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Old 05-27-2016, 04:23 PM   #11
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this way cool idea. i like it. use car ac for the bus, hm..
concerned about how much energy would have to go into turning the compressor though. after all said and done and time vested it may be cheaper to have gotten roof mount rv ac unit i think.
i am still toying with the idea of using my window mount ac unit from house in the driver window though.
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Old 05-27-2016, 04:30 PM   #12
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Rotary compressors these days draw very little off the engine. I had a '67 Mustang ragtop with a six and automatic. When the huge old factory compressor kicked in, the motor would often die. I switched to a system with a Sanden rotary and it would freeze you out with the top down and the idle never seemed to change. Sometimes newer can actually be better.
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Old 05-27-2016, 05:31 PM   #13
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Originally Posted by jazty View Post
I'm guessing that when the A/C companies say that their unit is inverter-based what they really mean is that they incorporate a VFD. That's an ideal solution when the accessible power is already AC, but since I have the option to start with DC I should be able to get better efficiency from using a DC step-up converter (the one I have has been tested to be 95% efficient).
Yep. Actually the incoming power doesn't matter: the first thing a variable frequency drive does when fed with ac input is rectify into dc. Then, usually, there's a three-phase inverter converting the dc back to variable-frequency and possibly variable-voltage ac.

I'd love to find a source for the pieces out of one of those inverter air conditioner units.. specifically, the hermetically sealed three phase compressor and maybe the inverter board too. I guess replacement parts for an inverter mini-split shouldn't be hard to find.
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Old 05-27-2016, 06:03 PM   #14
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Reread my post. Do as you want. I will
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Old 05-27-2016, 06:34 PM   #15
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Yep. Actually the incoming power doesn't matter: the first thing a variable frequency drive does when fed with ac input is rectify into dc. Then, usually, there's a three-phase inverter converting the dc back to variable-frequency and possibly variable-voltage ac.

I'd love to find a source for the pieces out of one of those inverter air conditioner units.. specifically, the hermetically sealed three phase compressor and maybe the inverter board too. I guess replacement parts for an inverter mini-split shouldn't be hard to find.
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Pick a unit? I can give you model numbers for ac only or heat pumps/ac and can find a number for full tech. Support if needed?
They don't like when you start re-arranging there stuff but I can tell you it has been done and you might have to pissem off but they will support there equipment even if you have to move the circuit boards to get the hot gas bypass or to twin units together inside the units because they were shipped wrong.
TRANE,MITSUBISHI,LG is way above CARRIER,DAIKEN as far as equipment maintenance support.
Even on brand new install?
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Old 05-27-2016, 06:52 PM   #16
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inverter units are in fact driven with a VFD... they are running 3 phase power to the compressor... so they have to rectify to DC then crate the A/C pohases with inverters and run a VFD...

there is LOTS of specs for compressors on the internet regarding KW capacity at various RPMs.. you have to find out who made the compressor you are looking at then look it up on the OEM site for it.. MOST automotive compressors are swash-plate type Sanden / Seltec style... sanden 508 (they have new numbers for the new ones) is onbe nunber that is real common.. most compressors have a minimum RPM of 600 - 800 (compressor RPM).. you can decent cooling in the 800-1000 RPM range..

to make that window unit work right you would need a TxV instead of the capillary tube the use now... with the capillary tube you have no ability to vary capacity.. even speeding up or slowing down the compressor wont help you.. too slow and you'll fail t omake liquid and wont properly return the oil to the compressor.. too fast and your head pressure is through the roof.. if you cycle out on high pressure you will have as TOUGH time restarting it...

ive custom built plenty of A/C units before but a window unit is not what id start with.. you likely have a single shaft fan motor so you would need a separate fan on your condenser(more power usage). and if you want to shrink the size of your unit to use the evaporator inside you have the condensate to deal with... most window units dont have a proper drain pan.. you'll have a double-shaft motor...

if I were dead set on usiong an inverter and that window unit.. id use a bigger inverter that could handle the cycle rather than attempting to rig something together that seemingly could work but definitely not be efficient and may be hard on said compressor...

like I say you have a SHOT if you run a TxV .. then you can run the compressor at various speeds and the TxV takes care of proper refrigerant flow and ensures oil return..

