most dc-dc psu cut power at 11V.
I'm just curious. Sometimes I run my carpc off the battery just to do some random stuff like syncing my music collection. I know that deep discharging lead acids is a bad idea. Could someone give some general rule as to how low I should run my standard lead acid battery down to? At what voltage should I turn off my computer to ensure that there is still plenty of juice to start my car, and to not damage the battery?
most dc-dc psu cut power at 11V.
Just test your car. I'm sure all cars are different. It's not about how low the battery can handle, but the minimum that your car needs, right? I let mine run down to around 10v by accident once and needed a jump. I drove around for half an hour converting gasoline to electricity before I was sure I had enough juice to start on my own.
Gen 1: Pentium 3 1GHz - ATX - 2005
Gen 2: Pentium M 1.6GHz - ITX - 2006
Gen 3: Pentium M 2.0GHz - 5.25" SBC - 2007
Gen 4: (coming soon: Core2 Duo - 3.5" SBC - 2009)
...it never ends
I accidentally left my inverter (and the 15" LCD connected to it) on in my truck, and it sat for four days.
It struggled a bit cranking, but it started up just fine. That was last week.
That's as close to a dead battery that I've had, fortunately.
AMD 3500+ 2.2Ghz, MSI K9VGM-V Motherboard,
Geil 512MB PC4200 DDR2-RAM, 7" Lilliput Touchscreen, 30GB HD
300 watt RMS 2 Channel MTX AMP, 500 watt RMS D-Class MTX AMP, 2 Front - 5 1/4" Sony Xplods,
2 Back - 6 1/2" Sony Xplods, 12" MTX Sub
I personally can run my system (with inverter) for about 1.5 hours before I start running into issues. Thankfully my car turns over pretty easy, but any lower and i'd have to jump.
If you're worried about your car cranking, i'd suggest a red-top instead. They have more cranking power than the yellows and will be more likely to start up every time. You aren't supposed to deep cycle them, but it sounds like you aren't looking to do that anyway.
If you run the battery down often, invest in a small battery charger. I've been thinking of installing a battery charger in my car (I have a big external one already)...so that I could plug it in and vnc into it at home to do updates, sync, etc... without discharging the battery. Your needs will vary from mine, as I don't like to idle my car very long and I need a full/nearly full good battery to start it. As a computer tech, I'll be VNCing often, so I'll be using the carputer without the car running. As an ex auto tech, alternators don't last as long if they must fully charge a battery and power all the electronics very many times (vs. just topping off the battery from the starters drain). Battery chargers are good
my car pc has been the cause of many flat batteries. Before i got the ignition wire wired to it i used to manually pull the inline fuse out to kill the carpc in the boot. But sometimes id forget and byt he morning.. cars as flat as a pancake. But all sorted now. However ive had screen up, carpc running with no engine running for over an hour or more and its fine. But then i do have a 1.9 diesel car and they generally have better batteries.
I dont like doing this now as i have a sub and amp aswell running. If in doubt you can get an extra battery and a split charging system which means your car pc will run off one battery and the starter motor for your car will run off the other meaning you can never leave your in an unstartable state however long you leave your aux devices running.