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Thread: Nevada 30A PSU - now nice and quite after a modification !

  1. #1
    dtrewren's Avatar
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    Default Nevada 30A PSU - now nice and quiet after a modification !

    Good evening guys,

    I have just bought myself a rig power supply to power my Yaesu FT-450D. I was running the rig from a Leisure battery with a smart float charger. Unfortunately, the Mrs complained about the fan in the float charger disturbing the peace and quiet (TV).

    So I bought a Nevada PS-30M linear supply. I wanted to avoid noisy switch mode supplies as I am mainly messing about on 20/40m. The supply was great, well made and did the business with very low ripple - I was a very happy Ham.

    That was until about 15 minutes into Hamming it warmed up and the cooling fan kicked in - pardon my French but 'Holy Mother of God' it was like a Harrier Jump jet at full throttle into a vertical climb from the deck !

    At this the Mrs suffered gimbal lock, went into a flat spin and said I was to leave and take all my 'rubbish' with me

    So I plodded off down to my workshop in the rain with the PSU under my arm to see what could be done - other than file for divorce !

    The fan is essentially connected via a very basic mechanical thermostat to the 12V supply so it is either ON or OFF. I decided as a first approach to run the fan relatively slowly all the time to keep the temperature down. However, should the temperature actually trip the existing thermostat I wanted to fan to come on full power as before.

    I had a bunch of 47ohm 10W resistors knocking about so simply connected one across the thermostat to run the fan but act as a current limit. This results in the fan running with a very low hum (almost inaudible even to the bat eared Mrs) but if the thermostat does switch in the fan will run full belt. With the fan running the voltage drop across the resistor is 6.6V so the fan is running at about 6V hence the slow speed as it is a 12V rated fan.

    I have been happily working 20m FT8 in a dead area at 60W resulting in a load of about 13A. FT8 has a fifteen second duty cycle, that has been running for about fifteen minutes and the full speed fan hasn't kicked in once.

    Back to being a happy Ham - photos and video attached.

    Cheers and 73s,

    Dave (G7IYK)



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    Last edited by dtrewren; Fri 5th Jan 2018 at 13:10.

  2. #2
    M0WAO's Avatar
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    nice one and solved in the spirit of being a HAM with some Smoke and Solder
    73 de Biton - m0wao - echolink 633710
    Elecraft K2
    dx-code

  3. #3
    M0WAO's Avatar
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    nice one and solved in the spirit of being a HAM with some Smoke and Solder
    73 de Biton - m0wao - echolink 633710
    Elecraft K2
    dx-code

  4. #4
    G0NMY's Avatar
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    Can I make an important suggestion based on my recent experience. While you are in the mood to modify your psu fit an overvoltage crow bar circuit to it. I never got around to fitting one and my psu went overvoltage last november, it took out 23cms atv transmitter, several cctv cameras and some 10GHz gear. A very costly result luckily my hf rig and 6m and 4 mtr transverters were not connected at the time. I could kick myself for not doing it.

  5. #5
    dtrewren's Avatar
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    A very sound suggestion Mark,

    Disaster loosing kit to a faulty PSU ! The Nevada supply already has an over current protection mode so it should be simple enough to detect over voltage and then hook into the same protection circuit used by the over current. I will have a look and see what I can come up with. Currently repairing a dual output switch mode supply which was being scrapped at work - very nice supply and confident a couple of issues have been identified.

    However, generally not a good idea to carry on debugging a supply which utilises rectified smoothed 240V mains after a lovely bottle of red wine - top tip

    Leave the repair until tomorrow me thinks !

    Dave (G7IYK)

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