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

[zanydroid]

It would be silent if PWM frequency is above human hearing upper frequency limit. But I never tried induction cooktop before. I may get one of those table top single burner units to experiment with.

Until I realized that the kHz frequency was layered on 120Hz I was confused by how noisy they were and how much energy I could hear.

Wikipedia says 25-50kHz as the operating frequency of induction burners so it is possible it will be silent.

Actually there are a lot of people I know in the cooking world that are triggered by the harmonics starting at 120Hz, and I had previously decided that they were SOL. But maybe induction cooktops should just include a few 3kW boost converters inside. The SMPS frequency should be much higher than 120Hz and also easier to manage than some buzzing induced inside the pans.

 

[AntronX]

Thanks to @Consumerbot3418 for sending me inverter board and parts from same model Midea AC unit. I was able to de-solder power modules to get part numbers. They are SIM6891M 600V 2.5A (400V DC max input rated) and SDM15G60FB 600V 15A IPM modules. Both should be OK to operate from 96 cell Li-ion EV battery pack.

 

[AntronX]

Thanks again to @Consumerbot3418 for sending me compressor as well. Now I have a spare or something to experiment with. I got it to spin using RC brushless speed controller powered from 60Vdc. Just enough to unstick the valve to let argon/co2 welding gas to flow through it to hopefully purge any trapped moisture from the air. Capped off the tubes and off to storage it goes for now. Hopefully doing this will prevent POE oil from going acidic and doing damage. I will probably replace it with fresh oil. Just have to figure out how to drain old oil and how much new oil to add.

 

[AntronX]

This project is coming to an end (for now). Weather is getting hot so I need it back in service. Installed junction box outside to route AC and DC power through. It's nice not having indoor power cord. Looks neater that way. Wrapped 8 turns of DC cable through FT240-31 toroid for EMI/RFI reduction. 3rd pic shows a hole and dam to keep condensate from reaching bottom of condenser and fan. Surprised this thing still cools after all the abuse.

 

[Vigo]

Dunno how i missed this the whole time. I missed my chance to contribute anything since i had opened one of mine last year and identified the voltage doubler circuit and thus the rough operating voltage etc, but a lot of the rest of this is over my head.

Mine has been sitting dormant since i installed a mini split in my room, but i intend to convert the Midea to a split unit and put it in a conversion van. Time will tell if i follow through. Thanks for posting all of this.

 

[AntronX]

Dunno how i missed this the whole time.

This forum is getting so big that some threads get lost in the torrent of new posts. Not a bad thing but does result in some interesting threads getting pushed down quickly. I usually browse by what's new.

Mine has been sitting dormant since i installed a mini split in my room

My next goal in this project is to install DC modded mini split. Will have this Midea run for another summer. It accomplished its main task of proving that inverter ACs can run on DC. That was the major reason I bought it to replace perfectly fine 5k BTU single speed box.

 

[Vigo]

As far as i know, anything that has a rectifier section and actually runs on DC, you could put DC straight through the AC cord and it would function, you would just be eating some pointless diode losses from passing through the rectifier section. But your way is nicer!

 

[AntronX]

Parts harvested from dead Aims 1500W 48V inverter that will become DC-DC converter for Midea aircon. E55-N2Z0Q 48V/120V 4:17 ferrite transformer good for 3kW surge. Measured 90nH primary leakage inductance with secondary windings shorted. Full bridge driver and rectifier circuit. SG3525 PWM controller (on breadboard) originally set to 36kHz. I will experiment with different PWM frequencies. VO3120 opto isolated 2.5A gate driver ICs harvested from scrapped UPS. MUR3060 fast rectifier diodes 0.73Vf at 1A. And 70N10F4 100V 60A 15mOhm MOSFETS I had laying around (6 of 8 original IRF8010 fets got fried). Will use 50V 1000uF Rubycon ZLH low ESR caps (not pictured). Kinda close to rated voltage but my batteries never go above 48V (4V/cell, 12S Li-Ion).

 

[toddincabo]

Installed junction box outside to route AC and DC power through.

