Laptop Battery Charging DC Voltage

I have a Toshiba Laptop Computer. The battery charger output is 19VDC, 3.42 Amps, 65 watts. I ordered a dc to dc converter for use in my car. The specs of the converter that I received are 12VDC input, 15 to 17.5VDC, 6.5 Amps, 90 watts. Can I use this converter to charge my laptop even with the lower voltage? In other words is the input voltage tolerance of the computer battery sufficient to allow me to use this converter without problems? Any help or advice will be greatly appreciated.

A maximum voltage of 17.5V is probably not close enough to the designed 19V. The problem you face is that all of the control logic and regulators inside the laptop may not have enough overhead voltage to work properly. They may kinda work, but it's certainly not going to meet spec to properly charge the battery pack. You run the risk of degrading and/or burning out circuitry inside your laptop by under-volting them.

I opened up the laptop and checked the battery specs. They show 10.8V/44WH. Somehow the computer must reduce the input voltage from 19VDC to some value to charge the internal battery. Thanks for your help.

Hawkeye57 said:

I opened up the laptop and checked the battery specs. They show 10.8V/44WH. Somehow the computer must reduce the input voltage from 19VDC to some value to charge the internal battery. Thanks for your help.

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Yes, there is going to be a charge regulator/controller circuit built into the one of the boards inside the laptop. All batteries (lead-acid, NiCad, NiMH, Li-Ion, Li-Poly, etc) have specific charging needs. These are typically things like charging current vs. voltage over time, charging modes, etc. These are taken care of by those internal charge controller circuits. If you don't supply them with enough voltage, they may not operate correctly, causing damage to the circuits themselves, and possibly damage to the battery.

A more correct solution would be to find a DC-DC converter that can be set to 19VDC and supply at least 65W, or buy a power inverter (12V DC to 110V AC), then simply plug your existing power brick into that. It's not the most direct or efficient method, but you can take advantage of someone else already having done the critical design work for you on the converters.