[fajimr]

I was going to post this in the Dumb Questions thread or even thought of starting a my own "Jim's Newbie Questions"  thread but decided (from my own experience looking for topics I remember seeing and then going back to look for) that I would start a new thread with an explicit subject so others might be able to find it.


While looking over this site I saw they had multimeters and, since I was going to order a learn to solder kit or two anyway, would get one.  Which one would best fit my needs?  I'll probably limit myself to this site as I will buy the other parts there so a discussion of other options although interesting, will not help me at this point.

http://omnitronelectronics.net/phpstore/index.php?action=category&id=92

thanks again for your patience

[AKSA]

Hi Jim,

Thanks for the post;  this is a damn good question!

To start out, you want an inexpensive meter you can happily destroy with inexperience without losing too much money.

Fortunately, since the advent of China as the world's factory, prices are not high.  There is a huge choice.

This is what you will need for building AKSAs:

1.  DC and AC volts to 200.  Higher is nice, but not strictly needed.
2.  DC milliamps to 200.
3.  Diode test.
4.  Resistance down to 1 ohm, up to a megohm.  On a DMM, the ranges are typically 200R, 2K, 20K, 200K and 2M.
5.  Transistor beta (hfe) test function.


You do NOT need capacitance, inductance, or frequency, or phase angle, or any of the fancy stuff.  If you can't get a beta test function that's OK, it's just handy.  You should not spend more than about $US30 on this meter, which is, of course, digital.

When you are thoroughly experienced (= two AKSA projects!!) you can graduate to the more expensive meters.  My advice here is a lower cost Fluke, arguably the best meters of all and made in Seattle, WA.  I have about four DMMs, but the best of them, and used ALL the time in my workshop, is an entry level Fluke Model 10, which is autoranging and cost about $US80.  The best Flukes are complex beyond reason - they can measure the mood of your Mother in law at 10 miles - but they cost the very planet we live on.

Hope this is helpful,

Cheers,

Hugh

[andyr]

... they can measure the mood of your Mother in law at 10 miles ...

Hi Hugh,

The only way I've found to measure the mood of my mother-in-law is rip the heart out of a chicken and see how it falls ... or do I mean rip the heart out of my mother-in- ... or am I just dreaming??  

Regards,

Andy

[fajimr]

To start out, you want an inexpensive meter you can happily destroy with inexperience without losing too much money.

does this have anything to do with an old post I read somewhere that you are not part of the "club" until you have jolted yourself across the room???  

[AKSA]

Jim,

My own thoughts on the matter are that you've not really been initiated into electronics until you've safely withstood a 500V jolt from a vacuum tube circuit.    

WARNING:  Don't try it.  I survived it ONCE.  I don't plan on doing it again.  But, like Terry the Tramp in Hunter S. Thomson's epic 'Hells Angels', I do feel I can take on anything now.......

Trick:  When working with more than about 120V, always keep one hand either in your pocket or by your side, NOT touching anything.  Stand on non-conducting carpet.  A shock on one arm is survivable;  a shock across both arms passes through the nerve center of the heart and sends it into fibrillation, usually resulting in death.

Ah, Andy, Mother's in Law!!  Aren't they wonderful creatures?  Fortunately I get along very well with mine.    

Cheers,

Hugh

[fajimr]

i see there is a very fine line between being supportive and brutually honest  

these are good things to know though... should there be new thread started:

"What I survived and why it almost killed me"

[Occam]

and who says that Darwinism isn't still an [electromotive] force in modern society?

[Seano]

Me. If Darwinism was real I'd have dead long ago!  

After two AC (light socket and power lead) and one DC electrocution (arc welder) I figure I'm either a reasonably good conductor or I have an exceptionally high capacity fusible link. Add to that the odd vehicle smash and fall from height I figure that either natural selection is not real......or I'm bullet proof.

As for a multimeter, I just bought my second and most expensive thus far. AU$75 for all the good stuff - continuity tester is a good feature!

[andyr]

Me. If Darwinism was real I'd have dead long ago!  

After two AC (light socket and power lead) and one DC electrocution (arc welder) I figure I'm either a reasonably good conductor or I have an exceptionally high capacity fusible link. Add to that the odd vehicle smash and fall from height I figure that either natural selection is not real......or I'm bullet proof. ...

I'm told a 9v lantern battery on the old tongue gives a nice jolt!  

Regards,

Andy

[MaxCast]

Make sure it has a stand so you can prop it up.

[Greg Erskine]

....and auto turn off.

