A Wholly Different Approach to Power Conditioning

Yesterday, at Northern Arizona University's "renewable energy fair", I stumbled across a method of power conditioning (generating sine waves) that might be more cost effective than the existing "audiophile choices". People who use solar power, or solar supplemented by the grid, employ these "charger-inverters" that generate a pure sine wave off of DC power. There are 4 or 5 brands out there, but 4 are owned by one parent company, Xantrex. Xantrex tells me that the cleanest unit is made by Prosine. Their models range from 1000 to 2500 watts. For instance, the 1000 watt unit will pass 20 amps peak, and will create a sine wave at full capacity with no more than 2-3 percent distortion. Unlike the PS Audio units, which generate a lot of heat (I may be wrong, but I think they are only 50% efficient), the Prosine charger-inverter is about 90% efficient. You get this for a retail price of about $1 per watt. So if your total system uses less than 1000 watts, you spend about $1000 on the charger-inverter (street price may be slightly less). As I noted above, they tell me the unit will pass the full 1000 watts without significant distortion of the wave form.

What would the advantages of such a system be? To some extent, cost. A PS Audio 1200-watt unit retails for $4000 (substantially less used), and from what I hear, requires some headroom in the energy it produces (i.e. you don't get the full 1200 watts). With this alternative, one would need to purchase both the charger-inverter and a battery bank capable of storing an evening's worth of listening for your system (actually twice that so that you don't often draw the batteries down beyond 50%). You can set up the charger-inverter so that if the batteries do fall down below a given storage, it automatically switches over to the grid and provides power via your local electric company. This would not happen often, but it's nice to have a backup. Batteries should cost around $300, so total system cost is $1300. Disadvantage - you have to keep the batteries outside your living quarters (fumes and such) and check the cells monthly for topping off with water. Advantage - if you live in a sunny area, you can add solar cells to the system and gather your own power. Advantage - you can also purchase a programmer unit and refill your batteries at off-peak times, thus saving about 20% on power. If you like, you could expand such a system to much of your household, thereby saving 20% on your power bills. If your fridge were included, you'd probably need to put a filter just upstream of the fridge.

To me, an Arizona resident, this is an intriguing option. Even without solar, it seems to make financial sense. Unfortunately, solar panels are still pretty pricey. One that generates 120 watts costs about $500, and given the standard assumption of 6 hours available sun during the winter, you would need two of them to store up 1.4 KW-hour for an evening's listening session. So, if you go solar, your total system cost is $2300. Unfortunately, given the utility likely charges about $0.15 for your daily 1.4 KW-hour, it would take 18 year to pay this off!!! Now we are getting into solar issues. An efficient household can run on 4 KW-hours. Conceivably, if you buy more batteries and 4 more panels (total cost somewhere near $7000), you could go off the grid entirely (using gas/propane for heat and drying clothes). Something to think about… ask TWL!!! The payback period for going off the grid might be on the order of 35 years or so - but you get clean power for your stereo!!!

Anyhow, back to the $1300 investment for a battery bank and a charger-inverter. I would love to hear what those who really know electricity, and have the time to check out this sine-wave generating charger-inverter, to get technical responses as to how well they think such a unit would work. Of course, with all those batteries sitting around, you could run some equipment off of pure DC (Hi again TWL).

The following link shows the specs on Prosine's 2000-watt unit. I couldn't find internet specs on the smaller unit. http://www.xantrex.com/products/product.asp?did=255

Thoughts? Impressions?
Hey Peter-

Great idea! My brother in Vermont has his entire house running on large solar panels hooked to a large bank of batteries in the basement. They claim the batteries can last for three days of average use should the grid fail. He also heats his water through the same panels. I had no idea the power was so stable. I'll forward on your post to him and get his impressions (he's an electrical engineer). Look forward to hearing input from those in the know here.

Personally speaking, I think the idea of DC power is a good one, as I have emailed with Twl (in the past) about the concept. I think it’s possible the power could be cleaner than what I achieve with my AC power filtration system (which now does a very good job).
My concern is how much will it cost to purchase the necessary equipment to convert a system (or partial system) over the DC power system? $1300 is probably a good guess.
I’m also aware that many of us have large wattage consumption systems (I don’t), or don’t have the space for the necessary batteries with short wire runs, or have invested large sums os money into AC power therefore are hesitant to spend additional money (or don’t have it).
I would love to hear my system on DC power compared to my AC filtration system to see if it sounded better and by how much.
I do know that the correct sine-wave generating charger-inverter is imperative, and I don’t know how the Xantrex would compare the excellent Studer inverters.
Yep, I use the Studer Inverter for the stuff that I can't power directly off the 12vdc from the batteries. I don't know exactly how the Xantrex compares to the Studer, but as long as it is clean, then you're ok. You MUST use a FULL-SINE WAVE inverter. Modified sine waves like the cheaper inverters produce are noisy as hell, and not suitable.
3% distortion is not too good. Your AC as supplied by your power company is supposed to remain lower than 5% at any given time. If it is above 5%, chances are, your pole transformer is defective. In comparison, the PS units are probably WAY, WAY below this, but i'm not sure. They don't post any specs on their website, so who knows. Sean
Sean, I think you'll agree that the issue is not necessarily what the power company specifies, but what is actually on your power coming into your house. The distortion they generate, is simply the baseline to which all the other crap from all over your neighborhood, and in your house, is added.

