Voltage Regulator

Discussion in 'The Projects Forum' started by davidk19380, Jul 6, 2011.

  1. davidk19380

    Thread Starter New Member

    Jul 6, 2011
    Here's my scenario. I'm a maker-wanna-be. I know enough to be dangerous, but not enough to make anything work on a consistent basis. My son and I have put a number of those simple kits together that make sounds, or flash lights, etc., so I can solder and understand the concepts of the breadboards, I just might not be able to have you draw me a diagram and be able to figure out where everything goes on the board. I'd like to learn though.. that counts doesn't it?

    I have access to a solar panel. The panel has 60 cells on it and generates around 34 VDC / 17Amps in sunlight. That might vary... I only checked it one time.

    I would like to make a circuit that will take that varying voltage/amperage from the panel and convert it to a regular 12V current at some amperage. Let's say for instance that I want to power a submersible pump that is rated for 12VDC/4.5Amps.

    1) what would the diagram look like
    2) pretend i'm a 5th grader and that I might even need to know what holes of a bread board to put everything into.
    3) i assume it would make sense that if the circuit can't create that 12VDC/4.5A then it shouldn't pass anything to the pump.
    4) I also assume that if this pump were to have a float on it, so that it only pumps when there's enough water, that wouldn't pose a problem for a circuit that is passing along unused electricity.

    I hope ya'll can help me out. You seem like such nice, helpful people. :)
  2. Zod


    Jul 3, 2011
    Here is but one way of doing what you want; http://www.play-hookey.com/analog/experiments/plus_12_volt_ps.html.

    If you use a 2N3055 instead of the TIP31, you will easily have the current you want.

    Unnecessary components are the transformer, the two rectifier diodes, and the filter capacitor on the left side, as you are starting with DC.

    Hope this helps..
  3. SgtWookie


    Jul 17, 2007
    Sorry Zod, that's just not going to work very well.
    David says he has around 34v @ 17A coming in; don't know how he measured that? But anyway, his load is 12v @ 4.5A.

    So, if we take the regulator input-output difference (34v-12v=22v) and multiply that result by the current: 22V*4.5A = 99 Watts of power that will be dissipated in the 2N3055 transistor and 12v*4.5A = 54 Watts power that will be dissipated in the load. While 2N3055's are actually rated for 115W maximum power dissipation, one would have to have a HUGE heat sink to dissipate that much power.

    Then there's the problem of the breadboard; they aren't designed to carry that much current. Go over a couple of amperes, and you'll be damaging the breadboard and melting those little jumper wires.

    Then there are the basic design problems with the suggested regulator. The 10k resistor is the only current source for the base of the power transistor, which will not provide anywhere near enough current to get 4.5a out of the emitter. Even if it did, the 2.2 Ohm resistor from base to emitter of the 2N3904 would limit the output current to under 300mA. 0.62v/2.2 Ohms ~=282mA, at which time the 2N3904 starts pulling current from the power transistor's base.

    What's really needed is some sort of switching regulator, but that would have to be built on a circuit board - and would be difficult for a newcomer to understand, let alone troubleshoot.

    I don't have a really easy solution offhand.
  4. wayneh


    Sep 9, 2010
    Let's suppose your panel, when loaded by the pump, can still produce 24v. A key problem you need to solve is that your electronics will need to dissipate as much power as the pump is drawing (or 12 of the 24v), maybe 50 watts or so. That's a HUGE amount of heat if it's in one tiny place like a 2N3055. You'd need a great heat sink and a fan to have a chance, and I'm still not sure it's possible to shed that much heat from that package. Reconfiguring the cells, if that's possible, to give less voltage and more current capacity might help. Well. it would definitely help with the huge ∆V problem, but it might reduce the times when the panel is able to run the pump. This stuff is complicated.

    Anyway, the overheat problem can be solved by using more than one power transistor in parallel, so that they share the heat loss duty.

    AARRGGH, gotta type faster to beat Sarge!
  5. KJ6EAD

    Senior Member

    Apr 30, 2011
    Last edited: Jul 6, 2011
  6. davidk19380

    Thread Starter New Member

    Jul 6, 2011
    Just a note... I measured the voltage and amps with a multimeter from my work.
  7. davidk19380

    Thread Starter New Member

    Jul 6, 2011
    Ok, so I looked at the replies and such and the links. Some of it makes sense.. some of it doesn't.

    A question back to you would be is this large solar panel not really that useful to mess around with, without getting a hefty inverter to handle it? I didn't realize that one panel would output some much voltage.

    A little history on this... this panel is left over from a recent installation on our roof at work. They installed 1600+ panels like this. I was just looking at the charts from earlier in the week and at one point they were generating 250KW AC (does that make sense?) Another reading was 299AMPS and 229V...

  8. wayneh


    Sep 9, 2010
    One man's garbage is another's gold. It really just depends what you want to power. You mentioned a 12V pump, and we pointed out the problem of dropping the excess voltage. But there are easy ways to do it. You could put 2 or 3 of those pumps in series, if that has some utility to you. You could put 12v, 50W lightbulbs in series, to make light that you might not need, but they would drop 12v in a controlled way since they're designed for the heat.

    The general answer to your question though is that you've discovered the problem with most alternative energy sources; they make widely variable outputs that are tricky to optimize. You get efficiency when source and load are matched, but that's a rare beast with alternative energy.