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

[T800mc]

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?

Yes that is what I have pictured with the prongs at either end.

I do have some spare LEDs I can play with here. I have some these if they will work:

Broadcom3.6 V Green LED 5mm Through Hole, HLMP-CM2H-130DD | RS

uk.rs-online.com

Vishay3 V Green LED 3mm Through Hole, TLHG4401 | RS

uk.rs-online.com

Vishay3 V Green LED 3mm Through Hole, TLHG4900 | RS

uk.rs-online.com

 

[marconi]

Right. Take your multimeter(MM) and select dc volts and identify which of the ends of the stubby item is +ve and which is -ve. Confirm 4.5V.

Now select dc amps on MM on a scale which will read 30mA.

Take an LED. Put long lead on the +ve of stubby item. Then put one MM lead on short lead of LED. Finally put the other MM lead on -ve of stubby item. Current should be 30mA or lower and LED lights up.

 

[T800mc]

Right. Take your multimeter(MM) and select dc volts and identify which of the ends of the stubby item is +ve and which is -ve. Confirm 4.5V.

Now select dc amps on MM on a scale which will read 30mA.

Take an LED. Put long lead on the +ve of stubby item. Then put one MM lead on short lead of LED. Finally put the other MM lead on -ve of stubby item. Current should be 30mA or lower and LED lights up.

The stubby item has + and - on it. When I connect red to + and black to - I get 4.5v.
If I connect the other way round I get -4.5v.

My MM doesn't do milliamps, I'll try and find another one.

Am I supposed to be doing this test on the lead with the resistor in it or normal one?

 

[marconi]

Your MM does do mA. Turn the knob so that its dot is at 6 o'clock - the last position going clockwise. the 'A' position without Hz beside it.

Use the lead without the resistor.

 

[marconi]

I did not have any single LEDs so I sent you a four LED panel indicator. Somes wires have been soldered to it from a previous project. Please study the attachment which shows you how the wires have been connected.

These LEDs only pass 10mA to light up so what I'd like you to do is connected all the wires on side together and all the wires on the other side together as I showed in my first attachment.

Then connect it up as I described in my #32 - all four LEDs should light up. Leave it on for five minutes. Note down the current you measure on your MM

Now connect up as shown in my second drawing and then connect to the Soap box as in my #32. Again all the LEDs should light up. Leave it on for 5 minutes. Note down the current.

Then tell me the results.

 

[T800mc]

Right. Take your multimeter(MM) and select dc volts and identify which of the ends of the stubby item is +ve and which is -ve. Confirm 4.5V.

Now select dc amps on MM on a scale which will read 30mA.

Take an LED. Put long lead on the +ve of stubby item. Then put one MM lead on short lead of LED. Finally put the other MM lead on -ve of stubby item. Current should be 30mA or lower and LED lights up.

I had to swap the red lead to the red port for amps, sorry. The LED

Your MM does do mA. Turn the knob so that its dot is at 6 o'clock - the last position going clockwise. the 'A' position without Hz beside it.

Use the lead without the resistor.

I had to move the red lead to left red amp plug too. The LED lit up and it red 0.015A
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I did not have any single LEDs so I sent you a four LED panel indicator. Somes wires have been soldered to it from a previous project. Please study the attachment which shows you how the wires have been connected.

These LEDs only pass 10mA to light up so what I'd like you to do is connected all the wires on side together and all the wires on the other side together as I showed in my first attachment.

Then connect it up as I described in my #32 - all four LEDs should light up. Leave it on for five minutes. Note down the current you measure on your MM

Now connect up as shown in my second drawing and then connect to the Soap box as in my #32. Again all the LEDs should light up. Leave it on for 5 minutes. Note down the current.

Then tell me the results.

Okay great I will try that when it arrives. Got to admit I wasn't expecting so much great help from a forum!
Does what I told you about the 0.015A mean anything?

 

[marconi]

Well done Sir. Yes the current measurement does. An LED like that will pass a current of about 15mA or 0.015A.

(I am only one of very many who like to help out when and where we can. Generally though we do not do 'step by step' for any electrical work which has safety or legal consequences but your question is not one of these).

 

[T800mc]

Well done Sir. Yes the current measurement does. An LED like that will pass a current of about 15mA or 0.015A.

(I am only one of very many who like to help out when and where we can. Generally though we do not do 'step by step' for any electrical work which has safety or legal consequences but your question is not one of these).

So if I needed instructions on replacing a contactor in a star delta starter it would be tumbleweeds? Lol

So does the information that is it passes 0.015A tell you something in partciular about the soap reactor?

