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Building my own SMPS

Discussion in 'General Electronics Discussion' started by Kaveyd, Jul 10, 2011.

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  1. Kaveyd

    Kaveyd

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    Jul 10, 2011
    Long Story:
    My cell phone dies. A lot. It's my replacement for a laptop/GPS/MP3 player/calendar/etc so I run out the poor thing's battery usually before 3 PM. I have a large messenger bag which I carry with me, and have been working on various designs for a portable power supply.

    My current ad-hoc supply simply consists of a 12v SLA battery hooked up to a car charger which bravely gave its' life for the cause. The battery is huge and bulky, and the car charger's efficiency is horrific. It uses a brother to the 7805 to simply bleed off all excess voltage as heat and supply 5v to the USB. Unacceptable! (It also has about 100mA of quiescent current, equally intolerable)

    I have a huge excess of NiCd and NiMH batteries, some still wrapped in cute little 7.2 and 9.6v packs. I'd like to get a bunch of these batteries in parallel and use this instead of a big lead brick.

    Short Story:
    I want to build a drop-down SMPS that can handle anything from 7-12 volts and drop it down to 5v with good efficiency (hoping for >90%) and at least 1500mA.

    I understand the concept of the SMPS and how it works, so my question is this:

    Suppose I took a low-amperage SMPS and simply tripled the size of the inductor. Would this allow a greater current flow? I know components inside the IC also have limits, but I would expect them to have higher tolerances than a measly 1500mA.

    Anyone have any suggestions? My current plan has been to buy an IC, follow the datasheet's prescribed circuit, increase the size of the inductor and find out what happens.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No.

    At the very least you would need an inductor of a similar value that would not saturate at the higher current and a pass device that could handle the higher current, also a diode capable of the higher current. The filter capacitors would probably need to be changed to handle the additional ripple current. If the device has a current sense you would need to change that too.
     
    Last edited: Jul 10, 2011
  3. Kaveyd

    Kaveyd

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    Jul 10, 2011
    Please excuse my ignorance, but...

    an inductor's value in henries does not determine where/when it saturates???

    This is news to me. It seems logical that for a higher current I'd need a new set of capacitors and new blocking diode, but there's more to an inductor than its' Henry rating?

    Let me start from the beginning:

    (as far as I know) an SMPS can change voltages via the inductor. Saturate the inductor from your input voltage, then connect the inductor to your output. The inductor attempts to keep current constant, and the voltage changes accordingly.

    Metaphor: Source voltage is a fire hose. Output voltage is a small drain in the bottom of a pool. To maintain an even pressure (voltage) at the drain, switch the fire hose on and off at a regular rate. The pool's water level (inductor saturation) will change, but overall pressure leaving the system is converted from fire hose pressure to drain pressure.

    Using this metaphor, increasing the size of the inductor (pool) allows higher current flow through the drain before water level (voltage) changes. A higher on/off ratio for the fire hose (input) would be required, but more water could flow before the pool is emptied.

    ...is this incorrect? Am I thinking about this the wrong way?
     
    Last edited: Jul 10, 2011
  4. davenn

    davenn Moderator

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    Sep 5, 2009

    increasing the size of the pool is analogous to increasing the voltage. bigger pool... higher voltage potential. its the drain hole at the bottom of the pool that determines the water (current) flow rate

    actually I will rephrase that slightly .......
    indreasing the depth of the pool will increase the voltage potential. keeping the depth (voltage) constant but increasing the area of the pool, will be like increasing the Amp/Hour rating of the battery

    do some google searching on step down buck converters and you will find circuits and ready made units that will do what you want.
    They are compact and highly efficient

    cheers
    Dave
     
    Last edited: Jul 10, 2011
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Saturation is determined by the core of the inductor. Presuming the core is other than air, there is a limit to the maximum flux in the core.

    Keeping everything else equal, increasing the number of turns to increase the inductance will decrease the current at which the core saturates because for a given current, the flux is proportional to the number of turns.

    Worse than that, increasing the inductance will reduce the rate of change of current over time. That means, for a given :eek:n time", the current can not rise as high. This will typically mean the SMPS has to operate at a lower frequency to permit longer ON times (This is not strictly true, but it does affect transient response).

