 A poser for the EE types, Weird battery problems |
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| lapuwali |
 Jun 2 2006, 11:53 AM
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#1
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Not another one!  Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743   |
Yesterday, my FIAT wouldn't start. No click, no lights, no nothing. Exactly like a flat battery. I pull out the voltmeter, and it reads 12.5v across the terminals. Hm. Can't find any obviously loose wires. Out of time, head off to work in the VW.
This morning, I look at it again. Still 12.5v at the battery. I throw a charger on it, anway. 2 minutes later, the car fires right up. Very puzzling. I'd not expect a battery so dead it couldn't even light up the e-brake warning light to show 12.5v. Comments? |
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| URY914 |
Jun 2 2006, 11:59 AM
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#2
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I built the lightest 914 in the history of mankind. Group: Members Posts: 120,983 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
Check the car end of the ground strap. Could be loose.
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| lapuwali |
Jun 2 2006, 12:02 PM
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#3
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
QUOTE(URY914 @ Jun 2 2006, 10:59 AM)  Check the car end of the ground strap. Could be loose. Nope. Both ends snug, and I see 0 ohms of resistance between the battery end and several ground points on the car. |
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| fitsbain |
Jun 2 2006, 12:03 PM
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#4
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Ask me if my car has rust!!! Group: Members Posts: 619 Joined: 25-February 06 From: Pittsburgh PA Member No.: 5,634 |
WAIT!!!
I know!!! It's a FIAT!!! (IMG:style_emoticons/default/owned.gif) Sorry man can't be of more help. Good luck finding it. |
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| Mark Henry |
Jun 2 2006, 12:13 PM
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#5
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
I've had dirty termanials do the exact same thing. Clean all your grounds, posts, etc. Tight doesn't mean you have good contacts.
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| URY914 |
Jun 2 2006, 12:15 PM
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#6
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I built the lightest 914 in the history of mankind. Group: Members Posts: 120,983 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
QUOTE(Mark Henry @ Jun 2 2006, 10:13 AM) I've had dirty termanials do the exact same thing. Clean all your grounds, posts, etc. Tight doesn't mean you have good contacts. (IMG:style_emoticons/default/agree.gif) They can look good from the outside and not be doing the job. |
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| Rand |
Jun 2 2006, 12:38 PM
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#7
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
QUOTE(Mark Henry @ Jun 2 2006, 11:13 AM) I've had dirty termanials do the exact same thing. Clean all your grounds, posts, etc. Tight doesn't mean you have good contacts. I've also had dirty terminals cause that exact behavior. When the solenoid won't even click, the first thing I think of is cleaning the posts and the insides of the cable clamps. A while back I ran into my first instant battery failure... was fairly new, measured full voltage, but there was an internal problem that caused it to fail when attempting to draw current. Traded batteries with another car and the problem followed the battery. |
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| lapuwali |
Jun 2 2006, 12:50 PM
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#8
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
All of the electrical connections were checked, cleaned, replaced, etc. The only thing that helped was charging the battery.
It's fixed now, and I drove the car to work today. It had sat for a couple of weeks, which is why I initially suspected a dead battery, but a simple voltage test showed the battery SHOULD have been OK, yet it wasn't. That's really the question: why would a dead battery show good voltage? Is there something about lead/acid batteries I'm not getting? The charger also didn't behave as though it were dealing with a nearly dead battery (has a ammeter on it, which usually shows a full 6A when charging a nearly dead battery, in this case, it showed a max of 2A, and slowly fell to under 1A, the usual case in a mildly discharged battery). I agree that everything points to a bad connection, yet that doesn't appear to be the case. The battery is 2-3 years old, and showed no other signs of weakness before this incident. A real puzzler. |
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| Rand |
Jun 2 2006, 12:57 PM
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#9
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
I'd be a little suspicious of that battery.
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| jsteele22 |
Jun 2 2006, 01:28 PM
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#10
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
I don't know about lead-acid batteries, but for run of the mill flashlight batteries (when they start to go bad), you can get a "good" volatge reading if they've been sitting with no load. If you apply even a slight load to them, the voltage will drop immediately. So for those batteries, a "battery tester" is more than just a voltmeter - it's a voltmeter with a load. So, I don't know if the same thing is true for lead acid, but you might check the voltage at the battery while the parking lights or something are turned on. Or you could bring it in to the shop and say "Fix It Again, Tony !" |
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| MartyYeoman |
Jun 2 2006, 01:35 PM
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#11
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Senior Member Group: Members Posts: 1,520 Joined: 19-June 03 From: San Ramon, CA Member No.: 839 Region Association: Northern California 
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If it's a lead/acid battery, check the electolite level. I've seen considerable changes in battery operation just by adding a little dist. water.
