[RFC] FT-991A fan mod

Discussion in 'Radio Circuits, Repair & Performance' started by PY2RAF, Jul 9, 2019.

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  1. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi there, list! o/

    I consider my FT-991A fan a bit noisy and I was considering replace it.

    My FT-991A ships a Panasonic ASFN60371 fan. After checking its specs (link), I have found that its noise is rated at 30.5 dB(a).

    Browsing in Digi-Key inventory, I have found a similar size and quieter 27 dB(a) SunOn fan (link).

    By comparing the specs, I found that the SunOn fan has a bit more of air flow (23.5 CFM vs 21.8 in Panasonic) but something really caught my eyes here: The power consumption. Pin it.

    By reading the FT-991A schematic, I see:

    1. Temperature is measured in both V/U and HF boards by a LM20 sensor, providing THVU and THHF signals respectively.
    2. Q4030 (a SPDT switch) selects either THVU or THHF signals, selected by the Main Unit HFB signal.
    3. Q4030 COM signal feeds Q4032 LM2902 OpAmp (and Main Unit TH signal), which bias a few more transistors and finally delivers the power to the fan.

    The fan is a two-lead powered and has no tach (speed sensor) feedback.

    So here comes my question.
    The Panasonic is a ball-bearing fan rated 1.92W, while the SunOn features a proprietary magnetic-levitation bearing, and is rated 900 mW, a bit less than half the power. And this is what concerns me.

    So, taking into account how the fan is controlled (looks like varying the voltage), and considering that the SunOn is definitely way more economic power-wise than the Panasonic fan, do you envision that is this a feasible mod?

    Do you have any strong opinions on go / no-go?

    Appreciate well thought comments.

    73s de PY2RAF / Rodrigo.
  2. N7AWM

    N7AWM Ham Member QRZ Page

    I don't see anything wrong with it, and would think it would help save power when running off battery. Would though you would have gotten more reply buy now. Have you tried it yet? Would like to know your outcome.
    PY2RAF likes this.
  3. KA9JLM

    KA9JLM Ham Member QRZ Page

    No go. The speed will not be the same with the same applied voltage.

    Or wire the new fan to run continuous.

    Fan noise lets you know the fan is running. I worry when the fan makes no noise.

    Good Luck.
  4. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hi there list,

    I gave it a try. Bought the fan in digi-key and in a few weeks it should be arriving here in Brazil, will let you guys know the outcome.

    I pondered that being more power-economic, it might tend to spin a bit faster than the Panasonic - Blowing more air and thus refrigerating faster too. However, might get noisier too.

    Will let you all know the outcome.

    My best regards and 73s;

    - Rodrigo.
  5. WA9SVD

    WA9SVD Ham Member QRZ Page

    Fan SPEED should not be a consideration; the CFM is what matters. (And of course, the noise level.) If a replacement meets the current air flow supply (or greater) it should be a decent recommendation, even if at a somewhat lower current demand. Hopefully, there are not other parameters that require a fan to use the original current , but that, too can be overcome.
    PY2RAF likes this.
  6. G4COE

    G4COE Ham Member QRZ Page

    Do keep in mind fans 'blow' direction and the air capacity it can shift.

  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    The voltage to make the fan run at the speed required to achieve the CFM rating is what maters.

    So speed does mater. And if it sucks or blows can affect the CFM rating. Some fans do not work well with back pressure, Or air flow restricted on the input.

    Noise just happens when air is moving.

    You do not get something for nothing.
  8. WA9SVD

    WA9SVD Ham Member QRZ Page

    YES, fan speed is related to CFM, and noise level. SOME fans (and their motor) are MUCH more efficient than others, so the noise level may well be less for a given CFM/motor speed.
    PY2RAF likes this.
  9. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hello there, QRZers!

    Well, that was a WIN.

    Replaced yesterday the fan and it is indeed quieter.

    On hand the new fan feels way lighter - Well, we're replacing a ball-bearing fan with a magnetic levitation fan.

    I tested the radio by doing FT-8 in FM band at full power (50 W) which is the most heat-stressful operation of the radio, in my case.

    It is interesting that the original Panasonic fan has a noticeable wail tone; the SunOn fan makes noise, of course, but mostly sounding like 'wind', with no companion wail.
    The step 1 fan state noise almost compares to the Panasonic. But as the radio gets hotter, the new fan is definitely more comfortable, especially by the lack of the wailing.
    The ramp-up ramp-down profiles are practically the same - didn't find any noticeable difference.

    Super straight forward, removed the top cover, removed the top shield (CAREFUL to not strand the speaker cable), removed the fan's 4 screws, exchanged the fans (PERFECT match) and to reassemble, reverse order.

    One noteworthy item is that I don't have the proper connector. But a Jumper Cable Connector will do the magic.

    That's it! \o

    73s - Rodrigo.
    W5TFC, W1TRY, SQ2TAC and 1 other person like this.
  10. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Updated version in https://github.com/rfrht/FT-991A/wiki/FT-991A-Fan-modification, including some thoughts involving Noctua fans.

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