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Does a 17" crt monitor need an exhaust fan ( to suck out heat ) ?

Discussion in 'Electronic Basics' started by Lim Pek En, Aug 6, 2003.

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  1. Lim Pek En

    Lim Pek En Guest

    I put a 8cm fan on my 17" Sony E200's grille, to suck out heat ( an
    awful lot ) made by its 120w consumption. I think its components
    will last longer, if they're cooler, esp if ambient air is >30°C.
    Am I right ? I plan to buy a 19" crt monitor ( produce even more heat
    ).
     
  2. If the fan moves the air in the direction it would normally move, only
    more so, it may well increase the life of the unit. But it will cause
    more dust to collect in the holes and on internal surfaces, so you
    should inspect it fairly often to make sure it doesn't get clogged.
     
  3. Lim PE

    Lim PE Guest

    | it may well increase the life of the unit.

    Thanks, I wonder why manufacturers do not supply even
    a fan point / seat on their crt monitor's grilles.
     
  4. But it will cause
    That is why in industrial computers the fans are not 'sucking' but
    blowing the wind into the PC, and this air is filtered.

    Pieter Hoeben
     
  5. Lim PE

    Lim PE Guest

    | catastrophic failure (and possibly fire) if the fan quits.

    Why not put a simple thermostat ( bi-metallic strip, failproof &
    cheap ) behind the crt ( hottest part ), to disconnect AC power
    supply if temperature is too high ?
    Is convection adequate for ambient air of >40°C in e.g. Saudi ?
    This 19" mntr www.ctxintl.com/products/crt_PR960FL.htm 's
    spec says it must not be used in air of >40°C.
     
  6. I doubt that it is.
    That kind of ambient temperature will almost certainly lead to a
    shorter useful life for most electronics, especially something with as
    must heat generation as a monitor. I would probably add a chimney to
    the case.
     
  7. I recall Iiyama quoted two MTBF on their 17" Diamontron (Trinitron clone
    from Mitsubishi) monitors some years back, at 25oC & 35oC ambient.

    Yes, design for convection since long-life fans are a high cost item
    and even there you could have an early failure re bath-tub curve.


    At least one monitor maker did fit a fan to their monitors - Hitachi,
    and quoted a higher ambient operating temperature. Unfortunately,
    they also stated if the fan failed the monitor would be damaged. No
    monitoring of the fan was provided - although it was a Sanyo unit.

    Yes, it generally does increase life - but remember that depends on
    cooling in terms of m/sec over the hot components requiring cooling.

    Industrial units do use positive case pressure as mentioned, which can
    be filtered (and must be if avoiding dust ingress is the objective).
    However,
    such filtering must be done carefully in terms of pressure drop & capacity.

    Small DC Axial fans are very poor at maintaining cfm against the static
    resistance of a filter - a resistance which rises with airflow additionally.

    With CRT tending to such low figures, a fan is a major cost item which
    may be better spent on other areas more user-perceiveable. However,
    for climates such as Saudi, without A/C CRT is not a good idea since
    the solar gain and thermal contribution of computers is very high.
     
  8. Fred Abse

    Fred Abse Guest

    Not usually the hottest part, apart from maybe an inch or so of neck.
    Heaters (say) 6.3V at 1 amp, that's 6 watts. Beam current maybe a
    milliamp at about 25kV, that's 25 watts, but most of it is dissipated
    over the area of the screen, which is huge.

    Most heat is generated in the PSU and scanning circuits.
     
  9. Lim PE

    Lim PE Guest

    | Yes, it generally does increase life
    thanks

    | cooling in terms of m/sec over the hot components
    I don't understand this.

    | if the fan failed the monitor would be damaged
    Why not put a thermostat ( bi-metallic strip, failproof & cheap )
    behind the crt ( hottest part ), to disconnect AC power supply if
    temperature is too high ?
     
  10. | cooling in terms of m/sec over the hot components
    Cooling airflow can be measured in many ways:
    o volume of air moved -- cfm
    o speed of air movement -- metres per second

    Some components don't specify cfm for themselves,
    but the air velocity over them in metres per second.

    I think the over-riding problem with modern CRTs is:
    o They are built down to a price
    ---- how they can contain the many components they do
    ---- and sell at such low prices
    ---- with margin for manufacturer + distributor + retailer
    ---- is incredible
    o A fan is a cost component
    ---- which can be designed out
    ---- whilst designing it in loses margin with little mkting benefit

    Vis., will customers buy a CRT with a fan or one without?
    For many, they might actually prefer one without re noise.

    What economic buyer population requires a CRT which can
    tolerate far higher temperatures (40oC+ v spec'd at 30oC)?

    Military may spec to 50-55oC ambient (Africa is 45oC right now),
    but they are also likely to specify no fan re single-point-of-failure.

    Frankly, I think most of the heat in a CRT is SMPS related:
    o 200W consumed in total by the PSU
    o 80% efficiency leaves 40W heat dissipation
    o Bigger monitors might dissipate 60-100W

    So the argument perhaps moves to PSU cooling.
    Convection cooling can work, just depends how it is designed.
     
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