battery decorations converted to mains tranformer

[Henhead]

I want to create a Xmas scene for my fire place. I want to wire a number of battery Christmas decorations together and run it off a single multi voltage adapter.

The decorations are led lights only (some change colour) ranging from led tree light (3 x aa) and a number colour changing snowmen (2 x aa) and snow men and robins (3 x LR44 Button)

I wanted to create a box stand that they will be stuck down to and then wired underneath (hidden) and run off a single adapter.

Is this possible? Safe? If so how would run the wires?

multiple feeds off one wire or chain each positive feeding the next and same with neg?

 

[GPG]

You could run them off a 4.5V wall wart all in parallel, Operating off batteries I dont think the current will be an issue

snowmen (2 x aa)

This will need couple of diodes to drop the voltage,

 

[Sadlercomfort]

Each light would have an led and a resistor to create a voltage drop and limit the current. (Apart from the button batteries)

So each circuit in each light is already designed for there battery voltages. If you can create several different voltage rails for each light it would be simpler.

If you used a single voltage for them all, you would need to find calculate which resistor is needed to create the right voltage drop for each(In addition to the resistors already in each light).

Diodes are useful to drop the voltage slightly, but it's more practical to use a resistor.

 

[davenn]

Each light would have an led and a resistor to create a voltage drop and limit the current. (Apart from the button batteries)

So each circuit in each light is already designed for there battery voltages. If you can create several different voltage rails for each light it would be simpler.

If you used a single voltage for them all, you would need to find calculate which resistor is needed to create the right voltage drop for each(In addition to the resistors already in each light).

That's not really the issue

the plugpack will be wired into the existing battery terminals of each unit so that it still powers the unit for the colour changes etc

As @GPG said, a diode will effectively drop the voltage enough to the lower voltage light unit

Diodes are useful to drop the voltage slightly, but it's more practical to use a resistor.

no is isn't,. because a resistor will also current limit and in this case that also isn't an issue .... a diode is ideal



Dave

 

[Sadlercomfort]

Okay Dave, would the diode voltage drop be unreliable though depending on the current?

 

[Martaine2005]

Hi Ash,
the diode would drop the voltage by approx 0.7v for each diode.
The resistors are more for limiting the current.
So two diodes at 0.7v is 1.4 volt drop immediately.
As for reliability, rectifiers are used in all AC to DC units.
So I would guess they are reliable.

Martin

 

[Sadlercomfort]

I read somewhere before about the diode voltage drop changing when the load current changes. But I guess that doesn't apply here.

So its be possible to use one voltage supply and create a series network of diodes to provide the necessary voltage drop

 

[Martaine2005]

I would guess that you can.. But obviously very inefficient. lots of diodes...
But yeah, it's possible..

Martin

 

[Sadlercomfort]

Yeah, it doesn't feel right to use them like that..

 

[Martaine2005]

But in this case, the OP has 4.5v and 3v. So two diodes are perfect for a voltage drop..

Martin

 

[Sadlercomfort]

Yeah it would be perfect

 

[Martaine2005]

Sorry Ash, not trying to tell you how to suck eggs! I think you are more knowledgeable than I am!
Sometimes, two heads are better than one!!

Martin

 

[davenn]

Okay Dave, would the diode voltage drop be unreliable though depending on the current?

the current in the circuit will also vary with varying voltage and load through a limiting resistor

 

[Sadlercomfort]

That's okay Martin!

There's always something to learn in electronics.

 

[davenn]

That's okay Martin!

There's always something to learn in electronics.

there sure is ... am always learning new things

 

[Sadlercomfort]

there sure is ... am always learning new things

I've accepted the fact that I'm never going to know everything.. but that's what keeps you open minded and makes electronics fun!

 

[Martaine2005]

there sure is ... am always learning new things

Put yourself in mine and all other 'learners' shoes Dave!
We will never know half of what you have forgotten!
So catching up is a no go! Going forward is likely!..But not guaranteed in my case
Uncle Chris only guides me after several large liquified grapes

Martin