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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / October 2005bizarre voltage measurement
I unplugged my battery completely, and put it on my garage floor. But my voltmeter still shows +4V from my car chassis to the +ve terminal, and 3V from the -ve terminal to the car chassis. In fact it shows various voltages to random other metal objects lying around. If I hold the battery in the air the measurements all go to 0.00 immediately. If I put it on a rubber mat I get measurements of about 0.5 - 1V. It is almost as if my battery is leaking current out the bottom of it (this would explain my car's problem with it going flat quickly). Has anyone heard of this happening before, or is there another explanation for what's going on? My multimeter has a new battery. >I unplugged my battery completely, and put it on my garage >floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 12 lines] > >My multimeter has a new battery. Diode rectification of nearby radio station signal. And/or sensing 60 cycle electrical field. If you look at this on a scope instead of a multimeter, you MAY see a 60 Hz sine wave. Lg > I unplugged my battery completely, and put it on my garage > floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 4 lines] > If I hold the battery in the air the measurements all go > to 0.00 immediately. Solved my own problem. There was all this gooey conductive crap sitting around the cell lids, and an invisible trail of it running down the sides of the battery and onto the bottom of it and then into the car etc. Gave the battery a thorough wash with hot soapy water.. no more phantom voltages :) >> I unplugged my battery completely, and put it on my garage >> floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 12 lines] >Gave the battery a thorough wash with hot soapy water.. no >more phantom voltages :) Every now and then, I wash my entire engine down, including the battery, and blow out the water with high pressure compressed air, and wipe stuff down, and run the engine to *burn off* any leftovers. Works for me. > Every now and then, I wash my entire engine down, including the > battery, and blow out the water with high pressure compressed air, and > wipe stuff down, and run the engine to *burn off* any leftovers. > > Works for me. Exactly the same thing I do every now & then to my vehicles. On Sun, 16 Oct 2005 01:17:46 GMT, "« Paul »" <" « Paul »" @houston.rr.co.tx> wrote: >> Every now and then, I wash my entire engine down, including the >> battery, and blow out the water with high pressure compressed air, and [quoted text clipped - 3 lines] > >Exactly the same thing I do every now & then to my vehicles. Along this line, I have an experiment for everybody on the n/g to do. I want them to go out to their alternators with a high-pressure AIR gun, and blow the compressed air through the alternator. YOU WILL SEE...A VOLCANIC ERUPTION OF CARBON DUST become airborne from the wearing of the brushes. WHY does this matter? Because, when carbon becomes WET, it becomes a conductor. Ask anybody who drives a car with a cracked distributor cap. Now what I do, is BLAST the alternator with a full pressure garden hose. That's what I do. Then, I *air dry* it with 90 psi compressed air. And now, I have a clean alternator, free of carbon buildup, open to fresh intake air and proper cooling. And I do this to everything. The throttle position sensor, the linkages. After all this *cleaning,* I relubricate parts that had the lube washed off with the high pressure water. You can eat off my automobile engine, and not get sick. It looks like it just came out of my dishwasher. Lg >>> I unplugged my battery completely, and put it on my garage >>> floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 16 lines] > battery, and blow out the water with high pressure compressed air, > and wipe stuff down, and run the engine to *burn off* any leftovers. Good idea.. now all I have to do is get an air compressor. My battery is still behaving a bit oddly though. When I charge it for any length of time, the battery water starts bubbling out from under one of the caps again. This happened once, and it wouldn't charge any higher than 11.3V, so I tipped some water out of it and then it didn't seem to happen again so I left it overnight to charge. In the morning I could hear the water bubbling out (although it did read 13.2 V). It doesn't look to the eye like it is overfull, but I suppose one of the cells is (only one appears to have lots of water coming from it). Is it dangerous to tip the battery on its side to pour water out? I'm a bit wary of doing things like that, given the strange noises it was making... >>>> I unplugged my battery completely, and put it on my garage >>>> floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 32 lines] >the battery on its side to pour water out? I'm a bit wary of >doing things like that, given the strange noises it was making... If you have a hydrometer ( available at any auto parts store ), you might want to read the Specific Gravity of the battery cell that is giving you problems, before replacing the entire battery. Something tells me there is something wrong with that particular cell. The numbers for what you should read on the hydrometer are included with the instructions. Lg If when charging a battery I see it bubbling from only one of the cells I assume that cell is shorted, and I would try to get another battery. Maybe the problem corrected itself (a piece of metal lead moved ) but if the battery doesn't perform well in the next few days I would assume it is still bad. Usually the old non sealed batteries will bubble if overcharged but they should bubble from all the cells equally and not that badly so I assume that cell is bad. And anything over 12.6 volts could be surface charge so try hook up a load to battery for a while and if it isn't around 12.6 after disconnecting load (like 11.5 (12.6-2.1) ) assume cell is shorted. > >>> I unplugged my battery completely, and put it on my garage > >>> floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 32 lines] > the battery on its side to pour water out? I'm a bit wary of > doing things like that, given the strange noises it was making... You are describing a battery with a bad cell. That is likely where the acid trail to the ground came from. It is 'acid' in there, not water! Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's >>>>Solved my own problem. There was all this gooey conductive crap >>>>sitting around the cell lids, and an invisible trail of it [quoted text clipped - 17 lines] > You are describing a battery with a bad cell. That is likely where > the acid trail to the ground came from. Right. I took it to the mechanic and they verified that it was a bad cell and sold me an expensive new one. They suggested that it might have been damaged by my alternator over-charging it, but I got another guy to check my alternator and he said it was just fine. It reads about 13.7V when I'm applying revs. > It is 'acid' in there, not water! Well, it looks like water, and I put water in when it is getting empty :) One thing that surprises me about battery acid is that it makes holes in my jeans when I spill it, but it doesn't really hurt my skin. > I unplugged my battery completely, and put it on my garage > floor. But my voltmeter still shows +4V from my car chassis to [quoted text clipped - 12 lines] > > My multimeter has a new battery. Depends on the type of voltmeter, especially its input impedence. If it is high enough input impedence it can read stray AC or even RF fields it picks up and can rectify it. Put a resistor in parallel with the probes- a few K should be fine. If it is one of the older non-electronic VOMs or car electrical testors, you should not see these kinds of things. Then it WOULD be weird. |
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