Multimeter Tutorial

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Doz
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Post by Doz » Tue Feb 06, 2007 10:19 pm

Marty wrote:gain - if your measuring the CCA of the battery - select a suitable scale.
I wouldn't want to try to measure the CCA of your battery with a multimeter, the test leads are just not man enough for that sort of current... and the meter probably won't have that sort of range , get an amp-clamp. Make sure it's the active sort for DC , cheap non-active ones tend to be AC only (just a current transformer)

Never forget seeing a supposed electronics engineer connect an AVO 8 (expensive at the time) across his car battery set to the 10 amp range , I don't think we ever did find the remains of the cut-out switch !!!! [-X #-o
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Post by Way2go » Wed Feb 07, 2007 2:18 am

tom wrote:"The advantage of measuring current is that it is non-invasive."
Unless you are using a clamp ammeter, it is not non- invasive and a clamp ammeter is of little use on a car. In order to measure current, the meter must be in series with the object being measured. How can this be done in a non-invasive way?
As discussed in this thread i.e.
ellevie wrote: Image
Inserting a fuse link connector to achieve this would not be classed as invasive by the majority of people.
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Post by tom » Wed Feb 07, 2007 8:24 pm

The majority of people are ignorant fxxkwits though.
It certainly would by me (you break into the circuit to install a measuring device), but then it is a very long time indeed since I trained as an electronics engineer, damn near 35 years, so I might be talking rubbish! :roll:
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Post by Way2go » Thu Feb 08, 2007 1:14 am

tom wrote:The majority of people are ignorant fxxkwits though.
It certainly would by me (you break into the circuit to install a measuring device), but then it is a very long time indeed since I trained as an electronics engineer, damn near 35 years, so I might be talking rubbish! :roll:
Tom, a difference between you and me is that I don't brand the majority of people as your term above and believe that most have a valid contribution to make. You want to beat me about the head that you trained as an electronics engineer but I too am an electronics engineer having trained with one of this countries foremost blue chip companies.

If you wish to rewrite basic principles and negate the need for current measurement then go ahead but you will be laughed at in knowledgeable circles and only followed by sheep!
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docchevron
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Post by docchevron » Thu Feb 08, 2007 1:51 am

It's usually me following the sheep...... :lol: :lol: :lol:

But they keep running away..... :wink:

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Post by cavmad » Thu Feb 08, 2007 6:01 pm

[quote="Way2go
Also it is wise to measure the total battery drain current when the car is switched off (parked state) because if this is anything signficant and the car is parked up for a period then the battery can go into deep discharge from where you can not bring it back to life. (Happened to me on a good battery in a Volvo where it was parked up fo a month! New battery only solution then.)[/quote]



Makes sense to me, had this a few times over the years and one of the electronics wizzards at work said what you mention above.
Incidentally for non-techies like me this part of the forum is invaluable and I look forward to tips, hints and repair advice from everyone. I don`t ever recall seeing any advice that was dangerous or misleading (unless I tried to fix the fault myself of course!) and while some might like to argue over the finer points to me any kind of tips are welcome.
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Doz
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Post by Doz » Thu Feb 08, 2007 6:54 pm

seen my fair share of halfwits .... ;) Dodging bits of flying AVO is only one of a million stories... Most people are keen to listen and get some advice before ploughing in an flamingoing it up ...

Still am an electronics engineer , and it looks like I've landed myself a job doing something interesting at long last .... sick and tired of the NHS ... (no pun intended, but it's relevent!!!)

I'm off to wrap a bit of washer hose round something warm ;)
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Post by tom » Thu Feb 08, 2007 8:03 pm

So, Way to go, you would remove the circuit protection to plug in an unprotected measuring device that will tell you how much current was being drawn before the fuse went. Fine.

When you are sitting in the charred wreckage, you might realise that you were wrong, and I picked you up for it because Oscar was trying to learn something without having to endanger himself or his property in the process.

I would sooner be ridiculed and right. Those of us in the knowledgeable circles of which you speak tend to think that way, which is why the sheep that follow me pay me very well for my services.
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Post by Stewart (oily!) » Thu Feb 08, 2007 9:01 pm

I read this thread hoping to learn something, If it had developed I was considering asking the moderators to make it sticky or move it to the hints and tips section, now its degenerating into something I am not enjoying, I`m off to drill holes in some spheres :shock:
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Post by docchevron » Thu Feb 08, 2007 9:05 pm

and I'm going to blow up the neighbours house.......because I can! :lol: :lol:
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Post by cavmad » Fri Feb 09, 2007 12:19 am

Hey, don`t knock it I`ve just learned the true meaning of condescending :roll:
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Doz
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Post by Doz » Sat Feb 10, 2007 11:02 am

I'd be a bit cautious about using the plug in fuse thing. Does it have any method of limiting current itself? If a fuse blows, and you plug that in instead, and it doesn't limit current, you could end up pulling a lot of current through a circuit not designed for such.

Put another fuse in, if it goes again, you have a fault, then it's off to find out what. Measuring the amount of current the fault is drawing is unlikely to help you.

When I was a college (many, manu moons ago) I was told electronics is powered by smoke. If you let the smoke out, it doesn't work anymore ;)

It's amazing how much smoke there is in insulated coper wire ;)

I hope I'm not being condiscending, I didn't mean to be.
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1982 Mini HL (No wheel trims, no wheels)
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Post by ellevie » Sat Feb 10, 2007 3:33 pm

...electronics is powered by smoke... :lol: :lol: :lol:

Reminds me of an anecdote about a remote island where the primitive inhabitants used to stand at the fence and watch planes coming in to land on a small airfield which had recently been built. After a while they went away and built their own version of a runway complete with watch tower and sat about waiting for an airplane to land... :roll:
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Post by tom » Sun Feb 11, 2007 1:05 pm

For those who would like to know the correct answers
I would suggest Maplin product WP94C £4.99 which is shown on their web site.

As for being condescending, I have to choose my words with care, so you didn't get to see what I should have said about people who post dangerous and incorrect advice!
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