Air Compressor < £500

  1. Jetex

    Jetex Member

    Messages:
    157
    Location:
    Luton, England
    I agree, this would be the best way to know which is a good compressor
     
  2. daleyd

    daleyd Member

    Messages:
    6,182
    Location:
    Wrexham, North Wales
    If its not pulling FLC then it's highly unlikely that the motor is not capable of that, more like the motor being overspecced for the pump. The motor will only pull the current that the load demands from it - which to be honest is probably not a bad thing as I'd rather have a bigger motor that's understressed than something close to the limit. The next size down would be a what, 2 hp? Throw in cold air, high demand, lots of stop/starts and it may well be that you'd be underpowered.

    I've yet to find a motor that isn't capable of what the faceplate says - if it's not pulling the rated current doesn't mean it's not actually that size motor,.
     
    morssdn and fizzy like this.
  3. TigTigger Forum Supporter

    Messages:
    109
    Location:
    UK South Gloucestershire
    The test results referred to in the posts above don't say under what conditions the current/power measurements were made. After initial start up I would expect the current to be well below the maximum as the pump is not working very hard. As pressure builds up in the tank the load on the pump increases, bit like using a bicycle pump to inflate an initially flat tyre. Measurements made just before maximum pressure is reached should provide a more realistic view of the maximum load current.

    However, it may well be that the pump only requires say 2 hp to operate at maximum pressure and therefore that is the maximum that will be drawn irrespective of the motors rating. So, the motors may well be rated at 3 hp, but if the pump never requires that much power you just have an over specked motor! The manufactures haven't actually been untruthful because they have not quoted the pump's maximum hp requirement.
     
    daleyd likes this.
  4. Jetex

    Jetex Member

    Messages:
    157
    Location:
    Luton, England
    Yes, you might think that. I did my tests from cold and these were the maximum current readings, in fact after the motor and cylinders heat up the current goes down, it does not seem to follow that more pressure in the tank puts any more appreciable load on the motor. I still conclude that on these imported air compressors the specifications are just fiction.
     
  5. Pigeon_Droppings2 Member

    Messages:
    2,219
    Location:
    london
    Too many variables to compute anything to any degree of accuracy I reckon....the time until fill approach does away with all the measuring and just looks at the end result.

    I do like a good brain teaser so I googled what 1 HP is....google reckons it's 750 Watts....so the minimum current for 1HP would be around 3 amps (I think????)

    So 3HP should be a min of 9A.....but that assumes the motor is 100% efficient....which of corse is nonsense.
     
    daleyd likes this.
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