To power the front lighting set, I use a 6 Volt, 10Ah sealed lead acid battery. The Smart lighting set I use (see here) originally consisted of a 2W normal light with a 10W spot. The battery power came from a 6V 4Ah nickel-cadmium battery which was designed to sit in the water bottle cage. This only gave a life of two hours with both lamps on... which was bad enough, but charging could only take place when the pack was flat or the pack would be destroyed by the memory effect, a particular characteristic of that type of battery which results in lower capacity if the battery is charged before becoming flat. This was obviously unsatisfactory... I tried to obtain a spare pack, but that would be more costly than buying the whole lighting set.
When replacing the power source, capacity was critical, as the two hour life I was getting was reasonable, but limiting. All rechargeable batteries have their capacity measured in Amp-hours, or Ah for short. In essence, if a battery has a capacity of one amp hour, it has the ability to supply a load of one amp for one hour. The original load of the lighting set was...
12W on full beam against a voltage of 6V
Therefore current taken = 12 / 6 = 2A
Now since the original pack ran the set for 2 hours, it must have been 4Ah (4Ah / 2A = 2h)
Presented with this problem, I thought about the best solution. Nickel-Hydride
batteries have a high capacity and can be charged at any point, but proved to be
expensive. Looking at the original pack, I suspected that if it were cut open,
it would contain five 'D' cells (such cells always tend to supply 1.2V... 5 x
1.2 = 6V) so it may have been possible to replace the original cells with
these... but that would have necessitated building a new charger. Costing this
option out, I found some 7Ah cells at
Strikalite, my
favoured battery supplier. These had excellent capacity compared to the original
pack, nearly twice that of the originals. This would have given me an
extra one and a half hours, but checking the cost, the batteries were £8 each.
This meant £40, plus the cost of the charger. I did also consider making a
separate battery holder from a plastic tube, but I would still have had to
charge the cells up... and the desktop charger I have only charges cells in
pairs. This was obviously a poor idea.
I had considered using a sealed lead-acid battery (the type used in cars, but sealed and maintenance free) for some time, but the weight and capacity had put me off. Whilst browsing at a radio rally last September, I came upon the Strikalite stand and had a good delve in the lead acid batteries. Talking to the assistant, he had a 10Ah 6V battery, and weighing it up, it wasn't much heavier than the battery pack that came with the lights originally. I found it had the advantage that I could charge it at any time (in fact it benefited from being left on charge when not in use) and a massive 10Ah capacity. Combined with the compact size, I purchased the battery and a suitable charger for about £25 pounds. With the extra capacity now available, I upgraded the lamp in the normal light to 5W with satisfying effect - and minimal hit on battery capacity. I do like to see where I'm going...
With a 10Ah capacity, it gives me about four to five hours life, and lives happily on one charge a week. The battery, as can be seen, sits comfortably between the seat post and carrier, sitting on the carrier struts, held in place with cable ties. The only work I had to do was to make a lead to connect the battery to the quick-connector on the lights. Details of that can be found here. One of the jobs for the summer is to make a more solid bracket and retention mechanism, but for now the cable ties do a fine job.