Power Consumption Question

[ResidentG33k]

Hey everyone. I have a Laptop connected to a power inverter to power my laptop while im at work. Because gas is soo expensive, i keep my car off but last time i did keep it off for about 4 hours, killed my battery. So I got a new battery from Costco and I wanted to know how long could I keep my car off without killing my battery? I work security which is why I sit in my car for such a long period and i use the internet through my phone to my laptop and I need some tunes so I listen to tunes through Sirius Satellite Radio (or should I say Sirius XM Satellite Radio - Because of the merger). *Specs Below*

Laptop:

Thinkpad T41

Power Adapter Input: 100v-240v~1.9A 50/60hz

Power Adapter Output: 16v==4.5A

Power Inverter:

Input: 13.8V DC==8A

Output: 115V AC~ 60hz 100Watts

My Battery:

Cold Cranking Amps at 32 Degrees F: 800

Cold Cranking Amps: 640

Car Stereo: Panasonic CQ-C3303U H/U

Sirius Satellite Radio: Stratus4

Stock Alternator for my 1997 Nissan Sentra

Any ideas of how long my battery could last on basic usage? I dont really listen to my radio loud with my car off... Let me know what you think and how long i could leave my car off without killing my battery and how long i'd need to turn my car on for to make sure the battery stayed charged. Been in my car for about an hour now and I've had the car off but started it about 10 minutes ago for about 5 minutes. Thanks!

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[BoxdGM 10+ year member]

cant help ya with an exact time but most inverters (everyone ive ever bought) has a low voltage cutoff, meaning that if you leave it on it will shut itself off with enough power to start the car.

My old crown vic had a remote start so if the power went out i would run an extension cord to the car to the inverter from a lamp inside and when the lamp had been on too long it would just turn off and i would use the remote start to start the car and charge the battery to get the light on again.

I can go to the drive in which plays 3 movies in a row without starting my car, and at the end it starts fine. The inverter is turned on by the remote wire from the deck so its on all the time even if im just using the radio plus my battery has to run 2 amps and the head unit.

It could have just been a dying weak battery or try a new inverted that says it has a low voltage cutoff

 

[ResidentG33k]

No Power Draw Protection on the Power Inverter. It almost killed my battery =/ Arent there smaller power inverters that draw less power? This was a power inverter that I bought from Walmart i think, its a 150Watt power inverter and plugs in to my cigarette lighter.

 

[helotaxi 5,000+ posts]

You need a big enough inverter to power the laptop. 150w is about as small as you can safely go. I'd get a second battery that is a deep cycle design. Draining a normal starting battery deeply will destroy it. You can deeply drain it without damaging it. I'd keep your starting battery under the hood and put the deep cycle in the trunk. Separate them with an isolator or solenoid. That way you can drain the deep cycle and your starting battery will still be good to start the car.

 

[DidUHearThat? 10+ year member]

If you plan on doing this often, you need to do as helotaxi suggested. I have installed a second isolated deep cylce battery because I like to use my system and other electronics for extended periods with the engine off.

It's hard to calculate your time exatcly, but my best guess is your already in a danger zone running your laptop/inverter/radio for even 1 hour with the engine off. The battery is new and strong, but it wont' stay that way with this abuse. It's not designed for this. You need a second deep cycle battery.

Also your charging time needs to be GREATER than your draw time. 1 hour off needs to be matched with at least one hour with the engine on. 5 - 15 minutes of charging time is just not enough to bring your voltage back up. You can install a voltage monitor to help you watch for voltage drops. When the voltage starts to drop, it will drop fast and keep going faster and faster. Called the sudden death syndrome.

 

[helotaxi 5,000+ posts]

The battery will recharge much quicker than it discharges when its only a low current discharge. That 150w inverter is only probably drawing 8A or so. The battery will recharge at a much faster rate. It's not optimal to recharge a normal battery that way when it's fairly deeply discharged but that's what will happen when it's being charged by the alt. The battery should be close to fully charged after only 15 min or less under those conditions.

An extension cord out of the question? Spare batt for the laptop?