Mini-split run off of DC directly? or??

tehno550tehno550 Registered Users Posts: 2
Is there a way (or a product, and would it make sense) to run an AC unit, ductless mini-split, off of DC directly?
Most of the high SEER mini-splits that are large enough for my target seem to be 220v as well.
What do most do for mini-split setups running off of a battery bank? Additional inverter? And on that front, if using an inverter, does it need to be pure sine, or are mini-splits ok using modified sine so I can try to pinch a few pennies on the inverter itself if possible.

Thanks

Comments

  • CDN_VTCDN_VT Solar Expert Posts: 492 ✭✭✭
    Re: Mini-split run off of DC directly? or??

    I have wondered that myself . if your input into the Mini-split (MS) is 220Vac what is your transformer to DC output ? Have you opened & measured yours ? I did check one from a friends MS and his was at 36Vdc when I checked it , but I always thought it varied the DC .. Being a guest & not wanting to dissect & look DUH , I left it there. I don't know if the DC internally is set as one voltage or if we have stepping .


    My units are still in new boxes X 3 .
    VT
  • tehno550tehno550 Registered Users Posts: 2
    Wanted to bump this up and see if there were any new updates or thoughts on this. 

    To clarify, I would like to run the mini-split off of DC directly to get rid of the odd chain of batteries (DC) to inverters (AC) to the minisplit (back to DC?)


  • Dave AngeliniDave Angelini Solar Expert Posts: 6,226 ✭✭✭✭✭
    There is very little loss in the conversions!  The loss is extremely small compared to the loss of the compressor doing the work!
    I have seen 2 different DC  mini-splits. Both were very expensive compared to state of the art 240VAC mini-split and the they consumed more power. I think the last one I saw was aimed at the commercial trucking market. You can search the forum BTW?

    The other concept to grasp here is that most of the time you are running during the day and there really is not a battery loss as they are charged. If you are offgrid then there always is loss at night along with the load. You design for that!

    I use to feel like this might be a good thing in 2007,  not anymore.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • WaterWheelWaterWheel Registered Users Posts: 362 ✭✭✭
    edited April 2016 #5
    This is the only 48v minisplit I could find.
    http://www.hotspotenergy.com/DC-air-conditioner/

    The other DC units all seemed to run on about 30v and want to use separate panels/batteries from your existing system.      I imagine you could use a transformer to drop a 48v battery to 30v but I have a different thought which I'll probably post later after a bit more research.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • BB.BB. Super Moderators, Administrators Posts: 32,800 admin
    foolami said:
    I imagine you could use a transformer to drop a 48v battery to 30v but I have a different thought which I'll probably post later after a bit more research.
    To be clear--Transformers are only used on AC systems (proper ratings, etc.)...

    There are DC to DC converters that can work just about the same as an AC transformer--Would they work with a DC mini-split--If you can find (or build) an appropriately sized converter--It should. But it is not a trivial exercise.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,226 ✭✭✭✭✭
    They appear to be using the Panasonic which is good. But, you still have to run DC wiring from the battery.  They spec 27 SEER equipment but who measures it?  You can buy 27 + SEER already at 240vac and install the outdoor unit any where you want easily with #12 wiring. I would like to hear from one of their customers. The conversion loss is pretty meaningless when the sun is out in decent sized systems. The concept is great but.....
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • vincevince Registered Users Posts: 79 ✭✭
    When I checked with Fujitsu about a DC connection to their split duct AC, they told me that it was not supported.
    Sunpower 3 x 435 watt panels, 48 v 215 AH battery bank (Sam's club), Midnite Kid and WBjr, Fujitsu 9RLS3 split duct AC, Outback FX 3048T + transformer 2000W 120/220V, GrapeSolar Fridge.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,226 ✭✭✭✭✭
    vince said:
    When I checked with Fujitsu about a DC connection to their split duct AC, they told me that it was not supported.
    I do not think any manufacture would let you make your own DC connection. The Hotspot is using a panasonic split but hotspot is the warranty deep pocket.

    Most all will not even support warranty if not bought from a licensed HVAC company. Even with a licensed install you mostly are on your own offgrid. 
    The good news is the name brand units are built to last and the 5 year warranty is an indication of that,
    even though many offgrid users just have to do what they can to get the unit running. Many offgrid homes are so far from HVAC pros they just learn the install and roll the dice with warranty. I did have a nice vacation in Hawaii installing for a client :)


    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • DRickeyDRickey Registered Users Posts: 22 ✭✭
    Essentially, conversion losses are less than transmission losses. We use monstrously thick wiring on the DC side because low-voltage DC current has high transmission loss. The power that goes from your batteries to the inverter on 1/0 cables as thick as your pinkie leaves it on a 14 gauge extension cord. And even if went 3 feet as DC and 60 as AC, then got converted back to DC, you probably lost more power in that 3 feet between the battery and the inverter than all the rest of the chain.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,226 ✭✭✭✭✭
    Definitely agree but for someone who did not need an inverter the concept of driving the split with solar panels only is very interesting. 
    The advantage is then lost when you are depending on Hot Spring to be in business and the loss of safety in running DC cables around a home. Many building departments do not want DC anywhere except at the battery location in listed equipment.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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