laptop - Do power adaptors automatically adjust current and voltage?
2014-07
usercr
I purchased a new power adaptor (19.5 V, 3.33 A, 65 W) for my Compaq Presario v3000 laptop, as replacement for the old one (18.5, 3.5 A, 65 W). It is listed as compatible with my laptop model.
Does the new adaptor automatically adjust based on current drawn?
David Schwartz
The new adapter will output 19.5V, or very nearly that, regardless of the current the laptop draws, unless it exceeds the supply's maximum output. It's possible that 19.5V is inside the safe input range for your laptop, and it's possible that 3.33A is sufficient. It's also possible that 19.5V is dangerously high for your laptop or that 3.33A is insufficient. But assuming whoever listed it as compatible knew what they were doing, then the ranges must safely overlap.
barlop
Sounds strange to me that the voltage isn't right.
Voltage has to be absolutely right. I tend to see it specified to 1 decimal place, so, it should be right to 1dp. Use the specified voltage.
When it comes to amps, the device uses what it needs. So the power supply's Amps need to be >= what the device needs.
I guess it's possible that when it's as high as 18V then 1V might not make or break it but that's a wild guess to say that and I wouldn't be keen on trying it. You're meant to use the correct voltage.
Questioner
Possible Duplicate:
Laptop power supplies, does current matter?
I have the opposite problem outlined in Laptop power supplies, does current matter?
My AC adapter (19 V, 3.95 A, 75 W, 3-pin) Part No. PA3468E-1AC3 for Toshiba Laptop L40 18Z is now useless. I am currently risking using an IBM Thinkpad adaptor (my old laptop) after checking the specification. The centre pin polarity is the same, I cannot currently find any references to Wattage output for the IBM adaptor - but the only difference I can find is in current and voltage.
The defunct Toshiba adapter is rated 19 V and 3.95 A. The IBM adapter is rated 16 V and 4.5 A.
I've used the IBM for several hours with no ill effect - risky I know! The lower voltage means that the battery isn't charging - but my concern is the higher current - 0.55 more.
Could this damage the sensitive internal electrics in the longer term - or is it unlikely to make a difference. If it works, which it does - could I confidently continue to use this until I've sourced a proper replacement?
Peter Mortensen
Here's the deal. The voltage SHOULD match (power adapters provide a steady voltage over a range of currents), whereas the current MUST meet or exceed.
If the voltage is too low, you'll get either nothing, or odd / failure behavior when the power draw on the system gets high. If the voltage is too high, you'll risk damaging the equipment you are powering.
If you have too low a current, you will either burn out the supply, trip a breaker or fuse in the supply, or the equipment will not work or fail unpredictably at high load.
If you have too high a current, the system simply won't draw as much power as the supply can provide. The supply might be a little less efficient, but no harm is done.
Peter Mortensen
The current rating is the amount that's available. It's not getting forced on the device that it's connected to. For comparison, you can plug your toaster into the same outlet as you'd plug your vacuum cleaner into, but the current they draw (and can handle) is quite a bit different. (This is for comparison to the output of the adapter, ignoring the AC input side.)
I'd be more worried about the undervoltage. It may put a strain on the voltage regulator in your laptop and may also put a strain on your battery (which you might consider removing while your using the mismatched power supply).
Turbo J
If the battery is not charging it should not do any damage. You might save a bit more by dimming the LCD.
Besides: 16V x 4.5A = 72W power.