Building a portable AC for my car

[OmCheeto]

The sun decided to burst out early today.
Currently collecting preliminary data.

 

[sophiecentaur]

There is another significant factor which I don't think has been dealt with here. That is the flow of air through the car. It's the main factor in Central Heating calculations and it is very important here. If you want the car not to be stuffy with recirculation air, you have to cool down all the warm fresh air coming in.
But we can really ignore the basics of a particular invention. The bottom line is to compare the heat transferred with a normal car AC with the 'negative heat' available in a few kg of ice. A car AC (Wiki figure) uses around 3kW of mechanical energy from the engine. A 1kW source of heat will melt about 10kg of ice in an hour. If you had 10kg of ice and could actually bring it into good enough thermal contact with the air in the car, you could have an effect almost comparable with a regular AC if you could actually melt it in one hour. That would have to involve some pretty clever heat circulation system which would be based on crushed ice.

 

[jim hardy]

uses around 3kW of mechanical energy from the engine

Just for estimating purposes...

3kw into a machine with EER of 8, same as a low priced room airconditioner, would be 24,000 btu/hr, two tons of refrigeration,
a ton of refrigeration being able to make a ton of ice in a day
which is 83.3 pounds in an hour

3kw making two tons of cooling should be equivalent to melting 167 pounds of ice per hour ?

check my arithmetic ?

 

[Planobilly]

I would run the wire direct to the battery with a inline fuse and a switch, The lighter is not the most well made device on a car and prone to failure to begin with.

With no engineering calculations at all, I can assure you that air being passed through a cold heat exchange unit blowing on your neck will be cooler than warm ambient conditions...lol

Everything you are talking about doing will work. How well? Who knows. What are the weather conditions where you live. Here in Florida at this time of the year would take a lot of ice to have much effect in this type of arrangement ..lol

Yes, fresh air is good but not a requirement.

If after you try all this and it does not work well enough for you. there are other less complex ways to deal with the issue.

I assume you only want to cool down people. Frozen bottles of water wrapped in cloth work fairly well. I do this some times on my boat which has no AC, and it is hot as hell here in Florida, so I know it works. How well does it work? A lot better than nothing, that is for sure.

Ask an engineer to build you a parking lot and leave him along and when you get back there will more than likely be a twelve story building there...lol Engineers are truly wonderful people, but most of them were asleep during economics class...lol

Have fun and go try your ideas and see how well they work for you.

Cheers,

Bily

 

[sophiecentaur]

there are other less complex ways to deal with the issue.

That is right without a doubt. The requirement was not stated at the beginning and any detectable change in the cab could be thought of as a success by the guy doing the project. But I wouldn't say that the possible outcome should be considered as "Air Conditioning as we know it".

check my arithmetic

I would do, if the problem had been stated in SI units. (I finished with Imperial Units, ten years after we did away with our Empire (lol) when I left school in the late 60s and they tend to bring me out in spots.) My calculation that 10kg of ice could produce a mild cooling effect over an hour seems to tie in, near enough with your answer.

 

[sophiecentaur]

The best value of cooling effect from ice would probably involve local cooling of the driver's body with partially insulated ice packs inside the driver's clothing.

 

[OmCheeto]

The sun decided to burst out early today.
Currently collecting preliminary data.

The data does not look good.

Thank god I used duct tape to put everything together.

 

[rbelli1]

two tons of refrigeration,
a ton of refrigeration being able to make a ton of ice in a day
which is 83.3 pounds in an hour

2 tons == 4000 pounds
4000 / 24 is about 167 pounds per hour.

about what I calculated after you correct tons per hour to tons per day in my estimate in post #10

If you put a heat exchanger in a block of ice and another directly on the occupant you should get some relief.

https://www.zoro.com/igloo-full-siz...TY3_FlLUZF_qXiP-SAVCVBoCBR3w_wcB&gclsrc=aw.ds

Fill that solid with ice and somehow melt it in 2 hours and you have the equivalent of a regular car AC unit.

Moving a 300+ pound cooler into your car is left as an exercise for the reader.

BoB

 

[iduhfuse]

Update: Canada Post is going on strike and therefore my rad is being delayed. Son of a gun! It might be a while until you hear from me next but don't worry. There will be pics and all. Also, cig lighter is 15amps. That's easily enough to power my pump 3A + 2, 0.5A fans. Total 4 amp draw lol.

