A smaller emergency lighting system

[adam2]

In another thread, I suggested how to install a basic 12 volt lighting system for use in case of long or short term power cuts, with PV charging.
The other thread is here
http://www.powerswitch.org.uk/forum/vie ... php?t=8246
Such an installation still has much to commend it if a good level of light is needed.

I give here though some suggestions for a much smaller and therefore cheaper system that uses the latest LED torch bulbs.
This requires the use of a lower voltage, in the 6 volts to 9 volts range.
The light is more limited, but ample for safe movement.
The lamps are 1 watt each, miniature screw base LED torch bulbs, they work from 2 volts up to 9 volts and give virtually constant light output over this range.

A number of MES lampholders should be installed, at least one per room.
In view of the very low voltage and current, bell wire or speaker flex is fine.

The battery should be a 6 or 7 cell nickel cadmium type of 4A/H, as widely used for emergency lighting. Expect to pay about £25.
The battery should last 10 years or more.
Connect a 2 amp fuse in series with the battery, a car type in line fuse holder is fine.

Charging may be from a small PV module of about 10 watts peak.
No charge controller is needed, just a blocking diode.
Consider mounting the PV module on a south facing wall as this maximises winter output and restricts summer output to avoid overcharging.

Nickel cadmium batteries are however tolerant of moderate continual overcharge. (when used as intended in emergency lights, these batteries are charged at about 0.25 amps continually, for years)

Conections are simple indeed !
Battery positive to fuse.
Other side of fuse to positive wires to lamps, and also to blocking diode.
Battery negative to negative wires to lamps, and also to PV negative.
PV positive to other end of blocking diode.
The lamp holders must have the positive connected to the center contact, if the other way around the lamp wont light, but no harm will be done.

Almost any number of lamps may be installed, but the run time will be much reduced if more than a few are regularly used.
The fuse and battery would supply over a dozen lamps, but the run time would only be a few hours.

With 2 lamps lit, the current used would be about 0.25 amp, and the run time about 16 hours without any charging input.
With a little charging each day, one might achieve a week at 4 hours a night.

Once the battery is run down, each days winter charging should give several hours use of a single lamp.
Summer use would be more.

Nickel cadmium batteries are tolerant of deep discharge and of crude charging arrangements.
They also tolerate extreme temperatures better than lead acid, though still best at normal room temperatures.
In emergency, the battery could be removed and fast charged by a simple improvised charging circuit, from either a vehicle or a mains supply.

Supplier details to follow,

[adam2]

The 1 watt LED torch bulbs may be obtained from ebay
http://www.ebay.co.uk/itm/TTS-1WCREE-Be ... 3f183802f9 Is a supplier that I can recomend (no connection)

The blocking diode and the bulbholders can be obtained from maplins
Blocking diode----------UK61R (or similar from another supplier)
Bulbholders------------RX86T (or similar from elswhere)

Twin bell wire or speaker flex from any electrical retailer, nothing special is required.

In line fuse holder, any common type will do as sold in car spares shops, and some 2 amp fuses to fit it.

Switches as required, any common type of mains or low voltage switch is fine.

PV modules, unless you have one search around for the best price, about 10wp. Larger will charge the battery quicker but may overcharge it in prolonged sun.

Battery must be nickel cadmium, 4 amp/hour and 6 cell (7.2 volt) or 7 cell (8.4 volt) Can be obtained from various sources, I may have a few spare to ESTABLISHED members, donation to powerswitch required.

INTERNATIONAL LAMPS have suitable 6 cell batteries in stock at £18.46, plus VAT, Phone 01279 442266.