Maybe microvolts if the meter is capable.
ammeter readings (1 Viewer)
- Thread starter Beckley
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Maybe microvolts if the meter is capable.
- Thread starter
- #22
I talked to a "genius" friend of my son and got the answer. 3 engineering degrees and an MIT grad. When the meter is set to AC volt and checking for DC voltage (simply stated) it looks for the top and bottom of the sinusoidal wave created by the battery and basically gives one a reading that is 2x the DC voltage of the battery. Bottom line is you get a misleading reading if you try to read a DC voltage when set on AC. Anyway, that solves the problem and I will measure the voltage coming out of the alternator and go from there. thanks for the help.
What meter are you using ?
Please look at the video. When the meter is set to read AC and you test the DC, if there is no AC it will read 0. I cannot understand what the degrees and MIT people are talking about. It really is a simple test.
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- #25
Your picture is showing exactly what we are talking about. You are showing 27 volts on AC which is 2x the DC voltage. My readings also showed 27V on the AC setting. I have a simple meter, not a dvom meter. I can't measure anything except the AC voltge and a battery doesn't emit 27 V AC. That is where the inaccurate meter reading is showing up. .My battery shows 13.5 volts on DC setting. Looking at previous advice, I was measuring at the battery and not at the alternator. That is why I was getting the strange readings that were 2x the Dc voltage on the AC meter readings
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- Thread starter
- #26
How exactly does a battery create a sinusoidal waveform?
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- #28
This is way beyond me, but in his exact words........."..I think it has something to do with the fact that the reader looks for the highest positive voltage it sees and because it believes it looking at a sinusoidal wave in AC, it reports the overall amplitude should be 2x the value it reads. It reads 2x from the bottom of the trough to the top of the wave. Since a car battery is actually 13.8 volts and the meter gives you an inaccurate reading of 27 volts."
Anyway, I noticed it reads 27 volts until the vehicle is started, than goes down to zero.
I do not know if it is a co-incidence , but, the video picture start has the test leads going nowhere. So the meter is reading 27VAC but not measuring anything. Are you using an analog meter. ? Please give make/model number of meter being used. I just went out and measured 3 different batteries , on AC, and got 0 volts. I started all 3 vehicles and ripple , AC, read about .025 VAC . That is 25 millivolts.
Well, not exactly. With the car off there is no sinusoidal waveform. A meter , in AC, is looking for a positive/negative transition and amplitude. A meter does read RMS in this setting but for this simple teat that is not important. So, if the meter is reading some alternating current on a DC battery, where is the AC coming from ? Give meter model number and maybe that will tell the tale.
This is why I need model number of meter. Reason is if a meter , in an AC setting, does not see any actual AC but perhaps reports only the positive peak and ASSUMES there is a negative peak, and guesses. That to me is not a meter. A meter in its simplest form will only report any AC it sees. If the meter is assuming, then it is not an accurate meter.
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- #32
Where did you attach the probes to get your readings? One of my meters is a LCD auto meter, CEN-TECH #95670 and the other one is a cheap Harbor Freight. Maybe it was even a Freebe. Like I said, with one probe on the ammeter B output and the other to a negative the reading was 27. once veh is started , it reads approx 12volts.dc. In AC it was near zero
First off I am using a Fluke 27. Both of those meters are Harbor freight you are using. I am not saying that is bad , but the quality may not be as refined as a Fluke. The reading of AC with the car off still boggles me why. Next, when started , with probes on battery, you should be reading between 13.5 to 14.3 or so. That means you are charging. If need be, turn lights on and any other item so as to draw energy and that will ensure regulator is working properly. I believe you said you were reading 18+ and that is not correct. Also, when you change to AC on meter , probes across battery, engine running, near zero is correct.
I wish I had a freebie Harbor meter to compare.
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- #34
Something isn't right. I don't want to drive to a repair shop if my voltage is spiking, so I am just going to spend $85 and replace the alternator and voltage regulator. Then....I wont have to keep fooling with this. I personally think the alternator is bad. I don't do electrical work often so that's why I skimped on the meter. It has really done a great job on everything I have used it on except this. I may just be hooking the probes up to the wrong places. Anyway, I really appreciate you trying to help me solve this problem. You really stuck with me.
Report back after new component replacement. We all learn new things when problems arise. Good luck.
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- #36
THX!
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- #37
It's working and unfortunately I can't tell you guys why. I was checking wires and created a spark. Then, the FJ40 ran like someone turn,ed the distributor 90 degrees. It ran terribly and sputtered smoke. It wouldn't run at idle. I thought about it overnight and decided to check my fuses before I did anything to the engine timing, plugs, etc. The "engine" fuse was bad and I replaced it. The FJ40 ran great! When I put all the parts of the regulator, alternator back together the voltage problem was solved. Like I said I have no answer. Don't understand what happened, but I am glad its working and hope it keeps working. Thanks again for all the advice. I learned a lot trying to diagnose the problem .
I wish i could have been there from the beginning with some test equipment. Glad it is working now.
