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Discuss My DC Fan wont spin fully, Only stutters and stops every 5 seconds in the DIY Electrical Forum area at ElectrciansForums.co.uk.

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  1. JackBoy
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    JackBoy EF Member

    Location:
    london
    I have a DC 24v Fan, which at full load uses around 7Amps.

    I brought a DC 24v 13A PSU Driver, which when i first tested the fan powered it just fine.

    After a week or so went by, I reconnected the driver again, and now the fan doesnt spin even 2% of what it did before.

    The fan just about rotates(not very fast spin at all) for half a second then stops for 5 seconds then makes a weak half a second rotation again.

    Around 2 seconds after I unplug the PSU Driver or dissconnect it from the fan, the fan spits out one last weak rotation attempt for a bit longer than half a second.

    Is the fan at fault or the PSU?
     
  2. Marvo
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    Marvo GMES....You absolute beauty. YOU ROCK DUDE!!!! Staff Member

    Location:
    South Africa
    Was the driver/PSU sold as a unit together with the fan of did you purchase them separately? If it was sold as a 'driver' it might be a constant current supply rather than a constant voltage type.

    Do you have a tester? Connect the fan to the power supply and test the voltage under load on the DCV scale.
     
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  3. JackBoy
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    JackBoy EF Member

    Location:
    london
  4. Pete999
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    Pete999 Trusted Advisor

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    " they was not sold together" sorry mate you're from London should have realised:cool:;):rolleyes:
     
  5. Richard Burns
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    Richard Burns Trusted Advisor

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    Richard Burns
    I would suspect that a component in the driver is overheating and cutting out.
    The power supply should be a constant voltage unit and should be able to power the fan without problem so I'd be asking for a refund or replacement from the PSU supplier.
    However if you have a couple of 12V batteries it would be worth just connecting the fan to them in series to check the fan works and measure the current drawn.
     
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  6. Marvo
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    Marvo GMES....You absolute beauty. YOU ROCK DUDE!!!! Staff Member

    Location:
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    I can't find any datasheet for the particular item you linked to on EBay but it looks to me like a unashamed direct rip-off of the MeanWell 350W constant voltage switchmode driver which I've used a lot in the past.

    Regardless, the supply should give a 24VDC output under an appropriate load so test the voltage with your fan connected and anything less than 23V and more than 25V send it back for a refund.

    Here's the MeanWell spec sheet but please note I can't guarantee you're unit is the same specs.
     

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  7. JackBoy
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    JackBoy EF Member

    Location:
    london
    @Pete999@Pete999 @Richard Burns@Richard Burns

    You lost me Pete999, can you elaborate?

    I purchased another of the PSU, and am having the same issues with it as the first.
    @Marvo@Marvo I tested the voltage without the fan connected, the voltage on the PSU reads 24.0V - on both PSU - which is just perfect.

    When connecting the fan, and then testing the Voltage the reading shows 0.2V, then every 5 seconds or so when the fan kicks, the Voltage jumps to around 1.0V.
    Lastly when unplugging the PSU, the fan has one big last kick after it is unplugged, the voltage of that kick goes up to 2.0V.

    Putting the Voltage test aside, I kept touching the fan wires to the PSU over and over, and maybe one out of 20 times the fan seemed to spin at full 24V and stay on until I removed the wires...
    It seemed that if I left the PSU on for a while w/o any load, and then touched the fan wires on the terminals after 40 seconds, I am more likely to get the fan to spin at 24V correctly. but if I keep touching the fan wire to the terminal it never seems to work...

    What could the voltage test indicate? And what could the scenario I posted below that indicate?

    Fan or PSU?

    Also guys one last question, I attempted to use this PWM 2Pcs PWM DC Motor Speed Control Switch Controller Volt Regulator 12V~40V 10A | eBay - http://www.ebay.co.uk/itm/152558432200
    with the PSU and Fan, is there anyway this could damage the PSU's?
     
  8. JackBoy
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    JackBoy EF Member

    Location:
    london
    I am also wondering whether to get a higher amperage PSU? 24V 20Amp, currently I have 24V 15A
     
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  9. Richard Burns
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    Richard Burns Trusted Advisor

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    Since you have what is a fairly powerful 200W fan it is possible that the initial start current of the fan may exceed the overcurrent protection of the PSU if this operates instantly and this shuts down the voltage output and then resets after a short time to start to power the fan which then overloads the PSU again, occasionally if you hit the right point in the output or the fan is still turning slightly then it may be able to overcome this and start normally.
    If this is the case, though it is very hard to measure for without an oscilloscope type monitor then a more powerful PSU may be able to cope without exceeding the overcurrent protection. If it is to the same spec as Marvo linked to then it can withstand an overload for 5s which should be in the order of 1000 times as long as required so I am not certain this is the case, but the symptoms point in this direction.
    Possibly applying a NTC resistor to limit the start up current maybe a way of assessing if this is the case and may resolve the situation at a much lower cost.
    The speed controller should have no perceptible back feed effect to the PSU as the input should be filtered and the fan shouldn't worry about the the input supply, it should be controlled readily.
     
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  10. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
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    Wilko Electrics
    As RB has said, it's possible the supply is shutting down due to startup load. I'd try a series resistance (maybe add in a car stop lamp?) and see if the supply will at least run up to 24V.
     
