2. tech-talk
  3. 1060530994

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?
peter_s
sean
6,231 posts
 
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
>
corona
132 posts
 
GM claims fuel cell technology will be available for home use in approximatly 4 years.
philip_psha5b7
28 posts
 
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.
peter_s OP
1,335 posts
 
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!!!
sean
6,231 posts
 
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
>
More to discover