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Author Topic: best way to measure amp draw with meter  (Read 1909 times)

Jim Layton

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best way to measure amp draw with meter
« on: May 03, 2017, 03:53:38 pm »

This has probably been discussed for ever but I could not find the right search term combo. I want to measure the amp draw of my PA systems, lighting, etc. I have my "small" JBL PRX rig and a Larger SRX/STX rig with iTechs/XTI 6002s. I want to see how much they draw at my events. I have a meter and clamp and have used this method on HVAC work in the past. I also have one of those line splitter plugs that allow you to clamp without cutting into the power cord. I plan on testing out my PA and monitors by using the splitter and meter at an upcoming event. I'll move the splitter around in between bands.

Any tips on what to look for? I imagine I will see some kind of peaks for sub hits (kick drum) and heavy screaming vocals.

I have always tried to give every amp or powered speaker a circuit but I am seeing I can combine a sub and cab and even a LED tree and not trip a breaker. I want to get a handle on what is really being pulled for amps

Thanks,
Jim
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TJ (Tom) Cornish

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Re: best way to measure amp draw with meter
« Reply #1 on: May 03, 2017, 04:19:09 pm »

This has probably been discussed for ever but I could not find the right search term combo. I want to measure the amp draw of my PA systems, lighting, etc. I have my "small" JBL PRX rig and a Larger SRX/STX rig with iTechs/XTI 6002s. I want to see how much they draw at my events. I have a meter and clamp and have used this method on HVAC work in the past. I also have one of those line splitter plugs that allow you to clamp without cutting into the power cord. I plan on testing out my PA and monitors by using the splitter and meter at an upcoming event. I'll move the splitter around in between bands.

Any tips on what to look for? I imagine I will see some kind of peaks for sub hits (kick drum) and heavy screaming vocals.

I have always tried to give every amp or powered speaker a circuit but I am seeing I can combine a sub and cab and even a LED tree and not trip a breaker. I want to get a handle on what is really being pulled for amps

Thanks,
Jim
The way it's done in the big leagues is via current meters in the distro, which have current transformers on each hot leg that are metered, and this data is occasionally logged or reviewed.  Your clamp meter is a lower-tech version of the same thing and will work. The problem with doing what you said is how to replicate a gig scenario in your shop.

Practically speaking, you may have at least as much success if you calculate the draw of your gear.  For amps and powered speakers, most publish power consumption at "1/8 power", which is about as much as they can draw before incurring damage.  Lighting loads should again be easy to calculate.
« Last Edit: May 03, 2017, 06:05:02 pm by TJ (Tom) Cornish »
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Bill Harvey

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Re: best way to measure amp draw with meter
« Reply #2 on: May 03, 2017, 05:48:23 pm »

I doubt you will see what you appear to be expecting. Most clamp on meters that I am familiar with will do a pretty good job showing of showing you the average current draw, and some of the pricier ones will even do a fair job of showing momentary peaks (for a slow definition of "momentary"), but as far as I'm aware it takes special equipment like a clamp-on sensor and a memory 'scope to show true peaks and transients so that you could see them. Kick drum transients would probably be on the order of a few milliseconds, and even if the clamp-on ammeter was somehow capable of responding that quickly, all you would see would be a flicker of digits. A recording power analyzer would work well, as would the aforementioned sensor/scope.

Disclaimer: There might be specialized tech out there of which I am unaware. If so, I would be very interested to learn of it...

Regards,

Bill
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Stephen Swaffer

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Re: best way to measure amp draw with meter
« Reply #3 on: May 03, 2017, 11:14:33 pm »

Considering the fact that circuit breakers are "inverse time delay", if the concern is "tripping" breakers you would have to compare the breakers trip curve against the average current over various time periods.

TJ's method is probably best.  Next best would be akin to destructive testing-chart/record amp draws until you trip the breaker then you'll know your limit-problem is-how close to the edge do you want to walk during a gig?
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Steve Swaffer

Jim Layton

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Re: best way to measure amp draw with meter
« Reply #4 on: May 04, 2017, 10:32:31 am »

The way it's done in the big leagues is via current meters in the distro, which have current transformers on each hot leg that are metered, and this data is occasionally logged or reviewed.  Your clamp meter is a lower-tech version of the same thing and will work. The problem with doing what you said is how to replicate a gig scenario in your shop.

Practically speaking, you may have at least as much success if you calculate the draw of your gear.  For amps and powered speakers, most publish power consumption at "1/8 power", which is about as much as they can draw before incurring damage.  Lighting loads should again be easy to calculate.

I'm small league-Haha. I understand the inability to see the nanosecond peaks on a meter. I am going to try it at my next event while the bands are playing. I am curious what I will see and where the numbers go with basic metering equipment. We used to charge A/C compressors with Freon by measuring the amps on the compressor. It was many years ago. Different animal.

So. I have read several commentaries on "the proper" way to calculate amp load for PA gear. I saw a method on SOS that went like this:

2 x 240W active PA speakers   
480W x 1.4 = 672W   
672 / 230 = 2.92 Amps   

I don't recall the "conversion figure" definitions.

