Charge a laptop with lower voltage
I want to charge my laptop using a 19V connector from a turtlebot. It has a special "Laptop charging connector" that delivers 2 Amps at 19 Volt (I measured 18 Volts though). I have a Lenovo that normally gets its power from an adapter delivering 3.5 Amps at 20 Volts. After I plugged my laptop into the turtlebot, the laptop started whistling like an old water boiler (but not as loud). The laptop detected that it was charging though. I didn't risk letting it charge due to the whistling. Can this Wattage difference be dangerous?
62 Answers
The whistling can be due to the switching converters in the laptop. These normally convert the 19 V from the adapter into the exact voltage that the battery needs (like 11.4 V for example). In some cases switching converters can enter a mode where the inductors in these converter circuits start making audible noises.
Probably in your case the turtlebot's output cannot deliver enough current at 19 V so the voltage drops and the switching converters in the laptop are trying to do their best to still make something usable out of that lower voltage.
The problem is caused by your laptop wanting to take more than 2 A of current which is the maximum current that the turtlebot wants to deliver.
Although it might work and charging will be slower I would advise against charging this laptop from the turtlebot, the turtlebot simply isn't powerful enough to charge your power hungry laptop.
Yes, the difference can be dangerous. How a battery should be charged depends on what kind of battery it is, and charging incorrectly can cause a battery to overheat, rupture, leak, or even explode in some cases. That includes supplying the wrong voltage, or too much current.
The laptop's charging circuits are designed to work with the laptop's adapter, so saying how they will behave with something else is speculation from anyone other than the manufacturer. They may or may not be able to safely charge your battery with the wrong supply.
In the best bad case, charging the battery with a lower amperage than it requires can build up its internal resistance, which shortens its life significantly. Again, all of this depends on the type of battery and on the specific implementation of the charging circuits, and you should consult the manufacturer of your laptop.
I'm surprised that this question was migrated from electronics.stackexchange.com. I feel like it's a simple electronics question that could have been answered there.
