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Data and monitoring: measuring electricity consumption on things without plugs

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  1.  
    • CommentAuthorRobinB
    • CommentTimeMar 28th 2011
     
    I know where to buy a plug-in electricity meter to measure power consumption of individual appliance with a plug e.g. the fridge but is there something I can get to measure the power consumption of our MVHR which is wired in? Ideally something that could be simply moved from place to place to e.g. to assess our heat pump, immersion etc.
    thanks
    RobinB
    •  
      CommentAuthorDamonHD
    • CommentTimeMar 28th 2011
     
    A clip-on meter *may* be able to do a reasonable job *if* you can (safely) separate out the live and neutral wires at some point and and clip on to just one of them. (Clipping on to a cable containing both will give a useless zero reading.)

    Rgds

    Damon
    • CommentAuthorRobinB
    • CommentTimeMar 29th 2011
     
    Hmmm, thanks Damon, I *might* try this, anyone any other suggestions?
    thanks again
    RobinB
    • CommentAuthorCWatters
    • CommentTimeMar 29th 2011
     
    You may have to break into the wiring somewhere (eg at the FSU). There is no other way to do it if you can't find somewhere where a clamp can be fitted around live or neutral only.

    Measuring low AC power isn't easy as there can be phase errors. Using one plug in meter my PC appears to draw 60W even when switched off using the switch on the back of the power supply.
    • CommentAuthorRobinB
    • CommentTimeMar 29th 2011
     
    That's so inaccurate as to be worthless! I suppose manufacturers must have more accurate means.
    Thanks for the info anyhow.
    RobinB
    •  
      CommentAuthorDamonHD
    • CommentTimeMar 29th 2011
     
    It's not always that bad; all of my plug-in meters are fine, and the clip-on ones will do a reasonable job (+/-10% probably) unless the load has a very odd waveform / load-factor, which is possible.

    They only cost ~£30 down Maplin, or you can geta free one various ways, or some libraries/councils lend them out.

    Give it a whirl.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 29th 2011
     
    May be worth looking at the upper and lower bounds of the electricity supply voltage and then deciding if any readings are so way out that you need more accurate equipment.
    Any resistance load can be checked (within a bit) with a simple multi-meter and then double checked with an clamp-on amp meter. Inductive and capacitance is a bit more tricky, but realistically how accurate do you need to be.
    My current logger is sensitive enough to know when an 8W CFL light goes on, and it logs every 6 seconds. If you are trying to find out fraction of a Watt parasitic loads, such as stand by loads, try working out what the load should be and see if that is detectable rather than see if you can detect it and then work out what it is.
    There is more than one way to skin a cat.
    • CommentAuthorRobinB
    • CommentTimeMar 29th 2011
     
    Many thanks, I'm not trying to be super-accurate but 50w out would be a waste of time. Off to Maplins or Amazon or suchlike. thanks
    RobinB
    • CommentAuthorRobinB
    • CommentTimeMar 30th 2011
     
    Damon - would it be this type of clip on thing - the kind usually for the whole house? http://www.maplin.co.uk/efergy-elite-wireless-energy-saving-meter-225407

    Also anyone brighter than me see the advantage of the 19.99 plug in meter over the 7.99 one on the same website?

    thanks
    RobinB
    • CommentAuthorwookey
    • CommentTimeMar 30th 2011
     
    If you are going to buy a plug-in meter make sure it can do small loads accurately - many can't. I know for a fact that this one can (down to 0.2W, I've got one), and it's inexpensive, and thus I recommend it: http://navitron.org.uk/product_detail.php?proID=339&catID=67
    you do have to read the answers whilst it's plugged-in though, as it has no battery so goes off when unplugged. This can involve neck-craning.
    •  
      CommentAuthorDamonHD
    • CommentTimeMar 31st 2011
     
    Take Wookey's advice. I tested the Efergy and its granularity was 100W.

    http://www.earth.org.uk/note-on-clip-on-power-meters-for-the-UK-REVIEW.html

    Rgds

    Damon
    • CommentAuthorBen1974
    • CommentTimeMar 31st 2011
     
    If the your MHVR is wired into a FCU there is nothing to stop you changing it for for standard 13A socket and putting a plug onto the MHVR supply cable.

    The plug and socket are a perfectly acceptable means of isolation for maintenance within the wiring regulations. (and even common sense!)
    • CommentAuthorjms452
    • CommentTimeMar 31st 2011
     
    With the advantage that if the plug socket was already there you probably don't need to be part P to wire a plug and plug it in!
    • CommentAuthorRobinB
    • CommentTimeMar 31st 2011
     
    Thanks I'll take your advice,and I thought granularity was for sugar. Yes it would be TOO sensible to have provided a plug and socket. The MHVR instrutcions specifically ask for it to be hard wired in. So that is what happened.
    Grrr!
    RobinB

    ps, Yes, Robins can growl
    • CommentAuthorCWatters
    • CommentTimeApr 3rd 2011
     
    Its so it can't be unplugged loosing ventilation.

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