Zener Diodes

chronorevolverchronorevolver Registered Users Posts: 6
Simple question!

How do you attach Zener Diodes in Solar Panels?

Comments

  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Zener Diodes

    You dont. Why would you?:confused:
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Zener Diodes

    Simple answer: you don't. :p

    Solar panels have internal bypass diodes like this: http://www.solar-electric.com/8ampbypdiod.html The purpose of which is to prevent shaded cells from being overwhelmed by reverse bias Voltage from non-shaded cells.
    And may have internal or external blocking diodes like this: http://www.solar-electric.com/blocdiod8amp.html The purpose of which is to prevent battery current from leaking back through the panels at night causing the battery to discharge. Usually these are found of small, stand-alone battery maintainers as large panels will be connected with a charge controller which should have enough internal semi-conductor circuitry to prevent the problem.

    Zener diodes are just about the opposite of blocking and bypass diodes, in that whereas they allow forward current most of the time they have a specific Voltage point above which they allow reverse current. They are most typically used in simple Voltage regulating circuits: an in-line resistor to the (+) side of the diode, the (-) being connected to ground. If Voltage exceeds Zener it is shunted to ground. This has to be able to handle the current potential of course.

    As solar panels are a current source not a Voltage source this type of regulation is not well-suited to solar electric.
  • UrbandialectUrbandialect Solar Expert Posts: 107 ✭✭✭✭
    Re: Zener Diodes

    zener Diodes will drop the voltage, you want a blocking diode, a rectifier diode, you hook it up to the hot(red) + lead coming off the panel, have the white part on the tip headed toward the charge controller or battery
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Zener Diodes

    My first thought was that he wanted to use them (or one) as a voltage regulator/charge controller. There are a number of problems with that idea, the most pressing being that zeener diodes, as Cariboocoot mentioned, have extremely low current handling ability before they overheat, short out and vaporize in a puff of smoke.
    Connect them to your solar panels only if you want to see what happens when they fail.
  • UrbandialectUrbandialect Solar Expert Posts: 107 ✭✭✭✭
    Re: Zener Diodes
    My first thought was that he wanted to use them (or one) as a voltage regulator/charge controller. There are a number of problems with that idea, the most pressing being that zeener diodes, as Cariboocoot mentioned, have extremely low current handling ability before they overheat, short out and vaporize in a puff of smoke.
    Connect them to your solar panels only if you want to see what happens when they fail.

    I was thinking i could use a zener as my charge controller, yall know how cheap i am, but the more i researched it the more i realized it was a dumb ideal
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Zener Diodes
    I was thinking i could use a zener as my charge controller, yall know how cheap i am, but the more i researched it the more i realized it was a dumb ideal

    do not worry as it is good to explore ideas even if they are wrong just to add to the general knowledge of what can or can't normally be done. i said normally because in some cases it may be an alternative if more parts are added to make up a more elaborate regulator circuit. this is not the best regulator to go with seeing as how we have much better ones out there and they are more efficient over zener types too.
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Zener Diodes
    niel wrote: »
    ... more parts are added to make up a more elaborate regulator circuit
    I see a power supply as a big "digital zener diode", a charge controller ... maybe a "programmable digital zener diode" 8)

    GP
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Zener Diodes

    you'd need allot of high wattage zeners to do any good by themselves. with other parts it is possible to tailor the voltage depending on the design you'd use and that means more parts as i said in the first place. this is still ancient power supply technology and is not as good as what we currently see in controllers these days.
  • mike95490mike95490 Solar Expert Posts: 9,359 ✭✭✭✭✭
    Re: Zener Diodes

    A zener can't make a good battery charger, it is a single, fixed voltage, and since it's a shunt type of regulation, it burns excess power as heat - more than a 50w array, all you have is a toaster!
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Zener Diodes

    A
    zener can't make a good battery charger,
    What about using a zener diode to power a low current led light source off of 12, 24 or 48 volt systems. It seems this might be a very price competitive use of zeners. Yes it would use more power through the series drop resistor but if the current it low, it wouldn't be much.
  • chronorevolverchronorevolver Registered Users Posts: 6
    Re: Zener Diodes

    Ah alright. I was curious because I was told to use a zener diode for my solar panel to reduce enough voltage to run a device without killing it. Now i have learned that it is not.

    http://www.youtube.com/watch?v=yCea7PztbtU&list=FLrnU3B5Ud8PKVE32WGAYGDw&index=1

    In this link, a 6 watt solar panel is being used to charge an iphone using

    Solar panel -> Female 12v cigarette socket -> Car adapter usb -> Iphone.

    my device takes roughly (7.5v x 1.05) 7.875 watts of power. and I have a 24w panel. I am trying to use the same idea on a slightly larger scale, while still be able to charge an iphone if I change out the plugs.

