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I have this projector which takes in 19v and has a power consumption of 65 watts.

I want to buy a 12v 6A car inveter, that plugs in the cigarette lighter, which would give me 72 watts.

The question is if it will drain the car battery if the engine is running or if there is any risk of frying anything up.

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  • \$\begingroup\$ I'd use a larger safety margin on the power specification. Depending on the quality the ratings may be inflated. To give you an idea of power, your car headlamps are 55 W each on dip. Most at risk of being fried is the ligher socket. \$\endgroup\$ – Transistor Aug 16 at 13:30
  • \$\begingroup\$ so I should get a 12v 10A inverter and worst case, my car lighter will be fried? Will the car battery get drained with the engine running? \$\endgroup\$ – Liviu Boboia Aug 16 at 13:34
  • \$\begingroup\$ Why not use a car laptop adapter and connect it directly to your car's 12V? Most of these can output 19V as that is (or used to be) a standard supply voltage for many laptops. It will be more efficient and more compact than a separate inverter and power supply. \$\endgroup\$ – StarCat Aug 16 at 13:38
  • \$\begingroup\$ Your battery will not get drained with the engine running, providing your car's alternator supplies more than 6A (which is probably the case). \$\endgroup\$ – StarCat Aug 16 at 13:39
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My advise would be not to use an inverter, but to use a direct 12V DC- 19V DC converter such as a >70W (preferably a bit more) Laptop power supply for use in a car, which will almost certainly be able to output at 19V.

Your only concern is finding out if the laptop supply comes with the correct plug for your projector.

The advantage is that converting 12V to 19V directly is much more efficient than converting 12V to 110/240V and back to 19V again.

If you're using a car cigarette lighter type plug, please note that they're not really suitable for suppying large currents for longer periods of time. They can get very hot and even melt.

Your car's alternator should be able to deliver the more than 6A needed to keep the battery charged when the engine is running.

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Most car cigarette lighters are rated at 12V and 10A.

I have run laptops in cars using a 150W modified sine wave inverter where the laptop was rated at 65W and using the supplied 240V power adapter. I would recommend only using a pure sine-wave inverter, which causes less stress on the power supply electronics.

Check your battery but is likely 70-100Ah and you don't want to drain the battery too much otherwise you won't be able to start the car and will damage the battery. A 70Ah 12V battery has a total energy of 70Ah x 12V = 840Wh. To minimise battery damage you probably don't want to discharge it below 50% or 420Wh. So 420Wh/65W = 6.5 hours.

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  • \$\begingroup\$ How does a 65W load drain a 70Ah (@ 12V) ~ 840Wh battery in an hour? Even if you drain the battery only to 50% (which would be advisable) you will still have 480Wh =~ 7 hours. That said, I would not use an inverter in this case. \$\endgroup\$ – StarCat Aug 16 at 13:43
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    \$\begingroup\$ No, I'm not wrong and I know what I'm talking about. You mentioned a 70Ah (Amp-hour) battery, which can supply (theoretically at least) 70A for 1 hour (OR 1A for 70 hours). The 70Ah is a standardized value usually given over a period of 20 hours (which should be stated on the battery). Since the load here is 65W / 12V =~ 5.4A, a 70Ah battery can provide 5.4A for a duration of (theoretically) 70Ah / 5.4A =~ 13h. Since you should not drain a lead acid battery for more than 50%, you should be fine for at least 13h * 50% = 6.5 hours. \$\endgroup\$ – StarCat Aug 16 at 15:50

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