 

[OmCheeto]

Update: Canada Post is going on strike and therefore my rad is being delayed. Son of a gun! It might be a while until you hear from me next but don't worry. There will be pics and all. Also, cig lighter is 15amps. That's easily enough to power my pump 3A + 2, 0.5A fans. Total 4 amp draw lol.

It's been my rule to never to pay more than $20 for equipment for an experiment, unless I've done the maths first.

My electrical power draw yesterday was 24.5 watts. (solar powered, measured with separate volt and amp meters)

one water pump: 0.194 kg/sec
one air pump: 0.0185 kg/sec​

My system thermal power was 67.2 watts (based on the temperature rise of the ice/water bath)

My guess is that the water flow rate was not the problem.

Still only into this problem for about $2.

 

[iduhfuse]

Update: all parts are in! Going to build this thing tonight! Will post pics of building process and final product. Testing will be performed tomorrow. Stay tuned

 

[iduhfuse]

Assembly and soldering went well. Ran out of time to finish cutting the lid properly and have to run out to get longer screws for the fans and rad. Wired it all up in parallel and did a test run. Runs perfect, but haven't tested water pump yet. Will finish tomorrow and post final build!

 

[Planobilly]

This is cool stuff! No pun intended...lol As you were describing all this, the photos you posted are just what I had in envisioned.

I also like to build stuff. Sometimes stuff I build works well and sometimes it end up in the trash..lol

Win, loose, or draw, it is always fun!

Cheers,

Billy

 

[rbelli1]

No pun intended

Seriously?

Win, loose, or draw, it is always fun!

Seriously.

BoB

 

[Planobilly]

LOL

I can't tell you how many times I dreamed of making some sort of "space suit" contraption to keep me cool in the boat and other hot places. Actually that idea comes up a lot about this time of year here in Florida!

Cheers,

Billy

 

[iduhfuse]

Okay it's finished! But I'm having problems
:(((...when I first flicked the switch on the pump ran and the two fans ran beautifully. Later when I adjusted everything switched it on again and one of the fans sort of took a while to turn on? Then I switched it on again later and only one fan came on. Again, now both fans are not operating ...wth?! Now, only the pump runs, I double checked all the wiring and its solid. I have no clue what's going on. Thought maybe the battery was draining so there wasn't enough voltage so I had the engine running for a bit and still both fans not operating. I'm stumped and need your help!

 

[Tom.G]

Methinks the H₂O entered the prime air mover. (At least that's better than the brown stuff entering the air conditioning system.))

 

[iduhfuse]

Methinks the H₂O entered the prime air mover. (At least that's better than the brown stuff entering the air conditioning system.))

You think water shorted the fans? *Cries*

 

[Tom.G]

First-pass guess based on next to zero knowledge. Dry 'em out, they may resuscitate. Or maybe there's just mechanical interference.

 

[jim hardy]

Got a datasheet for those fans ? Any notes in it about mounting plane ? Are they brushed or electronic ?

Fans 7-12V rated at 0.5 Amps

12 V ? Car runs 14, surely they're not that tender.
However - inductance of water pump could be generating a turn-off transient...reverse polarity spike when you flip the switch off
one of those cheap bicolor LED voltage testers would probably show, look for a green flash at turnoff
http://www.walmart.ca/en/ip/auto-voltage-tester/6000119380174try a flywheel diode ?

old jim

 

[iduhfuse]

Got a datasheet for those fans ? Any notes in it about mounting plane ? Are they brushed or electronic ?
12 V ? Car runs 14, surely they're not that tender.
However - inductance of water pump could be generating a turn-off transient...reverse polarity spike when you flip the switch off
one of those cheap bicolor LED voltage testers would probably show, look for a green flash at turnoff
http://www.walmart.ca/en/ip/auto-voltage-tester/6000119380174try a flywheel diode ?

old jim

I checked system running at 12.36 volts (car off) with multimeter. The fans are Corsair SP 120 High performance. Also can you send me a link for a flywheel diode?...i'm seeing diagrams. I have no idea what that looks like lol. OOPS ****Another thing I forgot to mention. I did remove the pump from the circuit and tested each fan individually. They both did not work.

