Multimeter help!
Discussion
I’m clearly getting old as I can’t quite work out my new multimeter and need help!
Trying to trace why my Jeep battery keeps going flat after a couple of days.
I’ve checked the battery voltage and cranking amps, and although both aren’t ‘perfect’ they are just about OK… battery just over 12.4v, cranking just over 10amps.
So I’ve moved onto (another) parasitic draw, and have set the multimeter in series to get a reading.
Looking for under 50 milliamps to be ‘ok’….
Does this show under that on the multimeter? I can’t figure out if the reading is 25 milliamps or much, much higher!
When I move the red connector to the left 10amp socket, there is no reading, this is the only one I get…
Trying to trace why my Jeep battery keeps going flat after a couple of days.
I’ve checked the battery voltage and cranking amps, and although both aren’t ‘perfect’ they are just about OK… battery just over 12.4v, cranking just over 10amps.
So I’ve moved onto (another) parasitic draw, and have set the multimeter in series to get a reading.
Looking for under 50 milliamps to be ‘ok’….
Does this show under that on the multimeter? I can’t figure out if the reading is 25 milliamps or much, much higher!
When I move the red connector to the left 10amp socket, there is no reading, this is the only one I get…
the cueball said:
I’ve checked the battery voltage and cranking amps, and although both aren’t ‘perfect’ they are just about OK… battery just over 12.4v, cranking just over 10amps.
I am more concerned with how you came to the above findings.12.4v is about 50% charged. A 12v battery is actually 6 x 2.1 volt cells in series, so a good/fully charged battery will read 12.6/12.7v and as a rule of thumb every 0.1 v down is a loss of 25% charge.
Also, how did you measure "just over 10 amps" as your meter is a 10 amp meter, so it will only actually read "just over 10 amps" at the most, after that it will blow the fuse, so it is unlikely you were measuring what you thought you were.
Paul_M3 said:
That’s 245 milliamps
No it’s not. It’s Zero amps because there is no lead plugged into the Amps terminal in the meter.Whenever you move the dial to Amps you need to move the lead to the A terminal.
When the selector is on Volts the meter internal resistance is (ideally) infinity and the meter is connected in parallel with the voltage being measured.
When the selector is on Amps the meter internal resistance is (ideally) zero and the meter is connected in series with the load.
If you have moved the lead to A and put the meter leads across a voltage the meter internal fuse is most likely blown.
To check the meter fuse remove it and then check it using the Ohms function.
If the fuse is OK you can then check for parasitic drain.
To check for parasitic drain you need to disconnect one of the battery terminals, put the meter in SERIES with the battery on the Amps setting and the lead in the A meter terminal. Don’t crank the engine as the starter motor current is WAY more than 10A and will blow the fuse.
Edited by paralla on Saturday 11th September 09:32
Paul_M3 said:
That’s 245 milliamps
So a tad bit over 50 milliamps then… lolE-bmw said:
I am more concerned with how you came to the above findings.
12.4v is about 50% charged. A 12v battery is actually 6 x 2.1 volt cells in series, so a good/fully charged battery will read 12.6/12.7v and as a rule of thumb every 0.1 v down is a loss of 25% charge.
Also, how did you measure "just over 10 amps" as your meter is a 10 amp meter, so it will only actually read "just over 10 amps" at the most, after that it will blow the fuse, so it is unlikely you were measuring what you thought you were.
I think 12.4 is more around 75% charged and on the very lower limit of a battery, but I gave it gave it a pass for now, as I think it’s more of a draw issue than a bad battery.12.4v is about 50% charged. A 12v battery is actually 6 x 2.1 volt cells in series, so a good/fully charged battery will read 12.6/12.7v and as a rule of thumb every 0.1 v down is a loss of 25% charge.
Also, how did you measure "just over 10 amps" as your meter is a 10 amp meter, so it will only actually read "just over 10 amps" at the most, after that it will blow the fuse, so it is unlikely you were measuring what you thought you were.
My mistake on the cold cranking test, I meant the voltage dropped to around 10v not amps…
paralla said:
No it’s not. It’s Zero amps because there is no lead plugged into the Amps terminal in the meter.
Whenever you move the dial to Amps you need to move the lead to the A terminal.
If I move the red lead to the A terminal the reading goes to zero though…Whenever you move the dial to Amps you need to move the lead to the A terminal.
Could there be a setting on the meter I’m missing?
paralla said:
No it’s not. It’s Zero amps because there is no lead plugged into the Amps terminal in the meter.
Whenever you move the dial to Amps you need to move the lead to the A terminal.
I think your wrong there. One lead is in the common (black lead), the other lead is in the up to 400mA fused position. Whenever you move the dial to Amps you need to move the lead to the A terminal.
