Laptop charging.

Jedi

I recently purchased this 60 watt fold up solar panel. I have tested the voltage output open circuit in full sun and it is about 19v to 19.5v. The current short circuit is over 5 amps.

I recently purchased this laptop. The AC power adapter specifies an output of 19v and 2.37 amps.

Despite the fact that the solar panel is producing double the necessary power the laptop will not charge. It doesn't make any difference if the laptop is on or off.

I am keen to know why.

Estragon

My guess is the voltage on the panel is sagging below the charge voltage with load.  Normally you would have a controller between the panel and the battery to manage this.  The charger internal to the laptop will be expecting a constant voltage from the AC power brick.

You should also know that Li-ion batteries are quite sensitive to charging voltage.  I wouldn't recommend charging directly from a panel.  

dennis461

Does the laptop provide any information? Does it say anything like "AC connected, not charging."  Does it have an icon which changes from a battery to a plug?

bill von novak

Jedi said:

I recently purchased this 60 watt fold up solar panel. I have tested the voltage output open circuit in full sun and it is about 19v to 19.5v. The current short circuit is over 5 amps.

I recently purchased this laptop. The AC power adapter specifies an output of 19v and 2.37 amps.

Despite the fact that the solar panel is producing double the necessary power the laptop will not charge. It doesn't make any difference if the laptop is on or off.

I am keen to know why.

Measure the voltage and current WHILE THE LAPTOP IS CONNECTED.  Ideally with a scope.  What you will likely see is:

1) 19.5 volts open circuit for a short time, zero current (the laptop has not started to try to charge yet)
2) A sudden dip to 15 volts or so, with current rising to 1 amp or something (laptop starting to try to charge)
3) A return to 19.5 volts and zero current (laptop saw 15 volts, and therefore gave up trying to charge)

Stage 2 might be only 100 milliseconds long or so, so you may miss it with a meter.  To avoid this problem you need:

1) A battery or large cap to store power and provide a lower impedance to the laptop
2) A voltage regulator to keep the voltage at 19.5 volts.

Easiest way is to do a 12V system plus battery and use a laptop adapter.  Or you could try a panel that can give you 19 volts at its maximum power point (most panels will not) and then use a 19 volt linear regulator.  You'd also need a largish capacitor to reduce the AC impedance.

oil pan 4

Or the laptop needs a PWM power supply and the computer will only accept a PWM signal.

Hooking a solar panel directly to anything but a charge controller is usually not a good idea.

bill von novak

oil pan 4 said:

Or the laptop needs a PWM power supply and the computer will only accept a PWM signal.

Hmm.  The output of a PWM supply looks just like the output from a linear supply.  I've never seen a laptop that will operate with one but not the other.

Do you mean signaling?  Some laptops (like Dells) require a digital ID signal in a third center pin before they will begin charging; it tells the laptop what power the adapter can support.