Home-based electronics lab

Discussion in 'General Electronics Chat' started by USNtron75, Dec 14, 2010.

  1. USNtron75

    Thread Starter New Member

    Dec 14, 2010
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    I was hoping somebody could point me in the right direction here. I'm in the process of slowly but surely setting-up an at-home-lab. For starters, I'm looking into purchasing a vintage ammeter (analog of course), so I can learn the fundamentals of properly measuring for current. And obviously, there are a multitude of ranges depending on the unit. My question is what amperage range would suffice, at least until I purchase a newer digital multimeter, for a hobbyist? I don't want to shell-out my hard-earned dough so as to place the unti in-series only to produce a surge. I guess, simply put, what is a good (sufficient) working amperage range for a newbie? I look forward to any/all response. Thank you.


    "Making mistakes is a gift."--Unknown
     
  2. #12

    Expert

    Nov 30, 2010
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    I received an ad from Harbor Freight today showing digital multimeters on sale for $3. I've used them. They don't last a year, but they are just right if you're going to blow your meter up by being a beginner. Buy two, they're cheap and they will get you enough experience to be trusted with a $100 meter.

    Just my opinion...
     
  3. elementalrage

    Active Member

    Jul 30, 2009
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    Why not buy a quality unit that will last? Why waste your time/money on something inaccurate? Start with a nice Fluke RMS multimeter.

    What kind of projects are you wanting to tackle?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    You start with the cheap stuff, BECAUSE you don't know how to use it yet. When you know what settings to use and what NOT to do with it. Then spend some money for a nice 'True RMS' Fluke meter.

    You'll cuss the day you were born if you pop for a high dollar meter and melt it down in the first week.
     
  5. someonesdad

    Senior Member

    Jul 7, 2009
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    Actually, you'll cuss the high quality meter's fuse replacement cost... :p I haven't bought fuses in lots of years, but I bet the Fluke-recommended replacements are at least $5-10 each today.

    Forget messing with an old analog ammeter; I don't think it would be worth your trouble unless you can get one for free. However, you can find scrapped equipment with good 50 μA or 100 μA meter movements and make your own ammeters using them. But it's easy for a newbie to ruin a microamp meter movement and it might be difficult for you to make the requisite low resistances. But it is an excellent learning experience.

    For plain ease, I'd also recommend buying a couple of the Harbor Freight $3 digital multimeters. They'll serve just fine for learning and you won't mind if you blow one up. Of course, as a newbie, you should be staying away from line voltages; do your learning with low voltage DC stuff in the range of 5 to 10 volts.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    There have been lots of discussion about the cheap meters on this site, they will last as long as you let them, and are decently accurate. You can make mistakes at any level, but meters overall are pretty rugged. You need to know where the fuses are and where to get replacements (Radio Shack can carry them).

    My standards towards meters includes not having the wires permanently wired to the meter. Some of the extra features on more expensive meters are nice (I'm not talking about true RMS), things like frequency counters and capacitance meters.
     
  7. Len Whistler

    Member

    Dec 10, 2010
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  8. elementalrage

    Active Member

    Jul 30, 2009
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    I guess that was my point. I highly doubt he's going to be working on extreme voltage or high current projects.

    I would venture to say that a cheap meter would have the potential for injuring it's user more than a decent unit would. If $5-$10 a fuse saves my skin... then I accept that cost.

    I'm very surprised that a lot of people are saying to buy the cheap meters. I didn't expect that.

    http://www.youtube.com/watch?v=M-FZP1U2dkM
     
  9. #12

    Expert

    Nov 30, 2010
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    That looks very much like the $4 meters that Harbor Freight sold last year. This years model is red and has a transistor socket, probably for measuring DC gain at one amount of current. Not very good, but it will tell you if the transistor has been ruined. Very handy for beginners :)

    ps, My fluke requires a 600 volt cartridge fuse, not in the 98 cent category!

    ps again, STAY AWAY FROM HIGH VOLTAGES! I have heard that these $4 meters turn into a ball of flame if you try to measure 440 volt power lines. I can't prove this is true, but just be safe. Don't be messing with stuff that can kill you just because you touched it.
     
  10. someonesdad

    Senior Member

    Jul 7, 2009
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    As stated before and in other threads, the Harbor Freight $3 meters are fine for low voltage DC and AC measurements. (I typically define "low voltage" to mean DC or AC voltages below around 20 volts; YMMV.) They'll meet or exceed the accuracy for typical analog meters and you simply can't beat the price. I know they also work fine on typical 120 VAC and 240 VAC line voltages because I've used mine to measure those voltages. However, they are NOT well-protected like the Fluke and other industrial-grade meters are (i.e., I wouldn't use them in an industrial or day-to-day setting). If you don't know the difference, then stay away from measuring line voltages until you can appreciate the differences.

    Since new analog meters will probably cost 3 to 10 times as much as the Harbor Freight meter, why mess with analog? There are times when I prefer an analog meter, but a newbie will do fine with these low cost digital meters, at least for learning tasks.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    I have several of the $3-on-sale Harbor Freight digital multimeters kicking around here. The worst part about them is the cheap meter leads that have a fairly high resistance and break pretty easily - along with the cheap sockets that are just brass tubes. But, what can you expect for $3?

