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  #41  
Old 11-08-2018, 03:37 PM
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Originally Posted by wpoll View Post
I have the same (well, very similar) meter, Andrew - I'll do the test on my 3.0d and post up the numbers here.

Great work!
Didn't get this test done this morning, sorry - torrential rain here and 7DegC. - not great conditions for such a test...
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  #42  
Old 11-08-2018, 03:37 PM
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Has to be. You lose an entire volt for every 0.005 Ω! With a thinner cable I can't imagine how bad.
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  #43  
Old 11-08-2018, 04:18 PM
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Originally Posted by andrewwynn View Post
Has to be. You lose an entire volt for every 0.005 Ω! With a thinner cable I can't imagine how bad.
It's a product of having the starter at the other end of the car from the battery!

The only other car I've owned that had this same arrangement was an old 1960s Austin Mini. The battery was also in the trunk/boot - because it just wouldn't fit anywhere else!!!

Starter current was a lot lower of course... it was only 850cc.
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  #44  
Old 11-09-2018, 02:35 AM
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You will see almost no voltage until you start to crank. If you see voltage like 0.1v wait until it drops, turn off any power draw like fan. You might see a negative value which will happen when power is coming up the right side cable.

70mm SQ is about 9mm diameter

Air con/fan always comes on as soon as you engage ignition to start so will turn that off....thanks
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  #45  
Old 11-09-2018, 04:30 AM
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Didn't get this test done this morning, sorry - torrential rain here and 7DegC. - not great conditions for such a test...
So I tried to get a reading tonight - no luck. I thought at least one of my meters had a peak hold voltage setting (or min/max) but they don't, and the start is so fast it was impossible to get any reading.

I have a Fluke ScopeMeter at work so I'll have a go with that next week - darn sure that has a peak hold (min/max) and even graphing/logging I think...
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  #46  
Old 11-09-2018, 08:31 AM
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Originally Posted by wpoll View Post
So I tried to get a reading tonight - no luck. I thought at least one of my meters had a peak hold voltage setting (or min/max) but they don't, and the start is so fast it was impossible to get any reading.

I have a Fluke ScopeMeter at work so I'll have a go with that next week - darn sure that has a peak hold (min/max) and even graphing/logging I think...

ANY Fluke surely more accurate than my digital voltemeter...plus there is noooo setting on my device to hold peak/min, so as mentioned if i can will have someone recording the device while i crank key, then check out recording in slower motion.....end of the day still need to know if my starter is doing odd things. IF all is in order owe you fellas an apology or dram or two.Then I reckon will be investing in a agm as I dont think that its a coincidence agms are in all modern stop start vehicles as opposed to 'normal' batteries. All will be revealed soon
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  #47  
Old Yesterday, 08:42 AM
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Originally Posted by wpoll View Post
So I tried to get a reading tonight - no luck. I thought at least one of my meters had a peak hold voltage setting (or min/max) but they don't, and the start is so fast it was impossible to get any reading.

I have a Fluke ScopeMeter at work so I'll have a go with that next week - darn sure that has a peak hold (min/max) and even graphing/logging I think...

Wayne?wpoll? ok well wired up my basic dmm to the + in engine bay and the other probe touching the inner sides of the dc lighter socket, set it to 20V got a reading that looked ok for battery at rest 13.0V, cranked engine, dropped down to 8.98V....not sure how I am gonna get the amp draw of starter via this info? if it was my starter an issue would it have dropped much more than this
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  #48  
Old Yesterday, 09:06 AM
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Originally Posted by andrewwynn View Post


Just performed the simple test of monitoring the voltage drop on the starter cable when cranking the starter.

I have a 2001 m54 gas 3.0i. The engine was slightly not cold (a few minutes of operation after sitting overnight then a minute or two rest when I realized I've been meaning to take this measurement for a while).

I started the car twice in a row the first was actually about 75/100v second start 63/100 and after waiting just 3-4 minutes took 75/100 again.

I'm going on gut to say my starter hasn't started the escalation of current into failure and is pulling between 200-225A.

