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HID light design

Discussion in 'Electronic Design' started by [email protected], Feb 16, 2007.

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  1. Guest

    Hello- I'm interested in building my own High Pressure Sodium lamp as
    a project. I've already designed a light reflector and mounted my
    mogul base to it, and insalled the bulb and so on. All I really want
    to know is if there's a way to cheap out on the ballast and ignitor. I
    know I can just buy the ignitor for pretty cheap but is there an
    easier way to simply substitute an iron core transformer from
    something else instead of paying up to 50 bucks for one online? I know
    the output has to be something like 4kv pulsed or something. Does
    anyone know what the requirements would be. Maybe if someone just knew
    what kind of transformer would be needed (example- how many turns
    primary and secondary, impedance in henries, resistance of the coils
    etc) in terms of electrical specifications. Also please note the
    circuit is to run on 120VAC. Thanks in advance -Carl
  2. For what? The ballast or the ignitor?

  3. I'd like to set up an outdoor thermometer. I have a decent location under a
    carport on the N side of the house. I've had a jumbo needle thermometer
    there for years, but its accuracy has always left something to be desired.
    A year ago, I purchased a cheap, wireless digital thermometer from Walmart.
    I didn't think I could mount the wireless sensor outside in place of the
    jumbo thermometer because it didn't look weatherproof to me, plus it used a
    battery, so I placed the sensor in a shed, also on the north side, and in a
    spot where there was ventillation. However, after about 3 weeks, the unit
    stopped working probably due to dead batteries.

    I'd like to find out my options. How can I get around the battery problems
    as I suspect temp extremes, etc causes failure quickly. And I'd like to be
    able to place the sensor in the location of the jumbo thermometer as I think
    the readings would have more accuracy there. I really can't run a wired
    sensor either.

    Thanks in advance.
  4. Buy better batteries?

  5. D from BC

    D from BC Guest

    Here's my wild idea...:)

    Find the solar rechargeable garden light and install the wireless temp
    sensor inside. Might be available at Walmart too...
    Figure out how to adapt the power.. Disconnect the light if needed.
    You get a bonus too..
    The garden light is designed be weatherproof.. :)
    D from BC
  6. Guest

    Get a Micro Temp Digital Infrared Thermometer from Cabelas and take
    the temp readings from a distance.
  7. D from BC

    D from BC Guest

    I checked the link..
    Taken from site:
    "Easily determine the temperature of anything
    Quickly canvas a stream or lake
    Determine hatches, spawning and feeding periods
    Countless other uses "

    I'd like to fill in the part about countless other uses :)

    Use it to stay away from sick people with flu fever.
    Use it as a rage meter when you piss the boss off..
    Use it to play hide and go seek in the dark..
    Check if that dried up pizza in the "by the slice" display is at food
    safe temperature..
    D from BC
  8. Guest

    On topic uses;
    1.) measure temperature of components on pcb.
    2.) determine if blower fan is actually cooling components in chassis
    3.) check if you left your soldering iron on without going back to the

  9. Guest

    BTW, DO NOT USE to measure temperature on aircraft flying overhead.
    That causes black helicopters to circle your house.
  10. ehsjr

    ehsjr Guest

    Don't know what went wrong with your
    theremometer, but it is unlikely that
    it would run good batterys down in 3
    weeks, unless something is defective.

    Here's a possible replacement:

    (watch out for line wrap in the above)
    I just ordered one, so I don't know how good it is.

    The site claims ~ 1 year life for the batteries. If that
    still is an irritation to you, you could try using NiCd's
    connected to a solar cell through a diode. There is a
    cheap solar light availalable at
    catalog # SPL-05 for $4.50. You could use the solar
    cells from that to charge the shed located thermometer
    sensor NiCd batteries.

  11. Dennis

    Dennis Guest

    I have an Oregon Scientific one that has been running over a year on its
    set of batteries. I use lithium batteries since this is in Minnesota.
    batteries will quit at about -4F, the lithium ones will go to at least -20F.
  12. 1. Quite a bit of the time in English-speaking portions of North
    America, outside the automotive industry, what technical types call a
    "lamp" is what non-technical types and auto industry types in Anglo North
    America call a "bulb".

