# Air Conditioning & alternator



## Fatboynotslim (Oct 25, 2011)

I am a newby and I have a simple question. I am converting a Saturn SL1. I am usinga double *Advanced DC FB1*-4001A double shaft. Why can't I run the AC and alternator of the back end of the motor and eliminate all this DC to DC convertor stuff and no Air con? I am planning on a 144V system. 
Would it run down my batteries to much?


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## Tesseract (Sep 27, 2008)

Fatboynotslim said:


> ... I am usinga double *Advanced DC FB1*-4001A double shaft. Why can't I run the AC and alternator of the back end of the motor and eliminate all this DC to DC convertor stuff and no Air con?...


No reason why you can't if you have a motor with a tailshaft. It requires a bit more fabrication work on your part, and it helps to idle the motor - especially if you run the power steering pump, too - but this is a reasonable solution.


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## piotrsko (Dec 9, 2007)

And in my experience it uses about 100 amps (16 hp) to power those accessories at 120Vdc. You have to decide if it is worth it. I no longer idle.


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## Tesseract (Sep 27, 2008)

piotrsko said:


> And in my experience it uses about 100 amps (16 hp) to power those accessories at 120Vdc. You have to decide if it is worth it. I no longer idle.


That's unusually steep... The worst EV I've seen yet as far as idle draw goes was the Volvo V70 station wagon that Seb/Rebirth Auto did about a year ago. The A/C in that beast took 8hp all by itself, but everything else amounted to about another 3hp - so 11hp worst case total on a 4800# station wagon that was packed to the roof with LFP (literally).

Smaller vehicles and/or those without dual-zone AC seem to use about 1.5hp for the alternator and another 1.5-2hp for the A/C compressor. Power steering is much more variable, but also much more intermittent - I have no good figures for that. Still, all in all we're talking about a typical load of 3-5hp. Sure that's a big chunk of highway cruising power, and you have to decide for yourself if that's a price worth paying - can't help you there - but regardless of that decision it is, indeed, possible to use the original alternator rather than a DC/DC converter.


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## piotrsko (Dec 9, 2007)

with everything on as far as electrical, the alternator draws 8 hp by it self, the Ps pump will draw 5 hp at lock, and the tranny seems to eat 3hp; so I see 16 hp consumed. I dunno, it is your logger saying 100 amps, the amp gage I have is uncalibrated.


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## Tesseract (Sep 27, 2008)

piotrsko said:


> ...I dunno, it is your logger saying 100 amps, the amp gage I have is uncalibrated.


Just to make sure, Logger reports *motor* amps and you have to multiply that by percent duty cycle (which it also reports) to get battery amps.


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## DJBecker (Nov 3, 2010)

piotrsko said:


> with everything on as far as electrical, the alternator draws 8 hp by it self, the Ps pump will draw 5 hp at lock, and the tranny seems to eat 3hp; so I see 16 hp consumed. I dunno, it is your logger saying 100 amps, the amp gage I have is uncalibrated.


It would surprise me if a manual transmission has a 3HP drag in neutral at "idle" speeds. It should be substantially less. If it is that high, check that you are using a synthetic transmission oil. The transmission will be getting less heat from the motor than an ICE. It will take much longer to warm up and have a lower operating temperature.

An automotive alternator is typically rated for 60 to 105 amps maximum output, and they'll only output their maximum when cool. They are fairly efficient, so the load shouldn't be substantially higher than their 1KW-2KW maximum output.


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## Ziggythewiz (May 16, 2010)

Maybe someone could do (has done?) the experiment, but I'm pretty sure a DC-DC would be far more efficient than converting electric to kinetic, and back to electric.


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## ElectriCar (Jun 15, 2008)

I have a Scangauge on my diesel truck. With the AC switched on the HP reading increases about 1.5HP. I would think my S10 compressor would be even less but it's a Chevy so I'd not be surprised if it were worse! I'm thinking of 2HP minimum, maybe 3 for insurance. Oh and driving it off a separate motor since I have no clutch and don't want to idle.


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