Power Inverters

Silas Pradetto

Silas Pradetto

Graduate Student
Jan 11, 2011
2,130
1
0
Land of Steady Habits
www.concertsunlimited.com
I'm not sure if this might be more applicable in the electrical section; it seems to be more about a power source than actual wiring, so I'll leave it here.

I have a few medium-small gigs where I need reliable generated power. Now the generator I normally use is owned by a friend of mine; it's a 68kVA diesel setup on a trailer that weighs about 6,000 pounds all said and done with 200 gallons of fuel. Sure, it's great and stable for big shows where I'm running lighting, sound, and who knows what else, but for a small setup, it's a bit of overkill.

This has me thinking: how can I generate enough power to run a small rig without renting and having to tow that beast of a generator around? I don't trust small generators. Should I buy one of the acclaimed $3000 Honda inverter jobs that will give me about 2 circuits worth of power?

Well, if an inverter generator is acceptable, then why not use an inverter with another power source? Like my truck, with its twin 1000 cranking amp batteries and 200-amp alternator?

This had me looking into power inverters for vehicles, and it seems I can relatively cheaply ($500) get a 5000 watt inverter and run it off the truck. I can tune the truck so it runs at any RPM I want so I can keep the alternator making big power; I can even install a second alternator since that was a factory option. In fact, most inverters have a peak rating of double their continuous rating, so that 5000 watt inverter could handle a 10000 watt load on bass peaks or whatever else I may throw at it.

Inverters come in true-sine and modified-sine varieties. I'm pretty sure I used a 3000 watt modified-sine inverter years ago for a parade gig and it worked fine. I can't think of one reason I need true sine output (I'm not running any motors, electric clocks, or other frequency-dependent loads). In fact, I think every piece of audio gear we'd ever use just takes AC and rectifies it to DC anyway...they don't care at all what they're fed with.

So, the big question: any reason why I can't set up a 5000 watt inverter on my truck to power a small sound rig?
 
Re: Power Inverters

I am sure you could, but this seems like an awful wasteful approach.

In the world of surf fishing, many people add this accessory, most often to run an electric compressor for filling tires. Still, I am not sure I would want to run anything else off of my starting batteries. I think it is also meaningful that every boat I have ever worked on that had 110V sytems for nonshore power use had independent gensets.
 
Re: Power Inverters

be ware of units with built in GFI.

I posted a longer reply when I went to post it decided I wasn't worthy or something.
 
Re: Power Inverters

Jay Barracato said:
I am sure you could, but this seems like an awful wasteful approach.
Click to expand...

+1

I wouldn't do it for a few reasons:

-added wear and tear on the truck engine from running for several hours

-Automotive Inverters can be weird with their output waveforms, grounding, buzz, etc.

-Large engine running all day to produce a fairly small amount of power

-You can dry hire rent out a generator, it's harder with a truck

-Generator is easier to hide behind a stage, and some shows I have worked, the fire marshall won't allow vehicles on site while the grounds are open to the public

-If your truck dies at the show, not only do you lose power, but you are stuck there

The Honda EU3000i's really are what they claim to be, they are pretty good for speaker on stick + sub rigs. If you need more capacity they make a cable to link it over to a second unit. You might see if there are any rental houses that have EU3000i's around you. That way you can own one, and rent a second one when you need the additional capacity. You could *also* probably get an inexpensive 3000W inverter used on Ebay or Craigslist and put it in your truck, that way if the generator goes out, you have a back up.

If you want a really awesome solution, you may want to look on Ebay or salvage yards for a 7-10KW small diesel generator from a boat or RV. Our local municipal stage has a 7KW ONAN diesel built into it with a California single phase output and that little thing rocks! I've considered buying one and mounting it to a small trailer or cart with maybe a 20 gallon fuel tank. You can run a fairly sizable rig with it.
 
Re: Power Inverters

As far as modified-sine vs. true sine, the extra harmonic distortion in the modified sine inverters can be hard on the front-end circuitry in SMPS, leading to reduced lifetime (the power supplies run hot).

Now, that 5kVA inverter, assuming an 85% efficiency (pretty typical) is going to be pulling ~490A at full load. That'll drain your starting batteries pretty quickly, especially with only a 200A alternator recharging them. Not to mention that starting batteries aren't really designed for continuous loads applied to them. And all this is assuming that you can get everything wired in and fused properly.

