AUTO AIR COMPRESSOR EFFICIENCY QUESTION 2

[Cherokeescot]

I wanted an opportunity to respond to the "most efficient auto ac compressor" but it was closed already. Here is some actual user experience in this issue. Restoring a 1977 VW van with factory ac. The original York piston compressor took 13 horsepower and man on a VW van, that is a heck of power draw! I put in all new original factory components and had a Sanden ROTARY built to fit the VW van. Horsepower draw was only four horsepower which is a phenomenal difference. I would have to go with Sanden rotaries over anything else I know of. FYI.

 

[tbuelna]

If you want to achieve max efficiency with your automotive A/C compressor, get one from a hybrid vehicle that is electrically driven. Even an engine driven A/C compressor that sucks up 4hp from an engine producing about 25hp during highway driving results in a fairly large loss.

 

[Cherokeescot]

Interesting idea. Do you know the current draw on one of these compressors?

 

[DanEE]

Doesn't answer the question on what the power draw is, but could easily be measured... According to this article, some of the earlier vintage Prius AC compressors ran off of the 3 phase AC from the inverter, but later vintages use 201VDC from the hybrid battery..

http://www.autoserviceprofessional.com/article/93187/Hybrid-vehicle-air-conditioning-service?Page=3

 

[DanEE]

In re-reading the above article there are ambiguities between the text and the image regarding the location of the inverter to produce the AC voltage (used in the Prius anyway) to run the compressor..

So I checked the factory service documentation (for the 2006 era Prius generation II vehicle). That vehicle has a 3 phase VFD (variable frequency drive) inverter (that is located in the main vehicle inverter assembly) putting out 201VAC 3 phase to drive the AC PM (permanent magnet) motor compressor. That compressor is a scroll compressor (which many vehicles, heat pumps, etc now use as most efficient technology AC compressor).

Given that the unit is driven by a VFD, the speed which the compressor motors runs is based on the cooling demand load (as do modern heat pumps that also now employ variable speed compressors) to attain high efficiency.. This is certainly an efficiency improvement over engine driven compressors running at some ratio of engine rpm regardless of cooling load requirement.

There might be some of the other hybrid vehicles that have AC compressors more easily adapted to another vehicle e.g. the inverter being separate from the main drive inverter. Although I would expect all of these to be AC brushless motor designs (and therefore AC multiphase powered) and, operating at the higher hybrid drive battery voltage (for higher motor electromechanical energy conversion efficiency).

BTW VFD electric motor drive technology along with PM (permanent magnet) AC motors (replacing older AC multiphase induction motors) have made significant inroads into factory/production type environments where production processes need variable speed control and improved electro-mechanical energy conversion efficiency.

 

[Cherokeescot]

Thank you for putting in so much effort to come up with an answer. I have several personal apps for this kind of a compressor, two are in boats, one a sailboat and the other a cabin cruiser with no a/c. This gives me a way forward without having to try a lot of different ideas. Im still not convinced the high voltage use on the hybrids and electric vehicles is the best (safest) way to go but it seems Ive lost this argument with the manufacturers.
The great risk is not only in an accident, especially in rainy conditions, but also the personnel who come to rescue those involved in the accident. Its really dangerous.
I have owned several electric cars. One was the GM and the other was the 'wedge' which was built in South Florida. I also experimented with both hybrid and electric cars in the sixties and seventies along with people like the old, original MOTHER EARTH NEWS folks. I know nothing about these Madison Avenue types who have bought the ppublication.
Thanks again for your information.

 

[DanEE]

You're welcome! I find this area rather fascinating especially how it is not just in the automotive area that we are seeing these new technologies..

That's also true in the electrical safety aspect of these systems also... There is no question that carelessness or lack of training around any form of stored energy can be dangerous.. People have been killed by car suspension springs and tire/rim failures..