    2. You wanna make your own ballast?

    Easier HPS ballasts for 120 volts AC are for wattages 35, 50, 70 and 100
    and the S55 version but not the S56 nor the H39-compatible version of
    150-watt. Easier ballast compatibility codes here are S76 (for 35 watt),
    S68 (for 50 watt), S62 (for 70 watt), S54 (for 100 watt), and S55 (for the
    easier 150 watt).

    Restrict yourself to one of these, disassemble a nice big heavy iron
    core transformer suitable for wattage at least that of your lamp, get an
    ignitor, find a place to get at least half a pound maybe a pound of magnet
    wire of all sizes mid-teens to low 20's, learn/know how to wind
    transformers and iron core inductors, then get back to me at
    However, I doubt you will make minimum wage or even half that using your
    effort to save on the cost of a commercially available ballast. I know
    how to make one, and I suspect I can make more money per hour picking
    up littered beverage cans for scrap aluminum value than I can save by
    hand-making an HPS ballast in place of buying one.

    - Don Klipstein (Jr) ()
  13. Guest

    What I mean to say is this: Most commercially available units at your
    local hardware store use an iron core transformer as the ballast, so
    isn't there a readily available piece of junk electronic device (such
    as an old tv or something) that I can hack open and grab a transformer
    from that will work? How about a flyback transformer. Or a step down
    transformer from a power supply (like out of a vcr or something) used
    in reverse with the output coil as the input coil instead. I'm not
    sure what is electronically required to light a 70w or 150w HPS light
    bulb, I think it's something like 4kv at low current to sustain the
    arc, and the ignitor is some sort of bimetal or capacitor used to
    create a pulse initially to start the arc. That said, I can get the
    ignitor, bulb and all other nessecary hardware, so I don't even really
    need to know much about that. What I need are some clues as to exactly
    what kind of transformer is needed. I'm pretty sure it can't be too
    tough. Aren't there some tolerances and forgiveness involved so as to
    allow me to make a direct substitution from somewhere else without
    causing a serious safety issue? -Evan
  14. joseph2k

    joseph2k Guest

    Part of what we are trying to tell you is that ballast transformers are the
    only thing like ballast transformers. About the only people who know how
    to design them are the industry insiders who design them. They bring in
    and train new ones about once a decade (for each of the major
  15. You ain't gonna make a 60 Hz ballast for an HPS lamp with a piece of
    ferrite that small. Easiest hack from a junk TV is if you can find a
    vacuum tube one and find the vertical output transformer. A decent iron
    core one in a vacuum tube TV set will have a core 2.375 or 2.625 or 3
    inches long, 3/4 to 1 inch wide, and about 1.98-2.5 inches tall (plus
    perhaps 1/16 inch each way for the mounting fitting whatever they call
    that). Those have E-I cores, and are easier to hack than most iron-core
    transformers with E-I cores since these are gapped and have all of the E
    pieces together and all of the I pieces together, AND these usually do not
    have any welds. (Many ballasts have welds.) Most other iron core
    transformers have the E pieces and I pieces interlieaved, and at least
    sometimes maybe often glued or at least effectively glued by some glop or
    None of these will work without serious modifications, many will not
    work even with any possible modifications, and most are not that easy to
    That is to start the arc. More typical is 4 KV repeated pulses.
    Capacitor and a triac and a few other bits.
    Let's suppose you get an E-I core with 1 square inch center leg, overall
    dimensions 3 by 2.5 by 1 inches. That may come from a 26 inch color
    vacuum tube TV vertical output transformer, or that transformer may have a
    core a little smaller.

