How to use a bloody multimeter

[Sir Stinkalot]

Hi All ....

I need help .....

I am in the process of changing over car stereos from one car to another prior to trade in ..... so far not so good.

I have managed to located and pair all of the speaker wires by touching them against a 1.5v battery until the speakers cracked ... great .....

Now I need to fund which ones carry the 12V current.

I have found some info from the net which tells me how to determine which wire does what but I need to use a multimeter to find which one is 12V.

After working at Dick Smiths I purchased a multimeter but unfortunately never worked out how to use it ..... I assume that to find the live 12V wire I need to turn the dial to the "V" rating .... do I put it onto 200m, 2000m, 20 or 200? I have the two probes one red and one black, but only I end of wire to test .... do I touch both probes to the exposed end wire or one probe .... and which one?

HELP .....

stinky

[jackruss]

woo hoo


First think make sure it is set to volts and its DC. Also that it is on the 20 scale.

If it doesn't have ac/dc you should be fine with just V ( for Volts),

Secondly, the car chassis is the -ve, so you touch the black lead onto body somewhere ( make sure its metal :-) and maybe even clear some paint off)

Then just touch the red lead onto your wire until the needle or reading changes.

If you want to check the principle, open the bonnet and touch the black lead to the -ve terminal of the battery and the red one to the postive lead and watch the needle move.

Then touch the lack lead to the engine or any exposed nut and see that the body is ground or -ve in the circuit.

Good luck.

JR

[bitingmidge]

... or you could get that annoying kid next door to lick the wires one at a time and tell you what each taste like... :D :D :D

Cheers,

P

[Honest Gaza]

Sir Stinkalot

The multimeter can be used to test for several things :

Continuity
Checking to see you have both ends of the same wire, or a working fuse, using the Resistance or Ohm settings of the meter.....make sure that there is no power connected to the wire.

Current
Checking to see how many Amps are running through a Circuit

Volts AC
Usually referring to 240V as in your home wiring....obviously very dangerous for the unwary

Volts DC
Batteries, Power Adapters, Cars

NOTE : If ever in doubt as to whether or not you have AC or DC...always best to select AC and set for the highest possible setting so as not to damage the meter.

In your case ( Volts DC ), there is normally a terminal on the meter marked COM for common and by convention, here is where you would normally plug in your black lead. As suggested, connect the black "probe" to some metal of the car ( even the case of the stereo will be earthed if still connected to the car wiring ), and use the red probe which will be plugged in to a terminal labelled "V" ( and probably coloured red ) to find the 12V lead from the car.

I hope I haven't simplified this too much....don't wish to offend. :)

[Sir Stinkalot]

Thanks all for the replies .....

I told the Stinkette when I came inside the problem that I had and said that I was going to log onto the net to ask the forum .... I then said I would be back in half an hour to get the answer .... I wasn't wrong.

The installation has gone well .... appart from a few blown fuses it should all go well.

As for electrical stuff I try and avoid it .... after changing a few light fittings a few months ago and making the entire fitting active I try and stay away.

The only time that I used the multimeter was at DSE when we had customers come in with cordless phone batteries .... we would pull out the multimeter and get some sort of reading ... then tell the customer the battery was stuffed and they had to buy a new one at overly inflated prices.

A now rocking Stinky.

[Wood Borer]

The only time that I used the multimeter was at DSE when we had customers come in with cordless phone batteries .... we would pull out the multimeter and get some sort of reading ... then tell the customer the battery was stuffed and they had to buy a new one at overly inflated prices.


Stinky thanks for confirming what is an issue with technology retailers.

Some of us have electronics and technology qualifications and experience which we use in our professions.

We get upset when we shop at a technology retailer who tries to bluff us into buying unecessary equipment. From the retailer's point of view most customers can be fooled by their unqualified staff but the unqualified staff get upset when it is demonstrated that they have no idea and the con is exposed.

OK, they are just sales assistants employed to operate credit card machines and press buttons on the till, but they should be aware of their short comings and that some of their customers may know a little more than they do. Rather than argue with the knowing customer, they might benefit from learning.

