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Registered
Join Date: Nov 2000
Location: Dallas
Posts: 3,603
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Dead Battery/Multimeter ?
Car has sat for 5 days and battery seems totally dead. I have a multimeter but unsure exactly how to use it. Could someone tell me what settings to put it on? I assume then I can put the jumpers on the appopriate posts and check the reading. The multimeter does not automatically check the range. Do I use AC? Sorry for the stupid questions and is there anything I can damage on the car by hooking this up wrong?
TIA,
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Buck '88 Coupe, '87 Cab, '88 535i sold, '19 GLC 300 DD Warren Hall, gone but not forgotten |
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08-15-2002, 10:22 AM
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Senior Member
Join Date: Mar 2000
Location: Lacey, WA. USA
Posts: 25,312
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You're more likely to damage the meter than the car. Select voltage. That is, you're not measuring resistance (Ohms), or continuity. You're not measuring dwell. You're measuring DC voltage. So, set the meter to a DC voltage setting and hook the leads up to the battery posts. The battery should have between 12.5 and 13.0 volts. Even voltages between 12.0 and 12.5 may start the car, but voltages below that will certainly not.
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Man of Carbon Fiber (stronger than steel) Mocha 1978 911SC. "Coco" |
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08-15-2002, 10:39 AM
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One more thing: Most DVM's have at least 3 sockets to plug the leads into. Make sure you use the one labeled GROUND (black) and the one labeled VOLT (red).
Do not use the one with a capital A or AMPERE. This one is for measuring Ampere (current). It has an internal shunt (sometimes fuse protected) that would short your battery and potentially could destroy your DVM. Ingo
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1974 Targa 3.6, 2001 C4 (sold), 2019 GT3RS, 2000 ML430 I repair/rebuild Bosch CDI Boxes and Porsche Motronic DMEs Porsche "Hammer" or Porsche PST2, PIWIS III - I can help!! How about a NoBadDays DualChip for 964 or '95 993 |
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08-15-2002, 11:52 AM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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88911coupe,
Your battery may still read 12 volts even discharged. A hydrometer is a better DIY tool for testing. To charge the battery, remove the ground (-) cable and connect a trickle charger (observe polarity; + and -) for at least 1 day, then check again with the hydrometer. This should tell you if the battery is still okay. An on-car load test goes something like this with your fully trickle-charged battery: 1. Remove the coil wire from the dist. cap and ground it so car doesn't start. 2. Connect multimeter to the battery 3. Crank engine for around 5-8 seconds while observing battery voltage. If voltage stays above 9 volts during the 5-8 second period, the battery is okay. If not, it's not ... okay. Don't let the battery cycle too often (discharge-to-charge = 1 cycle). This shortens the life of a battery. Hope this helps, Sherwood Lee http://members.rennlist.org/911pcars |
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08-15-2002, 10:19 PM
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Why do you need to disconnect the (-) negative wire prior to charging the battery? Thanks!
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08-16-2002, 09:40 AM
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Registered
Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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A couple of reasons to disconnect the battery cable when charging:
1) Isolates electrical system from the battery. You don't want a high amperage charger pushing electrons through any sensitive electronic circuits. 2) Related to 1. If you connect the charger incorrectly (wrong polarity), you will fry those sensitve elec. circuits and the alternator diodes. Okay, a third reason. If the cable connections are dirty/corroded, removing them will provide you a chance to clean them up bright and shiny. There might be more. Sherwood Lee http://members.rennlist.org/911pcars |
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08-16-2002, 08:02 PM
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1974 Porsche 911 Targa 3.6
