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Dirty-South Blues Harp forum: wail on! > 12 volt / 120 volt power inverters for busking
12 volt / 120 volt power inverters for busking
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kudzurunner
6219 posts
Apr 26, 2017
4:41 AM
I've got a question for the folks here who really understand electricity and electronics.

The Blues Doctors occasionally play the streets in battery-powered-amp mode. We're going to be doing that this weekend, in fact.

It would be nice, when doing that, to be able to use our small PA system, rather than singing through our amps. The PA system--I just checked--draws 70 watts.

When we've played a farmer's market around here, they have a gizmo that attaches to a 12 volt car battery. I've been poking around the internet and it's clearly something like this:

300 Watt Pure Sine Power Inverter - 12 volt

These sorts of units are available in a wide range of power outputs, from 180 watts through 5,000 watts.

If ALL we want to power is the PA, would the 300 watt unit have more than enough power, plugged into a regular heavy-duty car battery, to handle all the transients with no sag or other audible loss?

Also, since this unit would need to be paired with a car battery, what specs should the car battery have?
Tuckster
1562 posts
Apr 26, 2017
7:47 AM
That should do the trick judging from the specs you gave. I would use a new battery since you aren't charging it. The higher the amp-hours,the better.
STME58
1967 posts
Apr 26, 2017
8:21 AM
Some others who know amps (amplifier, not ampere) better than I can tell you if a sine wave inverter is necessary. Many inverters produce triangle waves or something else not quite like the sinusoidal waves the power company makes with their rotating equipment (thanks Tesla!) If your inverter is producing a sine wave, you are good in any case. Now you need to look at the power the inverter can deliver and the energy stored in the battery to see if you can drive your systems and if so, for how long. Add up the wattage of all your equipment, and that must be less than the wattage of the inverter. If so , your good to go, but for how long? Batteries are rated in amp hours (ampere, not amplifier) in general, for our purposes here, a watt is a volt times an ampere. to get 300 watts from a 12 volt battery, you need 300Watts/12volts = 25 amperes. If you battery can store 25 ampere hours, you can play for an hour. If it has 100 ampere hours, you can play for 4 hours. If it can only deliver a max current of 10 amperes, you can't play at all. So your battery must be able to deliver the current in amperes the inverter will require for the load your amplifiers will place on it, and it must store enough energy in ampere hours to run your amplifiers for the time you need. These specs are available from good battery suppliers.

PS: If your amplifier draws one ampere from the battery, than an amplifier hour and an ampere hour are the same. :-)

Last Edited by STME58 on Apr 26, 2017 8:32 AM
Jim Rumbaugh
1252 posts
Apr 26, 2017
9:24 AM
The Harmonica Club uses a Pure Sine Inverter when it does parades. We started with a 2000 watt inverter. I blew it up with a stupid move. I switched the polarity on the battery clamps. We now use a 600 watt inverter. This one has a power indicator showing how much power is being used. With 2 PA amps, rated at 50 watts out (RMS) each, or about 200 watts input, the meter barely moves. You may have a 70 watt PA, but it will not draw 70 watts continuously,it may peak at 70 watts.

Bottom line, 300 watt inverter is big enough. I just checked the link and the ad, Since the 300 watt unit is only $15 more than the 180 watt unit, I say it sounds like a good choice.
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theharmonicaclub.com (of Huntington, WV)

Last Edited by Jim Rumbaugh on Apr 26, 2017 9:25 AM
Fil
301 posts
Apr 26, 2017
10:20 AM
If you don't already have a battery to use, consider a 12v RV deep cycle battery rather than an auto start battery. Something like this is better for sustained inverter loads:

https://www.batteriesplus.com/battery/rv/deep-cycle/12/sli24mdc?gclid=CNj2i9zOwtMCFc1WDQodzucKPQ

70 watts is about a 6 amp draw, but as Jim says, that probably is not continuous. A deep cycle battery like the one in the link with 75 ah is plenty to handle that load and with a comfortable reserve for a gig.
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Phil Pennington

