-DIY- Powering a 3 volt LED from a 4.5V supply

[DPG]

Marconi, are you thinking the same as me, ie he has the resistor connected to the power supply, and is expecting the voltage to drop even without a load connected?

 

[T800mc]

Hello. four things first:

1. please draw me circuit diagram of what you have connected together.

2. Show me where you connect your voltmeter to measure 4.5V.

3. Do the LEDs glow?

4. Read out the colours on the resistor from one end to the other.

1. Drawing attached.

2. Shown on drawing.

3. No they don't.

4. There are no colours on the resistor, it's one of these:

Vishay 100mΩ Wire Wound Resistor 1W ±1% RS01AR1000FE12 | RS

uk.rs-online.com

 

[T800mc]

Marconi, are you thinking the same as me, ie he has the resistor connected to the power supply, and is expecting the voltage to drop even without a load connected?

That is what I did first. I tested it without having the lights connected. Connecting the lights too I get 4.5 volts.

 

[DPG]

Thanks. In that case, your answers to Marconi's questions will solve the mystery.

My bet, assuming the LEDs are lit, is that you are measuring across the wrong points.

 

[marconi]

Sir,

The resistor you have bought and wired in is 0.1 Ohms ie: 100milli Ohms/100mOhms.

I think you have clicked on the wrong value as you require 100 Ohms - check what I said earlier - is this for the Batman eyes?

So step by step you need to obtain some 100 Ohms resistors. Let me know when they arrive and I will talk you through it.

Meanwhile are you using a digital multimeter? Can you see the 'Ohms range'? Just switch to the lowest Ohms range and short the leads together - does the display read zero or near sero Ohms? Now measure the resistance of the LED with the leads connected one way round and then reversed. With one of these tests does the LED glow faintly? - you may need to reduce the lighting to tell.

Offer stands - do you want me to post you some 220 Ohm and 100 Ohm resistors? - they are only gathering dust in my man-shed.

The good news is that the SoapBox seems to work!

 

[T800mc]

Sir,

The resistor you have bought and wired in is 0.1 Ohms ie: 100milli Ohms/100mOhms.

I think you have clicked on the wrong value as you require 100 Ohms - check what I said earlier - is this for the Batman eyes?

So step by step you need to obtain some 100 Ohms resistors. Let me know when they arrive and I will talk you through it.

Meanwhile are you using a digital multimeter? Can you see the 'Ohms range'? Just switch to the lowest Ohms range and short the leads together - does the display read zero or near sero Ohms? Now measure the resistance of the LED with the leads connected one way round and then reversed. With one of these tests does the LED glow faintly? - you may need to reduce the lighting to tell.

Offer stands - do you want me to post you some 220 Ohm and 100 Ohm resistors? - they are only gathering dust in my man-shed.

The good news is that the SoapBox seems to work!

Oops, makes sense why it hasn't worked then.

I do have some 220 Ohm resistors too (he thinks lol). I could wire them in parallel like you suggested but I'm not sure how to do that.

If you really don't mind sending them to me I'll pm you my address, thank you.

Yes a digital multimeter. I will try that tomorrow.

 

[DPG]

Connect the ends of each of the two 220 ohm resistors together and you can treat them as a 110 ohm device.

 

[T800mc]

Connect the ends of each of the two 220 ohm resistors together and you can treat them as a 110 ohm device.

So they are next to each other? Both ends soldered together with a wire for each end of the double?

 

[DPG]

So they are next to each other? Both ends soldered together with a wire for each end of the double?

Yes, place the resistors together. Solder both wires together at each end. Google it and it will become obvious

 

[marconi]

Resistors posted today so should be with you Wed 19th.

 

[T800mc]

Resistors posted today so should be with you Wed 19th.

Resistors posted today so should be with you Wed 19th.

Thanks again, I shall have a play and report back.

 

[T800mc]

Resistors posted today so should be with you Wed 19th.

They all turned up great, thanks again!

I've put it together and the voltage still isn't dropping. See pic. I tried it anyway and the eyes don't light up.
Before I did anything I checked that the lead that goes into Batman head worked, put it in his head and attached a battery to the other end they lit up. Is it possible the soap reactor is somehow compensating?

 

[DPG]

So the LED lights when powered via the resistor from a battery?

But not when powered from the soap unit?

 

[T800mc]

So the LED lights when powered via the resistor from a battery?

But not when powered from the soap unit?

I meant the battery adapter with wires on it that goes in the head to replace the batteries worked just via the battery attached.
I just tried batteries through the resistor too and they lit up.

 

[marconi]

I reckon the Soap reactor contains circuitry such that each 4.5V 30mA output acts just like a battery without the need for the extra resistor. The no-load voltage is 4.5V but more importantly it will provide a current up to 30mA to illuminate the LEDs; as it provides this current the output voltage at the soap box socket will fall a little but not so much that it becomes less than the forward voltage requirement of the LED.

I will send you some LEDs to experiment with to confirm my thinking. If they are damaged then it does not matter but we don't want to damage those in the figurines.

I will draw out and explain the experiments in a later email - may not be today though.

When I look at the youtube explanations for the soap reactor the lead from the reactor turns into two thin wires at the end of which is a stubby cylindrical shape which substitutes for one or more 'hearing aid batteries' - this is inserted in lieu of the battery/batteries. Is this what you have pictured with the meter prongs at either end?

You will receive a 4 LED indicator (green, yellow, yellow, red) with wires already soldered on. Should arrive tomorrow 20 Aug.