Thread: Grrrr....Battery died

The dome light cant draw more than 2 amps ( and I would guess under 1 amp) @ 17 hours, lets say it sucks down 25 amps. a large car bat should be rated over 100 Amps, and I find most cars will turn over down to 80 Amps.

When you tried to start it, did it even turn over ? or was it like compleetly dead ?

I am kind of worried about this to, my car has a really testy starter.
It not like it will try to turn over if it is low, it will just click, and an alarm will beep for low battery.
I have an inverter, on a switch, and I am worried about forgetting to turn it off, I guess I will remember it as part of my shutdown cycle.
1. Turn off car
2. Turn off Radio
3. Flip off Inverter toggle switch

search for the dschmitt shutdown controler ( I have the link on another pc) it watches the accessory line of the car, when you start the car, it waites a couple seconds , and then turns on main relay ( hook to inverter) and has the ability to send the atx power on signal. then when it senses the car being turned off, it weaites 8 seconds, sends a shutdown command to the serial port of pc ( use with ups software) waits 30 seconds for shutdown, then cuts power to the relay.

Let me know if you need the link - he sells them for like 27.00

Originally posted by gizmomkr:
<STRONG>The dome light cant draw more than 2 amps ( and I would guess under 1 amp) @ 17 hours, lets say it sucks down 25 amps. a large car bat should be rated over 100 Amps, and I find most cars will turn over down to 80 Amps. </STRONG>

I'm very curious as to where you got that 80A figure. Starting current for my car (with it's easy spinning 1.3L wankel engine) takes over 300A to crank. I would imagine that piston engines take much more current as they spin much harder. 400-500A wouldn't suprise me.

Originally posted by Aaron Cake:
<STRONG>I'm very curious as to where you got that 80A figure. Starting current for my car (with it's easy spinning 1.3L wankel engine) takes over 300A to crank. I would imagine that piston engines take much more current as they spin much harder. 400-500A wouldn't suprise me.</STRONG>

That would make sense Aaron, since most car batteries are ratted in CCA's or Cold Cranking AMPS. My Suzuki swift had a standard battery rated at 340CCA, and I have just upgraded to a 440CCA battery.

So if a battery is rated at say 440 Cold Cranking Amps, we can assume that starter motors must need a few hundred amps at startup. Its a scary thought!

my battery is a heavy duty one with like 1200 CCA's. When I put the key in and moved it to the "ON" position without starting, everything lit up at normal brightness (including those annoying daytime running lamps--gotta disconnect those). As soon as I hit the "Start" button, everything went down and there was a weird clicking noise. I've had several cars, and even ones with bad electrical systems. This is my first truck, so maybe that noise is normal. I dunno.

I think there's some confusion here regarding battery ratings. You guys are talking about two different things. The CCA (cold-cranking amps) refers to the maximum instantaneous current that a battery can deliver. The Ah (Ampere-hours) refers to the total capacity of the battery. So a
standard battery can easily be rated at 100 Ah and 1200 CCAs.

"100 Ah" simply means that 2 Amps of current (i.e. running the dome light) will fully discharge a new battery in 50 hours. But the CCAs drop quickly as your battery is discharged. The 1200 CCAs figure will be valid only for a brand-new, fully-charged battery. So a used, 60%-charged battery will have a lot less CCAs, probably not enough to turn your starter. That little 2A dome light is quite capable of rendering your battery impotent in a few hours, especially a not-so-new battery.

wizardPC - the symptoms you describe are fully consistent with a partially discharged battery. There's still enough juice in it to run your lights and everything (say, 20 Amps), but when your starter motor tries to sink a few hundred amps at once, the battery can't deliver, so the voltage drops and everything shuts off. The click you're hearing is just the starter solenoid disengaging. No mystery at all.

BTW, here's a nice battery FAQ:
http://www.battery-index.com/dardencarfaq1.shtml

A quote: "CCAs are the discharge load measured in amps that a fully charged battery at 0 degrees F (-17.8 degrees C) can deliver for 30 seconds and while maintaining the voltage above 7.2 volts. Batteries are sometimes advertised by their Cranking Performance Amps (CA) or Marine Cranking Amps (MCA) measured at 32 degrees F (0 degrees C) or Hot Cranking Amps (HCA) measured at 80 degrees F (26.7 degrees C), which are not the same as CCA"

So with 1200 CCAs, your battery will give you 1200 amps for 30 seconds. Assuming things scale linearly (which they don't, but the figure is in the ballpark), that's 1 amp for just 10 hours...

In fact, according to the FAQ, the relationship between CCAs and Reserve Capacity (amp-hours, by a different name...) depends on battery design. Quite possibly, you can get a battery with the same CCAs, but a higher RC/Ah rating.

Aaron, just my rough guess after dealing with automotive stuff. (relays, starters, charging circuits)

Its hard to get exact figures on higher amperages ( with the equipment I have)

But if its of great concern to you, I can dig up specs from my friend (Sales / Tech for Honda)