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Modify a Dell Laptop Power Supply (PA-10)
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Very good idea ! - MagicManu
Nice hack. - russ_hensel
By the way, for certain values of the variable resistor, this Dell power supply will shut down it's output and will not turn it on again unless you disconnected it from the mains (in advance you need to rotate the variable resistor to a suitable value). For sure it was designed to provide a fixed voltage with a good efficiency and maybe a modification of + / - 4 Volts can be ok, but to have a nice variable power supply, not really. But for such mods, BeachsideHank made a useful comment about using a linear regulator :) (I think there are as well Instructables on this)
Thank you for your feedback! I wanted to check for myself the formula (on this Dell power supply it is Vout = 2.5 x (R41 + R42||R42A) / (R42||R42A) ). I used values of the resistors on board (see my schematic from the Instructable) and the output voltage (19,5 Volt), I expected to calculate 2.5 Volt from the voltage divider at the VSENSE pin, since this will be compared with the internal 2.5 Volt reference. (R42 || R42A = 1996 Ohm). Voltage divider output (R41 and R42||R42A) for 19.5 Volt input is 0.556 Volt. For a certain frequency, R41 is parallel with R41A, in that situation divider output is 17,17 Volt. Not sure why.
Thank you for your feedback!
I understand the objective now, thanks. These devices are notoriously compact and well seled, so this was a major acomplishment on your part. - BeachsideHank
Nice workout! - marc.deloor.5
nice job of re-using electronics. i got a box old laptop power bricks somewhere i might have to give this a whirl. if a guy wanted to he could mount the variable resistor in the case and have a variable power supply. also for those that like to mess with the math the formula is given in the data sheet to figure this out without the variable resistor. just gotta scratch your head a bit more :) so i did the formula given in the datasheet for practice, and replacing the bottom two resistors with one 12K resistor would get you to around 16.5V output.who needs to buy cheap wall wort's when you can convert high quality power bricks to your desired voltages! :) - rbusch
A heroic effort to be sure, but why not use something like an LM317 and regulate the voltage outside of the power supply? This question is not meant to diminish your useful Instructable either. ☺ - BeachsideHank
Thanks for your feedback! This effort was mostly on mechanical side, on the electronics was less effort. I think this was the reason: somewhere on the circuit I have only to replace a single resistor without considering the mechanical part of the project. This modified power supply will serve my Lithium charger only and can supply around 4 Amps max, while linear regulators can supply less current, have voltage drop on them, need extra heat sink, need a case too. I used a linear regulator for a bench power supply.
Modify a Dell laptop power supply (PA-10)
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Thanks for your feedback, it may work what you are saying. You can provide the correct voltage using 5 volt USB and a regular diode and using the USB charger you should be able to give a certain amount of current. Also you need to keep an eye on a clock, divide battery capacity to the current provided by USB charger to see how much time is needed to let it charge. One I'll experiment this:)
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i think really all you would need is a silicon diode because if I remember the voltage drop typically is about .7 volts so with the diode you would have reverse polarity protection and the perfect charging voltage as usb provides 5 volts, so with the diode it should be 4.3 volts. Haven't tested this but it seems in theory all you would need to charge with usb is a diode and a cable :)
Thanks for your feedback, I agree about lipos from ebay, you can pay a few dollars for a 6000 mAh :) I use recovered 18650 from laptop batteries. Regarding the electronics I used, that micro USB module may fail as well, but I trust it since I am using this for a while and on the other hand the voltage is lower.
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