On/Off swicth! I'm thinking a relay would do the job?

[albertc30]

Hi all.

I am new to electronics and am getting quite enthusiastic about the all thing.

Currently I am on a level 3 second and last year on electrical installations and as such, great part of this course has been about electronics to a degree.

I have setup my 25W 12V solar panel on my shed and used a set of 3 switches to energise my lights in the way that;

Electronic timer switch - set to switch on at a given time but lights won't come on at this point yet,
A push out door switch - this is when the lights come on given the timer is one
A bypass switch so to have lights on with the door closed.

As I am getting more energy being generated from my panel, I want to channel this to heat up 20 litres of water that will be used in the garden to wash some tools and hands.

I have come up with the following list of components;
1 container
1 immersion thermostat heater
1 heat sensor switch
1 12V immersion pump
2 small floating switches
1 small floating switch ( for the water butt) this will switch on the power to the pump. I don't want the pump working if the water butt is empty.

Now, my problem is on the use of the two floating switches for the water tank. One will be at the top and one will be at the bottom.

I know one would suffice but the thing is there is little water displacement until the water pump starts bringing water back in, which, mixed with the hot water will get it cold in no time. So, the top floating switches off the pump and the bottom floating switch will start the pump once the water minimum level is reached.

There are two stages water floating switches which would circumvent this issue, I know, however I am set to try and use these small floating switches jointly and make it work. trust me, I have thought of nothing else and done numerous drawings and I can't get my head around this.

Any help is well and truly appreciated.

Regards,
Albert

[pebe]

Hi. If you use a relay to start and stop the motor (started by the bottom limit switch), the top limit switch will de-activate the relay to turn off the motor. The problem is as soon as the water level drops a little from the full state the motor will restart, and I don't think that is what you want.

If your float switches close contacts when the water rises above their limit, then you can use a 555 as a bistable switch to operate a relay. Operation is quite simple:
When pins 2 and 6 are both low, the 555 ‘sets’ and pin3 (output) goes high. When pins 2 and 6 are both high, the 555 ‘resets’ and pin3 (output) goes low. Connect it up like this:

Connect negative supply voltage (V-) to pin 1 (ground).
Connect positive supply voltage (V+) to pin 8.
Connect pin4 to pin8 (keeps reset pin high).
Leave pins 5 and 7 unconnected.
Fit a 10K resistor, R1, between pin 2 and ground.
Fit a 10K resistor, R2, between pin 6 and ground.
Connect lower limit switch (LLS) between pin 2 and V+.
Connect upper limit switch (ULS) between pin 6 and V+.
Connect a relay between pin 3 and ground, and a 1N4148 diode across the relay coil (diode cathode to pin 3).

When the barrel is empty LLS and ULS are both open. So R1 takes pin 2 low and sets the 555. Pin3 goes high and turns on the relay and motor.

As the level rises, LLS closes and pin 2 goes high. The motor will run until the water level is high enough to close ULS. That takes pin 6 high and resets the 555, switching off relay and motor.

As the water level falls, ULS opens again but pin 6 now has no affect.
When the water level has dropped to almost empty, LLS opens and turns on relay and motor as before, and the process repeats.

Hope you find that helpful.