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Voltage & Current Readings When Checking Battery Drain?

Voltage & Current Readings When Checking Battery Drain?

Postby xjohndoe001x [OP] » Mar 09 2013, 3:43am

What Voltage and current readings should I be reading when I put the positive VOM probe on the battery positive terminal and the negative VOM probe connected to the Positive Cable?

Of course before I check I'll pull all fuses and disconnecting everything else except the ECM on my
'90 GMC Sierra, 5.7L TBI, 1/2Ton, 2WD
Sincerely Jon
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Voltage & Current Readings When Checking Battery Drain?

Postby Machster69 » Mar 09 2013, 4:11am

No more than 50 mA
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Re: Voltage & Current Readings When Checking Battery Drain?

Postby Sse1990 » Mar 09 2013, 6:16am

You will get a current reading, but not a voltage reading.
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Re: Voltage & Current Readings When Checking Battery Drain?

Postby xjohndoe001x [OP] » Mar 09 2013, 6:52pm

Sse1990 wrote:You will get a current reading, but not a voltage reading.


Eat a Snickers candy bar :-) I am sure you just had one of those.. .. .. Brain Moments.
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Re: Voltage & Current Readings When Checking Battery Drain?

Postby xjohndoe001x [OP] » Mar 09 2013, 7:01pm

xjohndoe001x wrote:What Voltage and current readings should I be reading when I put the positive VOM probe on the battery positive terminal and the negative VOM probe connected to the Positive Cable?

Of course before I check I'll pull all fuses and disconnecting everything else except the ECM


I want to make it clear that the engine is off and the positive battery cable is disconnected from the battery before proceeding with the for mention test
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Re: Voltage & Current Readings When Checking Battery Drain?

Postby Sse1990 » Mar 09 2013, 9:03pm

xjohndoe001x wrote:
Sse1990 wrote:You will get a current reading, but not a voltage reading.


Eat a Snickers candy bar :-) I am sure you just had one of those.. .. .. Brain Moments.



The way you are explaining the connection is in SERIES, that is for AMPERAGE, you will NOT get a voltage reading.

To read voltage, you have to have the meter connected in PARALLEL. PERIOD. As in POSITIVE on POSITIVE and NEGATIVE on NEGATIVE.

Also you have to make sure the leads are plugged into the proper terminals on the meter, other wise you can damage the meter, and with higher amperage, damage yourself if the meter explodes due to improper use.


Pretty simple. Not sure why you think I had a brain moment.



Here is a basic schematic of how you connect a meter

image.jpg
Meter connection
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You cannot have current without voltage

Postby xjohndoe001x [OP] » Mar 11 2013, 8:36pm

I am sorry if I angered you, I thought you'd get it. Really though you will get a voltage reading on both of those schematic, if of course you have your VOM set on voltage. Go try it. You cannot have current without voltage but you can have voltage without current as in a free battery, current is a product of voltage.

If you'll notice, to the VOM both circuits are the similar. In your parallel circuits the VOM will only see the battery in series with it in a CLOSED circuit, it will not interact with the load.

The other circuit it is also closed with nothing to stop the current, unless your load has a resistance of say, a billion ohms, and so the VOM will read voltage.


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Re: Voltage & Current Readings When Checking Battery Drain?

Postby Sse1990 » Mar 12 2013, 12:00am

Voltmeters are a HIGH resistance configuration, that way, the meter is not the path of least resistance and you get a proper voltage reading. If you connect it in series, then you are now affecting the voltage reading you are trying to obtain since the meter will most likely have a higher resistance than the circuit and you aren't getting a proper reading.

You are trying to test for a parasitic draw. By connecting the meter in series like you first mentioned, you are only testing for current, since ammeters are LOW resistance configuration as to not interfere with the readings (current flow) you are trying to obtain, hence the reason why your DMM or DVOM has different connections on it. Low resistance connections for amperage only and your high resistance connections for all other testing.

Sure you may get a voltage reading in series, but it is WRONG.

So back to the original question, connected the way you are connecting it, check for current and any voltage reading connected in series will not be accurate.

I do however like how you drew the flow in red, not the conventional wrong way of positive to negative, but the correct way of negative to positive flow.
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A

Postby xjohndoe001x [OP] » Mar 12 2013, 2:01am

Are you saying that if I was to test a battery alone like the diagram below I wouldn't get the correct reading? The battery and meter would be in series? How about if one or more loads were also in series with the battery and meter? Why don't you actually test this out because I have many many times in class, that is one of the first circuits learned and ..Wait.. .. .. .. .. .. just then and it always works.

I was lead to believe that yes the meter does add to the circuit but it was so calculated that the amount added could always be accurately subtracted giving you a correct reading, otherwise they wouldn't be any good.

37289
P.S. I am going to unsubscribe from this thread, ask someone else please.
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Re: Voltage & Current Readings When Checking Battery Drain?

Postby Sse1990 » Mar 12 2013, 2:17am

I'm talking about your first question about connecting the meter in series with the vehicle. You want to read the current. Any voltage reading will be I accurate.

You may play with this in class, but I deal with this in the real world as an industrial electrician where proper readings and testing is VERY important and done wrong can be deadly.

You do realize what I am saying about connecting a voltmeter in series with your vehicle. The volt meter is high resistance and it's resistance will be what voltage you are reading, not the vehicle.

When your talking about testing a battery alone, and talking about testing a parasitic draw on a vehicle, it's like comparing apples and oranges.

If you want to compare properly, you need to leave the load "vehicle" in the circuit.

Just trying to help.
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