Laptop Power Supplies

[hollis_f]

OK, I have two laptops each with thier own power supply. Both have the same plug, the same polarity and the same voltage (19V). The only difference is that one is rated at 1.6A and the other at 5A.

If I were to attach the 5A power supply to the lappy that came with the 1.6A power supply am I correct in assuming that all would be fine as the lappy would only draw 1.6A.

Contrarily, would attaching the lappy with the 5A power supply to the 1.6A source cause the power supply to overheat as it tries to pump them electrons through too quickly?

When I'm away with both laptops I'd like to just bring the single power brick.

[OdiN1701]

The 1.6A supply wouldn't be able to power the 5A laptop so it probably wouldn't charge right - or if it had no charge you may actually cause damage to the laptop.

You are correct that the 5A supply should provide the 1.6A laptop with the appropriate power - however, efficiency of power supplies comes into play here as well. The 5A supply will likely generate more heat if only 1.6A is being trickled out of it because it's designed for more than that. Probably will decrease the life of the supply, but who knows if you'll ever notice that - probably won't.

I would get a multimeter or find someone who does and have them test the actual voltage that is coming out of each supply, just to make sure.

[Xtreme2k2]

I wouldn't suggest doing it.

[neil_g]

I wouldn't suggest doing it.

likewise id be very cautious. if the psu is going to generate more heat it may do it to an extent where it could burn out and cause a fire hazard. possibly.

[OdiN1701]

BEFORE DOING IT:

This is important - the supply has to have a voltage regulator! You need to check that.

If you are only drawing 1.6A from a 5A supply without a voltage regulator - suddenly you aren't getting 19V anymore, but higher - and that can fry your laptop - or at least the power board inside.

If it has a regulator it should keep the voltage output at 19V regardless of how many amps your device is pulling.

This is your main concern.

The 5A supply may heat up running 1.6A only, but it shouldn't be too bad as far as fire hazzard. Monitor it during use and if it gets too hot, stop using it. I bet it would be fine though.

The 1.6A supply though - if you run 5A through it you could melt the wire and start a fire and all sorts of fun stuff, along with possible damage to the laptop.

If you don't have any idea what I'm talking about - don't do it :p

[MaxxuM]

OK, I have two laptops each with thier own power supply. Both have the same plug, the same polarity and the same voltage (19V). The only difference is that one is rated at 1.6A and the other at 5A.

If I were to attach the 5A power supply to the lappy that came with the 1.6A power supply am I correct in assuming that all would be fine as the lappy would only draw 1.6A.

Contrarily, would attaching the lappy with the 5A power supply to the 1.6A source cause the power supply to overheat as it tries to pump them electrons through too quickly?

When I'm away with both laptops I'd like to just bring the single power brick.

The 5A can be used on both or either. It simply has a higher rating than the 1.6A. The only down side is that if there is a surge on the line the 5A transformer may allow too many amps to the 1.6A laptop and burn it out. The other way around (1.6A on 5A laptop) may underfeed it and over time damage the laptop. Most modern laptops will warn you (if the battery has juice) that you are overvolting or undervolting your laptop.

Think of it in a sink metaphor... The pipes are the amps and the water is the volts. More amps (bigger pipes) the more volts (water) will be able to flow. Amps or Volts, the device will only (unless there is a problem) draw as much volts as it needs. The only issues is surges from the power company getting through the transformer.

It's been a while since I did any electrical work, but I think thats about right.

Edit: Sorry I mangled that because I was on my way out to lunch. The 5A transformer is perfectly fine in other words.

[OdiN1701]

You got that mixed up. It will only draw as much Amps (current) as it needs - if it needs more than available, that's what becomes an issue and you are underpowered which can damage the device (5A device on the 1.6A supply).

If a supply is spitting out 50V and you plug a device into it that only requires 20V, you'll likely damage that device seriously.

[MaxxuM]

You got that mixed up. It will only draw as much Amps (current) as it needs - if it needs more than available, that's what becomes an issue and you are underpowered which can damage the device (5A device on the 1.6A supply).

If a supply is spitting out 50V and you plug a device into it that only requires 20V, you'll likely damage that device seriously.

Yea, it's been a while - I got it the other way around. Still, the 5A transformer should be fine because either device will not draw more than 5A (the other 1.6A). He cannot use the 1.6A transformer for the 5A device because it cannot supply enough current. 5A ok, 1.6A no for the 5A laptop.

I'm thinking of it in terms of a house with 2x120v +1 neutral coming in from the pole. Most circuits will be 15-20, larger devices 30-40 and sub-panels 50-100. As long as the gauge is correct for amperage, the voltage of the device is rated as 120v and the total amperage does not exceed the breaker rating all is fine. So, for the above user, the only difference is amps therefore it is rated for 'more' draw than is actually going to be used. Theoretically, he could add another 1.6a device that draws 19v to the 5A transformer and still be perfectly fine because total draw is still under 5A. Correct?

[OdiN1701]

Yes you could run two 1.6A devices off of a 5A supply. The really important part is the voltage regulator when you're running devices that use less current on that supply. I don't imagine it not having one though.

[OdiN1701]

Think of it in a sink metaphor... The pipes are the amps and the water is the volts. More amps (bigger pipes) the more volts (water) will be able to flow. Amps or Volts, the device will only (unless there is a problem) draw as much volts as it needs. The only issues is surges from the power company getting through the transformer.


Not quite ;)

There are three main units when concerning power - Voltage (Volts), Current (Amps) and Resistance (Ohms).

With the pipe analogy, the water pressure would be Volts. The flow rate (how much water is coming out) is current. The size of the pipes would be resistance.

Increase resistance (smaller pipes - it makes it harder for water to enter = more resistance) and your flow of water (current/amps) will be reduced. Volts aren't affected because your water pressure is the same - it just has more resistance and that is why you get less current.

[MaxxuM]

So, as long as the 5A transformer is rated at high enough watts (which the OP said was identical), then all is fine. I believe it is watts/volts = amps drawn

hollis... just plug in the numbers from each of the devices. As long as they are both under 5A you're peachy.

Watts ________ / Volts 19 = _______ draw must be <= 5A

[MaxxuM]

Not quite ;)

There are three main units when concerning power - Voltage (Volts), Current (Amps) and Resistance (Ohms).

With the pipe analogy, the water pressure would be Volts. The flow rate (how much water is coming out) is current. The size of the pipes would be resistance.

Increase resistance (smaller pipes - it makes it harder for water to enter = more resistance) and your flow of water (current/amps) will be reduced. Volts aren't affected because your water pressure is the same - it just has more resistance and that is why you get less current.

Yep, I believe I came the to the right conclusion but from the wrong street. It's been yeas since I worked on power.

[OdiN1701]

So, as long as the 5A transformer is rated at high enough watts (which the OP said was identical), then all is fine. I believe it is watts/volts = amps drawn

hollis... just plug in the numbers from each of the devices. As long as they are both under 5A you're peachy.

Watts ________ / Volts 19 = _______ draw must be <= 5A

Yeah P (Watts) = V (Volts) * I (Ohms) is the normal equation.

As long as the supply has regulated voltage, as long as you do not exceed the amperage rating, you're fine.

Watts don't really matter.

If you have a 90W power supply that is 5A, you're going to be putting out 18V. Simple math. Watts don't really come into play. If you exceet the wattage rating of a power supply, you are simply drawing too much current (Amps).