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Measuring Amps

Old 11-08-2005, 01:08 PM
  #1  
RiverPlane
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Default Measuring Amps

I need help on measuring Amps with my Multimeter. Any tips?
This is how my multimeter looks like:
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Old 11-08-2005, 01:29 PM
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hoppy
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One battery lead needs to be run through the meter. For instance: Connect a short lead from the negative battery connection to the COM on the meter. From the 10 AMP connector on the meter, run a short lead to where that battery lead was connected. Set meter to 10A position. REMEMBER - these meters usually have a short (10sec?) time that they can handle the full current without burning up. Minimize the time that the meter is used. It should only take a second or two to get the measurement, than shut it down or smoke could come out of your meter.

DO NOT CONNECT THE BATTERY DIRECTLY TO THE METER ON CURRENT SETTING. IT WILL SHORT THE BATTERY AND BLOW THE FUSE ON THE METER. ]

If you are trying to measure the current delivered to a load from the battery connect the meter in SERIES with the battery and load. If this doesn't mean anything to you PLEASE get help from someone knowlegable in electricity.

Last edited by Red Scholefield; 11-08-2005 at 03:11 PM.
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Old 11-08-2005, 01:55 PM
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RiverPlane
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Thanks Hoppy
This also applies for LiPos?

I have the horrible thought that you are trying to measure the capacity of the battery with this meter. You cannot do this.

Last edited by Red Scholefield; 11-08-2005 at 03:12 PM.
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Old 11-08-2005, 01:55 PM
  #4  
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What I find very helpful is the craftsman inductance meter. It clamps around one lead of the battery and thats it!!! Fire the motor up and just look at the reading...its that simple. Make sure the meter can read DC amperage though....most do not.
I FOUND IT !!!!!!
here is the link to it......this is an outstanding meter!!!!!
http://www.sears.com/sr/javasr/produ...id=03482062000

I hope I have helped
Vammy
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Old 11-08-2005, 02:19 PM
  #5  
sailr
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Default Reading Amps

What's the mystery? Why don't you just purchase an Astro Whatt meter? It will give you amps, watts, volts, mAh, etc. A world of info for only $55!
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Old 11-08-2005, 02:42 PM
  #6  
gouch
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This is how I normally do it. See the photo below.
Taking a photo is handy as you get an instant figure of both readings, you just need to make sure the camera is directly above the anologue meter, or it can "read" wrong

I leave the multi meter to measure volts. and use a shunt style amp meter for the heavy stuff.

I have tried numerous multimeters to measure current and find they obviously have major resistance or something. It may even simply be in the spindly wires? And I found the cheaper the meter, the worst it is.

Don't believe me?. Run the motor with the meter in circuit as per hoppys method, listen to the revs, now try it without and listen to the difference.
The fact that you can only run them for short bursts before they melt down only strengthens my argument, heat = more resistance as far as I have been led to believe.

It may not be a problem at low levels, but even with my latest meter (no fluke, but not total crap) anything above 10 amps or so and I can hear the motor not getting to the revs as it does without the meter. I use one of these analogue meters and fit it into a case with a lead made up with deans connectors so it fits up very quickly.

Vammy, I looked at those style of meters at our local electronic store, and apart from being about $A150 here, how accurate would they be at around 10 -30 amps if they have a scale up to 400 amps? Actually looking at the link, that meter says only AC amps in the main specs, maybe that is why it is quite cheap?


Hey electric gurus, what is that "law" or whatever, that states
"It is impossible to measure something without actually affecting the results" or something like that..... It's called "someones law" replace "someone" with the bloke who thought of it

This also applies for LiPos?
Riverplane: DC amps is DC amps, as DC voltage is DC voltage, no matter what the battery source. Just be extra carefull to not short anything out with Li-Po of course.

