Calculating amperage draw realistically

[jarrell]

I got asked for an upcoming gig about amperage, which I've never been asked before. I am providing the PA through which I play keys (including key bass), plus there is a mic for bandleader talking. We play at acoustic volume - neither saxes, pans or drums are mic'ed. The system I am bringing is 2 EV SxA360s for mains, 2 EV ZxA1s for monitors and my Kurzweil PC4. I would normally just bring the ZxA1s (which are 8") but because I am also playing bass, the 12" SxA360s work better.

 

My question is, how do I realistically calculate the amperage draw for this setup? I know the formula,

 

    watts / volts = amps 

 

...and have the watts listed in the owner's manuals, but I'm thinking the watts listed are the maximum the powered speaker can draw. I always set the speaker volumes to noon (I.e. half volume). 

 

What I have right now is:

 

Kurzweil PC4
    15VDC        2.5 A (how it is listed in the manual)

 

EV SxA360
    600 W     120V =     5 A  
                         x 2 =  10 A
EV ZxA1
    800 W     120V =     6.6 A  
                         x 2 =  13.3 A

Total  = 25.8 A

 

I swear I have plugged this system in at several places that I'm sure only had one 15 (or possibly 20) amp circuit. My Furman SS-6B power strip, which I usually plug both ZxA1s into along with my PC4 and sometimes a bassist's amp, is rated at 15 amps - just the 2 ZxA1's and PC4 would exceed that, at 15.8 amps. Of course, I've never had a problem with it.

 

I mean, I can just tell them 25.8 amps and be done with it, but if it causes some cascading freakout or some such, like for that much power draw, the band must play only in one location that is in the direct sun, while all the guests chill in the shade (has happened before), or some other inconvenience, I'll be regretting my amperage honesty.

[GRollins]

The Kurzweil's 2.5A at 15VDC is not the same as the current it draws at 120VAC. You're actually looking at 0.5A or less.

 

There are scads of variables here that I can't control or foresee, like how much wattage you use to play at 'acoustic volume.' Power required to play alongside an acoustic guitar is paltry. The volume to play along with a sax (and drums and...) could be quite a bit louder, depending on how loud the sax is played. Assuming consistent volume, wattage requirements go up by a factor of four for every octave you drop--in other words, bass and the left hand side of your keyboard are going to consume the lion's share of the power.

 

That said, your gear is likely specified at maximum volume. Actual current consumption should be less. A 15A circuit strikes me as marginal. I would suggest at least one 20A circuit, preferably two. Do not assume that two AC outlets are on separate breakers. If they are physically close to one another, they are likely to be on the same breaker.

 

Grey

[Coker]

The wattage listed is probably the maximum draw, which might occur only when powering up. Simply now powering each piece of equipment up simultaneously (such as when you turn on a power strip with everything plugged into it) would drastically reduce maximum current draw.  Also, as discussed in at least one other thread, speaker wattage can be grossly larger than current drawn by the electronics. For example, the ZXA1 specifications show power input at 0.6 amps at 115 v; 115 x 0.6 = 69 watts vs 800 w claimed speaker power.  Best to add up all the amps listed for each unit and see if that’s well under a 15 amp circuit.

[Reezekeys]

Just looking at one item, the EV ZxA1 - you say "800 watts", that's the power output through the class-D amp into the speakers, not a measure of the current draw from the mains. Looking at the spec sheet it says "120V: 95V–132V, 0.6A, 50–60Hz." There is a footnote after "0.6A" that says this is a measurement at "1/8 power." I'm pretty sure this is because class-D amps don't draw a constant amount of current - it varies with the program material and how loud you want things. Manufacturers seem to have settled on "1/8 power" as an informal (or maybe formal?) measurement metric to describe what they feel is an "average" or typical use case. Maybe an expert here will correct or explain more, but I'm pretty sure your calculation of each of your ZXa1s drawing 6.6 amps is a little off.

[The Real MC]

Watts produced by the amplifier is NOT watts drawn by the amplifier out of the outlet.  You really need to find the spec that lists power or current drawn from the circuit.

"Direct sun" as in the gig is outdoors?  Trust me you WILL turn up those EVs if you are outdoors.

 

Do not assume that you "never had a problem" plugging high power devices into your power strip is OK.  A power strip designed to handle 15A could still pass 20A, but the wires inside will get hot and start melting.  You won't see fireworks on day one, but it can be catastrophic with extended use.

 

I have also seen power strips "rated for 15A" but with the flexible power cable wires of 16ga which is legally (per NEC) only rated for 10A.  A 15A flexible (IE stranded wire) power cable needs to be 12ga or bigger.

 

The correct formula is the sum of the maximum currents drawn from main power (be sure to use the current rating for local voltage 120VAC or 240VAC).  If only wattage is listed (again NOT power produced by the amplifier) you calculate current from watts/volts.

