DC load center for new small house

Started by openplanet, June 02, 2013, 08:27:42 PM

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dgd

An interesting post, your years of experience with DC loads, DC to DC converters and conversion efficiences shows just how DC powering can be achieved successfully. 
The only viable alternative is to use an inverter to distribute AC then devices needing low voltage DC convert the distributed AC to DC.
Perhaps thats inefficient but with the ever decreasing costs of PVs to gain extra power the efficiency argument becomes less relevant.

One point you made intrigues me...

Quote from: zoneblue on June 28, 2013, 08:14:54 PM
...
Building Biology says that the earth has several low frequency resonances around the 10 hz range, that are critical to our health and well being. Hence the desire to avoid drowning them out with a much stronger 50hz signal.
...
The last 10Hz resonance (of significant amplitude)  here in New Zealand flattened  a major city with severe loss of life.
Where are these other(?) 10Hz resonances that are somehow critical to our health? published papers on this?

dgd
Classic 250, 150,  20 140w, 6 250w PVs, 2Kw turbine, MN ac Clipper, Epanel/MNdc, Trace SW3024E (1997), Century 1050Ah 24V FLA (1999). Arduino power monitoring and web server.  Off grid since 4/2000
West Auckland, New Zealand

phonetic

I have a 24volt DC dist loop wired through the house, using 6 gang wall plates: 2xRG6 coax 2xRJ45 LAN & 2xred/black 30amp Anderson power poles.

All my small gear with wall plugpacks, have been replaced with DC/DC converters all works a treat.
Home:
3.04kW Grid Tie.
Weekender:
6.08kW Off Grid. DC & AC coupled
32 of 190W (12+12 Array DC) (8 Array AC)
Midnite Classic 150 & Classic Lite 150
1.5KW AC coupled Grid Inverter
8 of 600 amp hour Surrette S600 flooded cell battery bank 24 volt 1200 amphour
Outback VFX3024E Inverter Charger, Mate 2.

zoneblue

Quote from: dgd on June 29, 2013, 05:21:52 AM
Where are these other(?) 10Hz resonances that are somehow critical to our health? published papers on this?
dgd

The Building Biology Institute hails from germany, where they can be a bit obsessive about things. The NZ institute has an extensive set of papers. 

See:
http://www.ecoprojects.co.nz/
http://www.hbelc.org/

Building biology is on the eco, slightly fringe end of building practice, ill grant you that, however in general its about getting all the synthetics, pvc, adhesives, composites, fibreboard, foams, acryllic paint etc etc out of the living environment. Sometimes known as SBS or sick building syndrome. Its fairly hard core, they use things like wool, cork and pumice for insulation. They also prefer to minimize the use of metal in roofing, reinforcing, even bracing, (and esp. bedding) to avoid faraday cage effect. Same reason, to allow the earths natural magnetism to percolate undisturbed.

Im certainly no expo\ert, however, and couldnt provide a strong argument for any of this.
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

Hialtitude

Quote from: zoneblue on June 28, 2013, 08:14:54 PM


Our base loads are:

- fridge 24v 70 watts about 40/60 duty cycle
- one custom atom server draws about 15 watts, runs on 19v via a 24-19v converter.
- two laptops run on 12 and 19v , with their own converters, about 12 watts each.
-
- NiMH, lithium and nicad chargers for various tools, all runs on 12 volts via dc converter.
- cordless phone, still working on that, but its 5.7V using a custom converter.

Hi, I'm very interested in your post.   Did you build your DC to DC converters as custom or can you buy them.  I can imagine that there's probably 24v to 12v converters, but the 24-19V sounds interesting. 

Also, is there much loss in the conversion, but I'm assuming that it's less than going from DC to AC and then back to DC?   I'd like to use this method for some projects. 

thank you for your time.  GP.

zoneblue

#19
The first time you put 0.5A into one of those and get 1A out is a real eye opener to how switch mode DC-DC conversion works.

I have quite a collection of them, but have avoided so far the route of large, name brand models such as those made by samlex. For a couple hundred dollars im sure they are good quality, but lack flexibility. I prefer many smaller converters, to match the ridiculous array of voltages used by stuff these days.

