Variable speed 12v Air conditioner

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Murray Argo

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Apr 30, 2021, 10:58:11 AMApr 30
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I currently have an sbms 40 set up with 200ah lifepo4 battery pack. 

I recently ordered and received a 12v variable speed air conditioner from alibaba. According to the data sheet, it will pull 600w on start up. I have it connected to a victron bp100, which is controlled by the the sbms. My solar is probably not going to be able to keep up so I ordered a mean well RSP 750 12, which will also be controlled by the sbms. 

My plan is to connect the shunt, that I already have set up, from the battery to a positive bus bar. I will connect the bp100/AC to the bus bar, as well as the RSP 750 12 to the bus bar. My assumption is that this will work and only the excess that the BP 100/ AC does not use will go through the shunt into the battery.

Will this work as I have planned?

Dacian Todea

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Apr 30, 2021, 12:31:41 PMApr 30
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Yes only the excess from the RSP750 will go to battery is the same thing with solar.
But if you always have access to grid electricity why get complicated with a less efficient 12V air conditioning.

Murray Argo

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Apr 30, 2021, 12:38:41 PMApr 30
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This is just a temporary setup in my van. I have cells on the way from china that will get me to 600ah. Then I have more solar ordered. So to answer your question, I do not plan to always have access to grid. I am just trying to figure out a way to get the system to work for an upcoming trip that I will have grid access. Also the 12v units are pretty small and easy to mount to a van. I just had to drill a 3in hole and make a bracket for the condensor 

Dacian Todea

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Apr 30, 2021, 12:45:03 PMApr 30
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The 12V units are way lower volume manufacture so typically the 12Vdc or 24Vdc compressors are much less efficient than modern new variable speed higher voltage compressors that are build in huge volumes by large companies that invested a lot of R&D in having efficient compressors.
It is easily possible that the 12V one is 2x less efficient and is not even less expensive so even if adding an inverter it may be more efficient. It is the same thing with fridges.

Murray Argo

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Apr 30, 2021, 12:53:31 PMApr 30
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I appreciate this insight. I probably should have asked before ordering and installing, but too late now. 

here is the unit I have installed. 

Dacian Todea

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Apr 30, 2021, 1:05:27 PMApr 30
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The spec for those is very limited and also hard to trust unfortunately.  Here is a guy that uses a ForestAir mini split https://www.youtube.com/watch?v=woZH85EiHNY

Dacian Todea

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Apr 30, 2021, 1:22:25 PMApr 30
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Of course you will use the 12V unit you already got and the reason I made my comments is in case others read this. I think in most cases when needing a larger fridge or air conditioning unit is best from an efficiency point of view to look at quality known brands units that run on 120/240Vac.

Murray Argo

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Apr 30, 2021, 2:35:26 PMApr 30
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This is interesting. So even with the inverter loss the 120/240Vac fridges and air conditioning are better?

Dacian Todea

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Apr 30, 2021, 5:43:15 PMApr 30
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I saw small 12V and 24V fridges that barely had a COP of 1 compared to quality Vac fridges for the large manufacturers that can have COP of 2 or 3
So if difference is 2x then the small 10 to 15% loss from an inverter will be insignificant.
It is just the economy of scale where quality of a mass produced product can usually be much better at similar price.

Dave McCampbell

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Apr 30, 2021, 10:45:24 PMApr 30
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Interesting, especially the sliding solar panels on Dacian's Forest Air link above.  Murray, your Alibabl air conditioner link at the bottom has info on the company's ability to produce 120v and 240v models also.  So no need for an inverter if you are on shore power.  Not clear exactly what compressor this company is using, but probably not Secop/Danfoss as they would be much more expensive.
The marine industry has a well developed air conditioning  and refrigeration capability using variable speed Secop/Danfoss compressors with COPs in excess of 2.0 if using them on slowest speed.  Most marine units come with an electronic control module that facilitates making connections, modifying voltage and attaching control devices.  There are even dual DC/AC voltage models.  There is an efficiency difference with these compressors of around 30% between using highest and lowest speeds, so we have our refrig systems designed to use the lowest speed.  Proper insulation required for that, though; for refrigerators R20 and freezers R30.  Water heat exchange adds to efficiency, but is not easily possible on land installs.  Thanks for the interesting links above.

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