[mgalusha]

I recently picked up a used Fluke 8050A off of eBay. This is without question the best meter I've ever owned. It's most endearing feature is a "relative" mode. It allows you to compensate for the resistance of the leads or to measure the relative change from one voltage/current to another.

These were around $400 USD when new but can be had for under $100 used and a little more for one that's calibrated. There is also a 8050A-01 version that has rechargeable batteries so that it's portable. It's a bit large to be portable but it might be a worthwhile option for some folks.

[econ]

Re:the electrocution thing.

What the heart requires is 50 to 100 milliamps during particular parts of its cycle to set it into fibrillation or stop it altogether. That doesnt sound like a lot of current . Fact is the skin's natural resistance  is 5000 ohms when the skin is dry . So with 240v mains and using Ohm's law I =V/Ryou may just reach the threshold if all the current flows through the heart.  Fortunately, it rarely does. Our skin is rarely dry though so resistance is typically lower than 5000 ohms. But  cardiac  arrest IS one of the leading causes of death from electrocution.

 The paradox is that voltage can be very small and still be fatal. If it can deliver  50 odd milliamps  to the heart that is all that is required. Say you have a cut on your finger  (ie youve brached the 5000ohm barrier) and you have wet hands and youre standing with bare feet in a wet garage  and you touch the live 12v terminal of your car battery   well  it may be goodnight Louise

 Some people are at greater risk like  the person with a pacemaker
where the wire placed within  the heart will act as a beautiful conductor straight to the hearts electrical system.

The more common  problem of domestic type electrocution is involuntary muscle  contraction . You may not be able to let go of that live wire and the current that then flows can cause burns ,  the muscles which make you breathe may go into spasm resulting in asphyxiation, and nerves which themselves are electrical conductors can be destroyed. Your brain for example  is a big bundle of nerve networks. This is by no means an exhaustive list.

 None of it is good . So earth your cases and dont even think about  touching anything that may be live no matter what the voltage.

 

[ginger]

Multimeter selection from those webpages.

Forget the M1004 dirt cheap job - will have dirt cheap probes which fall apart all the time.
The DM-3700W for $14.95 does everything you need
BUT
I would opt for the VC-9802 at $29.95 - Overload protection and auto switch off so that when you walk away having forgotten to turn it off, it won't have dead flat batteries next time. Holster gives some protection when you drop it. Will survive most of the abuse you can chuck at it and does everything you need.
Cheers,
Ginger

[fajimr]

thanks ginger for the recommendations.. I went ahead and ordered the 14.95 job last week, not thinking about all the "little" details you mention which usually turn out to be so important.  If Hugh is correct, I may have a chance yet to purchase another  


econ- thanks for the info... it IS good to know.  But my newbie question is:  How do I make sure the case is grounded?  

Does Hugh provide precautionary measures in his building/testing instructions or is it assumed that people know such things???

can't wait to get the kits and start the real learning.....

[Occam]

I just recieved my Velleman DM970 -
http://www.allelectronics.com/cgi-bin/category.cgi?category=760&item=DVM-890&type=store
actually I ordered it from hosfelt.com for $6 cheaper, $39, but All has a picture.
Its auto-off, and I bought it specifically for its added (limited) capacitance measurement feature, which most don't really need.
I can't opine on its long term reliability or performance, but it does seem reasonably priced for what it does.

But I did order these hook test probes from All. I hate alligator clips -
http://www.allelectronics.com/cgi-bin/category.cgi?category=760&item=MTC-21&type=store

FWIW

[AKSA]

Hi Jim,

You wrote:

Does Hugh provide precautionary measures in his building/testing instructions or is it assumed that people know such things???

The answer is yes, particularly on the wiring of the mains circuits for the transformers, switch and snubber.  This is important, and I include a suggestion to use a professional electrician if in any doubt whatever.  This warning is far stronger than the typical warnings seen in the US, because our mains is 240V, markedly more dangerous than yours in the domestic environment.

I'm also pretty emphatic on chemical warnings too.  The fumes from soldering are toxic, and identified as such, with suggestions for standing to one side of the workpiece and ensuring adequate ventilation.  I also suggest use of Coke to remove tarnish from some brass escutcheon nails, and exhort the builder NOT to drink the Coke after this procedure.  After all, the taste is appalling..........

Cheers,

Hugh

[fajimr]

The answer is yes

that's what I figured Hugh, as I've come to expect no less    

just checking what other skills I might need.  let's see now:  stand to one side,  don't smell the fumes, keep one hand in my pocket, ground the case, don't stand barefoot in water or touching another live piece of equipment especially with cuts on my finger, don't drink the coke... all the while trying to melt solder onto tiny pieces of wire and a pcb board...... no problem