5 ms·

Is it dangerous to use a high output power charger, like the HP TouchPad one, with a low consumption device, like a phone?

• sciwiz 14y ago
  Haven't had any problems with my Galaxy S3.
• dhbanes 14y ago
  No, the current rating is the maximum output of the charger. It's up to connected device to draw as much current as it needs, rather than the charger pushing the current into the device.
  • zokier 14y ago
    Afaik it's not that clear cut. If some kind of fault occurs in the device causing it to draw more current than designed then the lower power charger could be safer assuming it has some kind of current limiter or fuse. Ie high power charger would happily give faulty device more current possibly causing more damage (heating up, exploding batteries etc), while a low power charger could prevent that by tripping a fuse or limiting current. Of course I'm not sure if this is applicable to USB chargers which all are relatively low power.
• coin 14y ago
  It's as dangerous as plugging in a 60 watt lightbulb into an 1800 watt (15 amp) circuit
• tisme 14y ago
  No, but it is inefficient. A larger charger will have a larger 'dead load', the internal consumption of the charger. So if you plug in a very small consumer into a such a charger then percentage wise you're losing a lot of energy to heat.
  • kens 14y ago
    Author here - it's a bit more complicated than that. For a linear power supply (old-fashioned wall wart), all the unused power is converted to heat, so you'd waste a lot of energy. But for switching power supplies (such as USB chargers), theoretically only the power that is needed is used, so the efficiency shouldn't depend much on the load. In practice, larger chargers might have better overall efficiency since they can implement better circuits (for space and price reasons). But larger chargers might not optimize as much for low loads. So it's hard to say offhand whether a large charger or small charger would be more efficient for a smaller load. I did a quick test to see what really happens, plugging a Samsung phone into a iPhone charger and an iPad charger. In both cases, the charger used 3.0 watts of wall power. (The phone was turned off and charging since if it is turned on, the load fluctuates a whole lot as the phone does random things.) So my conclusion is that the size of the charger doesn't affect efficiency.
    • tisme 14y ago
      For the general case, all other parameters being equal (supply mode, quality and so on): bigger charger -> larger dead load. An iPad charger is not a 'large' charger, it's a fairly small step up from an iPhone charger, since you are reporting 3.0 watts of 'wall power' but your multiplication of scope measured values does not correct for power factor you are likely off by quite a bit on both measurements. GP mentioned a HP touchpad charger to charge a phone, I don't have a HP touch pad charger here but the specs are quite terrible [1], you'd have to measure with that specific charger to answer the specific question or you'd have to do a comparison of a large range of chargers with accurate measurement methodology in order to really answer the general question. As it is your conclusion contradicts practical engineering and I'm afraid it will not hold up in a better test, which would be to try a number of switched mode supplies of various sizes designs with various loads. Plugging in one device and doing a hasty (wrong, ignoring phase shift) measurement does not warrant your conclusion. To measure efficiency you're going to have to take the power factor[2] into account, this can be quite hard to do, and theoretical efficiency doesn't matter for a practical test (you're measuring, not theorizing). The wave forms that switched mode chargers [3] output and consequently the kind of load they represent to the grid is so irregular that most non-caloric and power factor corrected measurements will give values that are not accurate. That noise that is present on the output wires will be to some extent visible on the input side. A normal Watt meter will work best with transformer based supplies or resistive loads, accuracy for small switched mode loads will be anywhere from 'so so' to 'terrible' depending on the make and model power meter. Good brands (for instance Fluke) do most calculations right and will be able to deal with CFLs and other phase shifted loads, bad brands (I won't name them but they're killing it in the domestic watt meter department) will give wildly in-accurate results. But even a quality meter like a Fluke will still have trouble with this kind of spiky load, especially if it is small. It would probably be a good idea to (properly) describe your test rig along with the results it says: "I measured the AC input voltage and current with an oscilloscope. The oscilloscope's math functions multiplied the voltage and current at each instant to compute the instantaneous power, and then computed the average power over time. For safety and to avoid vaporizing the oscilloscope I used an isolation transformer. My measurements are fairly close to Apple's[15], which is reassuring. " But you can't really do it that way and get accurate results, instantaneous power draw using a switching supply changes several hundred thousand times per second and is likely phase-shifted so a simple multiplication is not going to work. Accurately measuring (low) power draw from switched mode consumers is a really tricky problem, it's easy enough to read some numbers from a display but I can assure you that this is not a simple problem to work on if you want to get meaningful results. [1] http://en.wikipedia.org/wiki/HP_TouchPad#Power_adapter http://en.wikipedia.org/wiki/HP_TouchPad#Power_adapter [2] http://en.wikipedia.org/wiki/Power_factor http://en.wikipedia.org/wiki/Power_factor [3] http://en.wikipedia.org/wiki/Switched-mode_power_supply http://en.wikipedia.org/wiki/Switched-mode_power_supply