Bike Light Battery

Lights with dead batteries

The Magicshine LED front lamp is one of the cheaper and brighter bicycle lights.
Scores of the various Magicshine models and their clones can be seen on trading sites like www.dx.com
I've accumulated a number of them over the years.
Magicshine 808,  1000 lumen claimed and working on 8.4 volt Li-ion battery.
Magicshine, 600 lumen claimed and working on 4.2 volt Li-ion battery.
Two clones of slightly different shell shapes working on 8.4 volts.

In spite of slight differences in detail they all have in common a hard anodised aluminium shell, a LED light engine usually claimed to be by Cree, a very solid aluminium reflector and a 22mm standard diameter LED driver PCB with illuminated push button and an often confusing selection of modes. One of mine has three brightness levels, a flashing strobe and a flashing S.O.S! Another has just three modes, bright, dim and strobe. The whole thing comes apart easily so that anyone with reasonable soldering skills  can replace a dead driver board or LED with a new one, also from China.
See here for a Magicshine teardown.

They aren't perfect. The beam is circular with no top cutoff so you must be careful not to dazzle oncoming traffic. Fortunately, the often maligned rubber o-ring handlebar mount makes it easy to tip the lamp down a little while on the move. The mount is maligned because the lamp can move all by itself but that's easily cured by putting a wrap of rough cloth tape around the handlebar under the lamp saddle and rubber band.

Another imperfect thing about them is the Li-ion battery pack that comes with them. All of mine have died within a year and the same fate has befallen replacements I have bought, regardless of the price paid. I must say that when the battery pack with my second Magicshine died within a week, the Hong Kong based vendor only wanted to see a photograph of the battery pack with the shipping docket and they then sent me a replacement immediately. The new one lasted somewhat better but still fell well short of the theoretical recharge life of Li-ion batteries.

See the picture above of my various lamps with just some of my dead battery packs. I think the no-name tabbed 18650 cells inside are just plain cheap. The shrink wrap holding the packs together is often far from weatherproof too. I notice that the latest battery packs advertised with the lights are plastic cased but I've given up on buying Chinese battery packs.

I decided to buy protected 18650 Li-ion cells by a reputable manufacturer, put them in some sort of series/parallel holder and recharge them individually. So here's what I got in the mail from an Australian Ebay trader who appears to be honest and knowledgeable.

Soshine S1 charger and Blazar/Panasonic Li-ion cells

The four cells purchased are based on made-in-Japan Panasonics of 3400 mAh and are claimed to be the highest capacity 18650 cells available as of 2014. The importer and many experts say that individual cells advertised with capacities up to 5000mAh are either wishful thinking or lies. The importer says that he sends these Panasonics  away to China to have a protection PCB added and to be rewrapped. The protection PCB makes the standard 65mm 18650 cell grow to 69mm long. The charger is a four cell Soshine S1.
Li-ion cells are very fussy about charge and discharge voltages. It's the price you pay for the high energy density of the chemistry. Charging one above 4.2v and discharging below 3.0v results in complete failure at worst or permanent loss of capacity at best. For those reasons a protection circuit is essential to disconnect the battery when it reaches the voltage limits when charging or discharging. Unprotected cells made up permanently into a pack should have one protection PCB made to suit the pack voltage configuration which protects all cells in the pack. Individual cells should have their own protection usually attached to the base end under the wrapper. The only exceptions might be when the protection is built into the equipment to be powered and into the dedicated charger that comes with the equipment.
You should visit an excellent Danish website  here which explains all about protection PCBs and has up-to-date reviews of li-ion cells and chargers. I'm gratified that my Panasonic cells and Soshine charger received the site owners approval.

A closer look at the cells

The next problem is how to hold the four cells together in a series/parallel pack that can be mounted on a bike but allows the individual cells to be easily removed and placed in the charger. In this case Google is my friend only insofar as it told me that battery holders for 18650 cells are practically non-existent.  I did find some older posts on bike forums by some inventive souls who  designed and moulded suitable holders in various plastics. They sold them to other needy cyclists as a cottage industry. However, at this time of writing all of them have given up in exhaustion.

