Resitor Help Needed

Discussion in 'General Electronics Chat' started by gregkinder, Jan 27, 2013.

  1. gregkinder

    Thread Starter New Member

    Dec 25, 2012
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    Thanks for any help you can give I am a novas on circuits. Here is what I need help with I have an electronic air filter that quit working. I took one end of the caps & unsolder them & tested they test good I then tested resistor #1 & it is open. On the resistor is is stamped TRW 8402, 836-0151. I searched & could not find this number. The diagram shows it to be a 30Meg but does not show the watts The questions that I have is... How may watt resistor do need? I think this is a thick film power resistor is that correct? Where can I buy just one on line. I use to go to a local store & just show them what I wanted & they knew what I needed but they are gone now.
     
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  2. Salaja

    New Member

    Jan 27, 2013
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    i dont know the markings, but 30 meg is a lot for a resistor. the formula for power is P=V^2/R, so if you use a 0.25 watt, 30Meg resistor, it will take about 2.7kV to melt it.

    so unless this air filter runs on over 2.7kV, a regular 1/4 watt resistor should work. even a 1/8 watt resistor would be fine up to 1.9kV.
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,981
    3,708
    These ion air "filters" do run at high voltages to create electrostatic charges on particles. In my opinion, even 2.7 kV seems low for this application. It might operate as high as 30 kV or higher. It is worth some extra investigation or CAREFUL experimentation. Notice that the voltages used has damaged the existing resistor so I wouldn't go any smaller in power handling.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,415
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    How do you know the 30MΩ resistor is open?
    Most meters cannot read beyond 20MΩ.
     
  5. BReeves

    Member

    Nov 24, 2012
    412
    64
    Burnt and cracked would be enough for me to say replace it.


    I would replace it with three 10meg 1/4 watt resistors in series rather than just one 30meg 1/4 watt. Not sure what the voltage is but you would have less chance of an arc-over with 3 series resistors.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    An ordinary 1/4W resistor cannot be used in a high voltage circuit because it will arc. It is made with a helix cut in it and the helix spacing is very small. The helix will arc. It is rated for only 250V or less.
    A special high voltage resistor must be used.
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I just found a couple ionizers and the appear to operate in the range of 6 to 10 KV for static ionizers. Some with a blue spark run at even higher voltages.

    No mater what you elect to use for your resistor replacement, remember that resistors have both a maximum power rating AND a maximum voltage rating. At 6kV, you can easily exceed voltage ratings on a common 1/4 watt carbon or metal film resistor, even if you put 3 in series (still 2kV per resistor).

    Look here for a reasonable replacement.

    http://www.ohmite.com/cat/res_slimmox.pdf

    Alternatively, check Wikipedia.com for court case between Consumers Report and Sharper Image (Ionic Breeze) where consumer reports claimed these units do not perform well (compared to HEPA FILTER) and gave all ionizers a FAIL rating. Sharper image sued but consumer reports won.
     
  8. MrChips

    Moderator

    Oct 2, 2009
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    Sorry, I hadn't seen the photo.
     
  9. KnRele

    New Member

    Jan 7, 2013
    20
    8
    TRW ( http://en.wikipedia.org/wiki/TRW_Inc. ) used to make all sorts of things, from spacecraft down to components, including resistors.

    The number 8402 looks to me like a date-code, week 2 of 1984, which may correspond to the original date of manufacture. Not that this seems to matter too much, as we know this is a 30 Megaohm resistor for a high-voltage (tens of kV?) application.

    On googling, I found a website of a German company, SRT-Restech, that seems to have these kinds of resistors (high resistance and high voltage) available.

    http://www.srt-restech.de//index.php?option=com_content&task=view&id=36&Itemid=86

    They might have something suitable. Just putting in any randomly available resistors at these voltage level would be hazardous. I've seen what happens when too high voltage is applied to components not designed for them -- the results are on the messy side, unless what one really wanted, like the Mythbuster guys, was a big bang...