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| URY914 |
Jun 2 2006, 01:36 PM
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#12
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I built the lightest 914 in the history of mankind. Group: Members Posts: 120,983 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
Was it a full moon? (IMG:style_emoticons/default/confused24.gif)
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| mightyohm |
Jun 2 2006, 02:27 PM
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#13
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Advanced Member Group: Benefactors Posts: 2,277 Joined: 16-January 03 From: Seattle, WA Member No.: 162 Region Association: Pacific Northwest |
Hi James,
One failure mode of lead acid batteries is that they will float to normal voltage, but as soon as you try to draw current, the battery will act like it has tremendous internal resistance and the voltage will drop to zero. Monitor the voltage under load (turn on the headlights) and you will probably see this behavior. bondo might know the physical reason but I speculate it is a battery chemistry thing, not to be understood by us EE types. |
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| Brian Mifsud |
Jun 2 2006, 03:14 PM
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#14
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Mechanical Engineer Group: Members Posts: 981 Joined: 3-March 03 From: Penngrove, CA Member No.: 384 Region Association: None |
Are you sure the solenoid was/is happy?
If it comes to it, best place for best quality rebuilds on any BOSCH starter or alternator is RELIANT ELECTRIC on 5th Street in San Francisco. Had Mercedes Diesel, Porsche, Moto Guzzi alternators and starters all completely rebuilt there.. top quality work done on site, not "SENT OUT". |
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| draperjojo |
Jun 2 2006, 03:34 PM
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#15
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sixstrings Group: Members Posts: 411 Joined: 26-December 05 From: Salt Lake City Utah Member No.: 5,317 |
I agree with Jkeyser, I've found several times where a cell in the battery shorts or goes dead and it will indicate full voltage until a load is applied. Have your battery load tested. Also throw a digital meter on the battery. If the battery is just sitting there with out the engine running for a while, it should read 12.4 to 12.8 volts. Crank up your engine and hopefully the alternator brings up the battery voltage to approx 13.8 to 14 volts. If not, you may have issues in the charging circuit.
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| lapuwali |
Jun 2 2006, 03:36 PM
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#16
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Not another one! Group: Benefactors Posts: 4,526 Joined: 1-March 04 From: San Mateo, CA Member No.: 1,743 |
QUOTE(Brian Mifsud @ Jun 2 2006, 02:14 PM) Are you sure the solenoid was/is happy? If it comes to it, best place for best quality rebuilds on any BOSCH starter or alternator is RELIANT ELECTRIC on 5th Street in San Francisco. Had Mercedes Diesel, Porsche, Moto Guzzi alternators and starters all completely rebuilt there.. top quality work done on site, not "SENT OUT". The solenoid seems perfectly happy. Turned the key and NOTHING happened, not even the e-brake light came on. Charge it for a bit, and everything works again. It appears that this really is just some weird battery thing I'd not seen before. I didn't try to meter the battery loaded, only unloaded. I expect that was the issue. Live and learn... |
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| Rider914 |
Jun 2 2006, 08:16 PM
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#17
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Member Group: Members Posts: 276 Joined: 13-April 04 From: Palm Beach Member No.: 1,923 |
Did you check the voltage with the headlight switch on? If you are still getting 12v check on the clamps to the battery don't just put the probes on the teets. Then move on down the line, main fuse, fuse block, starter. It must go away somewhere.
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| So.Cal.914 |
Jun 2 2006, 08:23 PM
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#18
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"...And it has a front trunk too." Group: Members Posts: 6,588 Joined: 15-February 04 From: Low Desert, CA./ Hills of N.J. Member No.: 1,658 Region Association: None |
QUOTE(lapuwali @ Jun 2 2006, 11:02 AM) QUOTE(URY914 @ Jun 2 2006, 10:59 AM) Check the car end of the ground strap. Could be loose. Nope. Both ends snug, and I see 0 ohms of resistance between the battery end and several ground points on the car. If your ground was working your V/O meter would show resistance between the the strap and the ground points you mentioned. Check ground again. |
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| Rand |
Jun 2 2006, 09:45 PM
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#19
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Cross Member Group: Members Posts: 7,409 Joined: 8-February 05 From: OR Member No.: 3,573 Region Association: None |
QUOTE If your ground was working your V/O meter would show resistance between the the strap and the ground points you mentioned. Huh? Are you thinking infinite resistance? Or how many ohms would you say is normal with a good ground? |
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| Rider914 |
Jun 2 2006, 10:25 PM
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#20
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Member Group: Members Posts: 276 Joined: 13-April 04 From: Palm Beach Member No.: 1,923 |
QUOTE(Rand @ Jun 2 2006, 07:45 PM) QUOTE If your ground was working your V/O meter would show resistance between the the strap and the ground points you mentioned. Huh? Are you thinking infinite resistance? Or how many ohms would you say is normal with a good ground? With a good Fluke multimeter you should get between .5 and 2.5 ohms. There should be some resistance in the wire and connections but a less accurate meter will show 0 ohms. . . |
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