Electronic sound and light module question

[Gazzalene]

JimB, I hope you will see this post.
I have ordered the module from Germany, will be faster than uk!
Also ordered the wire and resistors and plenty of LEDs .

working out the number of lights the truck "could" use would reach close to 30!, I do not need all these BUT I did not get into
how many I could run with the 7.2v battery? 5000mah.

I do not understand if 30 single led runs ARE the same has 15 dual led runs OR 10 triple led runs?

do not want to get the wiring all done to find out I used too many leds

thanks

 

[JimB]

I did not get into
how many I could run with the 7.2v battery? 5000mah.

OK, the capacity of the battery is 5000mAh (mAh is milli-amp hours).
Earlier we set the LED current at 20mA, so if we connected one LED to the battery it would run for 5000/20 = 250 hours.
If we had all 30 LEDs illuminated at the same time, the battery would run for 5000/(30x20) = 8.33 hours.

All this is a bit theoretical and those times may (will) not be exact.
The more load you put on a battery, the less useful capacity it will have.
But lets not worry about that.

I do not understand if 30 single led runs ARE the same has 15 dual led runs OR 10 triple led runs?

If they are connected as I showed earlier, yes they will draw the same current from the battery.

A little problem that occurs to me...
When I asked about the LEDs, you said:

The LED bulbs are 5mm and 3mm plastic domed type. the spec says 3.4v , 15-30ma

3.4v sounds about right for a white LED, but other colours red and yellow will have different voltages, and so will need different values of resistor to limit the current.
You may also want to adjust the brightness of the LEDs,
reducing the resistance will make them brighter,
increasing the resistance will make them dimmer.

JimB

 

[alec_t]

Depending on your battery voltage you may be able to save some current by connecting a couple of LEDs in series, e.g. the left and right brake lights could be two series-connected red LEDs sharing the same 20mA current path. This would be more efficient than individual LEDs each in their own 20mA current path with a total current of 40mA.

 

[JimB]

Depending on your battery voltage you may be able to save some current by connecting a couple of LEDs in series, e.g. the left and right brake lights could be two series-connected red LEDs sharing the same 20mA current path. This would be more efficient than individual LEDs each in their own 20mA current path with a total current of 40mA.

True.

But, the original "specification" was for a LED with a forward voltage drop of 3.4v, so two LEDs in series would be 6.8v.
This 6.8v does not leave much headroom for the current limiting resistor, and as the battery voltage drops the light intensity will vary considerably.

Also Gazzalene states that his electronic knowledge is quite low, so my thinking was to keep it simple by sticking to the principle of one LED and one resistor per line.

JimB

 

[alec_t]

Agreed, series-connected white LEDs won't work well, but red LEDs should. But simple is good.

 

[Gazzalene]

JimB, sorry to start the posts again, i wont keep on I promise : )
I did remember the amount of leds question and the run time with 5000mah.
I have been buying leds and seen 3.4v and 5v did not see 5v initially. from the specs the yellow/white and red all have same voltage?
BUT my how many leds came about seeing a little article and this showed a 9v battery powering 3 leds only due to voltage limitations.
from your great diagrams I know how to wire the leds BUT the how many leds can I use in series/parallel is beyond me,sorry, can not just get it.

 

[JimB]

JimB, sorry to start the posts again, i wont keep on I promise : )

No problem.

I have been buying leds and seen 3.4v and 5v did not see 5v initially. from the specs the yellow/white and red all have same voltage?

One of the big mis-understandings with basic LEDs is that they are a current operated device rather than a voltage operated device such as a good old incandescent light bulb.
In the mind of non-electrical people, the meanings of the words current and voltage are one of the same thing. The reality is that they are different properties of electricity.

As for the "voltage rating" of LEDs, different colours of LEDs will have different voltages across them when they are operating normally. There is no way around this, it is all down to the chemistry/physics of the active materials used in LEDs.
All basic LEDs require a current limiting resistor when operated from a constant voltage source such as a battery.

As time has gone by, LED manufacturers have incorporated the current limiting resistor into the LED itself. This makes life easier for manufacturers, they can just use one component, ie the LED, instead of two components, ie the LED and the resistor.
So now we have LEDs with a true voltage rating, ie they are designed to operate from a fixed voltage such as 5v, 12v or maybe 24v.

Where does this leave us?
Without knowing exactly which LEDs have been purchased, it is impossible to make any further suggestions.

JimB

 

[alec_t]

Can you post a link to the specifications of the LEDs, or at least to the adverts for the LEDs?