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Common beliefs related to electricity

Chrono HelixChrono Helix Registered User regular
edited June 2008 in Help / Advice Forum
1: When recharging rechargeable devices (mp3 players, handphones etc) you should only do so when the battery is flat. Otherwise the battery life will shorten.
2: Leaving a lightbulb on continously for a long period of time is more efficient (uses less electricity or leads to longer bulb lifespan) than having it turned on and off a few times over the same period of time (doesn't have to be rapidly changed, could be a few hours in between flicks of the switch)

Are both of these true? Why?

Chrono Helix on

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  • exisexis Registered User regular
    edited June 2008
    1: When recharging rechargeable devices (mp3 players, handphones etc) you should only do so when the battery is flat. Otherwise the battery life will shorten.
    2: Leaving a lightbulb on continously for a long period of time is more efficient (uses less electricity or leads to longer bulb lifespan) than having it turned on and off a few times over the same period of time (doesn't have to be rapidly changed, could be a few hours in between flicks of the switch)

    Are both of these true? Why?

    As for 1, as far as I'm aware it depends on the type of battery. Certain types (eg Nickel-cadmium) have a memory effect, which causes the maximum capacity of the battery to decrease each time it's charged from more than completely empty. Lithium-ion batteries have no memory effect, and I believe they're now standard in most digital cameras. Lithium-Polymer batteries are common in mobile phones now, these also have no memory effect, I think originally they were mostly Nickel-metal-hydride, which suffered from memory effect also.

    So it depends. Lithium batteries it doesn't really matter. Nickel batteries it does.

    edit: While checking facts I found this kind of interesting:
    Wikipedia wrote:
    Unlike Ni-Cd batteries, lithium-ion batteries should be charged early and often. However, if they are not used for a long time, they should be brought to a charge level of around 40% - 60%. Lithium-ion batteries should not be frequently fully discharged and recharged ("deep-cycled") like Ni-Cd batteries, but this is necessary after about every 30th recharge to recalibrate any external electronic "fuel gauge" (e.g. State Of Charge meter). This prevents the fuel gauge from showing an incorrect battery charge.
    I remember my old phone would show full battery, then as soon as I sent to text, drop down to one bar and turn off a few seconds later. I suppose that was why. Hm.

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  • JAEFJAEF Unstoppably Bald Registered User regular
    edited June 2008
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  • WillethWilleth Registered User regular
    edited June 2008
    Electrical devices will use a greater amount of electricity during the act of turning them on than they do by leaving them on for the same amount of time - this is because there is a slight electrical surge at first. With lightbulbs it doesn't matter, but with things like cars it can be more efficient for your battery to leave it running while you run into the house for two minutes to grab your coat. This is also why 95% of the time a lightbulb will burn out when it's turned on rather than while it's already on.

    With phones and such I tend to recharge when fully flat, but for me it's more to do with the device readout - my laptop, for example, tells me I have 30 minutes remaining based on the average charge/discharge time (I think), and I want it to be accurate. The easiest way of doing that is by only charging it when it's fully discharged.

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  • Synthetic OrangeSynthetic Orange Registered User regular
    edited June 2008
    2: Leaving a lightbulb on continously for a long period of time is more efficient (uses less electricity or leads to longer bulb lifespan) than having it turned on and off a few times over the same period of time (doesn't have to be rapidly changed, could be a few hours in between flicks of the switch)

    How the hell did this one even arise? The answer is NO.

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  • 1ddqd1ddqd Registered User regular
    edited June 2008
    Actually, and this comes with a big grain of salt, Mythbusters proved that there was no discernible difference but that theoretically, if you were to switch a light on and off rather than leaving it on for hours at a time, you would use more switching it on and off.

    Theoretically. MythBusters. Yeah, it was a boring episode.

  • whuppinswhuppins Registered User regular
    edited June 2008
    You see a lot of beliefs like the light bulb one, and I think they spring from similar debates with much more complicated, less efficient systems like car engines and HVAC systems. For these types of things, there's at least a legitimate discussion going on. It doesn't really carry over to something as simple as a light bulb.

  • tsmvengytsmvengy Registered User regular
    edited June 2008
    whuppins wrote: »
    You see a lot of beliefs like the light bulb one, and I think they spring from similar debates with much more complicated, less efficient systems like car engines and HVAC systems. For these types of things, there's at least a legitimate discussion going on. It doesn't really carry over to something as simple as a light bulb.

    I remember reading a study that someone did about this where they took into account the cost of the bulb vs the wear and tear from turning it on and off and decided that the threshold time for leaving the light on was 3 seconds or something like that. So if you're going to leave the room for 3 seconds and then come back, leave it on, otherwise turn it off.

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  • MidshipmanMidshipman Registered User regular
    edited June 2008
    I'm pretty sure that the thing about light bulbs is referring to the old heavy ballast fluorescent lights (the kind with long tubes that often flicker for a bit before turning on). Newer fluorescent bulbs (any of the compact ones for example) don't use nearly as much power on start-up. Even with the old lamps it was probably only wasteful if you were turning a light off for only a few minutes.