Last Edited by Fil on Apr 26, 2017 10:21 AM
kudzurunner
6221 posts
Apr 26, 2017
10:28 AM
I love this place. Thanks, guys.
rainman
201 posts
Apr 26, 2017
10:47 AM
For all your Busking needs.
DEVICE RUN TIMES:
Headlamp 300+ Charges
Smartphone 100+ Charges
POV Camera 200+ Charges
Digital Camera 100+ Charges
Tablet 45+ Charges
Laptop 20+ Charges
Desktop Computer 12 Hours
Printer (printing) 1-3 Hours
Printer (idle) 1-2 Days
32" LCD TV 8-12 Hours
Game Console 6 Hours
Vacuum Cleaner 1.5 - 7 Hours
Drill 1-5 Hours
Blender/Processor 4 - 6 Hours
Washing Machine 2 - 3 Hours
Refrigerator (cooling) 12-24* Hours
Chest Freezer (cooling) 1-2 Hours
Home Alarm System 7-9 Days

https://www.bhphotovideo.com/bnh/controller/home?O=&sku=984437&gclid=Cj0KEQjwioHIBRCes6nP56Ti1IsBEiQAxxb5G7td2EwRqA-aSiXf0ouhcKMT1ihx0K6OjPccTVQnMn0aAl_f8P8HAQ&is=REG&ap=y&m=Y&c3api=1876%2C%7Bcreative%7D%2C%7Bkeyword%7D&A=details&Q=

This one is a little more affordable.

http://www.xantrex.com/power-products/backup-power/xpower-powerpack-1500.aspx

Last Edited by rainman on Apr 26, 2017 10:59 AM
nacoran
9444 posts
Apr 26, 2017
10:50 AM
I don't know if they are practical yet, but there are some hits on Google for solar busking.

This guy's rig is smaller, but it also seems to be from 6 years ago.

https://vimeo.com/15235580

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Nate
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Jim Rumbaugh
1253 posts
Apr 26, 2017
11:38 AM
@ RAINMAN

The more affordable unit puts out "modified sine wave". I would go with the products mentioned above for "pure sine wave".

I used a modified sine wave inverter for a PA with a transformer in the the power supply. It buzzed and produced a shock when holding the mics. I recomend going pure sine wave.

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theharmonicaclub.com (of Huntington, WV)

Last Edited by Jim Rumbaugh on Apr 26, 2017 11:38 AM
rainman
202 posts
Apr 26, 2017
11:47 AM
Yes I saw that Jim and suspected it might be a problem.
STME58
1968 posts
Apr 26, 2017
7:10 PM
Jim, if you got a shock from the rig, I suspect there was more wrong than just a poorly synthesized sine wave input. The buzzing I might expect, but I would defer to those who know amps for questions on how the quality of the power input would affect the sound.

Once you have a battery and inverter setup, adding solar is easy. All you need is a photo-voltaic panel and a charge controller. The panel will charge the battery and extend the play time. Three hundred watt panels are common these days and that would run the whole system when the sun is out leaving the battery to keep you going when a cloud passes or after dusk. It would be easy to make a system you never needed to plug in to charge. I have built such systems, but I have not used them for music. If anyone wants help spec'ing out the components for such a system, let me know and I can give some guidance.
kudzurunner
6222 posts
Apr 27, 2017
4:27 AM
Rainman:

The unit you've suggested--the Xantrex XPower Powerpack 1500--looks like exactly what I need in every respect. Can everybody here take a look and give me one reason why it's NOT the perfect street busking powerpack?

STME58
1969 posts
Apr 27, 2017
7:57 AM
That looks like a well designed unit. Xantrex had some trouble when they were bought out in the early 2000's. I finally bought an SMA inverter for my solar plant after installing several Xantrex units that were basically dead on arrival. I expect they have those issues worked out now. Know any other companies that had a great reputation, lost it by turning out crap for a few years, and then got thier act together and recovered thier reputation?

The critical points I see in the data sheet are 1500w output. 51 amp hour capacity at 12 v (612 Watt hour) AGM battery, and modified sine wave power. On the first two issues you have plenty of margin. You could run at a full 300 Watts for 2 hours and you are nowhere near peaking over 1500 watts. The Absorbent Glass Mat battery is an excellent choice, It won't spill and you don't have to water it. I would like to hear an amplifier expert weigh in on the effects of non sine wave power on an amplifier. For electric motors and computer chargers this is not problem, and I expect it is fine for amplifiers, but I really don't know.

