924Board.org

owenexile · Posted: Fri Dec 18, 2009 2:56 am Post subject: Battery Question

Hi ,
How long does it take to recharge the car battery if it was on 2V? it seems i left my headunit on while i was working on the car for the past 3 weeks , so now my Batery is totally flat , i drove around after jump starting it for about an 1 hour and when i turn of the car , the starter gave the engine about 1 turn before running out of power.

I tested the altenator and its charging on 13.5V

Thanks
_________________
924 1982 N/A
For some reason theres always a earth problem somewhere with this car...

!tom · Posted: Fri Dec 18, 2009 3:07 am Post subject:

Lead acid batteries do not, in general tolerate deep cycling well.

Your battery may have failed permanently after that.

It will take several more hours to completely charge your battery, if it will hold a charge at all. However, you should have had enough surface charge to turn over the engine if it had been off for only moments.
_________________
78 924 NA
5-lug

emoore924 · Joined: 13 Apr 2004 Posts: 2822

short answer: several days at 2v.

The alt will not charge a dead battery, it only replaces the energy that's used during a "normal" start cycle, and what's used when you run the lights, wwipers, etc.

!tom · Posted: Fri Dec 18, 2009 6:52 am Post subject:

9XX Girl! · Posted: Fri Dec 18, 2009 8:22 am Post subject:

If there is enough power in the battery to get a spark to bump start it, there will be enough power to start it charging.

Best to use jump leads. An alternator needs a voltage to tell it to charge as it is a separately exited AC generator. Under normal conditions this is done via a series lamp (the red one with a pic of a battery on it). If you cannot get this lit, prior to starting and then extinguish when the car idles, you cannot guarantee it will charge.

but if you have 13.8v while the engine is running sounds like you got juice going in. Without measuring the battery voltage under load, or clamp testing the charge current, its hard to tell. Get a local service center to load test your battery... or you could measure your battery voltage with the engine running, the headlights on, fog lights on, the heater on, the heated rear window on, hazards on, rad fan on and, your wipers on. it should be able to hold a minimum of 12v at 950rpm. if not look at fan belt, battery leads and engine grounds, alternator leads, red battery light, battery or alternator. But get stuff tested, it can get pricey swooping stuff on a fault finding mission.
_________________
924 (84) N/A 2 ltr - 5 Speed - BLACK - Project (looking for 200BHP, any ideas!)
924 (81) N/A 2 ltr - 3 Speed Auto - SURINAM RED (Metallic) - Near Original Spec (sticking with originality)
BOTH ON THE ROAD, BOTH USED EVERY-OTHER DAY

datatrain · Posted: Fri Dec 18, 2009 1:30 pm Post subject:

If you've bought an alternator lately and I've had to buy one for each car. They come with a BIG RED tag that says " Do not attempt to charge a dead battery with this alternator. Use a proper battery charger"

It's good advice and a battery that's been flattened completely wont have enough terminal voltage for the charger to sense it's connected.

I have seen it take over an hour on a charger before the terminal voltage rises enough to activate the charger cycle.

In all cases the battery was resurrected ( a christian term I believe) and provided service for several years afterward.
_________________
'78 924 NA with Collector plate
33 year old car, with me for 21 yrs
Mint '92 318i BMW
Near mint '98 Buick LeSabre
VE7HFR

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Emoore924, !tom, 9XX Girl and datatrain are all correct here although their opinion varies. Here`s how.

A dead flat battery (2V) will not draw much current (A) at all, regardless of the alternator or charger capacity. It will take some hours at a low current for the battery to gain charge and increase in voltage. As voltage increases, so will the current (amperage) drawn. As battery voltage approaches its fully charged value of 14.2V the current drawn will decrease.

Earlier alternators like the stock Bosch unit will output a charge once the field is excited and continue to do so while the engine is running. Even though it may be a 75A alt the dead battery will only draw milliamps at first. After an hour or so it may be drawing a few amps. Keep driving all day and the battery may get close to charged.

Later model cars with later style alternators, such as the GM CS series (charging system) rely on sensing the battery voltage to control the regulator for optimum charging. If the battery is flat or even below say 12V the alternator will not charge it at all. The alternator "sees" it as a flat/ damaged/no battery and to protect the alt, battery, wiring, and most importantly the vehicle electronics (ECU, ABS, etc.) will not output at all.

The best advice in your case is to connect your battery to a small 2-4A charger and leave it connected for a day. Allowing the battery to slowly gain charge and trickle charging it to capacity.