    Now, my 24w panel would be too much for said devices and I am just trying to figure out a way to run the devices no problem using only the solar panel.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Zener Diodes

    The problem is you're trying to take the output of a solar panel which varies in both Voltage and current and turn it into a power source that doesn't vary in either Voltage or current.

    I think you're going to have to investigate the possibilities inherent in IC Voltage regulators like an LM723, along with a few extra support components.

    Circuit design is not my field of expertise. Besides, I'm so out-of-date it would probably be based on a 5U4. :p
  • chronorevolverchronorevolver Registered Users Posts: 6
    Re: Zener Diodes

    The solar panel can be adjusted to be the same if need be. My reasoning was that, for example a 25v panel would output 25v at optimal output. Something that would reduce the voltage received to 7.5v. As sunlight decreases, the panel for example would produce 17v which is reduced to 7.5v, far more power than is necessary, than running a 7.5v panel powering a 7.5v device, then it receives less power and the device will no longer operate or charge.


    I didn't think it would be this difficult to throttle the voltage of a solar panel to a certain value.

    It was supposed to be 25v -> something to throttle to 12v -> 12v car adapter proceeds to use whatever voltage it needs like 7.5v for one device, or a 5v device like an iphone.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Zener Diodes

    Except that solar panels are current sources, not Voltage sources.
    A little bit of light hits them and the Voc goes right up. A Voltage regulator is going to try and regulate Voc, which applies a load to the terminals causing the Voc to drop like a rock until enough light falls on the panel that it can produce some current. Meanwhile the regulating circuit has switched off again and the Voc has shot up again and the regulator tries to clamp it down again and ... eventually the panel will manage something along the lines of Vmp * Imp. But as far as the panel is concerned, maintaining Imp is what's important. Put more load on (i.e. try to sink excess Voltage) and it will allow V to drop so long as it can maintain I. You could end up with a panel producing full I at some small portion of V and a regulator going nuts trying to manage this into a fix V*I output within the right range.

    In short, this makes it a bloody awful power source. Perfect for charging batteries though, since you want max I at the low V point of the discharged battery and then have it taper off as V increases.

    A simple circuit isn't going to do it without risk to the device being powered. The closer the panel's spec are to the loads, the easier it will be. You're after <8 Watts of power from a 24 Watt panel. In overly simplistic terms that means 16 Watts has to go somewhere. Try for something like the PWM used in simple charge controllers substituting a capacitor for the battery part. Just enough cap to smooth things out and keep the thing running and just enough pulsing to keep the cap charged. When the panel is disconnected it produces nothing, so there's no "excess" power that needs to be shunted anywhere.

    Thirty years ago I would have known what I was talking about here. That's no longer the case, I'm sorry to say. :blush:
  • chronorevolverchronorevolver Registered Users Posts: 6
    Re: Zener Diodes
    Except that solar panels are current sources, not Voltage sources.
    A little bit of light hits them and the Voc goes right up. A Voltage regulator is going to try and regulate Voc, which applies a load to the terminals causing the Voc to drop like a rock until enough light falls on the panel that it can produce some current. Meanwhile the regulating circuit has switched off again and the Voc has shot up again and the regulator tries to clamp it down again and ... eventually the panel will manage something along the lines of Vmp * Imp. But as far as the panel is concerned, maintaining Imp is what's important. Put more load on (i.e. try to sink excess Voltage) and it will allow V to drop so long as it can maintain I. You could end up with a panel producing full I at some small portion of V and a regulator going nuts trying to manage this into a fix V*I output within the right range.

    In short, this makes it a bloody awful power source. Perfect for charging batteries though, since you want max I at the low V point of the discharged battery and then have it taper off as V increases.

    A simple circuit isn't going to do it without risk to the device being powered. The closer the panel's spec are to the loads, the easier it will be. You're after <8 Watts of power from a 24 Watt panel. In overly simplistic terms that means 16 Watts has to go somewhere. Try for something like the PWM used in simple charge controllers substituting a capacitor for the battery part. Just enough cap to smooth things out and keep the thing running and just enough pulsing to keep the cap charged. When the panel is disconnected it produces nothing, so there's no "excess" power that needs to be shunted anywhere.

    Thirty years ago I would have known what I was talking about here. That's no longer the case, I'm sorry to say. :blush:

    Alright, thanks you have been very helpful. Do you recommend that I aim for 8 watts? 9?
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