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Old 09-15-2018, 07:15 AM   #10
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Join Date: May 2008
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Default Re: Modifying laptop adapter for 12v

^ That should work in theory. However, if the battery is low enough in charge, it could try to pull too much current from your adapter and trip it. The diodes will do nothing to limit the current. You will also want to check the voltage on the battery with the 15V adapter. A regular diode will typically start with a 0.6-0.7V drop and then go higher under load. So that should keep the battery charged up to about 14.4V. But be careful! You don't want to do is keep the battery voltage too high, as that will kill the battery over time.

Lastly, I suggest checking how much power the radio unit is pulling in "standby" mode (i.e. when the accessory signal gets toggled off to indicate there's no key). If it's just a few mA or less, maybe put something like 3x-4x 300-470 Ohm resistors in parallel between the diode output and the battery. That way, even if the battery is discharged, it won't trip your adapter, because the charge current will be limited by those resistors (to around 190 mA or less and each resistor will be dissipating about 0.9W or less).

Last edited by momaka; 09-15-2018 at 07:17 AM..
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