That means 0.75/212.5 means about 3.5 mΩ cable resistance.

If you take the voltage drop measured from the cig. lighter socket to the B+ jump point under the hood and multiply by 285 you should arrive at starter current.

Somebody with access to a clamp ammeter could perform the voltage drop measure to get a more accurate value but this will get you in the ballpark.

It also will give you trend and comparison info. Eg. Take the measurement at 30C and 0C it will be a lot different.

So back testing: 0.75v x 285 = 285*0.75 = 213. The immediate restart (oil still on all the journal bearings etc) was .63*285 or 180A both numbers seem right on target.

I was able to have the shrink wrap on the B+ hold my positive lead to make it very easy to do the measurement.

At some point it will be nice to have a control taken to measure the current draw and voltage drop at the same time but the 285 figure will probably work very well for most people to get a sense of if their starter is wearing out.

I'll take the measurement on wife's car when I'm in the same zip code as the car to DOUBLE my sample size.

Best if your meter has a peak scale (in fact probably a requirement. I just tried to watch live and only saw .30v or something. Maybe with analog meter you can watch the needle.

After I get a bigger sample size and especially if I can get a simultaneous clamp ammeter reading I'll make a thread about the topic and post more details.

1.38v would be 392A for comparison.

I just saw your theory Andrewwynn, and sorry if I repeat

on starting voltage dropped from 13.01V(fully charge battery)to 8.98V, to clarify of course it never stayed there it then stabilized and the time frame we are talking about is 4-5 seconds as it cycled through below readings



so 13.01 rest 12.65 cranked key 12.49 8.98v then up to showing 14.36v


so my maths, lets take the 12.65v as the battery voltage yes?
12.65(soon as truned key)-8.98(lowest reading whilst cranking)=3.67v drop


voltage drop of 3.67v X the 285 figure(not sure where you go this from?)= starter draw?
in this case it would be 1045.95W (which ahmmm is way over the norm )am i correct in the way I have calculated this? is this even possible to get such a draw?
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Last edited by omodos; Yesterday at 09:42 AM.
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  #49  
Old Yesterday, 09:15 AM
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Originally Posted by andrewwynn View Post
You will see almost no voltage until you start to crank. If you see voltage like 0.1v wait until it drops, turn off any power draw like fan. You might see a negative value which will happen when power is coming up the right side cable.

70mm SQ is about 9mm diameter

hmmm i reading your notes above must have done something wrong,says I should see no voltage until i start to crank? I never read this instead when the probe was dead center in the lighter socket indeed got no reading and thought this is wrong, so then as mentioned touched inside barrel of ligher socket that gave me reading of 13.01 v that i thought was the battery voltage, I then cranked and watched the meter reading drop, thinking that this was voltage drop you were referring to...please note my meter is one of these exxactly
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Last edited by omodos; Yesterday at 09:37 AM.
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  #50  
Old Yesterday, 02:33 PM
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Originally Posted by omodos View Post
hmmm i reading your notes above must have done something wrong,says I should see no voltage until i start to crank? I never read this instead when the probe was dead center in the lighter socket indeed got no reading and thought this is wrong, so then as mentioned touched inside barrel of ligher socket that gave me reading of 13.01 v that i thought was the battery voltage, I then cranked and watched the meter reading drop, thinking that this was voltage drop you were referring to...please note my meter is one of these exxactly
I think you've misunderstood what you are testing here... you are trying to measure the voltage drop in the main cable due to the starter current. Once you know this voltage drop, you can calculate the starter current draw (using ohms law).

This voltage should be less than 1v but may be a bit more in your case. It also very hard to measure this voltage if you meter doesn't have a peak hold function....

To measure this voltage drop, put the black lead from the DVM on the B+ terminal in the engine bay.

Put the red lead from the DVM on the centre contact in the cigarette lighter socket in the dash.

You should see a voltage very close to zero.

Now start the car and note the voltage that appears during cranking. It could be between 0.5 and 1.5v so set your meter to a low voltage range before testing.
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