Electric AC compressor

[Tins]

Does anyone have any experience with these? I’m toying with the idea for my OKA.

[BradC]

I saw one go into a Torana recently. They're pretty thirsty, but then it's often easier to put in a bigger alternator than it is to find space for another mount and belt.

[Tins]

OKA has air. Yeah, right. Hard to believe they come from your neck of the woods. And were used on mine sites. I don’t know if the original one actually works because the whole thing is nightmarish and I would like to start from scratch. The alternator upgrade would be easy, but if they’re thirsty then my idea of running it engine off probably wouldn’t fly.

[prelude]

Yes I have. Not in an OKA though :)

I believe I once did a write-up on the setup in my Range Rover P38 on here but I can't find it so I'll jot down my experiences here:



power hungry indeed
not as efficient as a split unit for a house
can work with engine off


About power, the most seen/used AC compressor is about 18cc and pulls around 97A according to spec, they can even go over. Add to that the rest of the car that needs to run and you are talking serious power. My standard 120A alternator for my range was certainly not up to the task and an aftermarket 200A unit had overheating issues when loading up to 180A or so. It is not easy to find after market uprated alternators that will do their max rating at 100% duty cycle! I ended up using two hitachi alternators from a VW phaeton which do 190A each and are water cooled so I could plumb them into the cooling system of the car and keep things stable with ample overhead. (I had the space for the original AC compressor for the second alternator)

Overall, if you look at the specs for the 18cc unit mentioned above it will have a COP of around 2.7 that is a far cry from a decent mini-split unit for a house which can go up to 5. Thing is of course that I used the existing HEVAC stuff already present in the car and simply rerouted the piping and plumbed in the electric unit. But still, even with the best conditions (ie sized evaporator and condenser) you would still not get the best efficiency possible. This might not be a problem as long as the engine is running but my third point:

The beauty of an electric setup is that it can work whilst the engine is NOT running, as long as you have a beefy battery bank. For me that was the reason to replace the belt driven AC compressor to begin with :)

Regarding cooling capacity; I found the unit on the highest setting to be quite sufficient to cool my range down to acceptable levels in 35c heat. I have not been able to try it on warmer days. The unit is capable of 3.17Kw of cooling according to the spec sheet. I reckon that should be enough at least to keep you cool in all but the most challenging conditions.

The beauty of an electric AC compressor is that you can place it virtually anywhere you have the space for it. It cools itself with the AC gas so it can operate even in hot areas like an engine bay (mine sits next to a hot V8). An added benefit is that the condenser can also live anywhere you like, on the roof, underneath the car, etc. It does not have to sit in front of the radiator where it is generally placed in most vehicles that come with AC. The compressor itself is not really that loud, I should think the OKA will be louder anyway. The added fan(s) for the condenser however can add quite a bit of noise since you need ample airflow to cool the thing down properly.

Anyway, should you want to know more details just let me know, I worked on it for months and experimented quite a lot with it as well (including blowing one up...)

Cheers,
-P

[BradC]

Overall, if you look at the specs for the 18cc unit mentioned above it will have a COP of around 2.7 that is a far cry from a decent mini-split unit for a house which can go up to 5.

That is almost entirely down to the relative lack of condenser in a vehicle. Those mini-split condensers have massive areas relative to anything you can fit into a car. I significantly improved the AC in my old Volvo by shoehorning in the largest and thickest condenser I could fit. The lower the head pressure the more refrigerant the compressor can move, so a real increase in capacity.

With an electric compressor, lower head pressures will directly translate to lower current draw.

[Tins]

I should think the OKA will be louder anyway.

You got that right.

The OKA is also a big volume to cool. I might rethink. I don't really need to cool the rear section, as I can open the windows and the roof pops up. But the cab, with the noisy old Perky between the seats, that's another matter.

[RANDLOVER]

Perhaps you could but in a door or a curtain and temporarily shut off any rear vents if any.

[prelude]

@bradc yes, that does help. Mind you though the range rover does have a significant slab of condenser but it is indeed not very thick. Removing heat (and thus recuding pressure) is the main goal and in a hot and crowded engine bay you need quite the fan to push enough air. I have replaced the stock vc fan with the largest thermofan on the market (it is actually an OEM version of the one in the ineos grenadier). it's a massive almost 50cm across unit that pulls well over 80Amps at full tilt (brushless DC as well).

@tins The volume is not really the problem I have found. Mind you, older range rovers, like mine, are basically glass houses on wheels due to the enormous amount of glass compared to other vehicles. the 3-ish Kw unit managed just fine with 35c and thus full sun through all the windows. I recorded the measurements somewhere if I find them I'll let you know. If the OKA is less glass or you can shade the rear and roof windows and has at least a minimal amount if insulation there should be no problem at all, whatsoever.