    Generally speaking, higher current SMPS (at least those which have to topology we're talking about) use lower value inductors. Take a look on a computer motherboard and locate the inductor(s) used to generate the low voltage (and high current) core voltages.
     
  6. Kaveyd

    Kaveyd

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    Jul 10, 2011
    Aha! It all starts to fall together now. Thanks for the help and advice - I'll be doing research on some converter ICs, and will be posting more info once I have it.
     
  7. Kaveyd

    Kaveyd

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    Jul 10, 2011
    Update!

    I did some research and bought some components, and am now moving into the build stage for a power supply.
    I ordered the LT1076-5 chip from DigiKey, and although I'm not too thrilled with a nominal 85% efficiency, a 2A output is nice.

    I originally planned to follow the instructions on the chip's datasheet to the letter, but started to question my sanity when I couldn't find any components on DigiKey that fit the bill. Instead of a 200μF capacitor, I had to get a 220μF. The same thing with the 500μF, I have a 550μF instead.

    I'm not freaking out over capacitors that are 10% over recommendations, I'm mostly surprised that DigiKey didn't have such common items in stock!

    Modifications from the original design: instead of a single 550μF capacitor to smooth the output, I'm going to add a few scavenged capacitors from dead electronics. A nice, even power supply is never a bad thing.

    I have one last concern:
    I've heard that board design (keeping traces short) can be critical to making an SMPS work properly and efficiently. Since the LT1076 has pins that don't fit in zeroboard, I'll be drilling my own. I'm not too confident I can get everything to fit together easily and simply...

    But that's for the next update!
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    But... 200uF is not a "common item". 220uF is, because it is in the E12 series of values.

    Note that if you have read the datasheet, then you have been referred to this document also.

    It contains the following sage advice:

    Page 20 is the most important read for you right now as it talks about the capacitors you need. You don't mention that the capacitors are low ESR, and so I'll assume the ones you have are not. Low ESR caps have a limited life, and I would not advise you to salvage them.
     
  9. Kaveyd

    Kaveyd

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    Jul 10, 2011
    Thanks for the reference - I had actually never seen that guide before and it has been very helpful!

    It was a bit of an epiphany when I realized that the size of the input capacitor was irrelevant because it is largely resistive at the chip's operating frequency... Thus the ESR is the deciding value. So simple, yet so easy to miss.

    Attached is a photo of a 'dry run' I did, simply putting all the components in place to verify they will fit. Since the board is mostly just getting in my way, I think I will wire the circuit point-to-point and then embed it in epoxy resin to prevent short circuits. (Just in case of failure, the caps will not be permanently embedded)

    [​IMG]

    Thoughts? You have been incredibly helpful, I can't thank you enough!
     
    Last edited: Jul 18, 2011
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I would use the matrix board to provide some rigidity. I'm hoping that you're not suggesting that you'll make it "dead bug" style.

    Potting is not a bad idea, but beware that it prevents free airflow and thus may compromise cooling. Also note that capacitors have a life (and not a long one) in applications like this, and you may wish to allow them to be replaceable.

    You may be well advised to place some small (say 0.1uF) capacitors in parallel with your larger capacitors. Check with the application notes however, some devices get a bit sad if the output capacitors have too low an ESR.
     
  11. Kaveyd

    Kaveyd

    15
    0
    Jul 10, 2011
    Wired the circuit up, dead bug style. Right now it looks like a bird's nest of wires, but there are no shorts and the wire is fairly rigid.

    Initially I had trouble in getting the circuit to work, it output ~0.5V below the input... Then I discovered I'd placed a filter capacitor incorrectly. One quick fix, and now we are happily outputting 5.81V nice and smooth.

    Tomorrow I will upload photos and data from an efficiency test. Stay tuned!

    RE your advice: I plan to pot the lower half after mounting it in a large heat sink. The top half contains the capacitors, so replacing them will remain possible. I attempted to look up their datasheet and was dismayed to find nothing at all! I anticipate replacing these caps with low-ESR ones soon.
     
  12. Kaveyd

    Kaveyd

    15
    0
    Jul 10, 2011
    Efficiency test completed, with disappointing results.

