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I have Toshiba satellite l505 laptop and the ac-adapter is damaged. i found new adapter but it's output is 19v 3.4a and the output for the laptop is 19v 4.7a. is that safe to use the lower voltage?

  • This question over on Electrical Engineering has some very good information on power supplies. – Hennes Jun 2 '13 at 10:20
  • Is there a sticker on the back of your laptop that states its current requirement? Which exact L505 do you have? Some need as little as 3.42A and some need as much as 6.3A. – David Schwartz Jun 2 '13 at 10:30
  • yes it states 19v and 4.74a – Sherif Sabry Jun 2 '13 at 13:33
  • It'll probably work, but may overheat. The danger of fire is small and of explosion is negligible. I wouldn't hesitate to use such an adapter in an emergency/short-term situation, though I'd keep checking it for overheating (too hot to hold comfortably) and would avoid stressful activities (eg, gaming, where you hear the CPU fan revving up.) – Daniel R Hicks Jun 2 '13 at 13:36
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Understanding Voltage and Current.

An analogy with water in pipes is often helpful in understanding the basics of electricity.

Voltage is like water pressure. It is a force. If the force is too strong your pipes will burst. Too low and your shower may not work at all.

Current is like flow-rate. Litres per second or how fast your bath fills. It depends on how big your supply pipes are. If your water supply has a low flow rate, you won't be able to fill your swimming pool in 10 minutes. If your water supply can fill your pool in 10 minutes, you can still use it to connect a drip-watering system for your pot-plants that only draws a cupfull a day of water.


Voltage

If the laptop requires 19V you should use an power-supply that provides the same voltage. If the power supply voltage is significantly more, it will damage your device and could start a fire. If the voltage is less, the device will not work, actual damage is less likely.

Current (Amps)

If the laptop need to draw 4.7A, your should use a power supply that is capable of providing At least that number of Amps. More is ok. Less means the device will probably not operate correctly.

Further information

See Choosing power supply, how to get the voltage and current ratings?

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    To add a specific example to this, when I first got this Toshiba A75 (as a repair salvage), it came with a 90 watt adapter (19v x 4.7a). It would be usable at the dimmest screen setting, and only for light tasks like web browsing. The laptop would stop charging the battery under any kind of load, and overheat... eventually turning off if the load continued. Only after replacing the adapter with the required 120 watt (19v x 6.3a) did the laptop operate normally (and continue to do so to this day). – Bon Gart Jun 2 '13 at 12:29
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    Another consideration is that on some brands of laptop, the power brick must be digitally compatible. Dell supplies have a third pin that allows the laptop to sense their capability. If the brick doesn't have the capability, the laptop cuts its power requirements and often the battery won't charge. – Fiasco Labs Jun 2 '13 at 15:15
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Normally when you use adapter, that has lower power output than the device you supply power to requires, adapter will simply heat up and die. In case of laptops, where battery has some charging logic, it will probably not charge or take very long time to charge, depends on how you use this laptop. I don't know if the adapter will explode in this case though. I will certainly not recommend using lower amperage adapter than Toshiba specifies.

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