We occasionally get inquiries regarding the 12 volt Masterflux compressors for vehicle cabin cooling. Particularly we get these inquiries from automotive enthusiasts trying to use it to remove the load of a traditional AC compressor in hotrod or performance vehicle projects.
Although we sell electric compressors that run on 12V DC, they are intended for use in small cabinet cooling, refrigeration, dehumidification, and other specialty tasks. The reasons are related to power consumption for air conditioning and power conversion efficiency.
The largest Masterflux SIERRA-06 series compressor solution package we offer through REVOLT Electric Vehicle Components provides about 1.5 tons of cooling running at full power under optimal conditions and it draws up to two kW of power to do so. Most modern automotive air conditioning systems range somewhere around two-to-three tons for a small car, and sometimes greater than six tons for larger SUVs. This places even the highest performing Masterflux units at something of a performance disadvantage.
In general this 1.5 ton cooling capability is adequate for our primary market in electric vehicles due to the smaller total heat load, that is, countering only the sun’s radiation, but not factoring in a hot engine and exhaust system. Even so, the DC cooling system packages we offer are best used with as much “help” as they can get in our most sun intensive areas — window film, light-colored paint and interiors, window shades, and so forth.
However, below 48V DC, the limitation of the compressor design sets in. The terminals physically cannot handle more than about 50-55A. As a result, the lower-voltage models must run with reduced performance. At 12V, the SIERRA-02 is capable of a little better than a fourth of the performance of the high-voltage models, and still draws a relatively large 50A current to do so.
Even if it were possible to get the same performance as our high-voltage units at 12V, it would need about 200A to do so, which would require a very large alternator and massive copper wiring. Ultimately it would run at a greater cost of horsepower from the engine, due to losses in the alternator itself, and in the motor and controller. A standard engine-driven automotive compressor skips these mechanical-to-electrical and electrical-to-mechanical conversions, making it far more efficient and lighter overall.
We would love to be able to sell a reasonably-priced vehicle cooling solution that operates at 12V DC and we will continue to evaluate options as they become available. In the meantime, we do support the Masterflux units below 48 volts for specialized applications and encourage you to contact us if you feel your application is within their capabilities.