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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
twl
3,251 posts
 
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.
sean
6,229 posts
 
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
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twl
3,251 posts
 
Thanks, Sean. It's always nice to get a knowledgable opinion on what I'm doing.
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