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Thread: Solar voltage limiter?

  1. #1

    Default Solar voltage limiter?

    I want to buy a 6 volt solar panel for charging my cell phone while I'm camping. The problem is I know it can get up to over 8 volts in full sun...that would probably give me a nice cellular door stop. [img]/ubbthreads/images/graemlins/wink.gif[/img] Is there any way for me to limit it to 6v max, but not take away any of the voltage when it is below 6v?

  2. #2
    *Flashaholic* Brock's Avatar
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    Default Re: Solar voltage limiter?

    Depending on the phone you probably don't need it. I know the Nokia 51xx/61xx phones say they need 3.7v, but the AC plug from Nokia is putting out 7.5v with no load. If you can check the voltage of the walwart charger and see how high it is. Unless the solar panel is rather large the voltage will drop from the load of charging the cell phone battery, and most phones have built in charge controllers, to a certain voltage.

  3. #3

    Default Re: Solar voltage limiter?

    As another poster has pointed out you may not actually have a problem.

    Otherwise, you can easily put a zener diode of the voltage you wish to limit to across the output (suitable power diode of course). Be sure it's above the maximum voltage your charged battery might be or plan for lots of discharge current.......

    Solar cells have fairly limited ability to produce current, this is a safe and easy 'out'.

    Doug Owen

  4. #4

    Default Re: Solar voltage limiter?

    Hmmm...the charger that came with my phone (Sanyo SCP 8100) is rated at 5.4 volts. I have no idea if it will take anything higher or not, it hasn't been out very long so I don't think anyone has really tested yet. I don't really want to be the first to do so. [img]/ubbthreads/images/graemlins/wink.gif[/img] If I put a diode in wouldn't that also drop the voltage when the panel is producing lower voltages? The panel I want to get is rated at 6v/50ma.

  5. #5

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    zmoz said:
    If I put a diode in wouldn't that also drop the voltage when the panel is producing lower voltages? The panel I want to get is rated at 6v/50ma.

    [/ QUOTE ]

    Yup. It's subtract roughly .7 Volts *at all times*. Even when you don't want it. This probably means slower charging under all conditions.

    OTOH, a 5.4 to say 5.6 Volt one watt Zener won't......

    Your call.

    Doug Owen

  6. #6
    *Flashaholic* Brock's Avatar
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    Default Re: Solar voltage limiter?

    can you put a voltmeter on the supply that came with it? I would be willing to bet it is over 7v, but if you can meter it, that would be best.

  7. #7
    Flashaholic
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    Default Re: Solar voltage limiter?

    If you are concerned about the drop across the blocking diode, use a shottky diode, maybe even a high power one even though you're not drawing much current; a shottky will only drop about .2 to .3 volt.

  8. #8

    Default Re: Solar voltage limiter?

    I measured it...almost exactly 6 volts...so under load I would guess it is very close to 5.4 volts.

  9. #9

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Evan said:
    If you are concerned about the drop across the blocking diode, use a shottky diode, maybe even a high power one even though you're not drawing much current; a shottky will only drop about .2 to .3 volt.

    [/ QUOTE ]

    I think you missed it, the goal was to reduce the voltage...

    (you'd just need more diodes and would still be inferior to a zener in the application)

    Doug Owen

  10. #10

    Default Re: Solar voltage limiter?

    While we're talking about this...do you think it is at all possible to damage the phone with under voltage?

  11. #11
    Flashaholic
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    Default Re: Solar voltage limiter?

    Couldn't you use a zener doide reverse biased between the pos and neg etminals of your solar pannel to limit the voltage output to 5v? It would dissipate everything over 5V through the diode, so you'd need a decently heafty one.

  12. #12
    *Flashaholic* Brock's Avatar
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    Default Re: Solar voltage limiter?

    Under voltage won't hurt it, but it will most likely just stop charging. Another thought is to get the solar panel in full sun and connect it to the phone and watch the voltage. Also if it is a bit high you could leave the phone on drawing a bit more power, which will drop the voltage a bit more. Or in full sun put a piece of masking tape over part of the panel. If you play with it and watch a meter while your doing it you will figure out how much to block, if you need to block any.