    I was dubious about their accuracy, so took one to work a few years back, and checked it using a Fluke Calibrator instrument that had itself just been calibrated, and compared it to a Fluke multimeter that had ALSO just been calibrated.

    I was surprised to find that with the exception of very low resistance values and higher current values, the cheap $3 meter proved more accurate overall than the Fluke handheld meter!

    This doesn't mean that the $3 meters are great, but they'll do OK for low-voltage stuff.

    The big caution on these meters is the way they're fused inside. The fuse is rated for 250v. If you were measuring line-level voltages and there was a power surge, the fuse may not be able to break the arc if the meter itself fails shorted. The result will be an extremely hot expanding plasma fireball that will consume anything it touches, including people. :eek: I'm not kidding. It would be like holding an exploding sun in your hand.

    Fluke meters use special fuses that are designed to break the circuit reliably even at high voltages; there is a silica material inside the fuse body that keeps the plasma ball from forming. These fuses must always be replaced with the same type/model fuse, or you will no longer be protected.
     
  12. tbfunk

    Member

    Dec 9, 2010
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    Your serious? What is this expanding plasma fire ball thing called? VERY curious!
    Excuse me if I am a little skeptical.
     
  13. Robin Mitchell

    Well-Known Member

    Oct 25, 2009
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    This is a very strange post, certainly sounds like a neewbie XD
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    #1 cause of death for linemen, electrical discharges, usually in the form of a fireball. You discharge 44000 watts in a millisecond and sustain, what is not to believe? BTW, I got that number from 220VAC and 20A, both are in American and European houses. A standard 110VAC 15 outlet is a potential 1650 watts. An arc is low energy plasma, we are talking high energy plasma. Of the high tension lines numbers in 100's of kilowatts (or even higher) are possible.

    Electrical safety classes emphasize this is exactly like an explosion when things go radically wrong.

    A engineer coworker was working on a 600VDC power supply with a quality DVM and it melted down inside. After the second one we concluded that there were high voltage spikes on the DC level, breaking down the protection circuitry and the DC discharge finished the process. When I opened the second one up the plastic inside (all of it) had been totally melted, and was very stringy. The only outside indication was a slight blackening around the LCD display. I sent one to our repair dept. as a joke (I was a metrology tech for a year, and had worked with these guys).
     
  15. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    This discussion of arc-flash caught my eye. A search yielded many hits, but they all seem to be lacking something.

    First the scary part: http://www.mseco.com/ArcFlash.htm

    [​IMG]

    Another link: http://www.arcflashtrainings.com/arc-flash-study-analysis/

    Accident report with 480V/200A breaker box:

    Mechanism:
    Now for reality: At what voltages and currents does arc-flash become a significant danger? Does a LiPo battery at 11.1V present a significant risk? What about 220V household at 20A? One thing seems clear. The lines feeding the main breaker box can probably provide much more current than the rating of the main breaker. So, in the case given above, the voltage may have been 480V, but the current might have been an order of magnitude higher than 200A.

    Does anyone have access to that IEEE article that might help establish at what point the danger becomes significant?

    John
     
  16. #12

    Expert

    Nov 30, 2010
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    Another rumor from #12...an electrician told me, "440 is the first voltage that will sustain an arc". He was speaking about voltages supplied to consumers, as in, 120, 208, 240, 277, etc. What he meant by, "sustain an arc" means, "when there is no fuse or circuit breaker to stop the fault". That happened to be the case that day because the 3 phase shut-off switch had failed and one phase was still connected when I went to work on the machinery. Don't worry, I'm still alive. Decades of habitual safety practices saved me.
     
  17. USNtron75

    Thread Starter New Member

    Dec 14, 2010
    12
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    I appreciate all the input. What would be advantageous about using an analog meter versus a digital one? And can any of you recommend a good text for learning the fundamentals of electricity? Experiments for newbies?
     
  18. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    An Arc.

    Like in this video

    The amount of power available at a 3 phase 480 volt panel is downright scary Another video showing the "low voltage" plasma . The video above is a higher voltage, but the same thing happens when lower voltages are put close enough together to arc (if you call 600V Peak-Peak "low"). The proximity is forced in a meter, hence the sand filled fuses used in Fluke meters.

    Another Demo of Just 480V 3 phase intentionally arcing If these vids do not make you spend the extra $150 on a good meter, nothing will. You never know when you might have to use it on higher voltage. Even 220 mains checking is a common task.
     
  19. Len Whistler

    Member

    Dec 10, 2010
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    [​IMG][​IMG]


    Anything with the 555 timer and 4017 decade counter. That's where I'm at right now.
     
  20. #12

    Expert

    Nov 30, 2010
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    @ post #17

    An analog meter is easy to see small variations on because the needle moves. Digital meters have some lag time between refreshes. You can miss seeing a glitch. My Fluke has a little bargraph that shows little changes better than the digital readout, but you know...I don't remember how many years ago I paid any attention to it. I have an analog meter, but I never use it. It's laying there on the bench and it just isn't important for me to pick it up. The digital meter is so much more accurate and easy to read, I wouldn't use an analog meter if I had one laying there.
     
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