Losing power through solar controlled transister.

Discussion in 'General Electronics Chat' started by Grashwi, Jan 6, 2016.

  1. Grashwi

    Thread Starter New Member

    Nov 25, 2015
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    1
    Hi all. I'm stuck, again. My project is a bug zapper using a camera flash like circuit to charge a large capacitor in parallel with a joule thief powering two UV leds to attract the bugs. Everything works perfectly. on a single 1.2v rechargeable battery these two circuits draw just over 100ma and run for hours on my 2500mah battery. I have good solar cells that put out over 200mah so recharging is handled well also. But, as it sits, it runs 24/7 and I thought that was both annoying and inelegant. So, I looked around and found the attached circuit which will block current while the solar panel is active but will let current pass when the panel is not charging. The problem is that I'm losing almost all my power for some reason. If I connect two batteries in series without the transistor I get around 3vdc. When I attach the solar panels and the transistor I still get around 2.5vdc. But, there's almost no amperage available. Those two batteries are both 2500ma and without the solar panel/transistor combo they provide all the power I need and more. When I connect the solar panel and transistor, and then block the light, I can't hardly get 11ma out. Barely enough to get the leds to glow even with the joule thief. I'm hoping this is obvious but my question is why am I losing all of my amperage when I go through the 3906 as in the diagram?
    Thanks in advance for any guidance.
    Grant

    SCN_0001.gif
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Please use paragraphs.

    Post voltage measurements for the transistor terminals.

    For the convenience of other Users, here's the schematic in the correct orientation:
    upload_2016-1-6_10-7-27.png
     
  3. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Voltages as follows. All vdc. Batteries alone 2.63
    While solar panels are on (charging)...
    B/E .55
    B/C 0
    C/E 0
    C/gnd 0
    B/gnd 3.14
    E/gnd 2.64
    While solar cells are off (dark)
    B/E .61-
    B/C .60
    C/E 0
    C/gnd 2.64
    B/gnd 2.03
    E/gnd 2.64
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Looks like it's working to me.

    You only needed to provide the voltages on the transistor terminals with respect to ground.
    Charging: Ve 2.64, Vc 0, Vb 3.14 -> transistor off
    Dark: Ve 2.64, Vc 2.64, Vb 2.03 -> transistor on (saturated)
     
  5. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    From the numbers the voltage seems to be working well. But, when I connect an LED directly across those batteries with a meter in line I get around 40ma. When I connect the LED between the collector and ground, with the meter in line, I get only 11ma. I don't understand why, if the transistor is saturated, why I am getting such a reduction in amperage. So, while I can drive my bugzapper and joule thief circuit directly off of the battery easily, if I try to run them off of this circuits collector to ground, I don't have enough power to work them. It appears that the transistor is restricting 3/4 of my amperage and I don't understand why.
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    You're seeing the effect of the internal resistance of your meter on measurements.
     
  7. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Shouldn't I be getting the same ma readings in both setups? In a direct battery connection, through the LED and meter, I get 40ma. If I connect that same led and meter between collector and ground I get only 11ma. With the transistor saturated shouldn't I be getting the same 'wattage' through both? I'm really missing something here. Taking power through the transistor isn't enough 'wattage' to power my project beyond a whimper while driving it directly off the battery works great.
     
  8. dl324

    Distinguished Member

    Mar 30, 2015
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    Are you using 2N3906 for the transistor?

    There is no current limiting resistor for either measurement (which is a bad idea if that's what you did)?

    Do you have another meter to measure voltages when you're measuring current? In addition to the transistor terminals, measure other terminal of the base resistor.
     
  9. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Yes, I'm using a 3906 transistor. I put in a 2705 just to be sure I didn't have a bad transistor and the results were identical. I do have a second meter and will do as you suggest - to measure voltage as well as amperage at the transistor and resister terminals. Not sure what your reference to a 'current limiting resistor' but I did not add any additional resistor when I measured current. I'll do the additional measurements and post the results.

    Dennis, thank you for your time. I certainly do not mean to waste it but I'm at a dead end as to why this simple concept isn't working for me.
    Grant
     
  10. dl324

    Distinguished Member

    Mar 30, 2015
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    No problem. It's good that you want to understand what you're observing. If anyone thought they were wasting their time, they'd find something better to do.

    Was the 50 ohm resistor in series with the LED for the transistor drive test?
     
  11. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Thanks Dennis. No, I had no resister in play when I took the measures I sent. From what I'm objectively seeing regarding the brightness of the led it's not under strain although I wouldn't deploy something with it directly across the battery without some protection. I'll take the followup measures with no resister in play either.
    Best regards,
    Grant
     
  12. ronv

    AAC Fanatic!

    Nov 12, 2008
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    What is it you want this to do? Turn on in the dark and off in the light?
     
  13. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Yes. This is a mosquito zapper. Two circuits in parallel - one charging a mesh with a high voltage capacitor, the other a joule thief driving two uv leds to attract. Works wonderfully at 1.2 vdc. I actually have a lot of battery and charging ability so I could afford to run this 24/7 but I'd really like to turn it off during the day. The circuit I'm struggling with would turn the current off while the solar panels are active and then release the current during the dark hours. So, yes, turn it off during the light. My problem is that I'm losing a huge amount of my current through the transistor when dark happens and I don't understand why. I expect to spend a little voltage to pay for the transistor but losing this huge amount of current at the same time is killing my idea.
    Grant
     
  14. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Maybe like this:

    upload_2016-1-6_21-5-19.png
     
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  15. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Sorry, I have no idea what this means.....
     
  16. ronv

    AAC Fanatic!

    Nov 12, 2008
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    It's a simulation of your circuit.
    On the left V1 is the voltage from your panel.
    The top part is like you were looking at the circuit with an oscilloscope.
    So the green trace is the voltage from your solar panel going up until it gets a little higher than the battery. (Vpanel)
    The red one is the voltage out of the transistor going to the 100 ohm load resistor. (Vout)
    And the blue one (IR1) is the current in R1.
    So I ramped up the panel voltage so you can see the transistor switch.
     
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  17. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    ok, you're talking to a real amateur here. This is a single pulse value? I'm looking for the transistor to act as a switch that would simply funnel full amperage through at saturation for the duration of the base being no longer under bias, when the solar panels are not charging. Idealy to applies bias to the basis of the transistor during daylight, blocking any flow, and then allows uninterrupted current flow when no bias is applied to the transistor. My measureable problem is that I cannot get full amperage through the transistor upon saturation even though I get voltage. I appreciate your input but can't understand how it applies to my issue. I only want the transistor to act as a switch, acting a couple of times a day. Not in some Mhz frequency. Why does the transistor cost me such a huge cost in amperage?
     
  18. dl324

    Distinguished Member

    Mar 30, 2015
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    Take the measurements I mentioned so we can tell how the transistor is biased when it's on.

    A better way to measure LED current through the transistor is to measure the voltage drop across the 50 ohm resistor and calculate current with Ohm's Law.
     
  19. Grashwi

    Thread Starter New Member

    Nov 25, 2015
    23
    1
    Will do then. I have to get my second meter but will then send values tomorrow.

    Regards
     
  20. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I think the reason you're not getting much collector current is that the transistor is being starved of base current. You have a 5k base resistor, but the base current has to flow via that and via the solar cell's internal resistance, which could be considerable when the cell is dark.
     
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