    How big is the solar panel or how many watt or mA is it rated at?

  13. #13
    Flashaholic
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    Default Re: Solar voltage limiter?

    You could always try a fixed voltage regulator.

    (or possibly a vairable one such as LM317 with a few resistors added)

  14. #14

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    FreeBSDboy said:
    Couldn't you use a zener doide reverse biased between the pos and neg etminals of your solar pannel to limit the voltage output to 5v? It would dissipate everything over 5V through the diode, so you'd need a decently heafty one.

    [/ QUOTE ]

    Yup, sure could, think I might have mentioned it a couple of times here......

    And given the 6 Volt, 50 mA output (.3 Watt), "decently heafty" isn't a factor since the smallest one you can buy (.5 Watt) is big enough for the job. Typical ones (1 Watt) are 'plenty big'.

    Doug Owen

  15. #15

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    UK Owl said:
    You could always try a fixed voltage regulator.

    (or possibly a vairable one such as LM317 with a few resistors added)

    [/ QUOTE ]

    Actually not. We don't have the voltage 'head room' to support this. LM317s need about 2.5 volts 'excess' to work.

    Even low voltage drop out regulators are a poor choice against the simple zener solution.

    Doug Owen

  16. #16
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    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Doug Owen said:
    [ QUOTE ]
    UK Owl said:
    You could always try a fixed voltage regulator.

    (or possibly a vairable one such as LM317 with a few resistors added)

    [/ QUOTE ]

    Actually not. We don't have the voltage 'head room' to support this. LM317s need about 2.5 volts 'excess' to work.

    Even low voltage drop out regulators are a poor choice against the simple zener solution.

    Doug Owen

    [/ QUOTE ]
    What he may need is some sort of switching regulator. I believe NatSemi has some flyback controller chips that are designed to work in situations like this.

  17. #17

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Entropy said:
    [What he may need is some sort of switching regulator. I believe NatSemi has some flyback controller chips that are designed to work in situations like this.

    [/ QUOTE ]

    Not really. If you check, the original problem was worry that the solar panel would go overvoltage and kill the cell phone. Such regulators don't work well at reducing voltages.

    I still think the zener's the call.

    Doug Owen

  18. #18
    Flashaholic* Burnt_Retinas's Avatar
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    Default Re: Solar voltage limiter?

    Fortunately, the easy fix is the common old "shunt regulator" used with small power solar regulation systems. In simple terms, it is as per Dougs posting - use a zener. There is no diode voltage drop so you'll get maximum voltage. Connect the zener across the panel's output leads. Remember - a zener is connected reversed biased ie the anode to the -ve of the panel and the cathnode (the end with the stripe) to the +ve of the solar panel. Connecting it backwards will short out the battery and burn up the zener.

    The panel is rated at 50mA so this would only be 300mW dissapation maximum when the zener hits it's breakdown voltage at maximum panel current rating. I'd use a 1 watt diode though, rather than a 400mW one. They are cheap too. Make the voltage of the zener 6V which will not damage the battery. The power from such a low power solar array is simply not enough to damage the battery, nor will the battery allow the voltage to go above it's 'normal' charged voltage with such small currents as once a battery reached it's charged status the excess energy supplied goes up as heat within the battery. Once again 300mW really is insignificant.

    You could as is also stated do nothing, probably stated due to the low power of the solar panel, but I'l prefer to err on the side of caution anyway for the cents it will cost for a zener.

    Chris

  19. #19
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    Default Re: Solar voltage limiter?

    With a larger input current, I would use a series pass transistor or in the case of this project that I am working on, I am using a Trace controller

    http://www.tri-met.org/max/yellowlin...quarterart.htm

    But, since your panel is so small - a zener is your cheapest solution

  20. #20

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Burnt_Retinas said:
    Fortunately, the easy fix is the common old "shunt regulator" used with small power solar regulation systems. In simple terms, it is as per Dougs posting - use a zener. There is no diode voltage drop so you'll get maximum voltage. Connect the zener across the panel's output leads. Remember - a zener is connected reversed biased ie the anode to the -ve of the panel and the cathnode (the end with the stripe) to the +ve of the solar panel. Connecting it backwards will short out the battery and burn up the zener.