So it looked like I'd have to make my own holder. The requirements are:
The cells must be quickly and easily removable.
The cells must maintain good electrical contact at all times.
The holder must be weatherproof and easily mounted on the bike.

That ruled out the very few plasticky holders for 18650 cells that I saw on websites in faraway lands. They looked like they'd be disappointing once I'd had them expensively mailed to me with their flimsy plastic and doubtful looking contacts. I'd also have to devise a weatherproof box to put them in. Another problem is that they'd probably be made for bare 65mm cells and a 69mm protected cell mightn't even fit.

Suitable battery contacts were essential and I found them at electronics distributor Element 14.
Here is the catalogue page for Keystone brand contacts, Cat.No.5204 for the coil spring negative contact and Cat.No.109-2 for the leaf spring positive contact. They're nicely made in nickel plated spring steel and are much more robust than the flimsy springs found in the ubiquitous plastic battery holders usually sold to hobbyists. I thought that with adequate preload they'd maintain contact with the cells.

Tube end-caps, contact springs and 18650 cells.

I'd already decided to put each set of two series cells inside pieces of 25.4mm square aluminium tube of 1.2mm wall thickness. This particular tube is sold here in big hardware stores for the home  handyman making modular storage and display units and it has an associated range of plastic connectors, including square end caps.
The internal dimension of the end caps is 19mm which means that a 18.4mm diameter Li-ion cell just fits inside. A spring contact with a 1/8" brass machine screw soldered to it can be inserted through a drilled hole in the end cap and gently tightened down on a thin layer of epoxy resin by means of a nut on the outside. I used my favourite JB Weld epoxy to ensure that the contacts stay there. The brass screws and some nuts and washers are for attaching the wires using ring terminals.

Terminal soldering jig with completed + and - terminals

 I soon discovered that holding the screw vertical with pliers in one hand while applying hot iron and solder with the other two hands does not work. I made the convenient third hand pictured. The label is for me, to ensure that I remember what it is and don't chuck it out months later.

148mm lengths of tube and completed endcap  contact assemblies

Almost there! Some measuring proved that the square aluminium tubes should be 148mm long. Fortuitously, light gauge PVC garden irrigation pipe of 19mm I.D. is an easy fit over 18650 cells. The internal dimension of the square aluminium is 23mm and the PVC sleeve fattens the cells up to 21.6mm. This makes a rattle-free fit and also holds the plus and minus ends of the cells in perfect alignment.
A couple of layers of cereal box cardboard  could also be fashioned into a battery tube with PVA glue and sticky tape.

Holder all put together

 More JB Weld glues the negative end caps inside, fastens the tubes side by side, attaches four little plastic cable tidy hooks and makes the two positive end caps into one unit with a bridge made from a drilled scrap of perspex. A narrow strip of grooved wood is glued over the negative wire coming up the side and the perspex bridge is left a little long on one end with 3mm holes to loop both wires through as a  strain relief.  Two punched strips of bicycle inner tube go over the hooks to hold the positive cap assembly on. The brass terminals on each end are painted with a US made glue-like product from a tube labelled "Liquid Electrical Tape"

170mmL. x 55mmD. x 25.4mmW.

All ready to be hung under the bicycle top tube in a neoprene bag. It could possibly be improved. I'd like to invent a better way to hold the positive caps on and I'll add some rubber o-rings for sealing around each cap when I get some. But it's not bad for stuff I found around the workshop or at the hardware store. The only really specialised bits were the battery terminals and they were fairly cheap and well worth it.
I'd really like to have Velleman 3D printer to print an entire plastic battery holder but a thousand odd bucks for a printer would buy a great many 18650 cells and bits of aluminium.
Next project is a two parallel cell pack for the 4.2 volt Magicshine.

For interests sake here is the measured current consumption for three of the lamps.
Lamp 1 Magicshine 808 1000 lumen 8.4 volt
High 1050mA  Medium 510mA Low 215mA

Lamp 2 Magicshine 600 lumen 4.2 volt
High 330 mA  Medium 210 mA Low 100 mA

Lamp 3 Unknown clone 8.4 volt
High 900mA Low 120 mA