The extra wear on your truck engine is real, and with only a 5-6kW load on the engine, you're likely well outside the efficiency band of the engine. So now your fuel costs go up.

I'm with the others on this, it's not worth the downside.
 
Re: Power Inverters

Rob Timmerman said:
Now, that 5kVA inverter, assuming an 85% efficiency (pretty typical) is going to be pulling ~490A at full load. That'll drain your starting batteries pretty quickly, especially with only a 200A alternator recharging them. Not to mention that starting batteries aren't really designed for continuous loads applied to them. And all this is assuming that you can get everything wired in and fused properly.
Click to expand...
+1 - 200A at 12v is 20A at 120V.

The Honda EUs really are worth it. In addition to the venerable EU3000, there is a newer EU6500:

http://www.hondapowerequipment.com/...ion=P2GG&modelname=EU6500i&modelid=EU6500ISAN

which provides 27A at 240V or 54A at 120V via an L14-30.
 
Re: Power Inverters

TJ Cornish said:
+1 - 200A at 12v is 20A at 120V.

The Honda EUs really are worth it. In addition to the venerable EU3000, there is a newer EU6500:

http://www.hondapowerequipment.com/...ion=P2GG&modelname=EU6500i&modelid=EU6500ISAN

which provides 27A at 240V or 54A at 120V via an L14-30.
Click to expand...

TJ, that little unit looks like it would do exactly what I want. It just sucks that it's so expensive.

I'm going to talk to my generator buddy who only deals with real-deal backup systems for commercial buildings and see if he can't get me a nice small diesel generator that I can pop in the back of the truck for these sort of gigs. I don't want a trailer, because that requires another truck. I think I can get a used/refurbished 10-20kVA diesel unit for less than $3k.

Others have made very valid points about inverters. It's more of a hodge-podge setup than I'd like to do, and I think it will end up costing me more in the end than I want anyway. Another SFN user has a 1500 watt inverter I'm going to mess around with, but I won't be using it for anything critical.

As I just mentioned in another thread, good business decisions are made based on ROI, not cost, so I need to suck it up and deal with it.

Thanks for the advice everyone.
 
Last edited:
Re: Power Inverters

I wonder what the technology looks like in some of the hybrid electric vehicles. They probably have much more robust charging systems, and perhaps IC motors optimized for steady mid RPM running.

Unfortunately it's all pretty new** technology but perhaps a fruitful place to look if you are really serious about this...

JR

** electric cars are actually very old technology but the hybrid gas motor/generator combination is still evolving.
 
Re: Power Inverters

John Roberts said:
I wonder what the technology looks like in some of the hybrid electric vehicles. They probably have much more robust charging systems, and perhaps IC motors optimized for steady mid RPM running.

Unfortunately it's all pretty new** technology but perhaps a fruitful place to look if you are really serious about this...

JR

** electric cars are actually very old technology but the hybrid gas motor/generator combination is still evolving.
Click to expand...

If I were really serious about this, my transmission has a PTO, with which I could drive virtually anything via a hydraulic link, or I could bolt on one of the Ambulance generators and have a ton of power that way.

I would think that with my truck making about 400 horse that I could build a pretty sweet 300kVA generator :) It might get a bit loud though...

It would be funny to advertise generator rentals, and when a client comes to pick it up, I say "hope you can drive stick, and keep it under 100!"
 
Re: Power Inverters

Bristish Gas has a system on their street pipe laying vans that uses a PTO from the vehicle main engine it's covenient for them because it allows them to tow a small digger behind the vans for quick response work to gas leaks etc, however the running costs are WAY higher than a dedicated generator/compressor and if they are doing heavy work or a long job on one site then they'll bring in stand alone devices.
Buy a small 7-10 Kva unit preferably with a diesel engine (much safer and arguably more reliable) run it till it pays for itself then punt it before it gets worn out and replace it etc.etc with some care it should make some money or at least not be a major cost to your business. In the UK petrol units tend to be frowned upon in public events by the powers that be so we're stuck with small cheap diesels or paying a few thousand pounds for a decent unit. G
 
Top Bottom