    The panel is rated at 50mA so this would only be 300mW dissapation maximum when the zener hits it's breakdown voltage at maximum panel current rating. I'd use a 1 watt diode though, rather than a 400mW one. They are cheap too. Make the voltage of the zener 6V which will not damage the battery. The power from such a low power solar array is simply not enough to damage the battery, nor will the battery allow the voltage to go above it's 'normal' charged voltage with such small currents as once a battery reached it's charged status the excess energy supplied goes up as heat within the battery. Once again 300mW really is insignificant.

    You could as is also stated do nothing, probably stated due to the low power of the solar panel, but I'l prefer to err on the side of caution anyway for the cents it will cost for a zener.

    Chris

    [/ QUOTE ]

    Oh...I must have missed something along the way here. So if I put in a 6v zener diode, that will limit it to 6v max, but will not drop the voltage at lower voltages?

    I definately don't want to just use nothing...$200 phone. [img]/ubbthreads/images/graemlins/grin.gif[/img] [img]/ubbthreads/images/graemlins/icon15.gif[/img]

  21. #21
    Flashaholic* star882's Avatar
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    Default Re: Solar voltage limiter?

    "Otherwise, you can easily put a zener diode of the voltage you wish to limit to across the output (suitable power diode of course)."
    You can also use a small zener and a power transistor.

  22. #22
    Flashaholic* Burnt_Retinas's Avatar
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    Default Re: Solar voltage limiter?

    Correct - no voltage loss. The zener is across the panel ie in parallel with the panel. You will only drop volts if a diode is in series with the panel. You WILL NOT loose volts using a zener in parallel with the panel. This is why the shunt regulator is so popular with low power panels. There is NO voltage loss. Higher currents will need different techniques as Inretech states, but this is not the case with your mod at 50mA.

    Remember, the zener must be reversed biased to work, otherwise it's just a *normal* diode and you will short it out with the batteries!

    Chris

  23. #23
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    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Doug Owen said:
    [ QUOTE ]
    Entropy said:
    [What he may need is some sort of switching regulator. I believe NatSemi has some flyback controller chips that are designed to work in situations like this.

    [/ QUOTE ]

    Not really. If you check, the original problem was worry that the solar panel would go overvoltage and kill the cell phone. Such regulators don't work well at reducing voltages.

    I still think the zener's the call.

    Doug Owen

    [/ QUOTE ]
    There are a few switching regulator architectures that work both when Vout<Vin and when Vout>Vin. Some of the NS chips were in this category, and (I believe) dat2zip's Wizard boards are a current-regulated variant of this category.

  24. #24

    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Entropy said:
    [ QUOTE ]
    Doug Owen said:
    [ QUOTE ]
    Entropy said:
    [What he may need is some sort of switching regulator. I believe NatSemi has some flyback controller chips that are designed to work in situations like this.

    [/ QUOTE ]

    Not really. If you check, the original problem was worry that the solar panel would go overvoltage and kill the cell phone. Such regulators don't work well at reducing voltages.

    I still think the zener's the call.

    Doug Owen

    [/ QUOTE ]
    There are a few switching regulator architectures that work both when Vout<Vin and when Vout>Vin. Some of the NS chips were in this category, and (I believe) dat2zip's Wizard boards are a current-regulated variant of this category.

    [/ QUOTE ]

    This much is of course, true. They are not, however, *flyback* converters. Flyback converters depend on the 'inductive kick' from that comes from interrupting the current through an inductor in series with the supply. The induced voltage is then added to the 'battery' voltage. Such circuits don't therefore work as down converters since when the output is lower than supply the transistor never switches but the inductor 'shorts input to output'.

    Again, even if we used the correct type converter for this use, it would be a lot more expensive and less reliable than the zener solution. Right?