 

[jim hardy]

Also can you send me a link for a flywheel diode?...i'm seeing diagrams. I have no idea what that looks like lol.

most any diode will do
it ought to be rated for as much current as the pump draws
if it's a 1 amp pump get a handful of in4001's they're dirt cheap and everywhere
1n400X series comes in various voltages , last digit is voltage rating in hundreds 1n4001 is 100 volt, 4004 is 400 volt etc but they're only 1 amp
probably these3 amp would be fine,
https://www.amazon.com/dp/B0087YKERK/?tag=pfamazon01-20

lifetime supply for two bucks ?

it goes right across pump motor terminals
end with the stripe to positive

Are the fans polarity sensitive? Do the instructions warn against reverse voltage?
I saw inductive kick from a Harley Davidson generator kill an expensive "Electric Frank" electronic voltage regulator... it's not something all designers think of.

I hope you find something simpler like a loose crimp connection

old jim

 

[Tom.G]

Good catch, Jim!

Diode: 1N4001. They are about 5 cents. Put one directly across the pump; reverse polarity so it doesn't conduct.
If that's the problem, the fans may be toast. So for good measure, the next time around, put a diode in series with with each fan.
EDIT: and a capacitor across each fan, maybe 0.1u to 0.47u.

I see you beat me to it Jim.

 

[rbelli1]

Don't bother with the 1N4001 diodes. Get 1N4007. They are 1000V and usually the same price as the 50V ones. If you ever need the higher voltage then you already have them. Get a bunch. Almost anywhere something just specifies a diode without any more information they will work.

For series diodes you will get better performance with Schottky diodes. It probably doesn't doesn't matter in this application but the lower forward voltage is useful for higher currents and applications where the voltage drop could be problematic. Don't use them for half wave rectification. The reverse leakage current is bad for polarized capacitors. And a bigger capacitor doesn't help. Or at least so I've been told !

BoB

 

[iduhfuse]

Don't bother with the 1N4001 diodes. Get 1N4007. They are 1000V and usually the same price as the 50V ones. If you ever need the higher voltage then you already have them. Get a bunch. Almost anywhere something just specifies a diode without any more information they will work.

For series diodes you will get better performance with Schottky diodes. It probably doesn't doesn't matter in this application but the lower forward voltage is useful for higher currents and applications where the voltage drop could be problematic. Don't use them for half wave rectification. The reverse leakage current is bad for polarized capacitors. And a bigger capacitor doesn't help. Or at least so I've been told !

BoB

Damn, I understood about a 1/4 of that hahaha. I will wait tomorrow until fans are completely dry. Who knows, maybe water did get into them (I'm hoping not) the rad wasn't even condensating yet but oh well. If the fans are shot, there goes $40...any other alternatives to push air through the rad?

 

[jim hardy]

I see you beat me to it Jim.

sorry - heat of the chase

Another trick would be run whole thing through a ten amp bridge
that way if cord to cigarette lighter plug gets wired backwards - no sweat, plus the bridge does the flywheel.

https://www.amazon.com/dp/B01HDZRYFI/?tag=pfamazon01-20

 

[Tom.G]

I just realized that 50V spikes are common in car electrical systems, and I wouldn't be suprised to see an occassional 100V spike. If those fans are the common 12V units sold for computers, they are brushless DC. The IC in them seems to be a Hall detector and commutator all in a 3-pin TO-92 package. Those would definitely need surge suppression/filtering on the power leads. The question is, what would be the most appropriate? Perhaps back-to-back 16V 5W zeners with a low amp fuse on the incoming power? What say, Jim?

@iduhfuse If the fans are dead, don't trash them. A post mortem would be helpful. Specifically, If there is an IC or transistor in them, let us know the part number and other markings on it. That way we can look for a data sheet and find out what their voltage rating is.

 

[jim hardy]

What say, Jim?

Don't forget that inductive kick reverses polarity.
When the switch opens
instead of current being pushed through the pump motor by the battery
the pump motor now tries to suck current through the switch, which of course it can't, and the only place it can get it from is backward out of the fans.
A motor's inductance can make a lot of voltage trying to do that.A flywheel diode let's the motor suck current , harmlessly circulating it around through the diode, with only one diode drop (-0.6V) which won't hurt anything.

https://www.westfloridacomponents.com/blog/what-is-back-emf-and-what-does-it-do/

old jim

 

[Tom.G]

I was trying to say that 50V to 100V spikes, of either polarity, are part of the automotive environment and was looking for some refinement to the idea of back-to-back zeners, perhaps with a bit of source impedance added. The flywheel, or freewheeling, diode at the pump would still be advantageous and is what joggled my memory of the noisy power environment.

 

[iduhfuse]

Not sure if this helps but I may need to mention that I have a 500watt amplifier hooked directly up to the battery for my speakers...