12/24/48 VDC Air conditioner

Thebes

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The dcairsales units seem to be for equipment cooling in small cabnets. They are all pretty undersized for residential use, but maybe in a very small bedroom. I don't doubt that they are more efficient than standard units, which are horrid for energy use. I'm sure they'd be a real blessing for cooling telcom electronics in remote areas.

If you are considering using multiple of these units for residential cooling, keep in mind that they draw more amps (watts = volts X amps, drop the volts and you raise the amps) and therefor could require some very heavy, expensive and perhaps even exotic wiring. You might find yourself better off with a high quality inverter and the most efficient AC A/C you can find, depending upon your cooling needs and the length of the wire runs. In my solar home I found it most economical to use AC for everything to take advantage of existing wiring, even though some DC items are more efficient. A big advantage with DC would be not having to worry about the compressor's surge and having an inverter that can handle it, I don't have A/C but I had surge troubles with my fridge at first.
 

gmiller261

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Thanks Thebes

Yes they are small. I run a 12K BTU AC unit in 900 sqft, so I figured that I would run 1 in every room, 3 for now.

According to their website the 10000 BTU/h (3000 watts) unit power consumption is:

600 watts @24a/24vdc-12.5a/48VDC.

The wiring is interesting, I did not think of that. What size do you think I need @24amps?

My 12K AC unit runs on a 30 amp fuse 230volt 5.5 amp draw.

I am trying to figure out if I can run mostly DC appliances so I can save money on inverters and spend it on solar cells.

The inverter I priced out was a XANTREX PPSW4024/D Dual Power Panel with bells and whistles for @7,500.00. That would buy me 6 x 315 watt of solar panels (52 volts @6.05 amps). So, correct me if I am wrong, according to P = I*V I should be able to double the amps (12) in a 24V volt system PER panel. Two of the above panels per 10K BTU unit. Then it would only depend on how many sunny days there are and how many sun hours they get.

I know I would still need a single smaller inverter.

So far I found DC refrigerator(17 amps @ 12volts) w/o/wo the freezer(44 amps @ 12volts), pool/H2O pumps and filter system and fans.

http://www.sundanzer.com/PDF/SunDanzer_Batt_Powered.pdf

Gary
 

Thebes

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Your wiring gauge will depend upon
#1 the amperage, if it has a significant surge you may need to factor that in.
#2 the distance
#3 the acceptable amount of temperature gain and voltage loss

I don't know what codes (if any) are applicable in the DR. In the US codes generally allow a smaller gauge of wire than is desired due to the voltage loss issues. Voltage loss from your batteries to your A/C when cloudy or in the evening might cause your A/Cs low voltage disconnect to kick in when your batteries still have enough juice. Heat is mostly an issue if the wires are enclosed in conduit, generally you up them to the next largest gauge. Codes may or may not be an issue, in the US other concerns dictate a heavier wire size. For a 60 foot run, I would guess (need to look it up) you'd need 6 gauge to keep the loss to acceptable levels, a seperate circuit going to each A/C.

If you can check on what the surge is (time and amps), and let me know the wire run, and I will look up the voltage loss for various gauges.

Also it sounds like the inverter you are thinking of is really a lot more than an inverter. I think you are talking a combination with a charge controller, circuit breakers, etc. I can find an inverter only, refurbed, and without the extras, in the states for under $2k that would do the job. I don't know about importing one to the DR or what else you might have there. Those power panels are mostly used in areas where they are required by code.

The 52v panels sound like they would be designed for grid tie inverters, what is the nominal system voltage (probably 36v?)? You might have trouble finding a charge controller that can deal with them. If you can you would need to either run your battery bank and appliances at the nominal system voltage, or use a MPPT (maximum power point tracking) charge controller capable of stepping the voltage down to a 24v bank; such inverters are more expensive but in some cases they are more efficient at putting the full power of the panel into the batteries (in cold, low charge conditions mainly).

You can not just take a 52v panel and expect 24v at double the amperage, the panel will only put out the maximum rated amperage at any voltage up to 52v minus wiring loss. Also realize that a 52v panel is actually less than 48v nominal system voltage, they raise the voltage quite a bit to deal with wiring loss between the panels and charge controller / batteries; some charge controllers can convert this for you (see above or google "MPPT charge controller")

The Sundanzers are supposed to be great fridges from everything I have heard. I don't know anyone who has one since they are a chest style and most people don't like that. BTW, they don't draw 17A, they take 17 Amp Hours per day (on average at specified temp); they are rated as taking 40-80 watts when running, with a surge low enough not to blow a 15A slow blow fuse.

Another excellent fridge (more expensive) is the SunFrost, I have a neighbor who has had one for 15+ years and loves it, availible ac or dc. I use an "ewave" that cost me $135 at a department store. While its small and takes more juice than a good fridge, I only needed to spend $400 for the panels to power it, so it saved me money over the others (and I get a decent freezer in it too).

My advice would still be to go with AC. I see DC as being a good thing only for small systems (remote cabin, RV, boat) or for always on loads when you don't want your inverter running 24/7 (cell phone chargers, answering machines, etc come to mind). I think you will find that in the long run you spend more money to set up a full sized house with DC appliances (harder to find and thus a worse value on average) and heavy wiring. I would need to know the lengths of the wire but I really think you will be spending a lot on it if you stick with 24v DC for everything; some of your wires might end up being long runs of welding cable (I've seen this!).