    Doug Owen

  25. #25
    Flashaholic* star882's Avatar
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    Default Re: Solar voltage limiter?

    "This much is of course, true. They are not, however, *flyback* converters. Flyback converters depend on the 'inductive kick' from that comes from interrupting the current through an inductor in series with the supply. The induced voltage is then added to the 'battery' voltage. Such circuits don't therefore work as down converters since when the output is lower than supply the transistor never switches but the inductor 'shorts input to output'."
    That's a boost converter, flyback converters are isolated designs and can step either up or down(as an example, I have a PC power supply with a flyback converter that steps 170v down to 12v).

  26. #26
    Flashaholic* Burnt_Retinas's Avatar
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    Default Re: Solar voltage limiter?

    Mike, Inretech,

    What is a "trace controller"? I've not heard of this and would like to know more. Any links to info would be nice.

    Chris

  27. #27
    *Flashaholic* Brock's Avatar
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    Default Re: Solar voltage limiter?

    Trace is a company, now Xantrex actually, anyway they make large charge controllers and voltage regulators. Typically in the 20 to 50 amp range, way overkill and over $ for what we are talking about here. But for large setups they are a lot more common.

  28. #28
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    Default Re: Solar voltage limiter?

    [ QUOTE ]
    Doug Owen said:
    [ QUOTE ]
    Entropy said:
    [ QUOTE ]
    Doug Owen said:
    [ QUOTE ]
    Entropy said:
    [What he may need is some sort of switching regulator. I believe NatSemi has some flyback controller chips that are designed to work in situations like this.

    [/ QUOTE ]

    Not really. If you check, the original problem was worry that the solar panel would go overvoltage and kill the cell phone. Such regulators don't work well at reducing voltages.

    I still think the zener's the call.

    Doug Owen

    [/ QUOTE ]
    There are a few switching regulator architectures that work both when Vout<Vin and when Vout>Vin. Some of the NS chips were in this category, and (I believe) dat2zip's Wizard boards are a current-regulated variant of this category.

    [/ QUOTE ]

    This much is of course, true. They are not, however, *flyback* converters. Flyback converters depend on the 'inductive kick' from that comes from interrupting the current through an inductor in series with the supply. The induced voltage is then added to the 'battery' voltage. Such circuits don't therefore work as down converters since when the output is lower than supply the transistor never switches but the inductor 'shorts input to output'.

    Again, even if we used the correct type converter for this use, it would be a lot more expensive and less reliable than the zener solution. Right?

    Doug Owen

    [/ QUOTE ]
    The circuit you describe is a boost converter (as used in the BadBoy and MadMax boards)

    As another poster mentioned, a flyback regulator has an output that is isolated from the input, and can operate with the output voltage inside the input voltage range. (This is excellent for producing regulated +12V from a car BTW.)

    I would consider an LM2585-based circuit to be more reliable than a zener - Depending on the solar cell, that zener may have to dissipate quite a bit of current. In a case where you're dropping from 8v to 6v, a flyback converter will also be more efficient.

  29. #29
    Flashaholic* Burnt_Retinas's Avatar
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    Default Re: Solar voltage limiter?

    I can hear what everyone is saying re switching regulators etc, and I agree a switching circuit for solar is good, as you can increase the current greater than that available from the panel when the panel voltage is above what you need, but also milk the panel for what it can offer when the voltage is below what you need, but for 50mA really? IMHO a switching circuit just isn't cost vs power effective for a 50mA set-up.

    You can't beat the 100% efficiency of a shunt reg like the zener. Of course this only holds true when the power lost with a shunt reg, when it kicks in, exceeds the power to drive a switching circuit. Keep in mind that even below this level a switching reg will be burning some power!

    Thanks for the "Trace" info too. Any idea what topology they use? Perhaps it's unique, or is it just that they happen to have a product that needs some peoples needs?

    Chris

  30. #30

    Default Re: Solar voltage limiter?

    Alright, I found a solar panel that is rated at 6v/200ma for the same price as the 50ma version. Will this zener diode still work fine at 200ma?

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