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Basic circuit battery help

Discussion in 'Power Electronics' started by Edgey, Dec 15, 2012.

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  1. Edgey


    Dec 15, 2012
    I am not too experienced with electronics theory so need a little help in selecting a power source for my 'beginner' project. I am also new to the forum so hopefully I have found a new base for electronic knowledge. I'm also not sure if my idea will actually be feasible.

    I ride a motorcycle all year round and if there are other motorcyclists in UK on here they will know it gets pretty cold, as such I'm doing a little project with heated grips. I have selected heated grip pads you can buy (cheap on eBay) which are usually wired straight into the vehicles battery, however for my own preference (removable) I would like to add a rechargeable battery source instead, this is the part I'm not sure is feasible or not.

    The grips I'm told are rated at 12V, 3A, which works out at 36W. The circuit will be a simple series circuit with on/off toggle switch. I have attempted a diagram below but as I'm unsure whether the conventional diagram is correct (right) I also drew what it would physically look like (left), apologies if my poor diagrams hurt the eyes of seasoned electricians :eek:


    Now my problem is what specification battery I should be looking for, I would like the pads to be powered for as many hours as possible, ideally 3-5 hours range minimum.

    Should the total battery bank voltage add to 12V? with generally as many mAh as possible? I see most rechargeable AA batteries are rated at 1.2V, does this mean I would require 10? Which may not be too feasible... Is there another rechargeable power source not too large in size which I don't know about of higher voltage output?

  2. davenn

    davenn Moderator

    Sep 5, 2009
    hi there edgey
    welcome tot he forums :)

    for a stand alone battery its going to have to be a big one
    eg a 12V 7.2 AH sealed lead acid or gel battery will only last a couple of hours at best
    thats around a kilo or so weight
    for 3 - 5 hours you would need something in the range of 15 - 20Amp Hour (AH)
    thats REALLY big and heavy

    by having a separate batter you are making it difficult for yourself
    as using the battery on the bike you are making use of the bike's charging system
    The other option would be to have your separate battery also charged by the bike's charging system, IF, it could handle the additional load :)

  3. Edgey


    Dec 15, 2012
    After about 2 hours trolling through Google earlier I suspected this was the case, but thought I'd post up anyway just in case. In light of this I'll think up some way to wire straight to the bikes battery with a fuse in a way that it's still removable.
    A common practice is to tap into the bikes wiring loom so that the grips cannot be turned on unless the bike is turned on, this prevents leaving them on and acquiring a flat battery whether it be yourself leaving them on or someone maliciously turning them on.
    As I want to be able to remove them I don't really want to tap into the loom, I'll go straight to the battery but with a somewhat hidden plug somewhere near the front of the bike so I can remove them easily and also unplug them with them left on the bike and know they cannot be maliciously turned on unless someone went to the effort of chasing wires and finding the plug, which is a lot of effort.
    Now I'm thinking about it I could also rig up a usb charging cable to go into this plug to power a satnav for the warmer months when the heated grips would be off the bike.

    Reason for the grips being easily removable is because I'm attaching them to the inside of my bar muffs rather than on my actual handlebars, I remove my muffs when I have to leave the bike in the rain, don't want wet muffs... shown below... By which I mean the setup... Not wet muffs...
    Depending how hot they get I may add insulating between the pads and the inside of muff & they will be covered by fabric, don't want to be melting my muffs!

    Thanks for the confirmation of my hours of searchings! Also thanks for the quick reply & warm (pun :)) welcome!

    When I get all the parts in and if it goes as planned I may put a project thread up, won't be soon though as the cheapest ones come from China, long delivery.
    Last edited: Dec 15, 2012
  4. donkey


    Feb 26, 2011
    edgey what is stopping you from accessing your loom and putting in a connector? something like a cigarette lighter socket.
    something else you have to consider is even though the little alternator on your bike is doing a great job of charging the battery now, if you start putting on too many accessories and you pull more current than the alternator provides you will end up with a dead battery at least..... at most I have heard of major stalls, disruption to fuel pumps that require the whole pump being replaced... etc etc.... on a bike there is not so much electrical gear but just be sure to see what the extracurrent is before adding too much
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