By creating an isolated power supply from battery, and a controlled AC inverting system, this creates a much cleaner, better regulated, and lower distortion supply, which is not subjected to all the other problems the mains lines are subjected to. It is a controlled, isolated, closed loop system.

Also, if you want to use a separate inverter/battery for each component, even the power supply intermodulation between components could be eliminated. This is something that is not often addressed, but is present in most systems.

I know you can't use a system like this with a high-power audio system, due to power drain considerations on the batteries. But for a low-power SET amp, and a typical preamp, it works great.
Twl: I agree with everything that you said. The only problem might arise from using dedicated inverters for each component. Since all the components share signal ( and possibly chassis ) ground, it is possible that the inverters might interfere with each other. Obviously, this would depend on the design of both the inverter(s) and the components being used. Sean
GM claims fuel cell technology will be available for home use in approximatly 4 years.
Sean is correct to be extra cautious about inverters. Professional studio equipment makers like eg Studer, mentioned by Twl's post, must have had very extensive R&D data and the solutions to overcome noise problems related to inverter operation. The solid state switchers or multivibrator mode pilot frequency & powerwaveform control circuitry which are necessary to convert dc back again to ac are about the noisiest devices around. In the same argument a larger current output capacity inverter of competent design will have a better power/noise ratio than that of a smaller one of the same design.

Thanks to this post, I now have some thoughts about not "reinventing the wheel", but may go wholehog with the professionals. I read somewhere about Isolated or Floating ac supplies... I am very curious to know what exactly the recording studios are using. This is a bread & butter matter to them, and their stakes are very high indeed.
TWL - does Studer make a charger-inverter? The charger part would be necessary for anyone without solar cells, or without enough solar cells to store the juice for a thorough listening session. I like the power company backup feature!

Regarding battery power. The rule of thumb is to have enough batteries so that you don't use more than half your storage between charges. So, I would think, even a high power system (e.g. 2000 watts peak) would work fine if you had say 4 kW/HR storage. Since the amps don't really use that much all the time, storage doesn't have to equal peak usage times period of listening. If all your amps are Class A... well, the storage requirements could get high. Batteries are not tremendously expensive. It's a battery issue, not an inverter issue.

As for the inverter components being very noisy - I don't know about that and would like to know more. I did see the waveform on an oscilliscope, and it looked very good. As TWL mention, a full sine wave generator (rather than a modified sine wave generator) would be required.

Please keep the ideas coming. This may be my "holy grail" of clean power!!!
Power inverters can produce relatively "clean" output in terms of AC if well designed, but they can also produce GOBS of RFI ( quite common ) due to the switching impulses that they make use of to convert the AC to DC. As such, you could clean up your AC supply and then infect the room and equipment with a massive does of broad-band RF splatter. This is the same thing that we ran into with Plasma drivers, as many of the amps used to drive them consisted of a 40 watt 27 MHz amplifier. This is the same thing as having a highly "souped up" splatter-box CB radio transmitting right in the same room as your stereo rig.

Can anyone say, "you can't get something for free" three times fast ??? : ) Sean
I wanta know where the "power professor" PsychicAnimal is on this discussion? Say THAT fast three time Sean! :D Regards, Robin
Peter, yes Studer makes an inverter/charger in its higher power units. They make up to 2kw models. The battery bank you mention is a large bank, and will take up alot of space, and require ventilation. But it can be done if you really want it.

Sean, I've found that my inverter doesn't seem to be a problem with RF. However, since in my past, I manufactured computer operated building control systems, and had to submit to FCC for testing, I did get some good experience in controlling local RF. Good shielding is a must, but many times the wires that come out of the box will act as antennas, and radiate the RF from these wires. Ferrite donuts placed at the outlet of the box where the wires emerge(all of them) will do alot to keep the RF under control.

Peter, I have my inverter placed right near the battery bank and use a longer run at 120vac. This keeps the DC wiring short which is critical since you will draw 10 times the current on the low-voltage DC wiring than on the 120vac wiring. Use the long wiring runs on the high voltage AC side. I use a ferrite ring around the exit hole for the AC and DC wiring. I have no ill effects that I can tell, from any RF radiation on my system.
I agree with everything that Twl has mentioned here. Good sized ferrite chokes that are properly placed and applied can / will make a world of difference in an installation like this. Keeping the DC supply lines as short and as heavy as possible are also the best way to go. Pumping DC over any distance becomes a very lossy proposition. That is why we use AC to distribute power and then convert it back to DC at the device.

Not that Twl needs a pat on the back from me or anyone else, but it sounds like he's got his system set up "the right way" : ) Sean
Thanks, Sean. It's always nice to get a knowledgable opinion on what I'm doing.