Oh, and always MAKE SURE you change the amp meter connection back to volts before you measure volts. A direct short WILL occur if you try and measure volts with the multimeter set up to amps. If you have a big 3S li-Po pack on the other end, good luck

Cheers
Paul
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Old 11-08-2005, 02:43 PM
  #7  
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Or you could always do what sailr said of course
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Old 11-08-2005, 03:27 PM
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Default uncertainty principle

gouch

"what is that "law" or whatever, that states
"It is impossible to measure something without actually affecting the results" or something like that..... It's called "someones law" replace "someone" with the bloke who thought of it"

I believe that is the Heisenberg Uncertainty Principle from nuclear physics.


John (guru of nothing)
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Old 11-08-2005, 04:05 PM
  #9  
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Default Amp meter

Go to http://www.sloflyer.com/ and scroll down to lower part of page and select General Electric , then pick Do it yourself amp draw meter. I have converted the probe wires using this and it is great as long as you don't exceed 10 amps. If you are using connectors for your battery other than JST connectors, make sure you match up the wiring directions accordingly.You may be able to buy probe wires to fit your meter and not have to modify the originals.
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Old 11-08-2005, 04:06 PM
  #10  
hoppy
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Originally Posted by gouch View Post

Vammy, I looked at those style of meters at our local electronic store, and apart from being about $A150 here, how accurate would they be at around 10 -30 amps if they have a scale up to 400 amps? Actually looking at the link, that meter says only AC amps in the main specs, maybe that is why it is quite cheap?

Cheers
Paul
Look again
Product Overview:

Multi-Meter, Multi-Tester Accessory
Multi-meter or scope
Item Weight
0.77 lbs.
General Warranty
1 year home use/90 days commercial use

Tester:
AC Current
Yes

Continuity
Yes

DC Current
Yes

Volts
Yes, AC/DC

I have the Sears item #03482062000 Mfr. model #55801 ($49) and it is actually quite good..... It is my first recommendation for modelers looking for a quick and easy way to measure current without introducing additional resistance/connectors/hassel into the measurement. You should buy one and than you too would be a fan.
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Old 11-08-2005, 05:26 PM
  #11  
RiverPlane
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Red Scholefield
I measure my batts on DCV 20 settings (look the picture above). is that bad? I'm worried about you coment:
I have the horrible thought that you are trying to measure the capacity of the battery with this meter. You cannot do this
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Old 11-08-2005, 08:19 PM
  #12  
hoppy
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Originally Posted by RiverPlane View Post
Thanks Hoppy
This also applies for LiPos?

I have the horrible thought that you are trying to measure the capacity of the battery with this meter. You cannot do this.
Yes, it applies to any current measurement.

Things to remember-
For current readings, one and only one lead is connected to the meter. It is connected in series between one battery lead and the ESC. The other battery lead goes to the ESC as usual.
Current must be below 10A. (or whatever the meter is rated for)
Measurement must be short (<10sec or whatever the meter is rated for).


I think Red is worried that you might connect the - battery lead to the meter's COM input and the positive lead to the 10AMP input. This would result in a direct short of your battery which would destroy the meter and the battery. Keep the questions coming, better safe than sorry.
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Old 11-09-2005, 11:35 AM
  #13  
gouch
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I think Red is worried that you might connect the - battery lead to the meter's COM input and the positive lead to the 10AMP input. This would result in a direct short of your battery which would destroy the meter and the battery
I got that impression too, that's why I mentioned it

The amp meter confusion was when I read this:

Sears item #03482062000 Mfr. model #55801
AC amps to 400A & AC/DC voltage to 400V ideal for on-the-job testing and trouble-shooting. Continuity check with audible signal, display shows the actual resistance. Auto ranging for quick reading

You should buy one and than you too would be a fan
Oh, I am a fan of them for sure, and have used them many times. I just don't want to pay what our local stores want for them! I have MANY uses for this as I work as a motorcycle mechanic and current is just another thing I need to measure on them. This is a very easy and fast way of doing it, no doubting that.
I am just curious of the accuracy as you are trying to measure very low in the outright range of 400 amps, but I will take your comment that: "you have one and are happy" as a : "yes, it is accurate at low levels"


