Email Detail

HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/NQOCIWYD722G4JX7MGZPJIUEJZFA3H7B/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "NQOCIWYD722G4JX7MGZPJIUEJZFA3H7B",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/FEXPG4RQD7ZO6OKCJGXPWK2R5QC6BZSW/?format=api",
    "sender": {
        "address": "karn (a) philkarn.net",
        "mailman_id": null,
        "emails": null
    },
    "sender_name": "Phil Karn",
    "subject": "[amsat-bb] Re: ARISSat-1 battery eclipse voltage decreasing",
    "date": "2011-08-14T02:56:15Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/4NSUMODGP55HMBJSVGDNBSCQQKTBLKPB/?format=api",
    "children": [
        "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/BKF5H2VK276YBEFJBYTHMTMOZLDVOV4V/?format=api"
    ],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 8/13/11 6:11 PM, Dave Guimont wrote:\n\n> How about you designing circuitry/program to charge \"cells\" individually\n> rather than the \"battery\".  Or has that been tried??\n\nThat's a great idea; I wish I thought of it first, but it was Lou\nMcFadden W5DID who published a paper at the AMSAT Symposium a few years\nago on a new modular power system.\n\nHis idea was to turn each cell into an intelligent energy storage module\nand to connect those modules in parallel to a power bus. There'd be a\nDC-DC converter between the cell and the bus so they could operate at\ndifferent voltages. If the cell in one module failed, it would\ndisconnect itself from the bus instead of dragging it down.\n\nHe found it a challenge to achieve high efficiency in the DC-DC\nconverter with low voltage batteries. For the lower voltage chemistries\n(e.g., NiMH at 1.2 V) it might be necessary to compromise by using two\nor maybe three cells in series per module. A lithium ion module would\nneed only one cell since they operate at a much higher voltage of 3.6V.\n\nThe beauty of his scheme is that not only would this be far more robust\nagainst individual cell failures than a single series string, you could\nfly several kinds of batteries to see which functions best.\n\nWith the proper command to a module controller you could perform a\ncontrolled discharge of its cell for a capacity test. That's kinda neat.\n\nSome modules could use supercaps. They have very high cycle lives\n(~500,000) but low energy density (0.35 watt-hour for a D-cell sized\ncap). You'd always discharge them first, or perhaps keep one in reserve\nto keep a computer going. Since they're capacitors you'd need the DC-DC\nregulator to produce a constant voltage as they discharge.\n\nThinking more about his scheme, you could program each module with a\ncommand like \"Keep the power bus at +12V by pumping up to 2A into it\nuntil you're 50% depleted\" or \"charge at 1A max unless the bus voltage\nfalls to 11.5V\". The computer could issue a new command at any time,\nsuch as one to stop all charging when the satellite enters eclipse.\n\nOne module might contain just a load resistor to act as a shunt\nregulator to keep the bus voltage from going too high.\n\nAnd one or two modules might contain high-density (e.g., lithium)\nprimary batteries as emergency fallbacks to keep things going long\nenough for the command stations to figure out what's going on.\n\n-Phil\n\n\n",
    "attachments": []
}