Thread: number of days of standby (S3) time.

Originally Posted by gnomad

Here's the rub: It is incredibly easy to kill an automobile battery. Automobile batteries are designed specifically *NEVER* to be discharged below 80% capacity. It only takes a few complete discharges to destroy a starting battery. Letting any lead acid battery sit fully discharged for any period of time is also a sure way to kill it.

Ok, so how about these "high performance" batteries. I don't need more cranking amps so the Optima Red Top really isn't it, but what about the Yellow Top? Is it all hype? Is it actually more tolerant of discharge? (I hesitate to call it deep cycle) I read pros and cons on these, what are the competitors? I'm looking for a battery which provides the cranking amps my OEM has but is more tolerant of discharging.

Originally Posted by kbyrd

Ok, so how about these "high performance" batteries. I don't need more cranking amps so the Optima Red Top really isn't it, but what about the Yellow Top? Is it all hype? Is it actually more tolerant of discharge? (I hesitate to call it deep cycle) I read pros and cons on these, what are the competitors? I'm looking for a battery which provides the cranking amps my OEM has but is more tolerant of discharging.

Yea those are good i used one and killed it 10+ times and it always came back alive once you charge it up. Ive been thinking about getting ether a red top for my car or keep the stock battery and stick a small battery in the radio cage for the pc standby.

Someone can correct me if I'm wrong, but I believe the amp-hour rating of the battery is defined as a measure of how much power it can deliver before it can't start the car anymore, using some average minimum cranking voltage, not the amount of power it can deliver before it's totally dead. that would of course differ by car. but I would guess that you won't have to be too conservative with the amp-hour rating, especially at such low current draw.

Also, just for reference, in the factory service manual for my VW (mkIII) it has a little blurb about testing the current draw with the car off, (and consequently, your method is exactly the same as the one in the manual), and it says that under normal circumstances, the car should be drawing less than 100mA. I have a feeling that's largely to indicate electrical problems, but since you aren't even double that amount I really don't think you'll have much trouble... especially if you don't regularly let your car sit for a week at a time. If nothing else, you could just run it that way for a while, and if it ever kills your battery, then that'll be an excuse to buy a yellow top or something

Originally Posted by evandude

Someone can correct me if I'm wrong, but I believe the amp-hour rating of the battery is defined as a measure of how much power it can deliver before it can't start the car anymore, using some average minimum cranking voltage, not the amount of power it can deliver before it's totally dead.

It's funny, me asking the questions, then correcting you when you're wrong (I'm cocky that way). But, I'm 99% sure an amp hour rating is total capacity. It's amps * hours, but at a 20 hour rates. So with 20AH battery you can draw 1 amp for 20 hours. or 500 milliamps for 40 hours (actually I think if you draw less than the 20 hour current you get a tiny bit more time). You also don't get a steady voltage over this time period.

I may be reading this incorrectly but doesn't the OPUS put the computer into complete shutoff status if the battery becomes too low to crank? I thought that I remembered reading that on the website? Although I do understand that USB devices and even the memory of the Motherboard may drain minute amounts of electricity, it would seem that as long as you crank your engine at least once a week, the computer shouldn't damage your battery in the long run. I have particular interest in this because I am going to Iraq in a few months and I do not want my battery to suffer a deep discharge that will make it crap out. My wife is more then happy to drive he truck so I am not extremely worried.

Originally Posted by Eternalodyssey

I may be reading this incorrectly but doesn't the OPUS put the computer into complete shutoff status if the battery becomes too low to crank?

You read my post wrong. I'm not using an Opus, I'm using an M1-ATX. It shuts off the power at 11V no matter what. greenman100 says that's about 50% capacity drain on my battery which really isn't good for it.

My drain was with EVERYTHING shut off except 5VSB (powering the RAM), if you have USB ports, network ports, keyboard ports powered up looking for a resume signal you'll draw more power than I.

My plan is to flip my kill switch if I ever leave the car for more than a day or two.

More information, and more questions.

Since my last test that showed 170-180mA in suspend, I've made two changes:

- I added a small kill switch which controls a relay, the relay controls the 12V constant to the m1-atx. I normally leave the switch "on" and the PC goes to
S3 when I turn off the car.

- I added a USB GPS mouse (BU-353), it's drawing some power when the PC is in S3.

So, this morning I did the same "whole car draw" test. This time I get 320mA in suspend. That's with the GPS locked on a signal (on the bu-353, the red led blinks when it's locked). If I unplug the GPS, I get a 290mA draw. I verified this by unplugging and plugging the GPS several times and got the same numbers. The GPS might draw more (or less) in suspend when it's not locked.

So, I'm the difference (minus GPS) is 290-180=110mA. It's got to be the relay right? I know there's some power to keep the contact closed, I just assumed it would be next to nothing (I guess ~100mA is nothing compared to the amps the relay is controlling).

This sucks. My relay almost doubles my draw. Are there "better" (use less power from the control circuit) automotive relays? Is there a better way to solve this problem? My first thought was to go back to the 25A/12V switch I found at Radio Shack. It's big, but it won't use any current when closed. Then I got to wondering whether I could reverse the relay wiring so that the 12V constant flows with the relay contact is open and not when it's closed. It's a Bosch-style, I think it's a double pole. Then I would draw ~100mA when the kill-switch was "off", still not good. There's got to be a better way...