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| Thread ID: 105360 | 2009-11-29 02:51:00 | Is my multimeter accurate? | Nomad (952) | PC World Chat |
| Post ID | Timestamp | Content | User | ||
| 834548 | 2009-11-29 09:53:00 | "For a AA battery in DC it reads 1.2V, in AC it reads 2.2." That's good as far as you've gone. That AA battery may be running a bit flatter than new. But did you measure your car battery directly at the battery terminals? Or some other point in the vehicle? |
coldot (6847) | ||
| 834549 | 2009-11-29 10:55:00 | Yeah I did measure the car battery at the terminal. At idle one was 12.5 approx and for a car that just driven and switched off was around 14. |
Nomad (952) | ||
| 834550 | 2009-11-30 01:00:00 | Old technology (lead-acid batteries) prevail as do old fashioned diagnosis . 13 . 6VDC is a good at rest voltage for a MODERN (post 1992-era) battery as they are all now lead/calcium and not lead/acid anyway . Your ECM keep-alive current draw is small and as such should not impact your battery in months, if not a half-year! Charging/running voltages are all temperature/load controlled and can run from 12 . 8VDC to 14 . 8VDC - but again that depends on the temperature of the battery and the charging status of the battery . Less than about 13 . 2-13 . 6VDC at idle indicates usually 1) something's using more that it's normal diet of electrons 2) the alternator's doing the AC-thing and putting out some ripple on the DC and that's bad! or 3) the alternator has mechanical problems like a slipping belt or the running speed is too low to make decent current . Batteries are like a bucket that gets filled of electrons (think water droplets) until it's full and the regulator in the alternator shuts it down or tapers it off to almost nil . The bucket (battery) has only one real job: to start the engine . If it does that and does it well and every time, then you can assume it is within normal/serviceable limits . If you measure the AC value on the DC output and see more than 0 . 013VAC there, the alternator's suspect and can harm the ECM/TCM/BCM . This rule is almost golden now as the digital devices on modern engines refuse to accept any AC at all! In the end here - I suspect either you're meter's screwed up or you are getting bogus results from probing the wrong areas and things at the wrong times with the wrong settings . Please refrain from using the OHMS position to test your battery . : |
SurferJoe46 (51) | ||
| 834551 | 2009-11-30 02:37:00 | What a load of unnecessary bullshlt, and SJ, you are the worst by a country mile. A simple question needs a simple answer. Set your meter to a DC range greater than 12 volts (20 volts is fine). Don't worry about measuring to 2 decimal places, there are too many variable to make that of any use at all. You should read something between 12 volts and 14 volts, depending on meter accuracy, battery condition and how recently you were driving. If it is between 12.5v and 13. 5v all is sweet. Turn your lights on and it should read between 12 and 12.5, depending on battery condition. If you want to learn something extra, try again on the AC range and you'll see a reading pretty much proportional to the quality of your meter. Cheap meters will read higher than quality meters. My DSE cheapie reads a used 9 volt battery at 8.9 volts on the DC range, as does my $7000 Fluke gear, but 18 volts on the AC range (can't do DC on AC with the Fluke, it auto-senses and sticks to DC). Cheers Billy 8-{) |
Billy T (70) | ||
| 834552 | 2009-11-30 05:35:00 | We used to have square wheels here too, but we found that every time the corners wore off, we had to replace them . "Recent" driving is for Harry Potter fans as is any meter that is so far off (ie: You should read something between 12 volts and 14 volts, depending on meter accuracy, battery condition and how recently you were driving . ) - if any meter is THAT inaccurate, then just stick with the 240Volt AC-to-ground system as finer electronics will certainly baffle ye . |
SurferJoe46 (51) | ||
| 834553 | 2009-11-30 08:04:00 | Nomad, there is nothing wrong with your meter PROVIDED you switch it to the right range. What happens is that some cheaper brands cheated in the manner they measured and displayed AC volts; with the result that if you inadvertently try to read DC on the AC scale, you get ridiculous readings. You won't be fooled next time. |
decibel (11645) | ||
| 834554 | 2009-11-30 10:26:00 | We used to have square wheels here too, but we found that every time the corners wore off, we had to replace them . "Recent" driving is for Harry Potter fans as is any meter that is so far off (ie: You should read something between 12 volts and 14 volts, depending on meter accuracy, battery condition and how recently you were driving . ) - if any meter is THAT inaccurate, then just stick with the 240Volt AC-to-ground system as finer electronics will certainly baffle ye . Fair do's SJ, I won't lecture you if you don't try to lecture me, but you must know that after driving for a while, battery voltage can float high under no load conditions . All Nomad wants to know is the basics, not chapter and verse . It isn't that the meter is wildly inaccurate (if on the right range and scale), it is the environmental variables (vehicle usage and battery condition) that are likely to influence the reading, and anything between 12 and 14 volts might be expected . As for finer electronics baffling me, I taught and examined in electronics for many years, with a considerable period as a national examiner so I know just a little bit about the subject . One thing I taught all my students was the KISS principle, which applies well to servicing of all descriptions: Keep It Simple Stupid! Don't look for complex problems until you have checked the obvious and eliminated the usual basic culprits . The other thing I taught them was to beware of creeping elegance, a lesson all servicepersons should learn . We never had square wheels here, we only had the round ones . Must have been a unique Yank invention to stop cars rolling backwards down hills, before they discovered the handbrake . :D Tiger could have used some though . :p Cheers Billy 8-{) |
Billy T (70) | ||
| 834555 | 2009-11-30 10:35:00 | What is creeping elegance in terms a dumb ass like me can comprehend? | prefect (6291) | ||
| 834556 | 2009-11-30 16:06:00 | What is creeping elegance in terms a dumb ass like me can comprehend? OK - - - - 1) A good battery is one that starts your engine . 2) A bad battery won't - but there MIGHT be certain circumstances that make it LOOK bad . A) Low charge rate from alternator B) small overnight drain on battery from accessory or ECM C) Electron zombies sucking the electrolyte outta the battery cells . D) Cheap Korean/Chinese meter E) Incorrect USE of meter 3) There MIGHT be a bad connection, but that is usually counter-indicated if the engine starts, the accessories work and can be trusted to perform as do so constantly . 4) Ughhh! I once found that the most dangerous person onboard ship was an ensign with a map and a compass . Take away either of those devices and they could be taught something practical-factors wise, anyway . Perhaps the answer here is to put the meter down and slowly walk away from it . :rolleyes: |
SurferJoe46 (51) | ||
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