There was a mention on the 32 Sedan Delivery thread about using A/C for electric cars on flathead powered cars, to reduce the power draw apparently. I would imagine expensive. Anybody have any knowledge of this application? No response on that thread, and searches only turned up individual units for personal or pet use. Not hard core trad, obviously, but those of us in the hot and humid South with flattie powered rides might be interested. Or is it just the newest have to have trick piece?
First of all, consider that there is a certain amount of energy required to remove heat from the air. That energy will be required no matter what form of air conditioning system is required, assuming the efficiency of them are all equal. You will require a much beefier generator/alternator in order to provide the power for the electric A/C system, and likely a much larger battery to run the system during periods of idling when the charging system is not quite providing the power needed to run the system. What is providing the energy to spin that generator/alternator? The same engine that would be spinning an A/C compressor. I'd suspect that an electrical system would actually be less efficient, all things considered. Here are some specs for a 12-volt R134 A/C compressor. Check out the current draw. Speed 1 Low Draw @ 12.0V 40A 2000RPM 0.92KW/hr or 3150BTU/hr Speed 2 Medium Draw @ 12.0V 60A 3000RPM 1.38KW/hr or 4700BTU/hr Speed 3 High Draw @ 12.0V 96A 4500RPM 2.15KW/hr or 7300BTU/hr
I did a little research on this a few years ago, when I wanted to add A/C to a vintage Capri that would have had a big, bulky style OEM Ford unit. I didn't want that, so after some searching around on the web I found a wide variety of electrically driven compressors that fit the bill. Evidently, they are used on boats, RVs, etc. where the location is either away from an engine powered compressor or where compressors can't be used on the existing power plants. They don't draw that much, either. Google around for them. At around 800 bucks, the price is reasonable, considering you didn't have to rig all those mounts, buy new pulleys, etc. to put a standard compressor on your engine. Gary
Vintage Air has some thoughts on the concept, and while there is possibly some bias towards their product, have a look at the power requirements. https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=30&ved=2ahUKEwjju6uq5vvlAhWOr54KHRgSA2QQFjAdegQIBhAB&url=https://www.vintageair.com/tech-topic-is-an-electric-compressor-a-good-option-for-my-hot-rod/&usg=AOvVaw07Anj2lSgwGXhWpKogN5-D
I was on the phone with Vintage Air last week, he said they are close to offering electric compressors themselves. I am mounting a 505 Sanden (same dimensions as a GM alt) on a 330 Hemi (not an easy feet) and he said it wont be too much longer before they offer an electric "mount anywhere" compressor. It would be nice and not foul up the engine bay. I would imagine an idle cutout and one of those 150 amp at an idle alternators would be in store.
Agree, there is no free lunch. It takes a given amount of energy, whether from the crankshaft or the alternator. I can see where the ability to hide the electric compressor is potentially advantageous. But you still need a given amount of energy, it's physics. Sent from my SM-J337V using The H.A.M.B. mobile app
Alternators have about 55% conversion efficiency. DC motors are about 75% efficient. An AC compressor takes about 5 hp to turn. Running it on an electric motor powered by the alternator powered by the engine takes 12 hp at the engine. Certainly not reducing power draw.
I wonder if that number is universal, or only for specific compressors? The specs that Ebb listed above, show about 3 HP.
Thanks for the responses! The HAMB rules, as usual. All were very enlightening. If an everyday Sanden, etc., only draws 3-5 HP, it will be hard to notice I imagine. My inquiry was first based on engine esthetics, and second on costs. As suspected, extremely high costs from a scratch install. Thanks for all your advice.
Electric driven compressors are usually smaller than belt driven. 2 or 3hp. Modern belt driven rotary are around 5. A big old York is more like 7. A bigger compressor will move more BTU's, so that may be important depending on the size of car, window area, and climate it's in.
Comments about typical belt driven AC compressor requirements are correct. Typically around 5 Hp plus minus. It all depends on the capacity you need. We once designed a roof mounted DC powered AC system for the Canadian military. (belt driven GM variable displacement compressor). We told them their stock alternator had to be replaced for a larger one. They didn't listen, and it wasn't long before we were told vehicles were catching on fire. You see, as supply voltage drops, DC motors compensate by drawing more amps. It is a downward spiral. Amps soon exceeded rating for the wire, and because there was no fuse, the wires melted causing fires. They finally did upgrade the alternator, but only after about 5 vehicles caught fire.
Electric cars are showing up in the wrecking yards. you could probably fine one in a U Pull It cheap enough. I have not looked into them but I got an idea hat they have a pretty big AMP draw so it would no doubt require more than your standard genny to feed it.
Another method of cooling does not use refrigerant or a compressor at all. I used to use small peltier junction coolers at a previous job. They do cool, but also draw several amps. Never considered them for automotive use, and technology has got to be improved the last time I used them. Just a thought Sent from my LM-V405 using The H.A.M.B. mobile app
Typical automotive AC Systems are designed for between 20,000 - 30,000 Btu/hr. For smaller 2 passenger interiors I'm guessing you could do with 10,000 - 15,000 Btu/hr assuming you have some insulation between engine and firewall, but it really depends on what type of climate you live in.
I am using the newest Sanden compressor on my 250 ci inline six, I hardly notice its on even at idle. I do speed up the idle a 100 rpm in the summer just so the engine fan runs a little quicker. I actually get better fuel mileage now with the A/C on since the windows are up, so the horse power loss must not be much.
I am not sure that either would be considered traditional. Unless of course you find problem solving to be traditional. LOL It seems to me that if your motor does not have enough zot to pull an AC compressor that you have a real dilemma on your hands. Your option is build more motor or open the windows.
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