If he wanted to read more than 400mA then he would need to move the red probe from the right hand connection (400mA) to the 10A connection (left one), of course if he’s tried measuring over 10 amps in the 400mA connection he will have blown the fuse.
Also if he’s seen over 10 amps when cranking (remember the amp meter averages out over a short period) it will have undoubtedly been higher at the instantaneous point of starting to crank (the fuse for 10A might be a slow blow type so still be ok).
As the meter appears to be reading still it appears the OP has got lucky.
Page 14 tells you all you need to know
https://www.drapertools.com/products/manuals/41820...
Edited by MB140 on Saturday 11th September 09:39
Edited by MB140 on Saturday 11th September 10:26
MB140 said:
I think your wrong there. One lead is in the common (black lead), the other lead is in the up to 400mA fused position.
If he wanted to read more than 400mA then he would need to move the red probe from the right hand connection (400mA) to the 10A connection (left one), of course if he’s tried measuring over 10 amps in the 400mA connection he will have blown the fuse.
Also if he’s seen over 10 amps when cranking (remember the amp meter averages out over a short period) it will have undoubtedly been higher at the instantaneous point of starting to crank (the fuse for 10A might be a slow blow type so still be ok).
As the meter appears to be reading still it appears the OP has got lucky.
You are right, I’ve never seen that in a meter before. If he wanted to read more than 400mA then he would need to move the red probe from the right hand connection (400mA) to the 10A connection (left one), of course if he’s tried measuring over 10 amps in the 400mA connection he will have blown the fuse.
Also if he’s seen over 10 amps when cranking (remember the amp meter averages out over a short period) it will have undoubtedly been higher at the instantaneous point of starting to crank (the fuse for 10A might be a slow blow type so still be ok).
As the meter appears to be reading still it appears the OP has got lucky.
Cranking amps for a Jeep will be above 50A for the entire time the starter motor is running .
The OP needs to understand the series/parallel bit though.
cueball,
Your Multimeter should have come with a 20 page manual!
If you haven't read it (it is a strong male tendency not to read the instructions!) or have lost it, see: https://www.drapertools.com/products/manuals/41820...
John
Your Multimeter should have come with a 20 page manual!
If you haven't read it (it is a strong male tendency not to read the instructions!) or have lost it, see: https://www.drapertools.com/products/manuals/41820...
John
paralla said:
You are right, I’ve never seen that in a meter before.
Cranking amps for a Jeep will be above 50A for the entire time the starter motor is running .
The OP needs to understand the series/parallel bit though.
Yep it amazes me how many people I have seen trying to measure current in parallel. They clearly have no idea how a meter actually reads the current flowing through it (passes all the current through a known value resistor (normally 10Mohms) and uses V/IxR to calculate the current, if you measure in parallel no only are you going to fCranking amps for a Jeep will be above 50A for the entire time the starter motor is running .
The OP needs to understand the series/parallel bit though.
k the meter not all current is passing through the 10Mohms resistor so your getting an incorrect reading any way. See the manual for this draper meter it uses 10MOhm impedance. also only samples 3 times a second so the reading the OP saw at cranking was way more than displayed on the meter. There are plenty of videos on YouTube that show you how to trace parasitic drains. OP just follow one of those.
paralla said:
You are right, I’ve never seen that in a meter before.
Really? Pretty much every multimeter has the same arrangement.Also, I imagine the reason the OP is getting a reading of zero when he moves to the ‘A’ socket now is because he blew the 10A fuse when he was messing around doing his previous testing…
MB140 said:
They clearly have no idea how a meter actually reads the current flowing through it (passes all the current through a known value resistor (normally 10Mohms) and uses V/IxR to calculate the current,
Surely it must be a low resistance that the current is passed through so as not to change the overall load on the loop you are measuring?E-bmw said:
MB140 said:
They clearly have no idea how a meter actually reads the current flowing through it (passes all the current through a known value resistor (normally 10Mohms) and uses V/IxR to calculate the current,
Surely it must be a low resistance that the current is passed through so as not to change the overall load on the loop you are measuring?Paul_M3 said:
You are correct E-bmw. It’s a bit funny that MB140 is talking about people not knowing how a multimeter works, whilst then going on to talk about the input impedance of the meter when being used to measure voltage rather than current. The resistance of the meter is very low when measuring current. It’s not an obvious spec to find in the manual, but is given as a burden voltage, normally in mV/A. If the current was being passed through 10Mohms the circuit would stop working.
Learning has taken place. I’ve only been wrong for 25 years. Apologies for the duff gen. Paul_M3 said:
paralla said:
You are right, I’ve never seen that in a meter before.
Really? Pretty much every multimeter has the same arrangement.Also, I imagine the reason the OP is getting a reading of zero when he moves to the ‘A’ socket now is because he blew the 10A fuse when he was messing around doing his previous testing…
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