Last Edited by STME58 on Apr 27, 2017 11:16 PM
rainman
203 posts
Apr 27, 2017
12:58 PM
My concern Adam is that it uses modified sine waves which might cause problems such as noise. The more expensive Yeti has pure sound waves. Maybe you could get Goal Zero to let you try one out ? They do have a couple other units that might work that are less expensive.
STME58
1970 posts
Apr 27, 2017
6:45 PM
In looking at tube amplifier physics and trying to understand it a bit more, I found that the AC is used in transformers and as heaters for the cathodes. After the voltage is stepped up by the transformer, it is rectified to near DC. In my understanding, the heating could be done with DC or AC and would not be sensitive to the shape of the AC wave if AC was used. The transforming process requires oscillation, but not necessarily sinusoidal. I don't believe a non sinusoidal input would bother anything here. I can imagine that the rectification process may be tailored to a sinusoidal input and that a non sinusoidal input might result in more ripple on the rectifiers DC output and thus add noise. If this is the case, the amount of noise introduced by the non sine input would likely be dependent on the specific circuitry. I would love to hear from someone who actually knows what they are talking about on this topic.

Last Edited by STME58 on Apr 27, 2017 11:14 PM
Jim Rumbaugh
1254 posts
Apr 28, 2017
10:48 AM
The problem with modified sine wave is that is has multiple jumps in voltage during each sine wave. IF your amp has a input transformer in the power supply, you can get spikes similar to an automobile ignition coil. Transformers don't like sudden change in voltage.

I do not know how modifies sine works with some of the newer power supplies that are more like a computer power supply with little or no input transformer. They "may" perform fine. I have no experience with this combination.

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theharmonicaclub.com (of Huntington, WV)

Last Edited by Jim Rumbaugh on Apr 28, 2017 11:01 AM
Tuckster
1566 posts
Apr 28, 2017
11:21 AM
I've been fruitlessly searching the Internet on this subject.I have found that the inverters that have non sinusoidal waveforms can generate noise. It makes sense since they generate either square or triangle waves. I think your first choice would be fine as it generates pure sine waves.
STME58
1971 posts
Apr 28, 2017
12:13 PM
Tuckster, when you say, "I have found that the inverters that have non sinusoidal waveforms can generate noise." Do you mean you have plugged an amplifier into a non-sinusoidal inverter and heard noise coming from the amp that is not there when you plug into a normal wall socket?
Tuckster
1569 posts
Apr 28, 2017
12:22 PM
No that was just what I found on the Internet. I found a paper on the effect on induction motors but none on audio amps.I did find a WikiPedia article on the sound of non sinusoidal waveform but am not sure they apply.I do know power transformers are designed to be optimum at 50/60 Hz.I don't know what frequencies are generated in non sine supplies. Still searching...

Edit: It could be that a steeply rising waveform like a square wave is saturating the iron in the xformer. The search goes on...

Last Edited by Tuckster on Apr 28, 2017 12:31 PM
Tank
3 posts
May 09, 2017
3:59 PM
I was playing Bass Horn with a band in the mid 90's, and did just that...used an inverter to power an amp.
Before I go on, I must explain that I've been a licenced Radio Ham since 1992, so have a decent grasp on the subject of electrics. My advice would be that pure sinewave inverter is the way to go, but you've got to remember that for 100w electrical output for 1 hour, you would need a battery of 15 A/h or above. The thing is, as batteries discharge, they give out less voltage, and many inverters are "voltage dependant" (if the voltage drops too low, typically about 10.5v, they shut down!) I used a 120w inverter to drive a 50w Bass combo at about half volume, with a 45A/h "golf cart battery", and from a full charge would get about 5-6 hours before it shut down. Inverters have become a bit more efficient in the past 20 years, so maybe you may get a bit longer with a modern inverter!? One piece of VERY IMPORTANT ADVICE: Use an RCD protector between your inverter and your amp/PA...safety first my friend!

Have a whale of a time!

Tank (aka Keith G7LPW) Norfolk UK
Jim Rumbaugh
1258 posts
May 11, 2017
12:31 PM
For us in the U.S.A., a RCE protector is what we call a "ground fault receptacle". ( I had to look up RCE protector)

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theharmonicaclub.com (of Huntington, WV)

Last Edited by Jim Rumbaugh on May 11, 2017 12:32 PM
Tank
8 posts
May 12, 2017
11:27 AM
Jim Rumbaugh: Thanks for that, I honestly didn't know what you guys call them. We call them R.C.D. (Residual Current Device) OR E.L.C.B. (Earth Leakage Circuit Breaker). No matter what we call them, they can be a life saver! ;-)

Best Wishes

Keith (aka Tank)


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