To make things simpler...I have read (here) about the how the transients won't always trip the breaker even though the draw exceeds the breaker rating. I've also read comments about  "hidden" appliances, fans and other equipment tied into a circuit. Been there too. I'm trying to get baseline figure so when I start counting outlets and breaker ratings I can be reasonably "sure" I am not overloading "assuming" nothing else is on it.

I often read how little amps smaller PA systems actually use. I suppose most of this experience is base on trial and error since you can't meter it accurately?

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TJ (Tom) Cornish

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Re: best way to measure amp draw with meter
« Reply #5 on: May 04, 2017, 11:58:49 am »

I'm small league-Haha. I understand the inability to see the nanosecond peaks on a meter. I am going to try it at my next event while the bands are playing. I am curious what I will see and where the numbers go with basic metering equipment. We used to charge A/C compressors with Freon by measuring the amps on the compressor. It was many years ago. Different animal.

So. I have read several commentaries on "the proper" way to calculate amp load for PA gear. I saw a method on SOS that went like this:

2 x 240W active PA speakers   
480W x 1.4 = 672W   
672 / 230 = 2.92 Amps   

I don't recall the "conversion figure" definitions.

To make things simpler...I have read (here) about the how the transients won't always trip the breaker even though the draw exceeds the breaker rating. I've also read comments about  "hidden" appliances, fans and other equipment tied into a circuit. Been there too. I'm trying to get baseline figure so when I start counting outlets and breaker ratings I can be reasonably "sure" I am not overloading "assuming" nothing else is on it.

I often read how little amps smaller PA systems actually use. I suppose most of this experience is base on trial and error since you can't meter it accurately?
Audio output is transitory.  Infrequent big peaks, lots of much lower levels.  The amplifier output wattage listed on marketing material has almost nothing to do with the power draw of the speaker, which varies wildly based on usage.  Turning down your level 3dB (a very small change) cuts your power consumption in half, all else equal.

Your calculations don't make sense, BTW.  Power consumption in watts = volts * amps, but that's not the whole story for what you're trying to do (instantaneous spikes may trip the breaker even if your average is below the rating, or not; external factors like ambient temperature change the trip point of breakers, supply voltage fluctuations, etc).

Break out the manuals, look up the 1/8 power power consumption number and run with that for your speakers.  Lighting loads and other devices can be read directly as they are steady state.  Then consider what Steve said - how close to the edge do you want to run?  What else might be on the circuit?

As fun as all this is, at the end of the day it typically boils down to experience.  You'll find out when you run out of power when the breaker trips.  You are correct though - you can run a lot of audio equipment on a circuit.
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Jeff Bankston

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Re: best way to measure amp draw with meter
« Reply #6 on: May 08, 2017, 05:05:25 pm »

I use my Fluke 336 meter. It also measures DC amps that has come in handy. I made an insert about a foot long with 10 gauge stranded wire and clamp the horseshoe onto the black wire. Make sure the arrow on the horseshoe is pointed toward the load.
« Last Edit: May 08, 2017, 06:09:45 pm by Jeff Bankston »
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Jonathan Johnson

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Re: best way to measure amp draw with meter
« Reply #7 on: May 19, 2017, 07:23:58 pm »

I use my Fluke 336 meter. It also measures DC amps that has come in handy. I made an insert about a foot long with 10 gauge stranded wire and clamp the horseshoe onto the black wire. Make sure the arrow on the horseshoe is pointed toward the load.

I didn't know AC was directional.

DC is, of course, so when measuring DC current it probably does matter which way the arrow points. I don't think it should matter for AC.
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Jeff Bankston

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Re: best way to measure amp draw with meter
« Reply #8 on: May 20, 2017, 05:49:50 am »

I didn't know AC was directional.

DC is, of course, so when measuring DC current it probably does matter which way the arrow points. I don't think it should matter for AC.
I worked as a commercial electrician for 20 years. We were taught to put the ct on the hot leg with the arrow on the ct pointed toward the load. If you have 2 or 3 hot legs and no neutral check each leg. It does matter for sure on DC and reversing the arrow will give a different reading. Check out page 5 of the Emon CT instructions.

http://www.submetering4less.com/downloads/demandinstall.pdf
« Last Edit: May 20, 2017, 05:57:14 am by Jeff Bankston »
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Stephen Swaffer

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Re: best way to measure amp draw with meter
« Reply #9 on: May 20, 2017, 09:36:04 pm »

Any time you are using a clamp meter, the ideal situation is to have the conductor centered in the clamp,  often this can be difficult/impossible.

When metering and monitoring multiple legs-especially if you are looking at phase relationships, I could see where having all of the CTs the same direction could affect the final reading.  The Emon is designed to monitor multiple phases for voltage and current simultaneously.  Apples to oranges when compared to the typical single phase clamp meter.

By definitition Alternating Current flows one direction half of the time and the opposite the other half of the time-I do not see how the direction could affect the reading when you are concerned about a single phase AC load-which is what the OP is about.
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Steve Swaffer
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