    Start with typical lamp voltage of 55 volts and typical line voltage of
    120 volts and a design of simple series inductor ("reactor") ballast.
    Voltage across the ballast steady-state is ideally square root of line
    voltage squared minus lamp voltage squared, meaning 106.6 volts ideally.
    Resistive losses in the ballast screw this up a bit to voltage across the
    ballast being less, but I think to about the same extent you need to plan
    for high line voltage and low lamp voltage - so plan for 106 volts.

    I have heard 12,000 gauss as being a reasonable design for peak magnetic
    flux density in steady state operation of an iron core magnetic component
    of such size using older type core materials. You can probably get away
    with 12,500 maybe 13,000, but I would avoid aggressive operation of a
    homebrew device for long where it is not under supervision. 1 square inch
    is 6.45 square centimeters. 12,000 times 6.45 times times 60 times 2
    times pi is 2.918 abvolts per turn peak. (The abvolt is CGS system
    voltage unit where K-prime is 1.) Divide abvolts by 1E-8 to get volts,
    and divide by SQR(2) to get RMS volts per turn - that is .206 volts per
    turn. For 106 volts, this means you need 514 turns for conservative
    operation, 475 turns even for aggressive operation.

    The window in a 3 x 2.5 x 1 inch E-I core with 1 inch wide center leg is
    1.5 by .5 inches. The largest size magnet wire that will fit that many
    turns even theoretically with typical insulation thickness is AWG 21, so
    optimistically you could cram in that many turns AWG 22. Kep in mind,
    the winding has to generate 4KV pulses, so you need thin insulation
    between layers (in addition to the coating that magnet wire has) plus
    some decent insulation between the core and the widning.

    I will continue the design process assuming that you manage to get 22
    AWG wire to fit. I give enough info below to let "someone skilled in the
    art" to redesign for a 35 watt HPS lamp without going astray enough to
    cause an actual problem should 23 AWG wire be required.

    For overall heating concerns, I would design for 12,500 gauss peak at
    most (494 turns) and allow at most 5 watts of heat to be generated by
    winding resistance when the winding resistance is elevated to what it
    would be at 100 degrees C. In fact, I would rather not exceed 4 watts
    winding resistance heating in a component of this size. 22 AWG
    copper wire resistance at that temperature close enough to 1 ohm per 50
    feet. The average turn in a half inch wide window on a 1 inch square
    center leg has four segments 1 inch long and four 1/4-circle segments of
    1/4 inch radius or .3927 inch ech, for average turn length of 5.571
    inches. 494 turns at this rate is 229.3 feet, worth 4.59 ohms. The
    roughly 1 amp typical current of a 50 watt HPS lamp means roughly 4.59
    watts of heat from winding resistance - borderline good for 50 watt
    and no way for 70 watt unless you have some really high temperature magnet
    wire and insulation (in which case you may be good with the roughly 1.4
    amps of 70-watt).

    Lamp amps is normally a bit more than ratio of lamp watts to lamp volts
    since the lamp (bulb) has power factor a bit less than 1 due to the arc
    characteristics causing distortion of voltage and current waveforms.

    So, let's go for the 50 watt lamp. Lamp voltage is nominally 55 volts
    steady-state (varies widely with age and condition for that matter). I
    guesstimate lamp power factor of .95 - 50 divided by 55 and divided by .95
    is .957 amp.

    Now for typical ballast voltage: I guesstimate 80 degree phase angle
    between lamp voltage drop and ballast voltage drop (ideally this is 90
    degrees). The ballast has voltage drop leading current by a few degrees
    less than 90 and the HPS lamp's arc has voltage drop leading current by a
    couple to maybe a few degrees.

    Cosine law is that line voltage squared is ballast voltage
    squared plus lamp voltage squared plus twice the cosine of phase angle
    times product of lamp and ballast voltages. Using 120V line voltage, 55
    volt lamp voltage, and my guesstimate of 80 degrees, the voltage drop
    across the ballast to the nearest volt is 99 volts. Divide by .957 amp
    and the ballast requires impedance of about 103.5 ohms.
    Assume the ballast has VA (volt-amps) of 99 times .957 or about 95, and
    6 watts actual power dissipation. This is getting to be an educated guess
    of mine, but I consider it reasonably accurate. Arc-cosine of 6/95
    is 86.379 degrees, sine of which is .998 so voltage across the inductive
    reactance is close enough to 99.8% of the total voltage across the ballast
    so basically unchanged from the above 99 volts to whatever extent that
    above 99 volts is a good figure for voltage across the ballast. That
    means inductive reactance is down only .2% from the 103.5 ohm ballast
    impedance that I got above (or from whatever it actually should be - close
    enough for an HPS lamp), so go for 103.3 ohms.

