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Thread: NTC Thermistor without bypass relay

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    Default NTC Thermistor without bypass relay

    Hi,

    I was looking at Corsair Rm550x (because it's a very silent PSU), for a build and i found something intresting. It has an NTC Thermistor but it lacks an bypass relay.
    I searched for other reviews of that platform and i found one of the Rm650i.
    The temp of the thermistor is at about 52 degree celsius and inrush current is in both cases lower than 50 amps at 230V wich seems to be good.
    The question is if the lack of bypass relay can affect the thermistor, PSU or hardware components, since the relay it helps for cooling down the NTC, bypassing the circuit once the PSU in on.
    The thermistor without an relay remains always hot or it's cool down after a while? If it remains hot will be affected the lifespan? If i shut down and power on PC repeatedly can affect the PSU internals or PC components because the thermistor goes hotter?

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    Default

    In the three years the RMx has been in production, NTC thermistor overheating has never been an issue.

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    Default

    NTC Thermistors for inrush current limiting have been used for decades in PSU. That's not new and they aren't that prone to failure if nothing went horribly wrong...

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    Default

    Quote Originally Posted by Al3xand3r View Post
    ... The thermistor without an relay remains always hot or it's cool down after a while? ...
    Without relay the thermistor remains hot as long as the computer is turned on. Thermistor only cools off after comp is turned off.

    ... If it remains hot will be affected the lifespan? ...
    Certainly more than if a relay by-passes it and it remains cool all the time, but NTC thermistors are designed to withstand the heat, and as said above they've done it for decades.

    Shit happens, however:



    The reason they introduced relays to by-pass the thermistor was not really thermistor longevity but overall PSU efficiency. An always online thermistor drains about 1% from PSU efficiency.


    Oklahoma Wolf once caught them jumpering the NTC thermistor (always off-line, no inrush protection) to boost up efficiency: http://www.jonnyguru.com/modules.php...tory7&reid=453

    ... If i shut down and power on PC repeatedly can affect the PSU internals or PC components because the thermistor goes hotter?
    Conventional wisdom says that always on (or always off ) is better for longevity than powering on and shutting down repeatedly.

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    Thanks all of you very much for the answers. Now is everythink clear.

    It seems like no reason to worry about since the chance for failure of the thermistor in a PSU whithout an bypass realay are the same as other components in that power supply.

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    Default

    The only problem a missing bypass relais can cause (besides minimal differences in the power supplys efficiency with a NTC not well suited) is a high inrush current if the computer get turned on again right after it has been turned off.
    The NTC can't cool down to ambient temperature in a couple of milliseconds.

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    Al3xand3r (11-11-2017), Per Hansson (11-11-2017)

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