Anyone Tried Cheapo Digital Display Ammeters?

[thehallofshields]

http://www.ebay.com/itm/0-36-DC-0-5A-10-50-100A-Ammeter-LED-Panel-Amp-Meter-Digital-Gauge-Display-4-30V-/390769212726?pt=LH_DefaultDomain_0&var=660209879736&hash=item5afba8fd36

They say they can do 0-5A. But do you think they'd do 0.01 or .001?

If not I'd just have to go Analog but I think these would be super cool on a Beavis (style) Breadboard Project.

[Jdansti]

I've never tried them, but the specs say the accuracy is +/- 0.1%. Normally accuracy is expressed as %full scale. So if full scale is 5A, then the accuracy is +/- 0.005A or +/- 5mA.

So a reading of 10mA could actually be anywhere between 5mA and 15mA. A reading of 50mA could really be somewhere between 45mA and 55mA and so on.  Not incredibly accurate. It just depends on your needs.

[karbomusic]

http://www.diystompboxes.com/smfforum/index.php?topic=108314.msg986944#msg986944

I have and the one I used appears to be within 1mA/mV:

http://www.diystompboxes.com/smfforum/index.php?topic=108314.msg986944#msg986944

It was more in the $15 range though.

[PRR]

> can do 0-5A. But do you think they'd do 0.01 or .001?

It's a 3-digit display.

5-exact Amps would show 5.00

So 0.01 would show 0.01. More-or-less. Sometimes it would show 0.00 and sometimes 0.02.

+ or - the basic accuracy, perhaps 1%, and 1% of 5.00A is 0.05A. So it is very likely to be way-off down there.

0.001 is totally out of the park. (These don't auto-range.)

What may be better.... 199mV is the standard voltmeter basic range. Wire such a VM across a 1 Ohm resistor. Now you have 0-200mA with dubious resolution around 1mA. If all your loads are under 20mA, use a 10 ohm resistor for 0-20mA with 10% measurements around 1mA.

Another aspect.... I've studied similar meters this week. A dandy 50A amp-meter turned out to HAVE to be wired in the Negative lead of the motor (because it needed some positive power to feed its little brain). That is not practical on my tractor where nearly all the Negative leads (generator, starter, most loads) are hard-bolted to the frame/chassis. It would be equally awkward where your negative lead is also the Common for audio (though for a single pedal with dedicated supply, you can get around this).

OTOH, for large AC current measurements, I am in love with the chinese volt/amp meters I installed in my house fusebox. AC is easier because you can use a current transformer, have complete isolation between the big power and the meter. But not useful in stomp-world.

[karbomusic]

Mine changes color depending on resolution to make up for the missing digits if that helps anyone... Actually I'm wrong, it's how it displays the decimal:

"There are four fixed display precision; the measurement range is 0-999.9mA-3.000A. When the measuring current is below 1A, it display ***.*mA; When the measuring current is higher than 1A, it display *.***A"

[Jdansti]

^ But don't confuse display resolution with accuracy or precision. The display may be able to show 0.1mA, but the readings may not be accurate. As PRR points out, the actual current might be 0.1mA, but the display might read 0.0, 0.1, or 0.2.

I don't understand the term "four fixed display precision". Precision is how well the meter can reproduce multiple readings under the same conditions. The term "precision" is often misused by manufacturers.

Say you aim a gun clamped in a gun rest at a target and use a mechanism to fire it multiple times. The distance of the hits from point of aim describes the gun's accuracy. The spread of the hits from each other describes its precision. If all of the shots hit way off from where you aimed, but are very close to each other, then you have low accuracy and high precision.

[karbomusic]

But don't confuse display resolution with accuracy or precision.

I know and I'm not, but I think I've been through this Q/A three or four times in different threads here now. I have 3-4 meters, none are officially NIST certified but between all of them the meter on my pedal board was averaging 1mV/1mA which is as good as the variance between every meter I have. That means it qualifies to measure anything else I trust (that I own) since I don't need sub mA accuracy, at least not right now.

[karbomusic]

I don't understand the term "four fixed display precision". Precision is how well the meter can reproduce multiple readings under the same conditions. The term "precision" is often misused by manufacturers.

I took it as the bad Chinese translation how many digits there are on the unit and that where the decimal displays is how you know if it is N.N amps or N.N milliamps. That's why I posted it anyway. It's a way to get two modes out of the same four digits. Can it be trusted launch the Shuttle? Absolutely not; accurate enough for what I built it for? So far, very much so even though I didn't expect it would be.

The original need was to make sure I wasn't exceeding my pedal board PSU rating since I build lots of pedals and add/remove them often (or anytime really, it's just too easy to place it inline based on how I designed it vs. hooking up a traditional meter once all boxed up and running), but it turned out to be more accurate than that.

[Jdansti]

And for $4, is a good deal!

[karbomusic]

And for $4, is a good deal!

Mine was $15! Sorry I went OT, I was talking about the one I posted the link to, not the ones at the top of the page.  

[duck_arse]

15$ = precision, OT = accuracy?

[karbomusic]

15$ = precision, OT = accuracy?

OT = Off topic. The one at the top of this thread isn't the one I have. I don't know what the extra $11 got me but it's as accurate as my other meters making it darn handy! But I don't recommend anyone buy the one I have, because yours won't be as accurate and I'll be in trouble.