Simple transformer question

[JeanTech]

Hi there

I'd like to know if the following statement is correct. I would like to use a 15V 2A transformer to power a 16V 0.8A laptop.

Will the 15V 2A transformer be sufficient? The way I see it is that the power rating of the 15V transformer is 30W (15V x 2A), thus the 16V 0.8A load (16V*0.8A=12.8W) should work fine.

Will this work and could it be harmful to the transformer (or load)?


Thanks in advance
JeanTech

 

[MrAl]

Hi,

Does the laptop require an AC input or DC input?
Is the transformer really a DC wall wart or just a transformer?

 

[JeanTech]

Hi

It requires a regulated DC input so it's not just a transformer.

Hope this helps
JeanTech

 

[MrAl]

Hello again,


Oh ok, so you are saying that your 'transformer' is really a regulated DC power supply then? That sounds like it would work.

 

[JeanTech]

Hi

Ok that's good news, so I was correct by using the power calculations to determine if it would work or not?

Thanks again
JeanTech

 

[BrownOut]

Whoa! How can a 15V regulated DC power supply work when 16VDC is required?

 

[JeanTech]

haha, that's my question - if it would work. Does the power rating make any difference, I mean that the power supply can source 2A at 15VDC. Can it not then source say 0.8A at 16VDC? Or is it impossible?


Thanks
JeanTech

 

[BrownOut]

15V@2A is enough power, but the voltage is too low.

 

[Jaguarjoe]

P=EI You can have a 15,000 volt 0.002 amp device and consume the same power as the 15 volt 2 amp unit does. For a proper substitution, you must determine if its AC or DC, if DC determine if its regulated or not, match the voltage, and provide a current equal to or larger than the original one.

 

[JeanTech]

So there is no way the larger current can substitute for the extra 1 volt?

 

[BrownOut]

So there is no way the larger current can substitute for the extra 1 volt?

No way. No how.

 

[JeanTech]

Ok, thanks I understand now. Thanks very much for all the help, I appreciate it!

Regards
JeanTech

 

[colin55]

It depends on the battery voltage. The 16v requirement hay have any overhead of 4v and supplying 15v will still work.

 

[vlad777]

Access current capability can not substitute missing volts but...
On my laptop it says that it needs 19V but I'm running it on 12V from ordinary PC PSU
and it works perfectly.
All components have some min ratings and also laptops have their voltage regulators inside them.

Another thing is that higher power transformer would have its idling voltage higher and this is your
chance for extra volt.

 

[JeanTech]

Does it still charge the battery on this voltage?


I found out that my laptop actually needs 20V at 3.5A. I will try to see if the PC PSU will work for that as well, but if you said it worked with your 19V, it would hopefully work for the 20V too.

Regards
JeanTech

 

[MrAl]

Hello again,


I had said that the 15v regulated supply sounds like it would work for a 16v input requirement because the voltage difference was only 1 volt. That's because many things can run on a voltage of only 1 volt less or 1 volt more. There's no guarantee it will work, but it should blow anything out to try. For example, i had used 6v for my 9v cordless drill and it still operated with decent success.

The problem is though if it really requires 20v instead of 16v then that is a totally different story. It may not work at all but it's probably worth a try.
If the current capability isnt there though that could be a problem. Without the current some things may not work.

 

[JeanTech]

Hi

I understand what you're saying. So if I could get a transformer of about 19V with more current than the 20V laptop requires it could maybe work?

 

[kinarfi]

If you use a 15 volt AC transformer and do a full wave bridge rectification and capacitor filtered, you will get 15 X√ 2(1.4142)- 2 X the diode vf = 21.21 - 1.2 = 20 volt and the internals of the computer will probably handle the difference, maybe. Good luck, hope your using it on an older computer.

 

[BrownOut]

Kinarfi, I agree with your analysis, but he said he's using a 15V regulated power supply ( although he has continued calling it a transformer ) Better vocabulary would help.

 

[JeanTech]

Hi

Sorry, yes I actually meant a regulated power supply.

Luckily, I also have a 16 volt AC transformer. That should work perfectly with kinarfi's idea.



Thanks for all the help, I should be able to power up the laptop now

Regards
JeanTech