measuring AC/DC Amps

[perfectbite]

Here is a question. If a Fluke 'tong' meter is built to indicate AC Amps passing through the conductors of an AC circuit, what is it indicating if it used on a DC Amperage producing device i.e. a car alternator. One 1/2 of the amperage or all of the amperage? Would it make a difference if the 'tong' meter were digital or analog? Would the Hertz rate make a difference?

[cato]

I don't think it is possible to say what the correction factor would be without a detailed analysis of design of the input circuit of the fluke and the frequency components (FFT) of the generator wave form. <p>I don't rememver enough calculus to be sure of this answer...but I'm pretty sure. You can use your Fluke as a good indication that SOME current is being produced in a particular leg of the alternator and maybe whether more or less current is being generated as you change engine speed...but I don't even think you can rely on a doubling of the reading as an indication that the current doubled. <p>When Ed sees your post you will get a more informed answer....but I thought this might tide you over in the mean time.<p>:-)

[rshayes]

Most of the "clamp on" ammeters form a transformer with the wire in the tongs forming the single turn primary of a current transformer. As a transformer, it will not respond to DC at all except for possible saturation of the transformer core if the DC current is high enough. At best, these will measure the ripple current on the alternator output, which has very little relation to the DC current.<p>A few of these ammeters use a hall effect element. These will respond to DC. The response could be either average or RMS, depending on the meter itself. The instruction manual should tell if it has response to DC and whether it is RMS or average reading. If ripple current is present, the RMS reading will be higher than the actual DC current.

[Chris Smith]

I think the 66% factor comes in to play.

[Edd]

Certainly assuming your current <<tong>> is the clamp on probe..wherein the unit opens up the core medium of its associated current transformer to enact entry and an AC sampling of your single current bearing conductor.
Either one of my two Fluke current probe designs would give the same response on DC, just a quick spike on a power on or off …heavier on off….condition, it being proportional to the strength of the conducted current. The unit being AC responsive.
Amprobe…that was the brand of the other 2 that I have….. and one of them has analog readout….nice for watching a current slow surging…the digital version just digit bobbles.., but, be it digital or analog….that is just the manner of the display so either ends up getting a readout for you.
Any Hall sensing units I have seen required very precise positioning of the current carrying conductor to the hall device, with conductor core diameter also being a critical factor. Therefore they were typically used in a fixed/lockdown situation.<p>I have never seen any auto alternators where the rect diodes weren’t onboard and in very-very close proximity, due to the high currents involved(potential losses). Some brands even use buss strips in place of solid wiring going to and within the diode matrix interconnect. Thereby access to the AC frequency area for a read would be inaccessible, even with trying to utilize a HP or Tek current probe and scope analysis within those cramped layouts.<p>73's de Edd
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[perfectbite]

From Chris Smith<p>"I think the 66% factor comes in to play." <p>Ah yes, the 66% factor, please remind me again what that is. I haven't got a bloody clue. <p>AND<p>Edd Whatley: How come this idiot computer can get me in a headlock and pin me every time I wrestle with it if my displayed name truly was perfect 'byte' (which it ain't). Answer me that huh? It is perfectbite as in a chomp out of a sandwich or the perfect set of my teeth impressions on this idiot PC tower although as I get older I have taken to calling it names between my clenched teeth. I then have to go and find the bloody dog (he slinks off and hides) and apologise to him because he thought I was angry at him. The eMac isn't much better but it does save what you were working on when it freezes up and you have to unplug the damn thing just to shut it off. If my handle were perfectbyte all would be sweetness and light as far as my PC and eMac were concerned. It ain't no sweetness and light it is sturm und drang! Last June I had a telephone appointment with a Microsoft Task Force Help desk person. He said "I have to give you a daily changing password so that your system can dial in here. Hang on." he came back and said "I can't give you the password, our computer's down! We'll reschedule this for tomorrow. OK?" This was bloody Microsoft! Perfectbyte? YEAH RIGHT, me and Bill Gates.

[haklesup]

Ideally, the clamp on meter probe will not measure any DC component. If you do get anything off your alternator, it is just ripple current or the big surge you get when you turn on or off current.<p>66% factor is that proportion of the answers that will make sense
(Sorry, just kidding. I couldn't resist, actually we do a lot better than that on most posts)