    103.3 ohms inductive reactance divided by 2, pi and 60 means inductance
    of .274 henry.

    Now, designing a gap to make this thing achieve an inductance of .274

    Inductance of a gapped inductor in abhenries (CGS inductance unit
    with K-prime being unity, which is conveniently same as nanohenries) is 4
    times pi times magnetic path cross section area times square of number of
    turns divided by effective gap thickness.

    .274 henry is 274,000,000 abhenries. Divide by square of above 494
    turns to get inductance of a 1-turn winding on same core with same gap, or
    1122.785 abhenries. Divide by core cross section area of 6.45 square
    centimeters, and that is 174.089 abhenries if gap is unchanged but
    magnetic cross section is reduced to area of 1 square centimeter. Divide
    by 4 and pi to get reciprocal of effective gap in centimeters being
    13.8536 or effective gap thickness in centimeters of .0721836.

    Next step - consider effective gap thickness of the core material. Go
    along the centerline of a path through half of this core and that is 4
    inches or 10 centimeters, a bit less considering rounding of flux paths
    turning through corners, so I would say 9.5 centimeters. Divide that by
    the permeability of the core material to get effective gapping of the core
    material itself - I am falling short of citable numbers here but I pull
    out of a hat 20,000. This means that the core accounts for .000475
    centimeter of gap, subtract that from .0721836 to get .0717 centimeter of
    required actual gap.

    Since a gap between an E-stack and an I-stack is crossed by magnetic
    flux twice, you need your gap between the E-stack and the I-stack to be
    half this, or .03585 centimeter or .3585 millimeter. It is fair to round
    this to .36 millimeter since an HPS lamp can easily tolerate power input
    being 10% off in either direction.
    4 sheets of 20-pound copier paper appears to me to be "in-range" here.

    There is another step: The winding needs a tap at roughly the 4% point
    (20 turns from one end of the winding I think) for the ignitor to make
    this ballast generate a 3-4 KV starting pulse. The tap should be close to
    whichever endpoint of the ballast has skimpiest insulation from the core,
    since the high voltage with respect to everything else will be at the
    other end of the winding. Given convenience of putting the tap in an
    outer layer of the winding, you need the inner layers of the winding
    adequately insulated from the core for the full 4KV.


    So, if you pull this off, what do you get? A homebrew ballast! It is
    not certified by UL or whatever other organization that does safety
    testing that could cost $$$$$! This means extra liability should a fire
    worth an insurance claim start at this thing, even if the fire started for
    a reason other than flaws in design or construction.

    MY WARRANTY: If anything goes wrongo, blammo or blooie or if any fire
    problems arise or if anyone gets electrocuted or so much as shocked into
    breaking someting (including body parts) or falling off a ladder or
    anything else even somewhat along these lines goes wrong from someone
    using info that I posted, I will refund what I got paid for posting this
    and no more. Info here is worth education only, and putting it into
    application has (maybe at best) risks typically adequately mitigated by
    having devices (whether or not made using info like that above) passing
    actual certification testing by a recognized safety certification body
    such as UL or CSA.
    If you want a ballast that does not require constant supervision by
    qualified technical personnel on hand to quickly disconnect power and
    quickly hit it with a sufficiently convenient and suitable fire
    extinguisher with both A and B ratings and to do adequately quickly
    whatever else ends up being necessary should the ballast go blooie, then
    don't homebrew it but buy something approved by UL, CSA or whatever.

    - Don Klipstein ()
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