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Voltage and Amperage

Discussion in 'Off Topic' started by shark2k, May 18, 2009.

  1. shark2k

    shark2k Member

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    Ok, so I'm not an engineer or scientisty guy or anybody like that that would understand the relationship between voltage and amperage so I'm hoping you guys can help me out. I've googled this for about an hour or so but couldn't come up with anything that answered my question simply or with a good example.

    Basically I am wondering what the relationship between voltage and amperage is. Let me explain why this came up. I was looking up electric lawn mowers (the Neuton CE 6 and the Black and Decker) powered by battery. The Neuton uses a 36-volt, 10-amp hour battery which gives it 360 Watt-hour. The Black and Decker uses a 24-volt, 17-amp hour battery which gives it 408 Watt-hour. Now, to me the 408 Watt-hour would seem better (and according to Neuton you should compare the Watt-hour rating of battery powered mowers. If this is the case then the B&D would be better, correct?

    Now, back to my original conundrum. I don't understand the relationship between voltage and amperage. I found something that stated basically voltage is how much electricity there is and amperage is how fast that electricity is moving (if at all) (this was found here: WikiAnswers - What is the difference between amperage and voltage) So my understanding from that would be that the 36-volt, 10-amp hour battery has more electricity but it would move slower and the 24-volt, 17-amp hour battery would have less electricity and move faster. Is that correct at all? And if so, wouldn't that make the battery for the Neuton better than the battery for the B&D?

    -Shark2k
     
  2. vfx

    vfx Well-Known Member

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  3. TEG

    TEG TMC Moderator

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    This probably won't really answer your question, but here are some ideas.

    Thinking of electricity like water is helpful.
    High voltage but low amperage is like high pressure water through a straw. It can squirt over a large distance, but it isn't going to knock you over.

    High amperage low voltage is more like a slow moving flood.

    The watts is like how much water you have.
    So if you equated one watt to one bucket of water you could transfer it two ways. You could dump the bucket on the ground and watch it dribble along... That is like high amperage low voltage. You could also spit the same bucket of water through a straw. It would be harder to empty your bucket you could squirt the water a lot further. That is like low amperage, high voltage.

    If you have high voltage and high amperage then think of a fire hose.

    So you can have two kinds of batteries with the same stored energy... Say 1kWh... So it can release 1 watt for an hour. You could have different types of cells in your pack so one could do it as 1 volt @ 1 amp, but another kind does it as 2 volts @ 1/2 amp, and another 1/2 volt @ 2amps.
    The differences in voltages affect how useful this pack would be at powering different devices. Given a particular lawn mower for instance it may be possible to get a more efficient electric motor that runs at a higher voltage.
    So the lower watt hour pack ~may~ be able to use its' watts more effectively. Another thing would be torque characteristics of the motor. I think the higher voltage (in your example) could get you a motor with more starting torque and it might be able to tackle denser grass. There is no guarantee from just knowing the pack specs though - you could have to find out motor specs and such. Also it is possible to have extra circuit convert the power flow to different volts / amps, but they are costly and take up room, so many low end devices just run the motor at pack output voltage.

    Some other thoughts -

    With higher voltage you can pass more current (watts) through a thinner wire but you need more insulation since higher voltage can jump through longer distances.

    Higher voltages get more dangerous as the electricity can start jumping through your skin. If you touch the terminals of a 12V car battery with your hands you generally don't feel anything. The voltage isn't enough to arc through your skin into your conductive blood. On the other hand a 120V household outlet can shock you if you touch the electrodes. With a million volt Tesla coil you can be 10 feet away and still have it arc into your body.

    Something like a Taser device can take a low amperage 9V battery and boost the voltage up and generate a 50KV spark that upsets someone's nervous system but doesn't have the amperage to set them on fire or burn them.


    Hopefully someone will correct me if any of these ramblings are techincally incorrect.
     
  4. TEG

    TEG TMC Moderator

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    (VFX jumped in ahead while I was typing!)
     
  5. vfx

    vfx Well-Known Member

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    Working smarter! (Now called "Dowding") :tongue:
     
  6. johnr

    johnr Member

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    Assuming both mowers are identical in motor horsepower, the B&D at 408 watt-hours would run longer on a charge ... on the other hand, a 36 volt motor is usually more powerful than a 24 volt, which would give the Neuton an advantage. Although this isn't always the case.
     
  7. shark2k

    shark2k Member

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    Thanks for the replies. I have a better idea now.

    -Shark2k
     

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