Input or Output [Inverter Question]

Discussion in 'Tech/Mech General' started by Langtoftlad, May 25, 2016.

  1. Langtoftlad

    Langtoftlad Funster Life Member

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    Ambition = Charging my E-Bike battery whilst driving
    Method = Bestek 300 Watt Inverter plugged into dashboard 12v socket.

    Before I try it out and possibly blow up the battery, the inverter or the van, have I got my sums right?

    E-Bike battery charger output labelled 42 volts & 2 amps which I reckon is 84 Watts?
    Van 12v socket is labelled 180 Watts

    So everything should be okay - right?
    :unsure:
     
  2. pappajohn

    pappajohn Funster Life Member

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    You need to know how many watts and amps input to the charger.

    2amps input @230v will suck 40amps from your battery @ 12v

    Easily do-able with the engine running but not via the fag lighter socket or a 300watt inverter

    Why do I think I got that wrong ?
    Brain fog today.
     
  3. Langtoftlad

    Langtoftlad Funster Life Member

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    Incase I wasn't clear - the inverter will be plugged into the van's cigarette socket & only used when the engine is running
     
  4. hilldweller

    hilldweller Funster Life Member

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    Looks good to me. 100W is only 8A so nothing. Worst case, a fuse blows.
     
  5. pappajohn

    pappajohn Funster Life Member

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    See, told you I wasn't thinking right.
     
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  6. Langtoftlad

    Langtoftlad Funster Life Member

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    Thanks for your 'input' ( :whistle: ) @pappajohn & @hilldweller

    I've searched the Interweb and although there are various threads on the subject, there's nothing definitive - some get into a tangle with the maths, some deviate on using an inverter with leisure batteries, whilst others say it works perfectly for them but without saying what kit they use.

    As you say - what's the worst that could happen :rolleyes:.
     
  7. Rapido925M

    Rapido925M Funster

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    I can't see a problem (y)

    84W is 84W. There will be losses as I assume you are converting 12Vdc to 230Vac (with your inverter) then to 42Vdc via your charger: they should not amount to more than 10% each, so call it another 16W [round ball-park figures] ie 100W.

    Your cig lighter will provide that (although specific 12V sockets MAY be only 8 (or 10) A but even they should be OK!).

    IF you charge the bikes with the engine off, you would be able to do it for 5hours without damaging your battery, I think - Gordon
     
  8. Jaws

    Jaws Funster Life Member

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    Yesssss but as already said, 100w equates to a minimum of 8 amps and unless it is a very posh inverter and extremely efficient I would guess at 10 amps draw at least.
    The standard cigar socket has a 10amp rating.. ( and believe me, they get REALLY flaky at much above 5 amps ! )
    I would suggest hard wiring the inverter via a fuse and or switch ) direct to the battery rather than use a socket
     
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  9. Jaws

    Jaws Funster Life Member

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    Just been on the Hella site.. The standard type )( Non Helar ) socket is rated nominally at 5 amps, the Hela ( Continental type ) is rated at 10 amps

    The standard ones in my Fiat have a big 5A MAX on the caps
     
  10. Bartyfixedit

    Bartyfixedit Funster

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    I would hesitate to use that inverter to charge a bicycle battery.

    The inverter concerned is a modified sine wave type as opposed to pure sine wave and you may well get problems with the charger. There have been many cases of chargers being wrecked by modified sine wave.
     
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  11. jockaneezer

    jockaneezer Funster

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    Last year, I bought a Machinemart 600 watt inverter on a vat free offer for about £40. I doubt it's anything but a billy basic quasi sine wave job, but it charges my 36 volt battery via the Kalkhoff charger when the engine is running. I screwed it to the outside of the bench seat housing the batteries (wire run is less than 18") and hard wired it in. You can hear the cooling fan cutting in and out frequently, but so far no problems.
    Also, driving on a particularly hot day last year, we plugged our 240 volt fan heater into it and ran it on the cold setting, directed at the dogs who were slowly melting under the table.
     
  12. Langtoftlad

    Langtoftlad Funster Life Member

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    @Jaws
    This what confuses me about electrikery mathematics...
    Where does the figure of 8 or 10 amps come from?

    My dashboard socket is labelled 180w
    No mention of amps.

    The battery charger is labelled with an output of 42v @ 2amps which I calculated is 84 watts.
    Why 8 amps?

    And then @Bartyfixedit says nay but @jockaneezer says yay.

    :confused: :confused: :confused:

    Is it going to be a question of suck it & see?
     
  13. Robin McHood

    Robin McHood Funster

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    If your socket is labelled 180W and assuming it has been wired up with correctly sized wiring you will be fine.
    Your load demand is 84W max, actually your charger will probably draw less than this most of the time. There are conversion losses for the inverter and the charger as @pappajohn and @Jaws etc have pointed out so the likely load on the socket will be just under 100W maximum.
    Make sure your plug is rated to at least 8A which it should be if it came with a 300W inverter and charge away!
    Otherwise install a new spur from your 12v fuse box with 25A fuse( so you can use the full capacity of your inverter) and hardwire the inverter.

    Oh and the 8A figure comes from the current required at 12V to allow you to eventually end up with 2A at 42V. 8A x 12v = 96W, 2A x 42V = 84W plus say 10W conversion losses on the 12V to 220v to 42v.
     
    Last edited: May 26, 2016
  14. Jaws

    Jaws Funster Life Member

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    If it is labelled 180w then it is a very good socket indeed and is rated at 15 amps

    To get amps from watts simply devid the watts by the voltage ( we will take the voltage as 12 v although it will be a bit higher )
    so 180 divide by 12 give us 15 amps

    To convert amps to watts reverse the sums.. 15 times 12 is 180watts
     
  15. Langtoftlad

    Langtoftlad Funster Life Member

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    IMG_20160526_124338.jpg

    So all 'should' be good
    Thanks one & all
     
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