- The first ones i got years ago at auction, they had obviously been made custom made in bulk for some kind of business application. They were nominally 24-13.8v (8A), but you could change the voltage divider on the sense end of it easily enough.  I once tried to measure the efficiency under typical load and was astonished to find that with the crappy meters i had it was near 100%. Couldnt tell the loss from the error! Big inductors and caps in them, ill add a pic below later.

- You can find all manner of cheap usb mobile/iphone/etc chargers,  12/24v car adapters, many of which you will find useful and easy enough to hack into off grid life. I also bought a couple of 80W HP car laptop adapters, designed for the corperate market, used off ebay. While designed for laptops, and decent enough quality, i found them to generally have poor thermal design, and lesser efficiency. I think the reason for that is because they have to run off 12 or 24vthey employ auto buck boost. Try to always use a higher input voltage, and buck mode exclusively. This is one big argument against 12v systems.

- You can get relatively cheap fixed voltage converters such as these, with a bit more amps.
http://www.ebay.com/itm/DC-DC-24V-to-19V-10A-190W-Step-DOWN-Waterproof-Power-Voltage-Converter-/321222894255?pt=LH_DefaultDomain_0&hash=item4aca6062af

- Lately i find these just little suckers in particular incredible value for money, $3 ea, and order them in 10 packs.
http://dx.com/p/mini-dc-dc-voltage-stabilizer-regulator-module-red-126106
They seem to have 'upgraded' that model lately to this one. $2!
http://dx.com/p/20083-adjustable-power-supply-voltage-regulating-reducing-module-blue-black-255394 (Has mounting holes)

There is also a version with current limiting, which are good for home brew led arrays.
http://dx.com/p/power-led-driver-constant-current-charger-power-supply-module-cc-cv-156788
(See also my led writeup in sig.)

All those little converters are good for 2 amps continuous, which is enough to run at most a (small) laptop.  These things have been powering our 2 netbooks without issue for the last couple of years, as well all the myriad other dc stuff you tend to have running around the place.

Had none die so far, and the adjustment is fine enough and stable. Set it to 9V, and a year later its still 9V. In a case like my wifi router, which is unhelpfully 7.5V, (which idiot thought that was a good idea), when the AC pack died, it was easier to flick one of those converters on it than try and find a replacement.

I have a couple of better meters now so i should have another go at measuring the efficiency. Like i said being so small they dont have a lot of filtering and i do tend to add capacitors on the input and output sometimes.

I should at this point confess that some of this is at present a real rats nest, but ive ordered some little baby boxes and midnite breakers and whatnot and its a summer project to make it nice and tidy ;)
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

ClassicCrazy

zoneblue - are those small DC/DC converters efficient ?  Do they get very warm at 2 amp load ? 
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable

zoneblue

The regulator chip doesnt really have a heatsink. Theres a bunch of through holes connected to a backplane pcb layer. Thats it. The chip is rated to 3A, but i derate it to 2A for this reason.

The inductor is small, i would say undersized, so there will be some loss there. But being (literally) 1000X  smaller and with variable adjustment makes them so convenient to use.

When say a net book is power up and charging at the same time, there is certainly some warmth there. I will try to measure the efficiency, but to do it accurately requires 4 decent meters, which i dont have. 
6x300W CSUN, ground mount, CL150Lite, 2V/400AhToyo AGM,  Outback VFX3024E, Steca Solarix PL1100
http://www.zoneblue.org/cms/page.php?view=off-grid-solar

ClassicCrazy

Well the touch test for efficiency  would work for me !  Can't you just take power in and power out ? Why four meters needed , to check the voltage while drawing current ?  I guess that is what those free Harbor Freight meters are for .
Thanks for the info on these - for a couple bucks I am going to get some to have around .

I bought one of the larger type 20 amp ones a few years back off of ebay but didn't think to make sure that the output was variable so it is stuck at 12 volts exactly  which was too low to run the radio I wanted to. I think it may have drawn too much power when not running anything. 
system 1
Classic 150 , 5s3p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system 2
 5s 135w Kyocero , 3s3p 270w Kyocera  to Classic 150 ,   8s Kyocera 225w to Hawkes Bay Jakiper 48v 15kwh LiFePO4 , Outback VFX 3648 inverter
system 3
KID / Brat portable