Excellent work, I'm going to be installing this exact model into my RV and would love to have the choice of AC or DC. Do you use a switch to choose between the two before powering on or does it not back feed in any way? Have you tested DC draw and amps with a "kilowatt" meter during use on a really hot day yet? Also, could you please give an estimate of the efficiency difference between the two using this mod or just AC plugged in? Thank you.

 

[AntronX]

No switch yet, still running on AC from 800 watt inverter. Worst case power draw (from grid) was 1200W on hot day and high setting. At low and medium setting there is not a noticeable efficiency difference. Main difference will come from using ~96% efficient DC-DC converter vs. 84% efficient inverter.

 

[toddincabo]

No switch yet, still running on AC from 800 watt inverter. Worst case power draw (from grid) was 1200W on hot day and high setting. At low and medium setting there is not a noticeable efficiency difference. Main difference will come from using ~96% efficient DC-DC converter vs. 84% efficient inverter.

Thank you. Could you please clarify the 84%? If you want to easily fill back in those holes you drilled you could use some stick putty like in photo, I do it all the time with the pack that comes with separate green and white sticks.

 

[AntronX]

I meant 84% efficient 48V DC to 120Vac inverter I use to power it from my battery. So far it seems OK keeping condenser outlet tubing dry. But I would not be able to detect slight cooling efficiency loss anyway.

 

[Brucey]

No switch yet, still running on AC from 800 watt inverter. Worst case power draw (from grid) was 1200W on hot day and high setting. At low and medium setting there is not a noticeable efficiency difference. Main difference will come from using ~96% efficient DC-DC converter vs. 84% efficient inverter.

I was thinking of getting a midea to keep the inverters occupied in the summer versus the oil filled heater in the winter. But I take pause when you mention that it really makes your 48/800 noisy with the power factor. I guess I could run it on the high frequency Delta 2 max instead.

 

[toddincabo]

I meant 84% efficient 48V DC to 120Vac inverter I use to power it from my battery. So far it seems OK keeping condenser outlet tubing dry. But I would not be able to detect slight cooling efficiency loss anyway.

OK, thank you very much, I'm looking forward to seeing where you go with this, this is great! I think I have it down from the photos where the cables are soldered, the resistors are attached (existing video screenshot), and the DC voltage range from your posts here. In the end, If you could possibly share a quick YouTube tutorial video for amateurs like me it would be greatly appreciated, especially by the RV crowd. I know I'd share that video. Thanks again and take care.

 

[Vigo]

I was thinking of getting a midea to keep the inverters occupied in the summer versus the oil filled heater in the winter. But I take pause when you mention that it really makes your 48/800 noisy with the power factor. I guess I could run it on the high frequency Delta 2 max instead.

I havent noticed any problem running midea 8k or 12k U units from my Growatts. I would highly recommend these units. If they had a good heat mode id like them better than the 2 actual mini splits i have.

 

[AntronX]

Come on Costco stop tempting me.

 

[Brucey]

Come on Costco stop tempting me.

View attachment 213898

I was close to buying one but a bunch of reviews mention it makes a bunch of noises including sqealing on the compressor. I can't tolerate that so ended up ordering an LG "dual inverter" 8000 BTU unit for sons bedroom, he loves things ice cold, and then I can bump up the thermostat for the central air.

https://www.amazon.com/gp/aw/d/B0B4PPM8W9

I did see that the Midea regular rectangular units have an option for heat pump heat that works down to 41 degrees...might get one of those for kitchen window, then can turn off the central AC, and then run that in heat mode during the shoulder season before it drops below 41 and then switch to the oil filled radiators for the colder days and nights.

 

[Brucey]

Come on Costco stop tempting me.

View attachment 213898

Limit 5.... just saying

 

[AntronX]

Limit 5.... just saying

Phone not included. Deal breaker.

 

[AntronX]

bunch of reviews mention it makes a bunch of noises including sqealing on the compressor.

High frequency inverter switching squealing is barely noticeable over outdoor fan noise. They have sound insulating mat around compressor to attenuate it. Other noise was from water getting flung onto condenser coil by the fan. It's not bad either. Can't hear either of those indoor.