go_away

Author Topic: Solar engine help (really more of a check)  (Read 786 times)

0 Members and 1 Guest are viewing this topic.

Offline z.s.tar.gzTopic starter

  • Supreme Robot
  • *****
  • Posts: 540
  • Helpful? 5
  • Linux Guru
Solar engine help (really more of a check)
« on: May 11, 2010, 04:46:44 PM »

I am building a little BEAM robot just to show at my presentation as I am unable to finish my big robot in time.
I've tried modifying the solar engine found here to work more as a power supply. The only real change I've made is to add the diode below the motor (which represents the load) and the wire to the left of it.

Will this work is my main concern. I tried modifying it a few days ago and it did not work at all. (I'm not going to troubleshoot it as it was really only a test run)

Key:
M1 = Load
D1 = Power Diode
R1 = 100K
C1 = 3600uF
T1 = 2n3906 PNP
T2 = pn2222

Yes I know the LED is also labeled as D1. Pretend it's D2.
The power source is a solar cell capable of about 6.5V@40mA if memory serves.
Save yourself the typing. Just call me Zach.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: Solar engine help (really more of a check)
« Reply #1 on: May 11, 2010, 07:10:49 PM »
Hi,

I cannot tell whether D1 (the one that we don't pretend is D2) is connected to R1 (which I decided to call the one marked R2, since there's only one resistor), since you don't use junction "dots", but if they're supposed to be joined, you are short circuiting the motor (+ the leftmost D1).

If they're not joined... To run the motor, the NPN needs to open and for this to happen, the PNP should go open.
The PNP won't open until it's base is ~0.7V less than the positive side of C1, but since the cap will be loaded down by the solar panel when there's not enough light, the base will never get below the emitter, except from the effect of the LED, which will keep it open when the voltage on the cap is reaching U_LED + U_eb (around 2.5V to 2.6V with a red LED).
Since the base of the NPN isn't kept in check, it might get very leaky, draining some of the current produced by the solar panel when the PNP is closed. A resistor between base and emitter (10k to 1M will get it in check.

A solar panel with data stating 6.5V and 40mA is not 6.5V@40mA.
The unloaded voltage is 6.5V (@0mA) and the short circuit current is 40mA (@~0V). This is at a light intensity roughly equal to full sun at noon in the summer.


The electron hole (or is it a quantum well) at the top of your schematic may influence results.


You know, Wilf has spend quite a bit of time with BEAMs, so I think it's safe to say that he would have made a similar circuit if it would do anything even remotely usefull. There's a plethora of Solar Engines out there and you could do worse than using a circuit unmodified.
If you just want a solar power supply to run the motor whenever there's enough light, pick a motor and a solar panel that will work in that setup and just use the panel, a (Schottky?) diode and a motor. It won't behave very BEAM-like though.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline z.s.tar.gzTopic starter

  • Supreme Robot
  • *****
  • Posts: 540
  • Helpful? 5
  • Linux Guru
Re: Solar engine help (really more of a check)
« Reply #2 on: May 11, 2010, 07:45:32 PM »
They are joined, sorry about that. I do jumps to signify which aren't connected as opposed to dots to signify which are connected.
And the solar panel should still be able to produce ~4V@30mA in reasonable conditions under load. The problem is getting it to work in lower lighting conditions where the power needs to be pulsed.

So let me restate my question: Will adding a diode and another wire allow me to operate the solar engine with relatively similar results but only have the current across the load travel in one direction?

Save yourself the typing. Just call me Zach.

Offline Soeren

  • Supreme Robot
  • *****
  • Posts: 4,672
  • Helpful? 227
  • Mind Reading: 0.0
Re: Solar engine help (really more of a check)
« Reply #3 on: May 12, 2010, 08:55:32 PM »
Hi,

And the solar panel should still be able to produce ~4V@30mA in reasonable conditions under load. The problem is getting it to work in lower lighting conditions where the power needs to be pulsed.
Do you want it to keep going (no pauses) when there's ample light and only get interrupted when it's too dark (where it then charges the cap and jerks forward a bit etc.)?


So let me restate my question: Will adding a diode and another wire allow me to operate the solar engine with relatively similar results but only have the current across the load travel in one direction?
Try this:
Remove the diode (i.e. back to the original circuit).
Move the positive connection of the panel from the T2 collector to the positive side of the storage cap.
(Almost like you did, but remove the diode and the PV+ to T2_base).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


Get Your Ad Here