There are parallels in the electrical design safety of the Toyota Hybrid Synergy design (the only one I've done extensive study of) and the practices used in high power UPS systems some of which have battery voltages summing up to 400 volts DC and above. DC systems (up to a point) are somewhat safer than AC systems in that the AC shock is more prone to stopping a normal heart beat. That aside, the Hybrid DC voltages are typically isolated from ground, as done in high power UPS systems. The Toyota battery safety disconnect plug in the battery is centrally located in the battery string so when pulled for example on a 201 DC battery stack, you are left with two 100.5 VDC battery strings still fully isolated from ground, and further isolated at the battery case enclosure by the main relays that open each output leg of the battery, Very similar to the same technique typically designed in the high voltage strings a UPS system.

To improve efficiency we are seeing other sources of parasitic energy loss (hydraulic power steering pumps, engine water cooling pumps for example) being replaced by VFD/PM drive technologies.

 

[Cherokeescot]

Now onto the vast subject of energy storage and batteries, I have some concern for Tesla's huge investment in battery production capabilities. I have never understood that. With enough of a hill to climb with a new automobile, for my money I think I would have looked for someone to supply the batteries to my specs. The problem, even short term, that I can foresee is the rapid technology advances in this field. Can they change gears in midstream if someone happens to come up with a better 'mouse trap'?

 

[RossABQ]

What Tesla can see very clearly is many millions is State and local tax subsidies (likely some federal money too) for making their own batteries. That plus eliminating the ~20% markup on actual manufacturing costs from a supplier gives them a big competitive advantage.

 

[Cherokeescot]

Ross, interesting perspective. I built my first solar energy system in 1967 and have been around long enough to see lots of things come and go. Many who relied on those subsidies you mention didnt make it. They are changeable as the weather and subject to political whims. Im not sure how much credibility I would personally put in such things. You are most likely correct but I cant help but see some unpredictable obsolescence factors involved in that industry.

 

[DanEE]

You are most likely correct but I cant help but see some unpredictable obsolescence factors involved in that industry.

I think that's a characteristic of any new emerging technological era..

It was true in the early days of automobile development, represented by the sheer quantity of early automakers that didn't make it through the consolidation phase...

True in the development of a national power grid.. the so called "War of the Currents" Edison promoting a DC system, Tesla backed to Westingshouse for an AC grid.

Was true in the early days of radio, with tremendous wars over patents, turf, etc.. Marconi, Deforest, Armstrong, Westinghouse and others..

And true in the early days of the personal computer, reflected by numerous companies we can name, but are no longer in the personal computer business as they became commodity products.

The Players seem to fall into these categories..
1. Companies that had the right idea, but too soon for the time and lack of suitable technology to implement.
2. Companies that invested tremendous R&D to advance the idea, but failed due to technological or other major problems, yet their technology helped others advance.
3. Companies that did nothing, except pontificate about how the idea to too far fetched, uncertain, and with doubt (so call FUD factor) only to later have their obsolete products over taken by #4.
4. Companies that had the vision and the guts to go for it, advanced the technology though their own R&D and spearheading others in the development of technology, and marketed successful products that did in #3.

Interesting wonderful times we live in to see this....

 

[gruntguru]

My understanding is that Tesla's plans for mass-market EV's cannot be supplied by existing battery manufacturing capacity.

Engineering is the art of creating things you need, from things you can get.

 

[JayMaechtlen]

I couldn't find the other thread you mentioned.
Didn't some of the axial piston A/C compressors have a variable stroke/displacement feature?
That would seem to be simpler and probably more efficient than making electricity, storing it, and using it to spin a variable speed drive/electric motor/fixed displacement compressor system.


Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[gruntguru]

This can be done without 200 VDC. 14V is probably a bit low, needing 100A or more to drive the inverter. Whatever happened to 42V auto electrics? I can remember when it was going to be the next big thing. Would have been ideal for variable speed electric ancillaries including AC.

Engineering is the art of creating things you need, from things you can get.

 

[GregLocock]

@Jay, yes the Delco V5 and v7 compressors were variable angle swashplate axial piston pumps. From memory ca 1988 the swash angle was adjusted by, or in response to, the high pressure line.

Sanden's scroll compressors also have some sort of variable timing, but I've never taken one apart.

Cheers

Greg Locock


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