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Can I use a NiMH battery in a NiCad charger?

Discussion in 'Power Electronics' started by moeburn, Jul 31, 2013.

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  1. moeburn

    moeburn

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    Jun 25, 2012
    Hello!

    I'm trying to make something useful out of this solar-powered outdoor night light, and I thought maybe turn it into a solar powered flash light, by using a bigger battery and a brighter LED. Could I just switch out the NiCad in the circuit for a NiMH, or do they charge differently?

    The battery that it came with is a 350mAh NiCad, and it uses a very very simple charging circuit (a single 4 pin chip, a N5819 schottky diode, and resistor).

    I think the diode is a blocking diode, to prevent the battery from discharging through the solar panel at night, but the chip doesn't appear to be a "battery charging" chip, it seems to be specifically designed for solar panels.

    It appears there is also supposed to be a 470uH inductor in the circuit, but there isn't one in mine. Here's the info I could find on the chip, but it was in Chinese:

    [​IMG]

    "Solar Lawn Light Controller ANA608-6
    Product Overview:
    Solar Lawn main use solar energy to work, when the day sunlight on the solar cell, the light energy into electrical energy stored in batteries, and then in the evening for the lawn by the battery LED (light emitting diode) to provide power supply."

    "Current regulation Reference: inductance value can be changed by changing the size of the input current, the inductor current relationship with the input reference to the following table: Inductance 150uH 100uH 82uH 47uH input current (input voltage 1.30V) drive white LED 11-13mA 18-21mA 22 -25mA 29-34mA Driver yellow LED when 11-13mA 20-24mA 24-27mA 30-35mA"
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    This is just a trickle charge at the max rate that the solar cell can provide, which is probably not much. So, yes, you could charge a NiMH battery the same way. A larger capacity battery might takes days to charge though.

    Bob
     
  3. moeburn

    moeburn

    41
    0
    Jun 25, 2012
    Thanks for the help!

    Yeah, I tested the panel connected to a 3v LED, and in max sun I only measured 5mA being drawn, the LED was pretty dim. Although that's why we use a battery. And it may take days to charge, but this flash light would only be used for a few minutes each day, perhaps it would be a brighter/higher current led than theirs, but I still think there would be a greater total charge each day than there would be total discharge.
     
  4. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    In that case, why do you need a larger battery?

    Bob
     
  5. moeburn

    moeburn

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    0
    Jun 25, 2012
    A) because i have a spare unmatched 1700mAh NiMH lying around, and it doesn't have a matching friend, and I don't have any other devices that can use just one AA, so I may as well use it in SOMETHING

    B) Because while it won't be used very often for very long (just to get me to and from garage at night, as well as to and from bathroom without tripping over cats), it would still be nice to know that if I needed to, I could use it for an hour or two, just in case the power goes out (happens often because we are on a buggy grid-tie solar gen system) AND we happen to be all out of alkaline AAs (also happens surprisingly often)
     
  6. BobK

    BobK

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    Jan 5, 2010
    Okay.

    Do you plan to use the entire circuit, and just replace the battery? Because a 1.2V battery will not run and LED without a boost converter.

    Bob
     
  7. moeburn

    moeburn

    41
    0
    Jun 25, 2012
    It won't run my 3v high brightness LEDs anyway. I'm not sure if I plan on just replacing the battery, or replacing the battery and the LED. Because their included LED is a 1.2v white, but I don't think it is bright enough for a flash light, I'll have to wait until night to see for sure.

    I would imagine I shouldn't try to get this circuit to charge TWO batteries, since I don't know if the IC can run at 2.4v, and I don't know if that schottky diode will be effective at 2.4v.
     
  8. BobK

    BobK

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    Jan 5, 2010
    There is no such thing as a 1.2V white LED, they are in the range of 3 to 3.6V typically. The chip includes a boost converter to up the voltage to drive the LED. That is why there is an inductor.

    Bob
     
  9. moeburn

    moeburn

    41
    0
    Jun 25, 2012
    Ah, ok, my bad. lol, I should have known, the schematic that I posted myself actually says their LED is 3.5-4v. Well boy do I feel like a knob.

    But there's no inductor on my circuit. Just the IC, a diode, and a 220 or 210 ohm 10% resistor, depending on if its red red brown, or red brown brown, i can't tell. Unless that resistor is the inductor, it is soldered into a hole labelled "L1", but I've never seen an inductor in a resistor-looking package before. It looks the exact same as the one in the picture in my first post, except the stripe colours are different.

    There's also a big unused square on my circuit, with 4 unused throughholes, labelled "S1". But it's not the solar panel voltage input, because that is labelled "S+"
     
    Last edited: Aug 1, 2013
  10. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Inductors do come in that kind of package, complete with color code. The one in the picture read 470, which matches the 470uH inductor in the schematic.

    Bob
     
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