 

Our band uses four subs with two tops for PA, monitors, bass amp, keyboards on a single 15A circuit outdoors and we have never tripped the circuit breaker.

You can ask for two 15A circuits, and initially use just one circuit; if you trip the breaker then you know you'll need the second one.

[D. Gauss]

buy this:  https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=asc_df_B00009MDBU/?tag=hyprod-20&linkCode=df0&hvadid=167125429392&hvpos=&hvnetw=g&hvrand=15440816143998263193&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003566&hvtargid=pla-306572288073&psc=1

 

[Delaware Dave]

The following are in my studio and ALL are used when we have a band practice at my house:

 

Peavey CS800 (driving 4 Peavey SP2G's)

Peavey CS400 (driving a Hartke 4x10 bass cabinet)

QSC USA400 (driving 2 JBL 12" monitors)

Peavey Butcher guitar amp (120 watt tube amp) driving a Crate 4x12 guitar cabinet

Fender Deluxe Reverb

Alto 8 channel mixer

Ramsa WR130 8 channel mixer

Digital effects unit for vocals 

Hammond Porta B 

Motion Sound LowPro/Pro3T leslie

Generalmusic Equinox 88 key Stage piano

Generalmusic Equinox 76 key synth

Peavey KB300 used to amplify the bass drum 

Peavey KB300 used to amplify the keys 

Both guitarists separately bring a various number of foot pedals

 

If I were to add up all of the OUTPUT wattages as you did there is probably 4000-5000 watts of output watts.  I am able to drive all the above from a single 15 amp dedicated line. In fact, at one point I used my Tripplite LC1200 on the front end which should "trip" if the draw were more than 1200 watts but it never did so that is a signal that I am not even drawing the 1200 watts to "trip" the Tripplite.  I no longer bother using that anymore.  The amps are up full tilt, i.e. practice is loud. As others have mentioned OUTPUT wattage is not the same as consumption wattage.  I see no reason for your concern and my guess is that if the electrical output line you are using is a dedicated line then 15 amps should be more than sufficient.

[Theo Verelst]

Power draw has various general aspects, like digital vs. traditional, serious power measurement at in and out, energy storage aspects, peak surges, and tripper activated versus unnoticed overdraw. Some of the not mentioned aspects.

 

Rating at equipment is often in terms of VA instead of Watt, which has to do with the phase of the drawn current with respect to the voltage, like the load can be inductive or resistive, and there are newer power draw characteristics compared with a traditional transformer plus rectifier inside the equipment, in general a switched supply forms another load on the line compared with lights and traditional amps. For instance the switch on may be regulated, but the control circuit in the digital supplies may draw seriously more current when the voltage drops significantly. Which may happen when more and more current is drawn over a single (long, thin cable) extension chord.

 

For traditional amps as well as for switched supply or switched amplification of various generations, the max power is the max it draws and therefor the max it could put out if the efficiency were 100%. Also, there's peak draw and peaks in the output power of a short duration. Switched amps also form potentially a non-linear load meaning some power meters and the mains might respond different to high power being asked, but no amp can generate more power at the speakers than it draws from the mains on average, that would defy the laws of nature.

 

I do not know at this point in time how all those plastic speaker on pole relatively low weight switched amps and switched supplies specify their power use and their output power, traditionally OP would be continuous sine power, and socket power would be VA as in the Watts drawn from the mains with a certain interpretation of inductiveness off the big transformer in the the device. The traditional setup in cases allows for significant peak power, whereas switched supplies usually have a pretty severe electronic current limit make a little extra power than the max spec probably not happen at all.

 

For normal band use, I'd require a solid, high amp socket with a thick (high amps) extension cord, WITH GROUND, and with preferably an over-voltage protector, and power the high power devices on one by one.

 

T

 

[stoken6]

2 hours ago, Reezekeys said:

Just looking at one item, the EV ZxA1 - you say "800 watts", that's the power output through the class-D amp into the speakers, not a measure of the current draw from the mains. Looking at the spec sheet it says "120V: 95V–132V, 0.6A, 50–60Hz." There is a footnote after "0.6A" that says this is a measurement at "1/8 power." I'm pretty sure this is because class-D amps don't draw a constant amount of current - it varies with the program material and how loud you want things. Manufacturers seem to have settled on "1/8 power" as an informal (or maybe formal?) measurement metric to describe what they feel is an "average" or typical use case. Maybe an expert here will correct or explain more, but I'm pretty sure your calculation of each of your ZXa1s drawing 6.6 amps is a little off.

This. I would probably factor about 1A for each speaker, and negligible for the Kurz. A single 15A circuit will be fine. Your experience with your Furman (and Real MC's experience) is supporting evidence. When my band brought our equipment, we asked for two sockets (UK, 13A 230V) - one for all the sound (1200W PA, four monitors, guitar amps etc.), and one for the lights (old school incandescents, probably about 1kW).

 

I would ask to have one socket dedicated to you - so nobody "accidentally" plugs in a space heater, hairdryer, or washing machine, or something.

