Large LCD power with inverter

**bleepjay** · 10-03-2005, 02:36 PM

I know this may be the wrong forum to post this in, but this resource is probably the only one on the internet that would have somebody smart enough to answer for me.

I have a 30" LCD TV which I am using in my car for tailgating. I have a 800w inverter that I am going to be using this for. The TV uses approximately 185W of draw, with a hi-def reciever that uses approximately 22W. I want to know how long I can run this setup without having the car running. I have a 2004 Jeep grand cherokee which supposedly has a 625 amp battery.

Does anybody know how long this will last without running the Jeep without killing my battery? I don't want to keep the car running all night, but will if I have to. If I only have to start it up like 15 minutes every hour, that would be fine too. I just have no idea where to start.

Thanks to anyone that could possibly help me with this.

-Jay

**KyferEz** · 10-04-2005, 12:22 AM

Jay, first you need to know that the 625 amps is CCA, or cold cranking amps. This does not help you to determine how long the battery will last running a constant load. You need to look for a rating called reserve capacity. That is the number that counts when determining this sort of thing.

After you know that, you can use our online calculator to figure it all out:
http://carpc.kyferez.com/Tools/Elect...Calculator.php
Click on the "Batt Discharge Time" link on the left.

Enter the battery's reserve capacity.
Enter 207 watts (185+22=207)
Enter efficiency. Just guess. I would use 50% to get the least expected amount of time it will run. Depending upon your inverter, it may be as high as 80% efficient or so.
Press Calculate

I would guess you can run the LCD and reciever for at least an hour with a fully charged, good battery. Just realize, deep discharging starter batteries like that will significantly shorten their lives. You should use a deep cycle battery instead.

Also, it will likely take longer than 15 minutes to charge a dead battery - but it is determined by the charging system in your vehicle. If you know the amount of current used to charge the battery in your vehicle (this is not the same as the alternator's output current), you can calcualte the charge time by going to the same link I gave you earlier, then click "Battery Charge Time" on the left, and enter the relevent info.

KyferEz