I believe that is the Heisenberg Uncertainty Principle from nuclear physics.
WOW, how did I even hear of it then? I am not worthy of even mentioning it! The only things I know about nuclear physics are what Homer Simpson tells me, and that aint much

Actually after a quick google, this is the Heisenberg uncertainty principle

The more precisely the position is determined, the less precisely the momentum is known in this instant, and visa versa.
uncertainty paper 1927

I'm not sure if that is what I was talking about. I don't even know what Heisenberg is saying ? It was definately "someones" law I was thinking of.....

Sorry for going OT, back to amps now

Cheers
PAul
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Old 11-09-2005, 02:44 PM
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Matt Kirsch
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If you have a Harbor Freight in your area, watch the sales. Every once in a while, they'll have a digital clamp-on multimeter for $9.99 that's similar in features to the $50 Sears meter.

For brushless motors, it's fairly accurate. Good enough for government work, anyway. Just clamp around one motor lead and run 'er up.
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Old 11-09-2005, 06:40 PM
  #15  
hoppy
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Reference the $49 Sears Clamp-On meter.
DC current accuracy - +/-3% of reading... 100mA resolution.

For a 10A reading that would be 10 +/-0.3A

Matt, I didn't think the Harbor Freight model could measure DC current.

"For brushless motors, it's fairly accurate. Good enough for government work, anyway. Just clamp around one motor lead and run 'er up." It won't work with the clamp on a motor lead without applying a fudge factor to compensate for the AC wave form, the meter has to be on a battery lead. Is that what you meant?
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Old 11-10-2005, 02:05 PM
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Whatt (pun intended) the multimeter approach won't get you is the summed totals going through the circuit over a period of time. I use my "watts up" meter from RC Electronics in series with my Li-PO charger and Li-PO battery to verify battery health. It is a 2000mahr battery. If I consistently show that after running it down to a "soft" response in the air, it only charges back up to 1000ma or so, then time to buy another battery. On larger planes, you can put it on board and get data on minimum voltage, max amps, max watts and min watts as well as amp hours, stored on the wattmeter. I paid about 50 bucks for this, plus shipping. Yeah, you have to put on connectors to match your system, but the information is worth it.
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Old 11-10-2005, 06:53 PM
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Here's a great deal on a great meter. The Astro 101 for $40.99 including shipping. It reads Volts, Amps, Watts and mAH. I use one of these for battery charging also so that I know the voltage and how much charge went in (mAH). This is a DEAL:
http://www.battlepack.com/Close%20Out.asp
Phillip

Edit: They were available with Deans connectors yesterday, I guess they already sold out. No big deal, for that price you can solder new connectors on.

Last edited by Jimmy Hoffa; 11-10-2005 at 11:07 PM.
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Old 11-10-2005, 07:01 PM
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Originally Posted by Jimmy Hoffa View Post
Here's a great deal on a great meter. The Astro 101 for $40.99 including shipping. It reads Volts, Amps, Watts and mAH. I use one of these for battery charge also so that I know the voltage and how much charge went in (mAH). This is a DEAL:
http://www.battlepack.com/Close%20Out.asp
Phillip

Edit: They were available with Deans connectors yesterday, I guess they already sold out. No big deal, for the price you can solder new connectors on.
Now that's a steal!
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Old 11-11-2005, 01:01 PM
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Geoff_Gino
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Hi Guys

Finally remembered to get the details off my amp meter.
It reads DC 100 amps and voltage as well, made by Maxx Products Inc. in Lake Zurich, IL, USA.

Great meter and looks similar to the one shown in the link above. Mine was bought in South Africa and I paid $ equivalent $55-00, but that is after import duties and dealer mark-up.

Great meter, easy to use and only has the one switch to select voltage or amps.

Geoff
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