The same applies to all industries including woodwork.

[Peter R]

One should be careful in using a voltmeter from say Dick Smith or any of the discount stores. Even though some voltmeters have 700 volts AC as a reading calibration I would not trust it on such voltages. A decent 240 volt meter will cost around $120 to $150 and anything below that is a toy.
However, the Dick Smith digital voltmeters are reasonable for 12V and 24v systems.
Always check that your voltmeter is working before using as you can get very frustrated with negative readings, which can be nothing more than a poor connection in the voltmeter leads.

Peter R.

[outback]

I have a $5.00 Multi meter from DSE.

it has been jjjjust great rewiring the house

[ozwinner]

Just found the font thingy huh?


Al :D

[Peter R]

$5.00, must have purchased it of Dick when he was an apprentice sparky!! Give it back, he might put in his museum.

Peter R.

[barnsey]

As an electro mechanical tradesperson there is so much I could go on abaout in this thread but I'll keep it short and sweet. ;)

Multimeters - which most people would buy are, within reason, quite functional for most applications. If you don't know how to use it for an application there is any amount of info on the net that will give you an explanation. You need to know this or you will blow out the meter and possibly yourself if you stick it where you shouldn't have been. :eek:

You wouldn't believe what I've seen done. :o

Honest Gazza gave good advice - if you are still a bit in the dark - read some more :rolleyes:

WB: Doesn't that get up your skirt - bloody SA sales assistants :mad:

Jamie

[Wood Borer]

Crow Eaters,

Barnsey means Smart Alec or Smart A#se not South Australian.

Some of the Sales Assistants are OK but some of them are a pain and with me their confident sounding lies results in either no sales or greatly reduced sales.

What concerns me though, I hear blatant lies from sales people on subjects I know well, but no doubt I am being told lies when buying other products and services, going to the doctor, dentist ....... a bit of a worry when a bloke has to be sceptical most of the time especially on health advice.

Anyway, back to the topic, good to know you sorted your problem Stinky.

[Iain]

Was this a classic case of an oversell? One of those little screwdriver thingy's (tech term) with a globe would have done the job here.
About $1.50 from the Warehouse.

[AlexS]

$5.00, must have purchased it of Dick when he was an apprentice sparky!! Give it back, he might put in his museum.

Peter R.

I'm still using a DS multimeter that I bought as a kit & put together in about 1978. Think I might replace it though, the battery's just about had it.

What, me a miser???

[barnsey]

WB

You should know by now that I don't know anybody called Alec and as far as I'm concerned any where south of here is south australia. :D

Jamie

[Wood Borer]

Jamie,

I buy my woodwork gear from MIK in South Australia and I just didn't want to get on the wrong side of them. Geez, what would they send me if I ordered an LN plane? Something in a plain parcel? :D

[barnsey]

WB
Yeah - that's happened to me :confused: Where do I put the batteries :rolleyes:

[Wood Borer]

Exactly, but Christopha could probably answer that one - check out his profile.

I am sure he knows how to use a multimeter to check the batteries in such devices.

[Peter R]

You blokes are right, there are a few things that would have done Stinky, like the 12 volt probe as technically described as a 'thingy', and there are some good cheap voltmeters that would be suitable for 12 and 24 volt systems....but the question was about using a voltmeter and that was answered very well, I thought.
I spent 30 years working with electricity, and I can say with pride that I never copped a bad dose of current either by accident or by carelessness. However, I have seen the effects of a survivors 240v experience and the burns of a 415v burst. It is not good, believe me.
Many times you will hear people that they have been thrown accross the room from a power supply, well in those cases you have probably only had a small bite as a full grip of 240V will make your muscles contract to a point where it is sometimes necessary to break an arm to get the hand to release. The toss accross the room is your own nerves reacting.
If you are a handyman a good voltmeter is a worthwhile tool and like any worthwhile tool it should be a good one.
The one clear electical killer of home renovators is a reversed polarity and a good voltmeter will pick that for you and that alone is worth the expense.
Am I preaching safety, you betcha!! I didn't get to this age by being clumsy.
Peter R.