How to make a battery pack for cycling at night
It's easy to make up a good soldered battery pack.
I have two NiMh packs that I've made myself. One is about 2.5 amp hour and the other is 4 amp hour, both rated at 12 volts using 10 cells in each. I made them from Sony batterys but most brands are quite good now.
You have to get the ones with the tabs on the top, but be careful because some have stainless steel tabs which you need to spot weld and some have tinned tabs. The tinned tabs are the ones you want.
Lay 5 cells side by side oriented so that the positive of one end is next to the negative of the other. To do the connections you have to bend one of the tabs backwards against its original bend, and you may have to trim off some of the tab but leave enough so they completely overlap for the width of the end of the battery.
Now you get some fine sand paper or steel wool and give the tinned surfaces a bit of a rub or else the solder won't stick to it properly, they seem to leave some sort of coating on them at the factory.
Next apply some solder to the surfaces but don't solder them together yet.
Use good solder which has about 70% led and 30%tin which has the lowest melting temperature. The secret to good soldering is to always keep things clean. Clean the surfaces before you solder them, make sure the soldering iron tip is clean and free of crud, wipe it on a cloth and apply fresh solder to it before making each join. The active component of the flux evaporates out of the solder very quickly leaving accumulated crud which is why it's important to always wipe the tip and apply fresh solder. (The flux is inside the solder.)
So now that you've tinned all the tabs, use electricians insulation tape to bind the 5 cells together so they don't move. Carefully solder all the tabs together. Because you've presoldered them you should only need to push them together with the soldering iron and the solder already on them should be adequate to make the joint. Wrap a heap more tape around it to make it firmer.
Make a second pack of 5 the same way.
Now solder some wire to the the main positive and negative of each pack, plus a short bit that joins the two packs in series. Allow longer length than you think you'll need.
I use special flexible wire from Farnell or Radio Spares which is like the wire used in multimeter leads, it has a lot of fine strands and flexes without breaking. Don't use single strand wire, it won't last long at all. Secondly, use red for positive and black for negative, that way there is no mistakes.
Use the wire to join the two packs instead of the tabs so as to allow for some flexibility of the pack if it gets jolted around on the bike. Wrap the lead wires about half way around the battery pack so that if you pull on the leads the force won't pull on your soldered connections.
Now that you've got it all together wrap a heap more tape around the whole pack so every part of it has at least three layers of tape over it. By now it should be a nice solid pack.
Now you need to put some connectors on it. The ones I use are from Dick Smiths, they are a whitish plastic and you can buy the pins separate from the plug. I use the two pin plug, it's designed so that it will only fit one way so you can't reverse the connections and blow things up, as an extra precaution I have one male pin and one female pin in each plug so there's no way I can get it wrong. My lights, chargers and battery packs are all set up with this arrangement. I use LED lights which are fed via a Luxeon current regulator which allows me to use between 8 and 14 volts and I have two NiMh batterys and two Lithium Ion batterys so I can swap between any of these batterys on my lights by simply unplugging one and plugging in the other.
I wrap the battery in bubble wrap and push it into a cut off water bottle which goes into the cage on my down tube. An important thing is to remove the battery from the bubble wrap when you charge it as the bubble wrap is a very good heat insulator and you'll cook your battery if it goes into an overcharge state. Lithium Ion batterys are especially susceptible to this. (I know from experience!)
I've been using my batteries for at least two years now without problems, my two old Gel Cell batteries are unused in the shed. (Lead acid batteries should always be stored in a charged condition, a flat lead acid battery dies very quickly.)
A good charger is the MW1768 from Master Instruments.
http://www.master-instruments.com.au/browse/Model/MW7168.html
It needs a 12 volt supply which might be a problem but it has a meter in it and will charge 12 to 14 volt packs which most chargers won't do. Master Instruments also have some other good chargers that are worth looking at.
Good riding
Links:
Home made Luxeon LED lights, 5 watt.