Electronics > Beginners

Help me create Low Voltage switching relay/circuit

(1/2) > >>

THATguy:
GOAL:
This is for a small handheld torch circuit - all parts should be regular that can be found in any electronics store NOTHING HIGH POWER OR HIGH END - I'm a simpleton trying to make a basic circuit! A similar circuit would be solar powered garden light ( to give  an idea of similar componentry, voltage & size of circuit).

I have two batteries fully charged. (~1.6v or so, over short distance - torch)
Only one will supply the load (single low voltage LED) at a time.
I want to keep parts minimal & circuit as simple as possible, I'd prefer not to use resistors, or bulky relay switches especially if that is lossy (no IC's unless one can solve this).
When one drops below a suitable voltage I wish for a switch to be activated that lets other battery begin supplying the load.

Had trouble finding switches or finding good info on how to make a transistor gate to do this.
https://imgur.com/gallery/JTbZ0IM
Figure 1. could I wire up a transistor similar to this - in some way that when voltage drops it switches off - but I would still need to link it with the second battery & more transistors somehow??
Figure 2. R in circle is a reed switch ( I know it would take more to get them functioning, just would be good if there was a switch that could turn it's self on into a permanent on position until switched off).

The battery charges up the cap, when the voltage drops it would go through & turn on the opposite reed switch. (Sorry, there is so much wrong with this circuit lol )
Just another brainstorm idea of how it could be done.

oPossum:
Choose D1 to be about 1 volt less than the low voltage. The relay will stay on until the voltage drops below that point.

Brumby:
In reference to the OP's diagram: I can't see how it could switch anything.  The diodes are back-to-back, which will effectively remove them and the capacitor from a low voltage DC circuit.

As for your inquiry, it lacks some fundamental information.

It's like saying "I want to transport some sand" without giving any idea of:
 - How much?  1kg or 500t?
 - How far? 5m or 5,000km?
 - How quickly? 10 seconds or 10 weeks?

To even begin to look at this, you need to provide - at the very least - the voltage and current that will be switched.  There will likely be other questions as well, but these will emerge along the way.

However, even here it is still worth describing the ultimate objective, rather than asking for help designing a particular solution that you have already chosen.

The reason is simple: there may be better, cheaper, easier and/or more reliable ways of achieving the end result.  There may be a design already in existence that does everything you want - and probably more - or one that can be applied to your needs.

There is a lot of knowledge on this forum, so you are likely to get some more useful ideas by being more specific in your requirements and less specific in the execution.

Brumby:

--- Quote from: oPossum on September 09, 2018, 02:07:37 am ---Choose D1 to be about 1 volt less than the low voltage. The relay will stay on until the voltage drops below that point.

--- End quote ---

That is a far more practical circuit - but it still based on an assumption about the voltage available.

THATguy:
Just a few volts and very short distance. A switching delay would be fine, keeping the current in the circuit is not critical.
Load is just a LED. That is the sole purpose, a torch with a back up battery.

I would prefer to not use resistors & keep all voltages just enough to turn the LED on - though if a few more LEDs are required to absorb a bit more excess voltage, or higher power LED that is okay.

(I appologise  for typos & attrocious spelling - on phone 😭 )

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod