Air Con and Power Steering

Technical discussion on converting internal combustion to electric
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Topgunsl
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Air Con and Power Steering

Post by Topgunsl » Wed, 03 Sep 2008, 19:28

Hello Everyone

I'm planning to use the existing airconditioner compressor and Power steering pump in an RX7 conversion replacing the ICE drive with separate electric motors to drive each system.

Has anyone any info on the typical power/torque demands for these systems in medium sized cars.   I'm assuming that the optimum speed of the pumps will be around 1,500 rpm.

Details of any similar conversions would also be great.

Cheers

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DVR
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Air Con and Power Steering

Post by DVR » Thu, 04 Sep 2008, 00:02

Hi Topgunsi!!
I've asked this same question on the DIY-EV forum.
To my question "Has anyone seen any hard evidence as to what is the smallest amount of power required to run a P/S pump and a A/C? I know that the MR2 P/S pump can pull 60 amp when under load what does that equate to as far as HP?"

I was told

"Some guy in the forum (sorry, don't remember who) said it took about 400 Watt to run the AC in his car. 60 Amps multiplied with 12 Volt (that's the right Voltage?) equals 720 Watt. One horse power is 735-736 Watt so that's a pony for the AC versus a galloper for the PS."

I don't know for sure if this is correct or not but 400W sounds a bit low. I do know that most people doing this use a 1.5 - 2 hp motor to run both systems . I've been considering using a DC treadmill motor for this myself.


So long and thanks for all the fish.

rhills
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Air Con and Power Steering

Post by rhills » Thu, 04 Sep 2008, 00:19

Hi guys,

I know little about refrigeration, but on my yacht I have an extremely efficient fridge. It uses a 12V Danfoss compressor and a tiny condenser. When running, it pulls a maximum of 4A. As my fridge has very thick foam insulation, I easily run this fridge day-in-day-out off a couple of 18W solar panels.

A refrigeration mechanic may correct me, but I'd have thought there wasn't a huge difference between aircon and refrigerator compressors so maybe one of these would be the way to go. You would probably need someone with aircon skills to help select the right compressor of course, but maybe its worth investigating.

If I buy a Danfoss compressor and controller together, do I get a discount Image ?
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woody
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Air Con and Power Steering

Post by woody » Thu, 04 Sep 2008, 05:11

Unless you're converting a Peel trident, I'm betting your car EV will be larger than a fridge, be less insulated, and soak up a fair few kW from our nearest star, and therefore need a few more neddies.

Your A/C is run pretty continuously when it's run, so you shouldn't undersize that motor.

The P/S is highest demand when parking and bugger all when you're going straight, so you can probably get away with a smaller motor which can only handle 800W for a minute or so.
Planned EV: '63 Cortina using AC and LiFePO4 Battery Pack

antiscab
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Air Con and Power Steering

Post by antiscab » Thu, 04 Sep 2008, 05:20

the AC in a car needs to be so powerfull for several reasons:
1) the starting temperature is almost always fairly high
2) cars have almost useless levels on insulation (think heat gain of 4kw+)
3) we all expect them to be cool within minutes, or well get to our destination before it cools down.
4) we normally dont care about efficiency (whats 2hp in 100?)

Matt
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antiscab
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Air Con and Power Steering

Post by antiscab » Thu, 04 Sep 2008, 05:23

not sure this counts as a data point,
but i will be using a 2kw 3-phase induction motor driven compressor for mine, or there abouts. (for 12kw of heat loss) Image

Matt
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2017 Renault zoe - 25'000km
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Topgunsl
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Air Con and Power Steering

Post by Topgunsl » Thu, 04 Sep 2008, 23:44

Thanks everyone. Food for thought!

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Air Con and Power Steering

Post by bga » Fri, 05 Sep 2008, 19:41

I have seen a project where they waere using a compressor out of a domestic inverter unit or similar. I think that the idea was to have only a single, easier to mount component for the compressor/motor. Involves a variable speed drive with suitable controller? Probably mechanically simpler, but technically more complex than the conventional motor approach.

I have wondered if power steering can be controlled by only running the pump when the speed is low and the steering wheel is significantly off straight, a timer maintains the steering assist pump for a time, or until the speed increases. The idea is that it will start then needed in a parking lot, but won't start when at a red light.

Cheers
Bruce Armstrong

Topgunsl
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Air Con and Power Steering

Post by Topgunsl » Fri, 05 Sep 2008, 21:39

From the reading that I have done the 2kW/2HP figure for the aircon seems to be about par for the course for the reasons outlined in the replies, albeit that it is a big demand on the batteries.   

The only scope to redude it would be to reduce the volume to be cooled (eg. closing off the back area of a hatch back., improving the thermal insulation of the metal areas and opting more for a cool breeze than a 23 dgree C passenger compartment.

I have also been working of an 800W peak demand for a PS motor at start up and something much lower for the average demand. I am toying with the idea of turning the pump off when the vehicle is not in motion.

Cheers

Steve

rhills
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Air Con and Power Steering

Post by rhills » Fri, 05 Sep 2008, 21:58

Hi Steve,

2kW, wow! If it were me, I'd be trying to find out the actual output from an auto A/C compressor and seeing if there was a 12V one that produced the same output. Alternatively, heat pump technology is touted as being very efficient, maybe there's an option there?

Interestingly, this Wikipedia page on air conditioning suggests that car A/C units consume around 4kW of a car's engine power.

Cheers,
Rob Hills
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Topgunsl
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Air Con and Power Steering

Post by Topgunsl » Fri, 05 Sep 2008, 22:21

Thanks Rob. Yes 3 to 4 kW does not surprise me if you want the full passenger compartment to be at 23 degress.

Cheers Steve

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Air Con and Power Steering

Post by a4x4kiwi » Fri, 05 Sep 2008, 22:53

Hi Guys,

Here is what I would do if I were doing aircon only. (note I am doing a 600v conversion)

1. buy a 2kw 3 phase induction motor (415v)
http://shop.automationdirect.com.au/cac ... l?cache=no

2. buy a suitable VFD like (415v) http://shop.automationdirect.com.au/cac ... l?cache=no or http://shop.automationdirect.com.au/cac ... l?cache=no

3. Set up a reversing valve from an old reverse cycle ac unit. (with the assistance of an AC engineer for the design) This will allow heating and cooling.

4. The amount of heating and cooling could be regulated by the speed of the motor.

If you throw the PS into the mix, you would probably need to run the AC pump as constant speed making it difficult to regulate the amount of heating and cooling.

The PS could be run from a separate VFD and motor (adding complexity)but you could set up the VFD to adjust the PS pump speed inversely proportional to vehicle speed. Perhaps even turn off the pump at 0 speed.

Mal

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a4x4kiwi
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Air Con and Power Steering

Post by a4x4kiwi » Fri, 05 Sep 2008, 23:01

I should add that if I were doing a 144V a conversion, I would use equivalent parts from the USA that are rated at 110v.
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antiscab
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Air Con and Power Steering

Post by antiscab » Sat, 06 Sep 2008, 04:08

yup, id have to agree.
2kw vfds are really cheap, so are the motors, probably even cheaper to buy than a DC unit.

Mattt
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2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
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