The older style flasher units are bimetal (thermal) units. However, newer ones are either
relay driven or solid state. The
relay driven ones use a
capacitor to trigger the coil.
When the
capacitor discharges its load, the
relay is triggered, turning on the lamp. Once the
capacitor has finished discharging, it will then re-charge. Whilst it is recharging it can no longer keep the
relay coil energized, thus the
relay breaks contact and the lamp turns off. This cycle continues until the
circuit is broken. (i.e. you trun off the indicator
switch).
I think I have a flasher
unit in my workshop somewhere that is inside a
clear plastic housing. You can clearly see the
capacitor and the
relay. I also think there may be some resistors in there to
drop the
voltage to something more suitable for the
relay coil. If I remember, I'll look for it and take some pics.
I am pretty sure that the older units actually draw more
power in heating up, where as the newer ones do not need as much
current.
Remember that relays are mainly used to control a device that requires a large amount of
current or
voltage.
For example, when you fit a set of spot lights to your car, you do so using a
relay. If you simply ran them off the same
power supply as your head lights, they would be very dim and eventually burn out the cable supplying the
power. What you do, is use the
power from the headlight
circuit (or from the
switch controlling them to
power up the coil in the
relay. You then run an appropriate sized cable from the battery or main feed for the
fuse box to connect to one of the terminals on the
relay (with an inline
fuse). The other
terminal on the
relay is connected to the spot lights and the remaining
terminal on the spot light is grounded.
The other use of a
relay is to use a low
voltage DC or
AC current to
switch on a high
voltage AC load. I used this
system to
power up the motor in my bore. The sprinkler
system runs off of 24V AC to operate the
solenoid valves and so I used the 24V feed to trigger a 240V
relay, which in turn powered up the
electric motor. Couldn't have powered it up just form using the 24V feed!
This application is similar. Use a low
voltage trigger to
power up a high
voltage device. I actually built such a
system to hire out to bands that cannot afford to hire out a lighting
system and operator. I use a DPST
relay to control 2x 240V outlets (into these they
plug 4 coloured lights (e.g. 2x Red and 2x blue) and place them either side of the
stage). When the
unit is powered up, the 2 blue lights come one. When the
relay is triggered, the blue lights turn off and the red lights turn on. It is a simple and cost effective way of changing their
wash.
The triggering is done using low
voltage DC and is done so by a standard guitar
foot switch and connected to the switching
unit by a TS to TS lead. By using low
voltage DC, if anyone accidentally unplugs the lead or damages it, there is no risk of
shock to them. All the 240V is contained within the sealed box.
This
system works very well and allows one of the band members to change their
stage wash by simply pressing a
button.
However, if you think that a 12V DC lamp would be bright enough, all you need to do is find a
power supply that is adequate to do your task and
wire that up to two switches. If you use SPST
momentary action
switch you could manually flash the lights at any speed you like.