    The power dissipation of the resistor is less of a concern than the voltage drop when the voltage is this large -- the insulation on the resistor has to withstand the voltage.

    For example, 30 kV / 30 MOhm = 1 mA, and 30 kV * 1 mA = 30 W. Now this is not likely to be continuous, but peak values when the ioniser is charging, so the continuous power isn't going to be that large (and the 30 kV is a guess anyways, though I would think it isn't too far off). But the voltage stresses do not average over time the same way as power does: 30 kV across a component that isn't designed for this voltage level is risky business.

    The ensuing fireworks is very likely to damage the rest of the components, both the transformer and the two rectifier diodes shown. At which time, the whole assembly might have to be written off, seeing as it is nearly 30 years old. If the resistor is hard to find, I'd think the diodes aren't any easier, and not to mention the transformer.
     
  10. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
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    From the looks of the schematic, the 30Meg resistor is part of a voltage divider used to light the Performance Indicator neon and possibly provide a bleeder function when the unit is shut down. If the unit is indeed not working, then I would look at the transformer, diodes or capacitors in the voltage doubler circuit.
     
  11. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    http://www.ebay.com/itm/KEV-1-22-Mo...-HV-High-Voltage-Resistors-4pcs-/251218059387

    http://www.ebay.com/itm/Lot-of-10-24-00-Mohm-Resistors-PN-A-8898694-264-/130689695384

    http://www.ebay.com/itm/KEV-1-36-Mohm-36M-ohm-36Mohm-1W-10kV-HV-Resistor-/250545305771

    Some eBay stuff, all of these will work.
    If you have doubts, install 2x 22 MOhm, it is not that much important for high voltage. The caps will still discharge, and the lamp will light up.

    I guess there are more problems than just the 30 MOhms resistor.
    If you replace it, you can see at least if the light goes on.
    The transformer filament might be gone too. I say filament, because these HV transformers use very thin wire. Many ionizers use a multiplier cascade, and only about 2kV on the transformer secondary.
     
  12. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    The original resistor clearly is not a 30W resistor.
     
  13. KnRele

    New Member

    Jan 7, 2013
    20
    8
    You are right -- but the question then is what kind of voltage is there. I was mistaken before thinking the resistor was being loaded with current pulses when something (an insect?) would enter the ionizer and be zapped. That is the one marked R2, in the flash focus of the picture.

    However, this R1 resistor, and the one marked R3, 2.2 MOhms, form a voltage divider for the "performance indicator" and the full operating voltage is across the series connection of these two, of which the R1 has the majority of the voltage. However, if this resistor is missing, the ionizer should still work, it will be just that this indicator won't light up. The lower power rating of R1 would put an upper bound on the operating voltage. As does R2, (13? K 22? W, hard to see) if it is expected to dissipate at most that when the "Push to test" is closed, the operating voltage is also limited.

    There might very well be something else wrong here.
     
  14. gregkinder

    Thread Starter New Member

    Dec 25, 2012
    2
    0
    Thanks for the replies so far. If I want to test the power supply not hooked up to the board & use a meter what kind of voltage should I be looking for?

    I did not know that my Fluke 88 would not measure the resistance on it.

    I am in automotive & have a digital graphing meter I would like to know what the voltages would be so I don't let the smoke out of my meter. I assume it will be an AC voltage due to the rectifiers on the board.

    In the automotive world it would take about 20kv to 30kv to jump the gap on the push to test button .

    Thanks for all the help.
     
  15. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    I found this with a Google search......

    The Honeywell F300E1035 is a complete system that includes the cabinet with the power box and 120v cord, access door, two electronic cells, two pre-filters and two post-filters. Ready to connect your duct and plug in.
    The Honeywell F300 maintains peak air cleaner efficiency over a wide range of cell dirt loading conditions through the use of a self regulating dual voltage high frequency power supply. The dual voltage increases particle charging efficiency with a high 8150v ionizing wire voltage and increases collection surface area through a reduced 4280v plate voltage. The dual voltage is a feature exclusive to Honeywell.
     
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