    In the absence of any nice tools or probes, I simply connected a brand new Duracell 9V battery (a known capacity) to the chip, then used the output to charge my phone. My phone records mA data and battery % in a CSV file, which I can then integrate to find the total power output by the circuit.

    In theory, this would work great. In reality, it either didn't work or my circuit is FUBAR.

    CAVEAT:
    This is just me, stabbing around with numbers and doing what seems logical. I don't know if what I'm doing is correct, accurate or even wise. But I'm trying!
    With data this radical, I'm going to run more tests to see if I can confirm the results.

    I tested the battery, fresh out of the box. 9.25V.
    Before I disconnected the circuit, the working voltage left was 6.5V.
    Simple math implies that the battery's average in-use voltage was 7.875V.
    The next morning, the 9V battery had recovered back up to 8.4V. (Just in case you cared)

    The average charging rate was a measly 260mA.
    260mA at 5V transforms into into 1300mW.
    At 7.875V, 1300mW transforms into 165mA.

    The ∑mA given to the phone is 134.9mAh.
    134.9mAh at 5V transforms into 674.5mWh.
    At 7.875V, 674.5mWh transforms into 85.65mAh.

    At 100mA, a 9V Coppertop should output a little over 300mAh (source).
    85/300 = 28.5% efficiency! Horrifying.

    Oh, by the way. Photos attached.