Min · Posted: Fri Dec 18, 2009 2:53 pm Post subject:

I agree completely with everything RC has said, however I would like to add that anytime you kill a good battery, you will be reducing its ability to maintain a charge. So if the battery that was killed in this fashion was already on its way out, you may have finished it off (without draining it out, replacing parts, and refilling it with new good battery acid). Trickle charge it at 2 to 4 amps for as long as you can get away with. I'd also like to mention that if the area you live in gets cold, and has gone below freezing, your battery will also have been damaged further. Battery acid will freeze if it does not have a good charge in it.

Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

Imafordguy · Joined: 06 Dec 2009 Posts: 189 Location: Eugene Or.

RC is 100% correct. Same for Min.

I would only add that when leaving a battery on a charger it is perferable to pull the caps, add distilled water if nes, and cover holes with a paper towel replacing caps after charging.

My grandfather preached that procedure. And I do know a guy who lost eye sight in one eye when a battery casing blew. He isn't the sharpest guy so he might of had other problems, But I understand that when a battery has a dead cell and is on a slow charge it can build pressure and blow the caps ans spray acid.
_________________
81 Porsche 924
84 Porsche 944(parting it)
66 Ford f100
66 AC cobra kit car(major project)
64 ford f100 (429 SCJ)
62 Studebaker golden hawk gt
61 baja bug (with bad opel 1.8, looking at ford 2.3 turbo to flovo)

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

One of the best investments I made last year was in a permanently mounted trickle charger for each of the cars. It stays in the battery compartment, and when the car is going to be parked for more than a day or so, I plug it in using a conventional extension cord. Out of necessity, I stored two of my cars outdoors last year, and kept them plugged in. Both cars started right up with no problems whatsoever even in the coldest of weather.

My point: I believe you will substantially increase the life of your battery by using such a device, particularly if you live in a cold climate like me. You can get these devices at Harbor Freight for $15, less when they have sales. Worth every penny.
_________________
erstwhile owner of just about every 924 variant ever made

9XX Girl! · Posted: Fri Dec 18, 2009 11:06 pm Post subject:

That idea is fine but its not for everyone. I park my car (outside) 50 yards from the sea front (9ft above sea level) and 800 yards from where I live. (i was on the waiting list for two years to get that parking space). There are public rights of way and a road between my car and my house making it imposable to run an extension lead. There isn't even any street lighting between my car and my house and i need a touch (flashlight) to find my car at night. I depend on having the electrical system in A1 condition and correct grade oil to get me through the cold months and although i do use the car daily, it sometimes goes a number of days without being used, i.e. it will be laid up between 20th Dec and 2nd Jan for instance. I see no reason even with the high humidity and freezing conditions we have here, why it shouldn't start firs time (every time) if well maintained.

In fact, the only time my car goes indoors is for its yearly 20min MOT safety test

The brake discs will be rusty though by new year

_________________
924 (84) N/A 2 ltr - 5 Speed - BLACK - Project (looking for 200BHP, any ideas!)
924 (81) N/A 2 ltr - 3 Speed Auto - SURINAM RED (Metallic) - Near Original Spec (sticking with originality)
BOTH ON THE ROAD, BOTH USED EVERY-OTHER DAY

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

In your situation, I would disconnect the battery leads when leaving the car unattended for more than a day or so, and not just for the protection of the battery

_________________
erstwhile owner of just about every 924 variant ever made

9XX Girl! · Posted: Sat Dec 19, 2009 1:01 am Post subject:

no worries, i got an isolator. this is not a pathetically worrisome time.
It's the Spring and Autumn Equinoxes during the end of March and September during the spring tides. If we have Easterly winds during this time the breakers brake over the car. I have to time getting in so not to get drenched and i don't have time to pop the hood to throw the isolator.
Its just get in and go.

Cars here don't last long. That said, my 25 year old Porsche has less rust on it than any other car i have ever owned.

These cars can take some punishment!
_________________
924 (84) N/A 2 ltr - 5 Speed - BLACK - Project (looking for 200BHP, any ideas!)
924 (81) N/A 2 ltr - 3 Speed Auto - SURINAM RED (Metallic) - Near Original Spec (sticking with originality)
BOTH ON THE ROAD, BOTH USED EVERY-OTHER DAY

Joes924Racer · Posted: Sat Dec 19, 2009 4:51 am Post subject:

Leavr it on the charger for awhile..seems to me the battery might be
toast as it should of restarted the car after friviong
around for an hour mine would and your alt putting out
correctly.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Rocco R16V · Joined: 03 May 2009 Posts: 497 Location: PNW

in my "toys" cars that arent driven at least weekly, I've switched to using deep cycle RV batterys, they have plenty of power for starting and last much longer when subjected to long periods of not being used.
_________________
"Government exists to protect us from each other. Where government has gone beyond its limits is in deciding to protect us from ourselves. "
Ronald Reagan