Question on batteries (one for the electricians)

rodgers73
rodgers73 Posts: 2,626
edited June 2014 in The cake stop
I own a Black & Decker cordless hedge trimmer that needs a new battery. B&D no longer make this style of battery any more but I can get a generic one from ebay.

The requirements are 18v battery with a maximum capacity of 1.5ah. I've seen a lot of similar style batteries with varying ratings on them but nothing that fits precisely.

If I bought an 18v battery rated at 3ah would that do any harm or would it work just as well as usual?

Thanks

Comments

  • capt_slog
    capt_slog Posts: 3,974
    The Ah numbers;- 1.5Ah means that (theoretically) the battery could deliver 1.5 amps for one hour or 0.5 amps for 3 hours or 0.15amps for 10 hours and so on. The Ah rating will not make any difference to the drill, a larger Ah just means that it will last longer.

    The only problem might be how the charger sees it, and if there is any feedback from the battery under charge to the charger.


    The older I get, the better I was.

  • nick-gti
    nick-gti Posts: 131
    it'll be fine the ah means it will run longer really on the 3ah battery in theory anywho
  • team47b
    team47b Posts: 6,425
    Volts times amps equals watts.

    Watts are the amount of energy you have, like fuel in the tank.

    18x1.5=27

    18x3=54
    my isetta is a 300cc bike
  • bdu98252
    bdu98252 Posts: 171
    Recharge it outside for the first few times in case your charger is not compatible. Battery fires during charging whilst not common do happen. However it generally applies to lithium batteries in phones and computers more than your battery drill style batteries which are generally lower tech. The quality of battery replacements on places like Ebay can be a bit ropey from a quality perspective.
  • ai_1
    ai_1 Posts: 3,060
    team47b wrote:
    Volts times amps equals watts.

    Watts are the amount of energy you have, like fuel in the tank.

    18x1.5=27

    18x3=54
    Sorry to be pedantic but it can get confusing if you're not accurate (and feel free to correct me if I have any errors!)
    Watts (W) = Power not energy
    Watt hours (Wh) = energy
    Amps (A) = current
    Amp hours (Ah) = capacity

    3Ah is the capacity of the battery. So long as the supply voltage is the same the hedge trimmer will draw the same amount of current and all will be fine. The current is determined by the resistance and the voltage. Battery voltage drops a little when it's under load. The bigger the load the bigger the drop. Often higher capacity batteries will maintain voltage better so the trimmer may draw slightly more current at times but it shouldn't be enough to cause any problems.

    You'll need to ensure the battery uses the same type of cell chemistry as the original one. The main types are Nickel Cadmium (NiCD) which is now largely obsolete, Nickel Metal Hydride (NiMH) were the main type used in power tools for a long time and Lithium Ion (Li-Ion) which have largely taken over in recent years. There's also Lithium polymer (Li-poly) which are fairly similar to Li-Ion but less robust and not used so much for power tools I think.
    If the hedge trimmer is designed to use Lithium Ion or Polymer cells then it will be configured to shut down before fully exhausting the cells as full discharge damages them. Also your charger will be designed for one or other type of cell and may either not work or may be dangerous if used with the wrong type.
  • rodgers73
    rodgers73 Posts: 2,626
    The generic batteries on ebay are all the same as I have now - the Li-Ion ones are clearly marked and are more expensive too so I doubt I'll buy one of them.
  • me-109
    me-109 Posts: 1,915
    As stated above, its rating is how much capacity it has, so just ensure that it is physically the same size where it matters, i.e. the bits that fit fully inside the device or form the mating surfaces.
  • drlodge
    drlodge Posts: 4,826
    Me-109 wrote:
    As stated above, its rating is how much capacity it has, so just ensure that it is physically the same size where it matters, i.e. the bits that fit fully inside the device or form the mating surfaces.

    This ---^ You can get higher capacitity battieries for mobile phone, but they are physically bigger so need a special back cover too.

    Think of a battery like a water tank.

    The capacity (Amp Hours) is the size of the tank - bigger capacity, bigger the tank!
    Curernt (amps) is the amount of water that flows
    Voltage is the height of the tank i.e. the amount of pressure the water exerts.
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • lesfirth
    lesfirth Posts: 1,382
    Ai_1 wrote:
    team47b wrote:
    Volts times amps equals watts.

    Watts are the amount of energy you have, like fuel in the tank.

    18x1.5=27

    18x3=54
    Sorry to be pedantic but it can get confusing if you're not accurate (and feel free to correct me if I have any errors!)
    Watts (W) = Power not energy
    Watt hours (Wh) = energy
    Amps (A) = current
    Amp hours (Ah) = capacity

    3Ah is the capacity of the battery. So long as the supply voltage is the same the hedge trimmer will draw the same amount of current and all will be fine. The current is determined by the resistance and the voltage. Battery voltage drops a little when it's under load. The bigger the load the bigger the drop. Often higher capacity batteries will maintain voltage better so the trimmer may draw slightly more current at times but it shouldn't be enough to cause any problems.

    You are not being pedantic. It is not a case of accuracy. The post is plain wrong.
  • drlodge
    drlodge Posts: 4,826
    Volts times amps equals watts.

    Correct
    Watts are the amount of energy you have, like fuel in the tank.

    No, incorrect. Watts is the rate at which work (energy) is done, so watts is more akin to the size of the engine under the hood. The amout of fuel in the tank is more like Watt-hours i.e. total energy available.

    The bigger the engine, the more work is done, so the fuel tank will empty more quickly.
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
    Find me on Strava
  • ai_1
    ai_1 Posts: 3,060
    lesfirth wrote:
    Ai_1 wrote:
    team47b wrote:
    Volts times amps equals watts.

    Watts are the amount of energy you have, like fuel in the tank.

    18x1.5=27

    18x3=54
    Sorry to be pedantic but it can get confusing if you're not accurate (and feel free to correct me if I have any errors!)
    Watts (W) = Power not energy
    Watt hours (Wh) = energy
    Amps (A) = current
    Amp hours (Ah) = capacity

    3Ah is the capacity of the battery. So long as the supply voltage is the same the hedge trimmer will draw the same amount of current and all will be fine. The current is determined by the resistance and the voltage. Battery voltage drops a little when it's under load. The bigger the load the bigger the drop. Often higher capacity batteries will maintain voltage better so the trimmer may draw slightly more current at times but it shouldn't be enough to cause any problems.

    You are not being pedantic. It is not a case of accuracy. The post is plain wrong.
    Stop being pedantic about my lack of pedantry! ;)

    I was trying to he nice about it.
  • JayKosta
    JayKosta Posts: 635
    The BIG questions are:
    1) Will the battery FIT into your device.
    2) Will your charger work with the new battery - same physical size, contact points, etc. Or does the new battery come with its own charger. Does the new battery indicate what type of charger is needed?

    Jay Kosta
    Endwell NY USA

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