    Here's the CSV data, in case you're interested:
    Code:
    DATE | TIME | mA | % | V | TEMP | ASLEEP | ???
    2011/07/20|19:30:10|-3mA|16%|3679mV|32.5ºC|2|2
    *** Charging begins.
    2011/07/20|19:31:10|567mA|16%|3679mV|32.5ºC|2|1
    2011/07/20|19:32:10|480mA|17%|3776mV|32.3ºC|0|1
    2011/07/20|19:33:10|472mA|18%|3776mV|32.1ºC|0|1
    2011/07/20|19:34:10|465mA|18%|3776mV|32.1ºC|0|1
    2011/07/20|19:35:10|271mA|18%|3776mV|32.1ºC|0|1
    2011/07/20|19:36:10|262mA|19%|3747mV|31.2ºC|0|1
    2011/07/20|19:37:10|257mA|19%|3747mV|31.2ºC|0|1
    2011/07/20|19:38:10|261mA|20%|3762mV|30.6ºC|0|1
    2011/07/20|19:39:10|258mA|20%|3762mV|30.6ºC|0|1
    2011/07/20|19:40:10|257mA|20%|3762mV|30.6ºC|0|1
    2011/07/20|19:41:10|255mA|20%|3762mV|30.6ºC|0|1
    2011/07/20|19:42:10|254mA|21%|3771mV|30.0ºC|0|1
    2011/07/20|19:43:10|249mA|21%|3771mV|30.0ºC|0|1
    2011/07/20|19:44:10|250mA|21%|3771mV|30.0ºC|0|1
    2011/07/20|19:45:10|248mA|22%|3781mV|29.6ºC|0|1
    2011/07/20|19:46:10|247mA|22%|3781mV|29.6ºC|0|1
    2011/07/20|19:47:10|241mA|22%|3781mV|29.6ºC|0|1
    2011/07/20|19:48:10|238mA|22%|3781mV|29.6ºC|0|1
    2011/07/20|19:49:10|242mA|23%|3791mV|29.2ºC|0|1
    2011/07/20|19:50:10|240mA|23%|3791mV|29.2ºC|0|1
    2011/07/20|19:51:10|239mA|23%|3791mV|29.2ºC|0|1
    2011/07/20|19:52:10|238mA|24%|3796mV|29.0ºC|0|1
    2011/07/20|19:53:10|233mA|24%|3796mV|29.0ºC|0|1
    2011/07/20|19:54:10|228mA|24%|3796mV|29.0ºC|0|1
    2011/07/20|19:55:10|233mA|25%|3806mV|28.7ºC|0|1
    2011/07/20|19:56:10|231mA|25%|3806mV|28.7ºC|0|1
    2011/07/20|19:57:10|230mA|25%|3806mV|28.7ºC|0|1
    2011/07/20|19:58:10|224mA|25%|3806mV|28.7ºC|0|1
    2011/07/20|19:59:10|163mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:00:10|59mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:01:10|2mA|26%|3767mV|28.5ºC|0|1
    *** Charging ends.
    2011/07/20|20:02:10|0mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:03:10|-4mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:04:10|-14mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:05:10|-10mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:06:10|-10mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:07:10|-9mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:08:10|-13mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:09:10|-17mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:10:10|-20mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:11:10|-11mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:12:10|-12mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:13:10|-14mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:14:10|-18mA|26%|3767mV|28.5ºC|0|1
    2011/07/20|20:15:10|-30mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:16:10|-21mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:17:10|-20mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:18:10|-23mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:19:10|-27mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:20:10|-34mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:21:10|-28mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:22:10|-26mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:23:10|-29mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:24:10|-33mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:25:10|-35mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:26:10|-35mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:27:10|-38mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:28:10|-32mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:29:10|-33mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:30:10|-36mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:31:10|-47mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:32:10|-39mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:33:10|-47mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:34:10|-39mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:35:10|-43mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:36:10|-45mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:37:10|-44mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:38:10|-48mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:39:10|-41mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:40:10|-41mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:41:10|-43mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:42:10|-46mA|25%|3762mV|27.8ºC|0|1
    2011/07/20|20:43:10|-45mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:44:10|-42mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:45:10|-43mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:46:10|-44mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:47:10|-48mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:48:10|-48mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:49:10|-61mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:50:10|-45mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:51:10|-46mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:52:10|-46mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:53:10|-49mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:54:10|-54mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:55:10|-46mA|24%|3737mV|27.2ºC|0|1
    2011/07/20|20:56:10|-47mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|20:57:10|-48mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|20:58:10|-51mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|20:59:10|-53mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:00:10|-48mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:01:10|-49mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:02:10|-49mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:03:10|-53mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:04:10|-58mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:05:10|-50mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:06:10|-50mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:07:10|-50mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:08:10|-50mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:09:10|-52mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:10:10|-56mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:11:10|-51mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:12:10|-51mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:13:10|-51mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:14:10|-56mA|23%|3728mV|27.1ºC|0|1
    2011/07/20|21:15:10|-61mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:16:10|-53mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:17:10|-50mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:18:10|-53mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:19:10|-55mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:20:10|-61mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:21:10|-53mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:22:10|-53mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:23:10|-53mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:24:10|-58mA|22%|3718mV|27.0ºC|0|1
    2011/07/20|21:25:10|-59mA|21%|3713mV|27.0ºC|0|1
    2011/07/20|21:26:10|-59mA|21%|3713mV|27.0ºC|0|1
    2011/07/20|21:27:10|-58mA|21%|3713mV|27.0ºC|0|1
    2011/07/20|21:28:10|-54mA|21%|3669mV|27.0ºC|2|2
    2011/07/20|21:29:10|-204mA|21%|3669mV|27.0ºC|1|0
    2011/07/20|21:30:10|-74mA|21%|3674mV|27.0ºC|2|2
    2011/07/20|21:31:10|-219mA|21%|3679mV|27.1ºC|2|2
    2011/07/20|21:32:10|-220mA|21%|3679mV|27.1ºC|2|0
    2011/07/20|21:33:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:34:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:35:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:36:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:37:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:38:10|-2mA|21%|3679mV|27.1ºC|0|0
    2011/07/20|21:39:10|-31mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:40:10|-7mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:41:10|-9mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:42:10|-9mA|20%|3708mV|26.8ºC|0|0
    *** I suspect this is the phone entering 'hibernate mode'
    2011/07/20|21:43:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:44:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:45:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:46:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:47:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:48:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:49:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:50:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:51:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:52:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:53:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:54:10|-51mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:55:10|-9mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:56:10|-9mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:57:10|-9mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:58:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|21:59:10|-5mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:00:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:01:11|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:02:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:03:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:04:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:05:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:06:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:07:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:08:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:09:10|-14mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:10:10|-8mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:11:10|-8mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:12:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:13:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:14:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:15:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:16:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:17:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:18:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:19:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:20:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:21:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:22:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:23:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:24:10|-10mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:25:10|-14mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:26:10|-18mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:27:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:28:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:29:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:30:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:31:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:32:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:33:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:34:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:35:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:36:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:37:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:38:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:39:10|-13mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:40:10|-7mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:41:10|-10mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:42:10|-10mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:43:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:44:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:45:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:46:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:47:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:48:10|-2mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:49:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:50:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:51:10|-2mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:52:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:53:10|-1mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:54:10|-13mA|20%|3708mV|26.8ºC|2|0
    2011/07/20|22:55:54|-8mA|20%|3708mV|26.8ºC|2|0
    2011/07/20|22:56:10|-8mA|20%|3708mV|26.8ºC|0|0
    2011/07/20|22:57:10|-8mA|20%|3708mV|26.8ºC|0|0
    *** I turn on the phone and examine it.
    2011/07/20|22:58:10|-186mA|20%|3708mV|26.8ºC|2|0
    2011/07/20|22:59:36|-96mA|20%|3708mV|26.8ºC|2|0
    2011/07/20|23:00:10|-8mA|19%|3698mV|25.5ºC|2|4
    2011/07/20|23:01:10|-178mA|19%|3664mV|25.7ºC|1|2
    2011/07/20|23:02:10|-193mA|19%|3659mV|26.0ºC|1|2
    2011/07/20|23:03:10|-201mA|19%|3654mV|26.2ºC|1|
    *** The phone is now plugged into a charger.
    2011/07/20|23:04:10|449mA|19%|3654mV|26.2ºC|1|1
    2011/07/20|23:05:10|566mA|20%|3820mV|27.0ºC|2|1
    2011/07/20|23:06:10|568mA|20%|3820mV|27.0ºC|0|1
    2011/07/20|23:07:10|567mA|21%|3840mV|27.2ºC|0|1
    2011/07/20|23:08:10|564mA|22%|3850mV|27.5ºC|0|1
    2011/07/20|23:09:10|566mA|23%|3855mV|27.5ºC|0|1
    2011/07/20|23:10:10|566mA|23%|3855mV|27.5ºC|0|1
    2011/07/20|23:11:10|564mA|24%|3864mV|27.5ºC|0|1
    2011/07/20|23:12:10|565mA|24%|3864mV|27.5ºC|0|1
    2011/07/20|23:13:10|565mA|25%|3874mV|27.7ºC|0|1
    2011/07/20|23:14:10|564mA|26%|3884mV|27.7ºC|0|1
    2011/07/20|23:15:10|563mA|27%|3889mV|27.7ºC|0|1
    2011/07/20|23:16:10|564mA|27%|3889mV|27.7ºC|0|1
    2011/07/20|23:17:10|561mA|28%|3894mV|27.7ºC|0|1
     

