the RS-232 port on my PC (two output lines controlling the relay and current sink, one input line checking the voltage detector). I wrote a simple Java program to first connect the charger for a few hours, then disconnect the charger and connect the current sink while polling the voltage detector every few seconds. It then calculates the capacity once the discharge is complete.

I wish my definition of "simple" matched yours! This is something I would have to invest a big pile of time & learning to accomplish (not that there's anything wrong with that).

Though I will say: thanks, because your post motivated me to decide I will study electronics a bit more this winter.

[Christ]

Originally Posted by rgathright

My biggest fear with building battery packs like this is what happens when you pull to much power and burn off the connectors?

I have seen Group 31 Marine batteries get so hot cranking an engine that they form a layer of carbon on the lead contact posts.

What would happen if you pulled to much juice out of a set of Li-ion laptop batteries?

How in the world would you find the break?

With a test light.

Open the Altoids tin, and test between battery cells.

[NiHaoMike]

Originally Posted by MetroMPG

I wish my definition of "simple" matched yours! This is something I would have to invest a big pile of time & learning to accomplish (not that there's anything wrong with that).

Though I will say: thanks, because your post motivated me to decide I will study electronics a bit more this winter.

The hardware is simple, the software is comparatively complex for me. In fact, if you don't mind physically moving the batteries to a charger, all you need as far as hardware goes is 3 NPN transistors and 4 resistors. If you can figure out how to write a program to read and write the control lines of a serial port (somewhat complex), it would be very easy to write a program to automate the measurements.

The very easiest to build is to take an analog clock and add a load resistor.

[jjackstone]

MetroMPG,
The lithiums in laptops are probably different chemistry than the ones from B&D(haven't checked for sure). B&D may be using the A123 lithium iron phosphate that are being used in the 36V Dewalt cordless tools. If so, they have a max voltage of 3.6 V/cell and operate near 3.2v/cell. The batteries from the laptops probably are some variation of lipo that have a max voltage of 4.2V and operate around 3.6v/cell. Careful mixing them.
BTW, I use the Dewalt packs to run my ebike. I use the lipo's to power the LED headlights and rear lamps on my tadpole trike.
JJ