Sunday, February 10, 2013

Battery Holders, Chargers, home brew gizmos.

Commercial Protected battery holder

The one thing that I thought I needed is a protected battery holder, since the batteries have  no protection circuit built in.  Plus some sort of keyed connector - when I got these on eBay, they came with the JST connectors sets - maybe it was a mistake since the listing doesn't mention it in the listing, but a welcome surprise.

Firecracker Battery holder

My first take at a battery holder. Kind of looks like a firecracker, doesn't it? Just took the battery and wandered around the local home supply store and tried different things. I love PVC, I found these gizmos that press fit onto the battery.  I scavenged some springs from an AA battery holder - drilled a hole in the end and ran the wire through.  Voila - dangerous, but serviceable. Made sure that it had all kinds of markings identifying which end is which. This plus a protector board, a JST connector will find its way outside to the weather transmitter.

The KahnFire Charger setup

The protection board in the circuit

And the charger

Added a trimmer to dial in the current for different batteries.  It's almost set to a short to get the 800 ma to charge the 18650s

A 18650 battery Charging fool

Fire Resistant Charge station
I have been having a seriously geeky good time the last week or so.  I have been filling my brain with everything Li-Ion and 18650 batteries in particular while waiting for the little pieces parts to show up.

Adafruit in their fantastic efficiency got me the charger in just a few days.  But it took a little longer for the "protected" battery holders to show up from China.  Two holders and two surprise sets of jst connectors had me down in the shop melting solder in minutes.

Since I trusted the Adafruit charger it got hooked up first. I think it was a mistake getting a 9v power pack for the charger - when charging the little  chip  gets quite warm to the touch.  The datasheet says the chip is thermally protected and will throttle back on the charging current if it needs to, not what you really want from a charger.  So I will dig around in the old phone charger box for the highest current 5v mini plug converter, less voltage, less heat.  Actually I do not care how long it takes to charge one of these  - I just sit next to the "fire resistant charging station" until the light blinks - about an evenings TV viewing.

It seems that most people use these cells to power flashlights.  Some of these flashlights have Cree LED and are driven at one amp plus constant current buck/boost switchers.  So having a 2200 mah battery for the hour or two run time you will need for this makes sense   However, even though I got a flashlight just to see what it is all about, I will be hooking these up to Arduinos and such which draw milliamps - I suspect that the batters will suffice me for a very long time - even if they are well past their useful life for high power applications.

Comment about Battery safety.  The charging part of the process is the most "dangerous".  I have read all the articles I could find about exploding Lithium batteries.  All of them I find are forced in some way, gimiked cells to cause an unstable situation, direct connection to a 12v car battery to an unprotected pack. These are unusual occurrences.

The thing that simply astonishes me is that people take batteries that have about the energy density of dynamite, that have elaborate safety mechanisms designed to outgas safely if some thing untoward happens.  Then they seal it up in a machined high strength aluminum tube without any safety overpressure blow out ports.  This is how to make a pipe bomb - not something that will take the abuse that a flashlight will over time.  When/if something happens - I will not be surprised, sorrowful and with heartfelt pity, but not surprised.

 I an good with the safety built into the cells, and the protection circuits I purchased, I can't make it any safer.  These batteries are safe if you don't go around poking them with sharp things or running over them, or something juvenile like shorting them out to just to see what happens, or putting them in high flying aircraft .  A little red and black magic marker to make sure I know which end is which, helps a bunch.

So I will use the same care I use with line level circuits / lasers/ gasoline / echant /  hypergolic concoctions.  I will pay attention to what I am doing, and never hurry. Nothing is so important that it can't wait until you are wider awake,  less stressed.......

More interesting details in next post