-Christopher
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Old 05-27-2016, 07:00 PM   #17
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Originally Posted by Jolly Roger View Post
Mitsubishi.com
Pick a unit? I can give you model numbers for ac only or heat pumps/ac and can find a number for full tech. Support if needed?
They don't like when you start re-arranging there stuff but I can tell you it has been done and you might have to pissem off but they will support there equipment even if you have to move the circuit boards to get the hot gas bypass or to twin units together inside the units because they were shipped wrong.
TRANE,MITSUBISHI,LG is way above CARRIER,DAIKEN as far as equipment maintenance support.
Even on brand new install?
have a couple of thoise mini splits in my basement.. one of them is torn apart as i used it for hardware abnd software DEV.. the VFD board in mine is not analog voltage controlled.. there is a special SPI bus protocol to control it.. you CAN use a full set of boards from one of these units to make the compressor run...

before the ducted ones were available.. I completely re-worked 3 of them and made ducted enclosures for the indoor units.. i also hacked the protocols to the indoor board so i could feed it whatever info I wanted to make the unit run in whatever mode and maintain whatever ideals I wanted.. I could set an arbitrary setpoint and then feed it the reading from the room sensor (my own value) so effectively i could control the compressor speed and output.. I use a zone blower damper system in the house and have one main blower.. I discarded the blowers fro mthe ductrless splits and by usiong dampers and my VFD main blower i can create whatever CFM i need across the coils..

the ONLY thing was I had to use a full set of boards from each uniut and i allowed their sensors to monitor the temps on my own coils .. each coil has 3 sensors... intake / middle / output so it knows the superheat and subcool this way of both coils.. the TxV is electronically controlled.. in essence by handing the unit manufactured sensor values for several inputs i can control them precisely.. been running this system 7 years in my home now without issue...

I would sooner start with a mini than I would a window shaker..

-Christopher
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Old 05-31-2016, 09:30 AM   #18
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Originally Posted by cadillackid View Post
to make that window unit work right you would need a TxV instead of the capillary tube the use now... with the capillary tube you have no ability to vary capacity.. even speeding up or slowing down the compressor wont help you.. too slow and you'll fail t omake liquid and wont properly return the oil to the compressor.. too fast and your head pressure is through the roof.. if you cycle out on high pressure you will have as TOUGH time restarting it...
Nice. A TxV will definitely be necessary to achieve my end result. Very nice. I've done some research and they appear to be relatively easy to incorporate into a system.

Quote:
Originally Posted by cadillackid View Post
ive custom built plenty of A/C units before but a window unit is not what id start with.. you likely have a single shaft fan motor so you would need a separate fan on your condenser(more power usage). and if you want to shrink the size of your unit to use the evaporator inside you have the condensate to deal with... most window units dont have a proper drain pan.. you'll have a double-shaft motor...
I suppose it's a bit silly to say that I was planning on reconfiguring the window unit. As I think about it further, the only things I'd end up using from the unit are the condenser and evaporator coils. Maybe the front end ductwork. I have a well suited DC PWM motor controller that could be used with some radiator fans I can pull off of an Outback. Based on the current design of the window unit, can I assume that the condenser fan should always be running at the same speed as the evaporator fan?

The other option I've been thinking about is ripping the A/C system out of a car, reassembling it into my preferred configuration and drive it with an electric motor. I've read that some modern car A/C systems use a TxV. I'm not sure I'd be able to pull the A/C from a modern car, though. But then again... Would the rental car company notice it missing?
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Old 05-31-2016, 09:53 AM   #19
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a repurposed car A/C isnt a bad way to go... also you very well may be able to snag a condenser and / or an evaporator from a member here ..

some of the people buiy busses with A/C but most all remove it as they want electric / RV A/C and not engine driven... some busses have 2 small evaporators mounted and would work good...

a window A/Ccondenser and an electric radiator fan is a great way to go and more compact than a car condenser...

-Christopher
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