How can I make my carputer run longer?

**Bobby Digital** · 10-22-2004, 02:31 PM

I've heard everyone talk about having their carputer run for hours without the car on but I can't seem to have mine running for more than about 10 minutes before hearing the inverter low voltage beep (man is that sound ever annoying!). I am running a pretty power-hungry system and I know an inverter setup isn't the most efficient but I think I should be able to get more than 10 minutes of run-time (it actually used to be about 20 minutes but it has slowly dropped to less and less over the past few months).

[edit]I have a 400 watt inverter hooked up to a normal 400 watt power supply.[/edit] It's all wired directly to the battery with 10 guage wire and I have a shutdown controller and small backup battery hooked up through a diode to keep it alive during crank (which by the way doesn't work all the time, ie. if I am getting the beep from the inverter and try to crank at that point it will die because the voltage is already low). I'm running a micro-atx board with all onboard components with an AMD XP 2000+ cpu and I have a desktop DVD-ROM and a desktop HD. The screen is a lilliput and I'm running 3 USB devices (GPS, touchscreen, wifi).

So ultimately I have 2 questions, firstly how long is the runtime of others with a similar system? Secondly, what can I do to increase the runtime? I would like to avoid spending a lot of money since I've already dumped so much into this "project" (projects usually have an end, this thing is forever ongoing).

**mushin** · 10-22-2004, 02:45 PM

Your decrease in runtime could be due to your wearing out the battery. Standard car batteries are *not* designed for deep discharging - they're designed to pony up the initial high current draw in order to start. If you're going to be running it off the battery alot, I recommend you getting a deep cycle battery.

Getting it to run longer really comes down to a) decrease system draw b) increase battery capacity. If you have the room, the easiest (and cheapest - there is a thread that mentioned getting used wheelchair batts free) way to significant increase is to y use multiple batteries in parallel.

**VanMan69** · 10-22-2004, 02:48 PM

If you keep draining your regular lead-acid car battery, it's gonna lose its ability to hold a charge, and drain faster each time, before it eventually dies.

I'd suggest getting a smaller PSU for starters. Find out the minimum your components require. 400W is a lot of juice, especially if you're taking that from an inverter, and I'm guessing it's a lot more than you really need.

If you're really looking for extended run time, look into an auxiliary battery. I think the people claiming hours of no-engine run time are probably using auxiliary battery systems, or have really light systems (on like 90W PSUs or something).

**pip** · 10-22-2004, 03:17 PM

1. Get a new battery as your current one has taken a beating.
2. Get a second, deep cycle (optima yellow) battery to run the PC.
3. Get the requisite gear to keep both batteries charged.
4. If needed, upgrade the alternator.
5. Replace the Inverter/DC power supply with a quality DC-DC solution such as the OPUS 150W.
6. Remove/turn off unused hardware/components you don't actually need.

In essence, provide a dedicated stable 12v supply and reduce the drain on it.

**ColdPhreze** · 10-22-2004, 05:03 PM

Do NOT replace the inverter with an OPUS. With a power hungery system (2GHz and above with a 3.5" hd and some other misc equipment, the OPUS will NOT be suficcient to power it. Look at any power consumption charts for AMD and Intel CPUs, then add to that the HD power consumption.

It is not that inefficient to use an inverter with a standard ATX power supply. It is only Slightly less efficient than a DC-DC power supply. Your problem is that you have an aged battery, it may be quite small in terms of current capacity (even when new), and you have a power hungery PC. Opus will only give you headaches.

I'm deadly serious. IF the OPUS works, it will not last long before burning up due to exceeding it's rated output. I am not making this up. I know several people who had OPUS power supplies and replaced them with inverters.

**Bobby Digital** · 10-22-2004, 05:10 PM

The battery is not being "drained" at all. It is going to the inverter's warning point (11V) at which point I shut off the computer. I don't think this is all that bad since the car cranks perfectly every time and the battery has never been down.

About the PSU, I thought that if it is rated 400W but the computer is drawing less, then it will only use what it needs. Is this not true? Is it drawing 400W no matter what all the time? If this is true then I will get a new PSU, but all logic would lead me to believe it only uses what it needs to power the computer.

Also do you guys think 10 guage wire is enough? Could moving up to a bigger wire help at all?

**Hcomplyr** · 10-22-2004, 05:25 PM

that is true, you will only use what power you need at that moment but P4s suck 100 watts at idle and up to 50% more when being stressed (AMD's are about equal) so there goes your 150 watt OPUS right there and thats just for your measly processor. an inverter with a full size ATX power supply will work much better for such a system.

I'm using 8 gauge wire and thats plenty for my PC and some other goodies running off it

**VanMan69** · 10-22-2004, 05:56 PM

Originally Posted by Bobby Digital

The battery is not being "drained" at all. It is going to the inverter's warning point (11V) at which point I shut off the computer. I don't think this is all that bad since the car cranks perfectly every time and the battery has never been down.?

Huh... the shutdown point on my inverters (a 135W, a 175W, and a 1250W) is closer to 10.2-10.5V. The battery is still being drained to that point, and the repeated drain to that point is going to decrease the charge it holds, even over that 1 volt.

**Bobby Digital** · 10-22-2004, 05:59 PM

I'm not going to the shutdown point, only to the warning beep, which is listed on my specs as 11V. The shutdown point is 10.5V, but I never allow it to go that far (as soon as I hear the beep I shut it down, mostly because my ears can't stand the high pitched sound).

**ColdPhreze** · 10-22-2004, 06:01 PM

Bobby, there are several things here:
Older batteries do not hold as much current as an equilivently rated new battery. Therefore, even though you have no problem starting the car, the pc will not run as long before the inverter detects low voltage. It all works linearly. As you drain current, voltage slowly drops. A dead lead acid battery is 10.5 volts, and 11volts is almost dead. To be safe, once the battery drops below 12 volts, it's time to start the car. Smaller or older batteries will drain much quicker than newer and larger ones. The fact that you said it used to last longer (20 minutes and now is less) is indication that the battery should be replaced... However, to play devil's advocate, it may just be that you have not given the battery enought time to fully charge before discharging it again. It takes several hours to fully charge a battery...

Also, the battery is likely quite small, as in the case for most 4 and 6 cylinder small cars.