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  11. JackBoy
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    JackBoy EF Member

    Location:
    london
    Hi guys, thanks for the replies.

    The problem is I dont have access to these components you are talking about.
    I am going to try buying a larger Amp PSU, do you think a 24v 20A should be ok to deal with the insurge? (my previous one in question was a 24V 15A).

    Or the next sizes up are 24v 25A, 24v 30A...
     
  12. JackBoy
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    JackBoy EF Member

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    london
    Also, I phoned the PSU supplier, they said that perhaps the fan is appearing as a dead short to the PSU, and therefore the PSU cuts out when it notices it.

    Could that be possible? wouldnt that make the fan faulty?
     
  13. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

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    cheshire/staffordshire
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    Telectrix
     
  14. JackBoy
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    JackBoy EF Member

    Location:
    london
    @telectrix@telectrix yep, thats exactly the path any electrical job I attempt ends up going, highway to f**king hell
     
  15. Wilko
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    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    A stationary DC motors appears (to the supply) as the resistance of the windings and so it's normal for the motor to try to draw a high starting current. I think you need to find a way to limit that starting current, as you could double your psu and it might not be enough.
     
  16. Richard Burns
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    Richard Burns Trusted Advisor

    Location:
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    Richard Burns
    Just place any resistance in series with the fan, as wilko says a light bulb for instance and see what happens, the fan might run a little slowly but it would prove the principle, an NTC thermistor is not expensive, this linked one is £1.84.
    The fan would likely be about 3 ohms so anything above 3 ohms should help, if this is the fault the PS sees.
     
  17. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    A mates 20A running fan has an 80A relay for a good reason .
    ( testing with 60W head light bulbs , cheaper than resistors )
    It not the fans fault ,
    (may be able to get an expensive fan with " Soft Start " )
     
  18. JackBoy
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    JackBoy EF Member

    Location:
    london
    @Richard Burns@Richard Burns @Wilko@Wilko
    @static zap@static zap Your right about that!

    Some good news, the 24v 20A PSU I purchased worked... Everytime I tested it the fan always spins unlike the 24v 15A, so it seems the startup current was the issue.

    Now if the fan only needs 7A to run, or perhaps 8-9A under bad air conditions, would using a Thermistor allow me to use only a 24v 10A PSU?

    I was thinking to buy the Thermistor Richard Burns linked to
    SL32 10015 Ametherm | Mouser United Kingdom - http://www.mouser.co.uk/search/ProductDetail.aspx?R=0virtualkey0virtualkeySL32-10015
     
  19. Richard Burns
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    Richard Burns Trusted Advisor

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    Richard Burns
    If you have a working solution then I would stay with that, if you are planning on making lots of these then try out some thermistors, the one I linked to starts at 10Ω and should present a resistance of about 0.1Ω once it is running which might slow the fan slightly. Possibly a lower initial resistance may still prevent the PSU cutting out but give a lower resistance once running.
    There are complex calculations with values I do not have to calculate which rating would be best to use but that one should be OK, just remember that they get hot so you will need to provide a barrier with ventilation to avoid risk.
     
  20. JackBoy
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    JackBoy EF Member

    Location:
    london
    @Richard Burns@Richard Burns I do not plan to have alot of these, however the reason I want to try a lower amperage is driver costs.
    The 20A driver I bought to test this was a cheap china one, costing around £30.
    If I get a quality 20A driver, it will cost me around £100, If I get a quality 10A driver, It may cost around £50, it seems wastefull to buy a quality 20A driver just to have that over-amperage for a startup surge and then not in use anytime after.
     
  21. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
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    Business Name:
    Telectrix
    old adage...buy cheap, buy twice.
     
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  22. JackBoy
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    JackBoy EF Member

    Location:
    london
    Well thats my point if you read my post correctly... Hence my reasoning to enquire about Thermistors...
     
  23. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
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    Telectrix
    worth a try.
     
  24. JackBoy
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    JackBoy EF Member

    Location:
    london
    I have bought the one Richard mentioned, will post an update back once I tested it.

    Although I now see another problem - if I was to stop the fan and try to restart it before the NTC has cooled down, a too high current maybe allowed to pass through it resulting in the fan not spinning again... are there any common ways to get around this?
     
  25. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    Fans definitely take a large surge at start up,
    (very likely to vary a little between units )
    Stick with a big safety margin and will still be working in 3-5
    years when componenets have aged .
    A dedicated timed startup circuit ,
    resistor ,thyristor ,relay + electronics .
    (bulb + relay ..cheap and dirty)
    Is a workaround to hot thermistor -restart problem!
     
  26. Richard Burns
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    Richard Burns Trusted Advisor

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    Usually there is an arrangement whereby the NTC resistor is taken out of circuit after it has performed its start up function, to employ this method would probably exceed the cost differential of the PSUs.
    If you were manually present then you could install a make before break switch to take the NTC out of circuit after a second or two, perhaps you could activate a relay on a RC delay that provides a lower resistance path so that the NTC will cool somewhat as a cheapish alternative.
    If the NTC is well ventilated then it should cool quickly and at least provide some resistance, since the 20A PSU could cope then the 15A must be close to not tripping so even a lower resistance than 10Ω may be enough to stop the overload operating. However the residual heat would only be a problem if the fan were switched on again quickly after stopping.
     

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