As mentioned above about the thermofan: those suckers really pull some power. Combined power draw for the AC components alone I estimated at around 180Amps for my application. Depending on where you place the condenser and indeed what size it is, you can probably get away with two smaller thermofans. There are also larger units of course and 24v versions, not sure the OKA is 12v? In any case, if you have to fit a second alternator you could consider a 24v unit just for the AC...

Cheers,
-P

[Tins]

@bradc yes, that does help. Mind you though the range rover does have a significant slab of condenser but it is indeed not very thick. Removing heat (and thus recuding pressure) is the main goal and in a hot and crowded engine bay you need quite the fan to push enough air. I have replaced the stock vc fan with the largest thermofan on the market (it is actually an OEM version of the one in the ineos grenadier). it's a massive almost 50cm across unit that pulls well over 80Amps at full tilt (brushless DC as well).

@tins The volume is not really the problem I have found. Mind you, older range rovers, like mine, are basically glass houses on wheels due to the enormous amount of glass compared to other vehicles. the 3-ish Kw unit managed just fine with 35c and thus full sun through all the windows. I recorded the measurements somewhere if I find them I'll let you know. If the OKA is less glass or you can shade the rear and roof windows and has at least a minimal amount if insulation there should be no problem at all, whatsoever.

As mentioned above about the thermofan: those suckers really pull some power. Combined power draw for the AC components alone I estimated at around 180Amps for my application. Depending on where you place the condenser and indeed what size it is, you can probably get away with two smaller thermofans. There are also larger units of course and 24v versions, not sure the OKA is 12v? In any case, if you have to fit a second alternator you could consider a 24v unit just for the AC...

Cheers,
-P
OKA has lots of windows. As a Disco owner I am familiar with the glass houses ting. OKA has a large glass area in the front. But it’s hard to see how anything could be less effective than what is there now.

[scarry]

With an electric compressor, lower head pressures will directly translate to lower current draw.

Lower head pressure will to some degree,but it is higher back pressure that pushes the amps up very significantly.

The higher the back pressure,the more capacity and work the compressor has to do.

Which is why we use MOP TX valves,and CPR valves on low temperature refrigeration systems,and a few other applications,such as large DX AC plants.


We actually came across a freezer room today,at a school,4 yrs old,a faulty compressor,they wanted another opinion.It is on its third compressor.[bigsad]
No MOP TX or CPR valve,are the main issues,there are others.
I wish fan mechanics(AC techs),would stick to AC......

[RANDLOVER]

It's amazing how much current just a thermo fan can draw, I had one of those battery monitors connected to my brother's car on the weekend and it was showing green with the alternator running but when the second stage fan kicked in it briefly changed to yellow!

[prelude]

@tins then I think that indeed if you can optimize the system without being limited to the constraints of the engine bay you might win some here and there. This does remind me of another topic here about the TD5 efficiency and other topics about after market AC/s in defenders and such. It's not just the condenser that has to do it's job (and the compressor having to make sufficient RPM when the engine is at idle) but it also very important to have a decent evaporator and blower(s) inside the car.

As mentioned before; I basically ripped the original belt driven compressor and VC fan out of my range rover, but kept all the rest of the system intact @scarry so yes I have a TXV just before the evaporator inside the range rover which at that point already was dual zone so it has two blowers, one for each side.

In short, my entire system was already very capable of keeping the car cool on even the hottest days, with the exception of slow traffic where the VC fan would not pull enough air and the two thermofans would have to help and even then I got to points where the over pressure switch would simply kill the AC for a while. With the large thermofan I do not expect that to happen again (and the much smaller electric compressor can probably never get to that point...). This in my opinion goes to show/prove that with a decently sized condenser, evaporator etc. even a smallish sized DC compressor can provide ample cooling, although it will never be as much as the belt driven one. If you put the smaller compressor on a less properly sized system, I doubt you will get great results.

@randlover yes, and do not forget the blower(s) that keep the interior cool/warm. My range has two and both of them are rated (well fused) up to 40A. I doubt I will ever see them do that under any circumstance but let's put all the theoretical maximums together: 100A compressor, 80A thermo fan, 80A blowers... and then the rest of the car to work. I had a victron shunt in my car for a while that measured -everything- and just the car running pulled 30A. So yeah ;)

Cheers.
-P

[Tins]

Lower head pressure will to some degree,but it is higher back pressure that pushes the amps up very significantly.

The higher the back pressure,the more capacity and work the compressor has to do.

Which is why we use MOP TX valves,and CPR valves on low temperature refrigeration systems,and a few other applications,such as large DX AC plants.


We actually came across a freezer room today,at a school,4 yrs old,a faulty compressor,they wanted another opinion.It is on its third compressor.[bigsad]
No MOP TX or CPR valve,are the main issues,there are others.
I wish fan mechanics(AC techs),would stick to AC......
Hey Paul, when you get time how about a car A/C 101 for us muppets? My early learning did not include it ( Army didn’t use it below the rank of General) and we always used to farm it out in my post military life. I would like to have a basic understanding. YouTube may be the younger generation’s centre of learning, but you never know who the teacher is.