 

[marconi]

Yes it does. Assuming you used a 3.6V green led and the open circuit voltage of the soap reactor is 4.5V then the internal resistance of the 4.5V supply is:

(4.5-3.6)/0.015 = 0.9/0.015 = 60 Ohms

For a 3V green led:

(4.5-3)/0.015 = 1.5/0.015 = 100 Ohms.

The soap reactor 4.5V 0.03A outputs are equivalent to a battery of 4.5V with an internal resistance circa 60-100 Ohms - see my attached diagram - the Thevenin equivalent circuit for the output.

You could work out the internal resistance more accurately if you measured the voltage across the led (the forward voltage) and used it instead of 3.6 or 3 in my sums above.

Do the checks using the 4 leds I sent you and report back and then I will confirm you can simply connect a Soap reactor output (4.5V 30mA) without an extra series resistor.

 

[T800mc]

Your delivery times are better than amazon!

0.026
0.008

Yes it does. Assuming you used a 3.6V green led and the open circuit voltage of the soap reactor is 4.5V then the internal resistance of the 4.5V supply is:

(4.5-3.6)/0.015 = 0.9/0.015 = 60 Ohms

For a 3V green led:

(4.5-3)/0.015 = 1.5/0.015 = 100 Ohms.

The soap reactor 4.5V 0.03A outputs are equivalent to a battery of 4.5V with an internal resistance circa 60-100 Ohms - see my attached diagram - the Thevenin equivalent circuit for the output.

You could work out the internal resistance more accurately if you measured the voltage across the led (the forward voltage) and used it instead of 3.6 or 3 in my sums above.

Do the checks using the 4 leds I sent you and report back and then I will confirm you can simply connect a Soap reactor output (4.5V 30mA) without an extra series resistor.

Your delivery times are better than amazon!
Leds turned up and I made an attempt.

Connecting it via the first diagram I got 0.026A
Connecting it via the 2nd diagram (hopefully I did it correct) I got 0.008A

The MM went off after 4.5 minutes but thats what the readings were. The 0.008 did dip to 0.007 fractionally at the end but that could have my grip slipping.

 

[marconi]

Thank you. You can connect you figurines using the connector leads without a resistor to the eight 4.5V 30mA outlets instead of using a battery/batteries, one output and lead for each battery you substitute for - do not use the the higher amperage outlets though. One 30mA outlet replaces one battery in a compartment eg: in the head. Please confirm all works fine.

There is something in this which talks about what the higher amperage outputs can be used for - meant nothing to me though.

View: https://www.youtube.com/watch?v=r8JXlyZ3TpA

 

[T800mc]

Thank you. You can connect you figurines using the connector leads without a resistor to the eight 4.5V 30mA outlets instead of using a battery/batteries, one output and lead for each battery you substitute for - do not use the the higher amperage outlets though. One 30mA outlet replaces one battery in a compartment eg: in the head. Please confirm all works fine.

There is something in this which talks about what the higher amperage outputs can be used for - meant nothing to me though.

View: https://www.youtube.com/watch?v=r8JXlyZ3TpA

Thank you.

I watched them before I bought the soap reactor. I just thought I'd be sure before damaging anything.

I've tried the stubby thing both ways round via the soap reactor and the LEDs will not illuminate. I tried the stubby thing with batteries attached and they lit up fine. Something about the soap reactor that won't light up the LEDs in Batmans head.

 

[marconi]

I wonder if the stubby thing is not making contact with the terminals of the battery compartment.

Take two pieces of wire and sellotape one piece to one end and the other piece to the other end of the stubby thing. Touch the free ends on the contacts of the battery compartment - may have to swap over to get the polarity right.

The soap reactor is turned on?
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A test: Using the stubby thing connected to the battery and inserted into the battery compartment please use your MM to measure the current through Batman's head LEDs.

 

[T800mc]

I wonder if the stubby thing is not making contact with the terminals of the battery compartment.

Take two pieces of wire and sellotape one piece to one end and the other piece to the other end of the stubby thing. Touch the free ends on the contacts of the battery compartment - may have to swap over to get the polarity right.

The soap reactor is turned on?
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A test: Using the stubby thing connected to the battery and inserted into the battery compartment please use your MM to measure the current through Batman's head LEDs.

I opened the other large stubby thing and tried that and it worked. Excellent! Maybe an issue with that other one. Thank you so much for your help! How can I repay you?

 

[marconi]

I do not need recompense because I like helping out. These problems occupy me and give me mental stimulation but if you feel inclined perhaps make a £5 donation to the NSPCC towards their very good work.

NSPCC - https://www.nspcc.org.uk/

I reckon some folk who may have been following this thread would like to see the working figures and a short ditty on your interest in these figures. Do you make films using them for instance? Pictures are always good.

Best wishes Marconi