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  • FellhandFellhand Registered User regular
    edited June 2008
    2: Leaving a lightbulb on continously for a long period of time is more efficient (uses less electricity or leads to longer bulb lifespan) than having it turned on and off a few times over the same period of time (doesn't have to be rapidly changed, could be a few hours in between flicks of the switch)

    How the hell did this one even arise? The answer is NO.

    Well it follows the same principles of physics that most systems do, in that it takes more energy to start any system than it does to keep that system going.

    So like with a light bulb it might take 5 units of energy to start it, but only 2 to keep it running once it's started (these are not units or concrete numbers, just trying to show that it uses more to start). As to whether it's more efficient than turning it off for a period and then turning it back on, it depends on how long of a time this is going to span.

  • SeptusSeptus Registered User regular
    edited June 2008
    2: Leaving a lightbulb on continously for a long period of time is more efficient (uses less electricity or leads to longer bulb lifespan) than having it turned on and off a few times over the same period of time (doesn't have to be rapidly changed, could be a few hours in between flicks of the switch)

    How the hell did this one even arise? The answer is NO.

    I think it's confusing efficiency for energy, and the efficiency of the lightbulb's duration. I believe you'll spend more energy but get more use out of one lightbulb by keeping it on, because the surge of energy when turning it on wears it out faster.

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  • fuelishfuelish Registered User
    edited June 2008
    Willeth wrote: »
    , but with things like cars it can be more efficient for your battery to leave it running while you run into the house for two minutes to grab your coat. This is also why 95% of the time a lightbulb will burn out when it's turned on rather than while it's already on.

    Explain. Your car constantly charges the battery. There is no gain from leaving the car running as there is more than enough juice in the battery to crank the motor over with no future strain on the charging system. There is no gain from leaving a car running. All motors use 0 fuel when off. Modern motors with fuel injection use fuel only when the ignition is firing. The alt on a car produces way more energy than the car needs. IMHO, cars in the near future will use something like the clutch on the AC unit to reduce load on the motor when it is not needed. When the batt is maxed, the alt will not be turning. When the cooling system is cool the water pump will not be spinning. I think this would be better handled by an electric pump, then it could spin at an optimum rate for cooling with out extra system load.

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  • WillethWilleth Registered User regular
    edited June 2008
    fuelish wrote: »
    Willeth wrote: »
    , but with things like cars it can be more efficient for your battery to leave it running while you run into the house for two minutes to grab your coat. This is also why 95% of the time a lightbulb will burn out when it's turned on rather than while it's already on.

    Explain. Your car constantly charges the battery. There is no gain from leaving the car running as there is more than enough juice in the battery to crank the motor over with no future strain on the charging system. There is no gain from leaving a car running. All motors use 0 fuel when off. Modern motors with fuel injection use fuel only when the ignition is firing. The alt on a car produces way more energy than the car needs. IMHO, cars in the near future will use something like the clutch on the AC unit to reduce load on the motor when it is not needed. When the batt is maxed, the alt will not be turning. When the cooling system is cool the water pump will not be spinning. I think this would be better handled by an electric pump, then it could spin at an optimum rate for cooling with out extra system load.

    You know a lot more about cars than I do. It was just an illustrative example of something that uses more power than a lightbulb.

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  • desperaterobotsdesperaterobots Registered User regular
    edited June 2008
    This thread is relevant to my interests. I always worry about charging things 'mid-charge' because 'uh-oh memory effect', which I remember was a huge problem with video cameras in the highschool media lab. Heh.

    Good to know!

  • GihgehlsGihgehls Registered User regular
    edited June 2008
    It uses more gas to start a car than it does to make one idle. That's what they are talking about. Also, with the turning on of the light bulb, you are more likely to have a light bulb pop because you are cold starting the filament, making it change shape rapidly. Leaving it on leaves the filament at the same size.

    Also read this http://forums.penny-arcade.com/showpost.php?p=2766808&postcount=8

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  • JasconiusJasconius sword criminal Flo-ridaRegistered User regular
    edited June 2008
    I heard the bulb thing with regards to florescent, not regular light bulbs.

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  • PheezerPheezer Registered User, ClubPA
    edited June 2008
    1ddqd wrote: »
    Actually, and this comes with a big grain of salt, Mythbusters proved that there was no discernible difference but that theoretically, if you were to switch a light on and off rather than leaving it on for hours at a time, you would use more switching it on and off.

    Theoretically. MythBusters. Yeah, it was a boring episode.

    No, they proved that it was never ever ever going to happen in anything approaching a real world scenario. It's a complete myth. It doesn't actually happen.

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  • fuelishfuelish Registered User
    edited June 2008
    Gihgehls wrote: »
    It uses more gas to start a car than it does to make one idle. That's what they are talking about. Also, with the turning on of the light bulb, you are more likely to have a light bulb pop because you are cold starting the filament, making it change shape rapidly. Leaving it on leaves the filament at the same size.

    Also read this http://forums.penny-arcade.com/showpost.php?p=2766808&postcount=8

    Only with a cold motor. Otherwise it is pretty much myth even when considering a carbed motor(Kind of off topic but a wasteful myth nonetheless)

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  • PheezerPheezer Registered User, ClubPA
    edited June 2008
    Gihgehls wrote: »
    It uses more gas to start a car than it does to make one idle. That's what they are talking about.

    Then "they" are completely and absolutely incorrect.

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