Just a small point on your calculations to size the required battery to supply the load via the inverter. You didn’t mention the power factor of the load, which adds to the calculated value.

So if you were measuring the current with a clamp on ammeter (which is what I have done for our busking equipment), and say you measured a total of 1.74 A on a 230 V single phase supply.

Then the result of multiplying 1.74 A x 230 V = 400 VA, not 400 W. It would only be 400 W if the power factors of the PA equipment was all equal to 1 or unity power factor, which it rarely is.

A typical load power factor would be 0.8 or maybe 0.9. Let’s say it is 0.8. Then in this case the load wattage would be 400 VA x PF = 400 x 0.8 = 320 W.

So if you were sizing the inverter then you would use the 800 VA value, as inverters are rated in VA or kVA.

But to size the battery you need to use the wattage value as the battery only supplies wattage, not VA (similar to a generator, where the diesel engine only supplies the ‘real’ power in watts and the alternator supplies the additional ‘reactive’ power in VAr, resulting in the overall ‘apparent’ power in VA).

So in this example when measuring 400 VA for the PA equipment and you want to double this value, i.e. 800 VA, to size the battery, then using the 90 % inverter efficiency figure (1/0.9 = 1.1), the 12 V battery current would be:

IDC = (800 x 0.8) x 1.1 / 12 = 58.7 A

And for a duration of 4 hours you need a battery ampere hour rating of 58.7 x 4 = 234.7 Ah [instead of the 293 Ah size you calculated using the 800 W value].

But bear in mind that this 234.7 Ah capacity value is the C4 rated or 4 hour rating. If you asked for a 234.7 Ah battery you would likely get a battery rated at the 10 hour rate, which is a battery rated to supply a load of over a 10 hour duration, not a much shorter 4 hour duration and therefore you will get a battery that is not big enough to supply your load.

Hope you don’t mind me chipping in on your post like this.

Barry

]]>STAGEPAS 300

Mixing capability

Mixing channels

4 Mono + 2 Stereo

Input channel functions

2-band PEQ, Digital Reverb (CH1-4)

On-board processors

Music/Speech

On-board amplifiers

Maximum output power @6ohms

150W + 150W

General specifications

STAGEPAS 300

Frequency response

-3dB

55Hz-20kHz

Components

LF

8″ (20cm) Cone

HF

1″ (2.54cm) Compression driver

Maximum output level (1m; on axis)

112dB

Total harmonic distortion

Less than 0.5% (20Hz-20kHz)

Hum & noise level

Equivalent input noise

-106dBu (CH1/2)

Residual output noise

-65dBu (Speaker out)

Crosstalk

Less than -70dB

Power requirements

Depend on area of purchase; AC100V, 120V or 220-240V; 50/60Hz

Power consumption

70W

Dimensions

W

275mm; 10-7/8in

H

455.5mm; 17-15/16in

D

255mm; 10in

Net weight

18kg; 39.7lbs (2x Speaker + Powered Mixer)

Accessories

Owner’s manual, AC power cord, 2x Speaker cable

Best of luck everyone with busking. ]]>

Any ideas how to ground my deep cycle battery and inverter when i am busking out in the open?

Is it necessary?

Thank you!

Mark

Did u get an answer on the venue? What was the solution? ]]>

However, I’m having difficulties validating my power measurements against the formulas.

Please let me know what I am doing wrong. “Thank You” in advance.

I purchased and used an ammeter (P3 P4400 Kill A Watt Electricity Usage Monitor) and measured the power usage of my total music rig in Watts, and in Amps using a standard US household outlet. At a loud volume, the ammeter read a maximum of approximately 181 watts, and maximum of approximately 2.4 amps.

Using the formulas on this website, these to measurements conflict with each other.

Using my 2.4 amps measurement, and the Amps*Volts=Watts formula, I get 2.4A*120V=288Watts ???

Using my 181 watts measurement, and the Watts/Volts=Amps formula, I get 181W/120V=1.5Amps ???

I can’t live with these discrepancies!!! Please help!!!

Music Rig:

2 powered 2-way 12″ speaker cabs (Alto TS212)

1 powered 18″ sub-woofer speaker cab (Alto TS218S)

1 Behringer XR-18 Digital Mixer

1 Line 6 HD500 modeling pedal board

1 Line 6 wireless guitar receiver

1 Shure U series wireless mic receiver

1 Sennheiser wireless In Ear Monitoring (IEM) system