Electrics 2
Low energy and low voltage electrical lighting comes in
two forms; fluorescent and halogen.
Fluorescent lamps do seem to be ideal until certain factors are taken into
account. Firstly, they need a voltage step-up circuit to make them work, unless
this is very well designed it is not very efficient and it will not be optimised
for long lamp life. needless to say, commercial models fall far short of this
ideal and tend to give less efficiency overall than halogen. There is also
a safety aspect. Fluorescent tubes are easily broken and as well as producing
dangerous shards of glass, the phosphors contain toxic chemicals, even more
so with the more modern lamps! Having said that, they do have their uses and
we shall delve further with this when time permits!
We have found that the various small, easily available, low voltage halogen lamps are are great on 12V dc as well. They come in two main varieties, one with a built in reflector with power ratings from 20-50W (and higher if you look about), and as capsule lamps for use in a wide range of fittings. These are made in 5W, 10W and 20W sizes (order the small sizes from electrical wholesalers, although most don't realise 5W versions are available!). The reflector type also come with a choice of beam width which can sometimes be handy.
For much of our domestic lighting 5-20W lamps generaly seem sufficient, with 20-50W lamps great for stage lighting etc! Whatever lamp size you use there are often times that you want to dim it in the same way as a mains lamp. This can be done with a simple circuit such as follows:
The 555 is a really cheap timer chip available anywhere on
the planet (almost!) in various forms, the 1N914 diodes can be just about
anything that rectifies(!), the device to the right of the 10ohm resistor
is a power mosfet suitably rated for the load (e.g, for up to 50W a BUZ11,
IRF740, etc., or one of those nice 65A devices from Maplin Electronics). Don't
forget a heatsink if switching a fair load (bolt to some metal somewhere).
The other device marked 24V is a zener diode of at least 1W rating, this protects
the mosfet from voltage spikes and the 1A diode across lamp absorbs the hefty
kick back from those little coiled lamp elements. A separate switch is still
required to operate the lamp as in a conventional dimmer.
We shall give more details on construction of this and other projects in it's
own section soon!
And lastly, for now, an often asked question: What are the standard voltage references concerning 12V lead acid batteries? Look no further!
Lead Acid (liquid electrolyte): Charge/discharge voltages:
SOC= State Of Charge
11.7V - Prewarning: SOC<40%
11.1V - Disconnection: SOC<30%
12.4V - Reconnection: SOC>50%
11.7V - Commence Equalisation charge (14.7V) (this means that if the
battery has reached this level of discharge or beyond, it should ideally receive
a charge at 14.7V)
12.6V - SOC<70% Cycle charge (14.4V) (this means that if the battery
has not been discharged beyond this point, it should ideally receive a charge
at 14.4V, the standard charge voltage like that on a car alternator).
13.7V - Final charge voltage
Temperature compensation: -4mV/K/Cell (ideally, but not often used!)
Continue for more info on electrical systems including rules and regulations.....NEXT
