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Combining notebook (laptop) chargers for more POWER ?

HauntedAccount

Apr 14, 2015
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Hello,

First of all, I am new here so sorry if I made any mistakes (including wrong box and everything).
My notebook charger recently died. I am looking to buy a new one but the problem is I have a 120W charger and they only sell 60W chargers locally (I can get a 120W model but it would be over-the-top expensive). I did some research and I found that chargers can be combined to get more power. I am looking to buy 2 identical 60W chargers and splice them together in order to get 120W charger (theoretically). The other problem is there might be a slight voltage difference between the two charger and that would resulted in an unwanted flow of electricity - which I could sove with a couple of diodes. Then another problem arise: There will be 60W (max) flowing through each diodes so choosing one would be quite a dilemma. I am looking at some Schottky's but the datasheets are quite perculiar (0.7V drop for a Schottky, wut) and it would be impractical. Can anyone shed some light on this subject? Are there any other problems that I should be concerned about?

TL;DR: Want to combine 2 60W chargers to get 120W. Need help choosing diodes. Any other problems?

Thanks in advance!
 

BobK

Jan 5, 2010
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Diodes are the wrong way to combine two supplies that you want to share equally. You need to use resistors instead. I would check the output of the two chargers, determine how much voltage difference there is at full load, then use resistors that would compensate for this difference i.e. drop more than that voltage at the rated load. For example, if the difference is 100mV I would calculate the resistor to drop 200mV at the rated current.

Bob
 

HauntedAccount

Apr 14, 2015
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Hello Bob,
Nice to see a reply. Unfortunately, I cannot measure the output as I don't have any device capable of doing so. Will there be any problems if I were to just hook them together straight (ground to ground, 19v to 19v, parallel)?
 

BobK

Jan 5, 2010
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Yes, the one with the higher voltage would supply all the current.

19V 60W gives me all the info I need. That comes out to 3.15A.

I would use resistors that drop 250mV. Which works out to 0.08 Ohm resistor. They would need to be 1W resistors, though I would go 2W for extra safety. You could go to 0.1 which would be easier to find. Be aware that they will get warm.

Bob
 

BobK

Jan 5, 2010
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You put a resistor in series with each power supply's + line, connecting the other sided of the together to go to the laptop.

Bob
 

HauntedAccount

Apr 14, 2015
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Sorry for not replying on time. Anyway, you mean like this (excuse my awesome drawing skill)? Do I need anything else to further ensure that I won't burn down any facilities and/or the charger itself won't drop dead? Thanks in advance!
OZL9tD9.jpg
 

BobK

Jan 5, 2010
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Diodes are used to make the higher voltage supply give all the power. Resistors are used to share power more equally. Neither will guarantee equal sharing, but resistors will do a better job of it.

Bob
 

HauntedAccount

Apr 14, 2015
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One final question: Can I plug your system in and expect it to work for a long period of time at fairly high load?
 

BobK

Jan 5, 2010
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Yes, as long as you size the resistors correctly.

Use P = I^2 R

Then use resistors that have twice that power rating.

Bob
 

ramussons

Jun 10, 2014
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http://www.edaboard.com/thread98883.html

I've been Googling around for a while now and these and many other guys says that I should use diodes. I'm confused. Care to explain?

Thanks

Diodes are used to provide, what is termed as, Isolation. If you have more than 1 stand alone power supply feeding a load, these "Isolation Diodes" prevent a faulty PS unit from "sinking" power from the other sources. They cannot be used to balance or share the load. In this particular application, it may not be required.

Resistors are used to reduce the imbalance in load sharing.
 
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