Hi all
Looking into BEAM circuits I have seen the use of the FLEDs (flashing LEDs).
http://solarbotics.net/library/circuits/se_t1_fled.html
Are they different from common LEDs and why should I use them?
Can I buy them somewhere nowadays or could I use something else?
Thanks

 

For sure you can buy them. They look like an ordinary LED but they have a "black spot inside".
https://www.kingbrightusa.com/images/catalog/SPEC/WP56BSRD-B.pdf
https://www.digikey.com/en/products...7310?s=N4IgTCBcDaIOoAUCsA2AQgZQEoBED0aIAugL5A

 

FLED? That seems to be an acronym that we've managed perfectly well without, until now.

 

FLED? That seems to be an acronym that we've managed perfectly well without, until now.

Do you think it's necessary for this kind of project?

 

Do you think it's necessary for this kind of project?

I'm curious now - what is the solar panel voltage and how big is the motor?

 

Two things here,First, using an uncommon acronym is a poor choice, and second, in this instance it is a VERY POOR CHOICE.
It appears in that linked article that it is used a a voltage sensitive trigger for a circuit momentarily pulsing a motor.

It may be that currently available flasher LEDs are different from the one in that linked article. And it is likely that there are better ways to trigger on voltage rise.
So while it may work, why bother???

 

I'm curious now - what is the solar panel voltage and how big is the motor?

He is talking about the little toys that charge a caoacitor through a small solar panel (like from a calculator) then discharge the cap through the motor for a little bit if movement.

Bob

 

I'm curious now - what is the solar panel voltage and how big is the motor?

typically 3V panels

 

Two things here,First, using an uncommon acronym is a poor choice, and second, in this instance it is a VERY POOR CHOICE.
It appears in that linked article that it is used a a voltage sensitive trigger for a circuit momentarily pulsing a motor.

It may be that currently available flasher LEDs are different from the one in that linked article. And it is likely that there are better ways to trigger on voltage rise.
So while it may work, why bother???

ok then what alternatives do you suggest?

 

The circuit is a very simple MPPT. In order to get the maximum power out of the solar panel, the panel voltage has to be kept at about 85% of its open-circuit voltage, so discharging it down to 1V is very inefficient. What is required is much less hysteresis (maybe 250mV) and much more capacitance. I also suspect that there is very little spare power to run the circuitry.

 

The circuit is a very simple MPPT. In order to get the maximum power out of the solar panel, the panel voltage has to be kept at about 85% of its open-circuit voltage, so discharging it down to 1V is very inefficient. What is required is much less hysteresis (maybe 250mV) and much more capacitance. I also suspect that there is very little spare power to run the circuitry.

They are basically toys... Do you suggest me using something else other than FLEDs?

 

ok then what alternatives do you suggest?

A uinijunction transistor could do it quite well, but while I have seen those circuits I have neither designed nor analyzed one.

 

The circuit is a very simple MPPT. In order to get the maximum power out of the solar panel, the panel voltage has to be kept at about 85% of its open-circuit voltage, so discharging it down to 1V is very inefficient. What is required is much less hysteresis (maybe 250mV) and much more capacitance. I also suspect that there is very little spare power to run the circuitry.

The panel is incapable of running the motor continuously, hence the charge / discharge cycle.

Bob

 

The panel is incapable of running the motor continuously, hence the charge / discharge cycle.

Bob

Exactly, an MPPT would keep the panel voltage at the optimum for maximum power by adjusting the output current.
This is my suggestion.
Current source plus 6x1N4001 makes a simple simulation of a solar panel.
1H + 1Ω simulates the motor.
I note that the reverse diode across the motor is missing from the original circuits. It would be essential to prevent damage to the drive transistor, but it is important to allow the current to continue to circulate in the motor.

 

The switching rate of the transistors and the low inductance of the small motor make the turn-off "spike" much smaller in such a motor. In addition, the voltage ratings of most transistors exceed the level of such a pulse of a small motor.

 

Exactly, an MPPT would keep the panel voltage at the optimum for maximum power by adjusting the output current.
This is my suggestion.
Current source plus 6x1N4001 makes a simple simulation of a solar panel.
1H + 1Ω simulates the motor.
I note that the reverse diode across the motor is missing from the original circuits. It would be essential to prevent damage to the drive transistor, but it is important to allow the current to continue to circulate in the motor.

View attachment 256724

What are you using instead of the FLED to create the trigger effect?
I don't understand the benefits of your configuration.

 

What are you using instead of the FLED to create the trigger effect?
I don't understand the benefits of your configuration.

Regeneration or positive feedback. It gives better accuracy. When the voltage on the R1/R2 divider is high enough to turn Q2 on, R4 gives it extra bias and switches Q1 fully on.