 

Cheers, Mike.

[Adam Burgess]

As @Reezekeys says, music program is usually measured at 1/8 power. If you had massive sustained sub bass notes going on, and the amps are hitting the red for more than a split second, you'll be close to the limit or both the rig sonically and power wise. 

I think the EVs would give in long before the power tripped.

I'm in the UAE, where the electrical system is based on the UK system (which is, of course, the best 🙂 ), so 13A/16A outlets are usual. Can run a decent sized bar rig and LEDs etc no problem on 13A. We can get over 3000W on a single socket. Admittedly, we run 230-240V so your current would be around double in 110V land. 

[D. Gauss]

really, why guess?  buy the doodad listed above.  i use mine ALL the time when I do remote full band recording sessions in old houses, barns, etc. where there's tons of gear, and power can be iffy to say the least.

[cphollis]

800 "music" watts is not 800 electrical watts, so you're way off.

 

I can run my 6 piece electric band on less than 15 amps @ 120 v (standard household circuit) going easy n the sub and with battery powered lights.  I doubt that you'd draw more than 5 amps unless you started crankin@g your sub to max.  That can draw a lot of power.

[Delaware Dave]

8 hours ago, D. Gauss said:

buy this:  https://www.amazon.com/P3-P4400-Electricity-Usage-Monitor/dp/B00009MDBU/ref=asc_df_B00009MDBU/?tag=hyprod-20&linkCode=df0&hvadid=167125429392&hvpos=&hvnetw=g&hvrand=15440816143998263193&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003566&hvtargid=pla-306572288073&psc=1

 

 

The OP question was 'calculating amperage draw' realistically.  The above seems to be the best answer so far.  That doodad does exactly what he asked for.

[Jim Alfredson]

A standard 15amp outlet should be fine. As others have said, you're not calculating the current draw accurately. 

[jarrell]

Thanks everyone for your input and advice. I now understand that the amplifier power output is different from the current draw input. I knew that it varied according to source material, but as I said these are the only specs listed. Well, 

11 hours ago, Reezekeys said:

Just looking at one item, the EV ZxA1 - you say "800 watts", that's the power output through the class-D amp into the speakers, not a measure of the current draw from the mains. Looking at the spec sheet it says "120V: 95V–132V, 0.6A, 50–60Hz." There is a footnote after "0.6A" that says this is a measurement at "1/8 power." I'm pretty sure this is because class-D amps don't draw a constant amount of current - it varies with the program material and how loud you want things. Manufacturers seem to have settled on "1/8 power" as an informal (or maybe formal?) measurement metric to describe what they feel is an "average" or typical use case. Maybe an expert here will correct or explain more, but I'm pretty sure your calculation of each of your ZXa1s drawing 6.6 amps is a little off.

That 0.6A is listed only for the ZxA1, so I assume at 1/2 power it would draw at the most 2.4A, or 4.8 for the pair. The SxA360s don't list that, but if roughly comparable (they are listed as less watts speaker output), that's under 10 for all 4 speakers, and the PC4 is listed as 2.5A, although it may be in fact less. Long story short, I just now told them 15A is what I need; I'm sure I'm fine.

[D. Gauss]

really. y'all seem hung up on doing all this iffy, speculative math when there's a reliable thingy that does it accurately it for you with ease. again, see above. worth its weight in gold. had mine for almost 20 years.  paid for itself when i found out that my fridge and basement dryer were on the same circuit even though the electric panel labeling said otherwise.

 

 

 

[stoken6]

7 hours ago, jarrell said:

the PC4 is listed as 2.5A

And just to repeat - that 2.5A is at 15VDC (from the output of the transformer/power supply). That transformer will not be drawing more than a fraction of the 2.5A from the wall outlet. 

 

Please buy D. Gauss's gadget if you like, but I think there's plenty of margin of error around the assumptions we've made in this thread to support a single 15A outlet. In fact, please buy it and run it during the gig - I would be fascinated to learn how much current your gig needed!

 

Cheers, Mike.

[The Real MC]

11 hours ago, D. Gauss said:

really. y'all seem hung up on doing all this iffy, speculative math when there's a reliable thingy that does it accurately it for you with ease. again, see above. worth its weight in gold. had mine for almost 20 years.  paid for itself when i found out that my fridge and basement dryer were on the same circuit even though the electric panel labeling said otherwise.

 

 

 

That meter only averages current which is not an "accurate" measurement of true current draw.  Current spikes - caused by low frequency thumping subwoofers - are diminished during the averaging.  The meter lacks a peak hold function which is more accurate, and I've been in the EE/automated measurement field for over thirty years as well as FOH engineering.  The poor craftsmen who always blame their tools are equally quick to dismiss math as "iffy", "speculative".

[cphollis]

On this topic, the same devices pictured here can also *limit* current draw. 

This is very handy if you don't want to blow your circuit breaker using your sub, or lights.