Also remember that if you opt for a high end Trace, you'll have it for a long time, many appliances will be replaced before it is (on average, YMMV).Exeltech might be a better choice as they are modular and have an even higher mean time between failures (18.5 years if I remember), plus are redundant.
 

gmiller261

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Nice reply. Thanks

Thebes

Yes, a separate circuit for each DC appliances. As you pointed out most DC appliances have little to no surge. No article, I?ve read, mentions surge power.

I am calculating 20-35 amps maximum for any one appliance. The following link refers to a 6mm wire (unsheathed) that is rated for 50 amps DC continuous. My runs would be in the 60 to 120 feet.

The panel info only mentions 52V, the nominal would be less, I expect. The Trace equipment I mentioned before is equipped to handle this type of panel.
http://www.affordable-solar.com/ase-dgf-50315w50v.html

I was under the impression that the 52V potential would be normalized to 24V (battery bank) through the controller/charger. This should allow the charger to double the amps charging. Excuse me for my ignorance if I am totally incorrect.

Thanks for the correction. It is 17 amp hours per day @ 90F. I used that figure as a mean value for temperature. So what you said is that it is much better efficiency than I stated. If it cools for 17 hours a day then it would actually be 1 amp hour. The article does state that they can operate with a 75watt solar panel with 5 hours of sun a day. That would make more sense. Thanks.

I have looked at the SunFrost and I agree they are more standard, but still ugly, I do not care about that.

I am glad to hear someone using the solar panels for driving an energy hungry appliance. Good for you.

Do you know how much your friend paid for the SunFrost? Here they sell anywhere from $850-1000.

I am hoping that with the advent of Hydrogen fuel cells and better solar cells, DC appliances would become more prevalent. If they do last me 10-12 years my kids could worry about replacing them.

I am looking for a ?small? monthly run rate in terms of $?s. I would rather send $25K on solar panels, kick a** batteries and DC equipment, if it truly means I will be spending 80% less per month to operate them.

And I do realize I could put that money in the bank and have the interest pay for my excess, but I am not that way.

Welding cables would be bad. I wonder what kind of RF they would put out and if your hair would stand on end when you walk over the wire?

My MTBF is less than 18.5 years.

Thanks very much for the conversation and information.

Gary
 

Thebes

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Jun 18, 2004
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What charge controller did you intend to used. I know that Trace just started making the Sun-Tie series, which are mainly intended for grid tie applications, I think they can have a battery bank too but don't know much about them. For the panels you are talking about you would need a MPPT charge controller, several companies now make them and Outback is probably the most well known for the technology. As far as I know the trace power panels all come with a Pulse Width Modulation charge controller like a c-60, that will only use 24v (nominal) of the 52v and will essentially waste most of the voltage of those panels going into a 24v (nominal) battery bank. Perhaps Trace has come out with a new Power Panel I don't know about though.

Last I checked (a few months ago) on MPPT charge controllers, they would be a good investment in terms of what they saved in extra panels for systems exposed to low voltage low temp conditions (Decembers and January in most US locations) and in such conditions would allow a smaller number of panels as systems are normally designed in temperate US areas to deal with December and the rest works itself out (A/C could well change this assumption). MPPT controllers are also used extensively for grid tie applications, that is to say when you tie your system to the electrical grid and backfeed it part of the time, taking electricity out when it isn't sunny and putting it into the grid when it is; some, but definately not all, grid tie inverters will also charge an auxillary battery back for use in the advent of power failure. Grid tie inverters are inverters and charge controllers in one and are generally MPPT; MPPT charge controllers are just charge controllers.

A wiring size chart figuring a 5% loss can be found at http://www.gosolar.u-net.com/Wire_sizing_chart_for_12_and_24_volt_systems.htm

According to it a 60ft run at 15 amps would need just over 8mm. For a 90 foot at 15 amps you need 16mm. These are the figures for 24v nominal systems. I just googled this particular chart but the figures are in line with others I have seen. You would have substainly better luck with a 48v system, you can get transformers designed to step it down at the point of use for cases where you can't find 48v appliances; I have never seen them used but have read about them.

You can see why I said you might need wires the size of welding cables. I just wired a 12v dc circuit for some friends today and it used 6 and 8 ga just to deal with a couple of low power lights and a small DC tv on a run shorter than you would be doing. They are using a Magic Chef fridge off of an older Trace inverter instead of going with a DC fridge. BTW, I think EMF/RF occurs mainly due to modulated sign wave inverters, then you get strange hums in some electronics.

A full size SunFrost for $850 US! That is a steal, even used! A 9 cubic foot fridge only retails at $1600 and a Full size fridge/freezer at $2800 in the US. I have no idea what my neighbor paid and it was long ago, but I'm sure it was over a grand even back then.
 
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gmiller261

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Thanks again, Thebes

And for the education.

I?ll check the charger type on the system. I?ll do some more homework on chargers. I did not know there was that much of a difference.

I did not think it would be wise to feed back into the DR grid. I was not expecting too.

I need to understand (through research) why the link on wiring mentioned a 6mm wire dong 50 amps. May be that was for 1 foot of run.

I contemplated 48VDC battery array but I wanted the Surrette 4KS25PS rated at 4V @ 1350 amp hours. At over $750 a pop I thought that $9K was excessive.

I stand corrected on the RF. It would be EM from a moving current. Wonder the health hazards from a dozen 12mm cables @ 30 amps would cause.

I thought the $1600 cost of the refrigerators were because they were selling you the solar panel and equipment. I?ll google and look for a price again.

Nice speaking with you and thanks for your real world information,

Gary