Midea U 12k power from DC (IT WORKS!!!)

[AntronX]

So i was doing annual cleaning on my Midea U 12kbtu window AC and decided to take it apart a bit more to see inverter/controller board and to try running it from DC power. I tried to power it from 120v 100ma benchtop supply and i got it to spin the indoor fan followed by power error displayed on temperature LED screen. I see there is power relay next to bulk capacitors. I have to figure out what its used for to make sure it does not break current under load which would fry it under DC supply. Nice to see passive 3mH PFC inductor inside but active PFC would have been ideal. My 800w inverter still hates this thing but will start it. EDIT: It works!

 

[Bluedog225]

Be interesting to see if you can get it to work.

 

[AshleyL]

What is the capacitor brand? Can't see clearly in the picture.

 

[AntronX]

What is the capacitor brand?

 

[AntronX]

Some contrast/brightness magic reveals Renesas RX24T8 32bit 80Mhz MCU that runs motor inverters and probably refrigerant cycle logic as well.

 

[AshleyL]

View attachment 191781

Hmm.....Samxon......A reasonable budget choice comparable to Teapo and Capxon.

 

[zanydroid]

My 800w inverter still hates this thing but will start it.

What happens when you try to start & run it?

 

[AntronX]

Hmm.....Samxon......A reasonable budget choice comparable to Teapo and Capxon.

Only needs to outlast 1 year warranty. In a couple of years condenser coil will rot anyway since it always sits in a puddle of water by design. I drilled a bunch of holes and dammed up condensation channel to avoid pooling water under the coil.

 

[AntronX]

What happens when you try to start & run it?

It runs it on medium speed but LF transformer buzzes louder than normal. It's only 800W Victron.

 

[zanydroid]

It runs it on medium speed but LF transformer buzzes louder than normal. It's only 800W Victron.

Ah OK so running it on something with the kind of PF you get for passive correction was asking for it. Did you measure the PF?

 

[AntronX]

Did you measure the PF?

No i forgot. Will do when I put it back together (if it starts haha).

 

[zanydroid]

Cool. Does this have heat? (I'm not sure it does). If it does then a fun project is to try disabling the low temperature cutoff (I know it's somewhat standard to disable on portables that lock out in the 40Fs by default).

 

[AntronX]

Cool. Does this have heat?

Nope, no reversing valve or TXV/EEV. Only cap tubes. Not at $300 price point lol.

 

[zanydroid]

LOL, i just noticed the new version is Matter-certified. Really bleeding edge stuff, and I can't find a thread saying what is exposed to Matter.

What would be interesting to have? Probably some temp sensors and changing the power level/set point.

 

[AntronX]

If they could make it continue to spin indoor motor to dry out the coil before shutting down that would be great. Pressing power button shuts it off and closes that useless vent flap which helps keep moisture around evaporator coil helping mold grow inside.

 

[fromport]

Only needs to outlast 1 year warranty. In a couple of years condenser coil will rot anyway since it always sits in a puddle of water by design. I drilled a bunch of holes and dammed up condensation channel to avoid pooling water under the coil.

Could you post a photo of that modification you made ?

 

[AntronX]

Will do. I just realized it runs a loop of condenser outlet tubing through that puddle to cool the refrigerant some more before expansion to increase efficiency. Oh well I guess it will run less efficiently now. I already poked too many holes under that puddle pocket.

 

[AntronX]

Well, crap. It uses voltage doubler circuit. Can't run it direct from 170V or 340V DC battery unmodified but it should run fine with cheap square wave inverter. Power relay is for bypassing PTC inrush limiter.

 

[rhino]

Somewhat related, I have that AC (smaller one) and the compressor never kicks on.. this was after only 2 seasons. Any ideas what I may need to check?

 

[AntronX]

compressor never kicks on..

Measure compressor winding resistance to look for shorts. If comp is OK then check internal fuse on controller board. Edit: If display lights up then main fuse is OK.