    Attached Files:

    Last edited: Jul 22, 2011
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,489
    2,830
    Jan 21, 2010
    A type 216 battery I suppose?

    Wow. That's actually quite impressive. I'm surprised the 9V battery could deliver quite so much power.

    However to measure efficiency properly, you need to measure the voltage and current into the regulator. You can't just assume what it is.

    Those small 9V batteries have quite a small capacity. Do some googling and find out what it is for your make/model of battery and compare it to the rating of the battery in your phone.
     
  14. Kaveyd

    Kaveyd

    15
    0
    Jul 10, 2011
    Unfortunately, I have no tools that can measure >200mA - so my tests are doomed to always have a fuzzy margin of error.

    Ran a second test, more detailed this time. I put 8 brand new NiMH AA batteries (2500mAh) in a pack and charged the phone, measuring the pack's voltage during use. Results are still disappointing, but better.

    I have two batteries for the phone, so I simply drained both and swapped them once the first was fully charged.

    Knowing the pack's voltage allows me to convert the output (known current and voltage) into watts, then convert back into current from a battery pack of known voltage. Since the batteries *should* contain 2500mAh, the final results give me a loss ratio.

    I'm again posting from my phone, so I can't provide detailed calculations, but the total output was ~1250mAh, or 50% efficiency.

    Photos ahoy:
     

    Attached Files:

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