Automotive aircon?

[rosssavage]

Stupid question time: I would like to install some cooling for my boat (Princess 385) for the upcoming summer. Boat aircon is heavy / massive / power hungry and most importantly v.v. expensive. How daft is it to try and modify a car aircon system and use that? I appreciate the output will not cool the whole boat, but may be enough for just the saloon or master cabin (switchable?). I could run the compressor from an engine power take off, or, to be really daft, how about using an old starter motor for when the engine is off...? Can a starter motor be used for long periods or will it over heat? How much current might it draw (I have 440 Ah battery bank...)? Appreciate this is a really silly idea, but I'm at work and bored...

 

[bendyone]

Best buy a free standing uint (B&Q £200) take it apart so it will fit somewhere and run it off an inverter.
Problem with a car type arrangement is getting rid of the heat as you have no radiator.

 

[thechevychase]

I agree with bendyone,pop over to B&Q in Slough when they have a sale on and buy a free standing unit. I paid £78 for one of their units in a sale and it's brilliant. Also great on this marina, as we don't pay for electric Don't think a starter motor would last long as most are not built for continuous running, it'll also flatten your batteries in no time.

 

[Heckler]

not such a daft idea, get the pump and controls off the donor car, get the evaporator and fan and box it up so that you can run ducting, you can get an external condensor that is normally used for a frdge system that fits thru hull into the water. et voila, only trouble is that you have to be pretty adept at "fitting" if you are good at spanners and making things, no probs, I could do it but could you?
Stu

 

[rosssavage]

Hi Stu,

Qualified as an aircraft engineer in 93, so I'm fairly confident I could make it work, however, having read the above posts ref the B&Q option, that seems more attractive as it contains all the bits I need in one box, and I already have an inverter so power should be ok. Thank you all for your ideas, i feel less stupid now.. I'll let you know how it goes should I have a go! Ross

 

[billskip]

"Qualified as an aircraft engineer in 93" ..............


Mmmmmmmm

 

[Avocet]

Starter motors definitely will NOT stand being run continuously. 30 seconds at a stretch is about maximum. also, I'd guess you'd have to be pretty handy with the heat exchange calculations to work out how much refrigerant to put in if you alter a car one to use a water-cooled condenser!

 

[tangofour]

Try looking for a continuously rated treadmill motor. They run off rectified mains DC , 2 to 5 hp available. With treadmill controller board you get variable speed too.

 

[rosssavage]

Avocet, ref calculations, I wouldn't try and mess with the heat exchange system, was thinking of using a radiator and fan to get rid of the heat, so using the existing car bits. Thats what I thought about the starter motor, but 30 secs use is under very high load, I was hoping an a/c compressor would not work the motor as hard...

Tangofour, thats why I come here, I would never have thought of of a treadmill motor, thank you!

Having said all that, the B&Q option still seems like the easiest solution..

Billskip, yeah, sorry, my mistake.. I joined BA as an engineer apprentice in 93, didn't actually qualify until 96. Then 5yrs on aircraft, and another 4 as an avionic senior development engineer. Next time you're on a BA 737 or Airbus, just think, I designed some of it.. Left to go to ops 2yrs ago now /forums/images/graemlins/smile.gif

 

[DavidTav]

Well I hope next time I'm on a 737 that the aircon isn't running from a starter motor!

 

[ccscott49]

B & Q, best idea. The car system is just that, a car system, all the cars I know have very small internal capacity to cool. Plus of course all the DIY involved, for a system which may or may not do the job or even work atall!

 

[rosssavage]

Davidtav,

No, unfortunately I had to work under very tight regulations pertaining to what I was and was not allowed to do on aircraft. Shame, I had some bloody great ideas while I was there! /forums/images/graemlins/wink.gif

 

[rogerthebodger]

Having designed a full aircon systen for my new Lavranos 50 ft I went through the sane thoght processed.

You need to do the sums.

Calculate the BTU required to cool the areas of your cabins and using the data supplied by the domestic/ boat air con suppliers find out the power required and you will find that to run of 12 volts you need an very very large battery bank.

I have 3 units 2 12000 BTU and one 18000 BTU.

these require about 5 amps at 240 Vac. converting without thaking losses into account you will need 100 amps at 12volt so to run uniy for 10 hrs per day will need 1000 Ahr time 3 3000 Ahr battery bank per day.

I will be running my units from a 5 Kva generator and at that size I will not be able to run all at the same time.

Also consider the air cooled units need lots of air to get rif of the waste heat.

I found some water cooled units used in shopping mails not as small as the boat units from cruseair and the like but not so noisy.

 

[Avocet]

I'm not sure a car radiator fan would be up to the duty of running for (say) 12 hours at a stretch - they generally cut in and out and do so quite rarely when the car is moving.

I understand that the compressor load would be much less than an engine being cranked but the motos just aren' designed even for continuous running even at no load. The brushes and bearings jus taren't up to it! When I was a kid I thought I'd put a car starter motor on my pushbike and tow a trailer with a battery in it - BOY did it take off quick! (but by the time I got to the bottom of the road the motor was smelling pretty hot)!

I don't know if would be too noisy, but how about a refrigeration unit off a refrigerated container lorry? All nice & self-contained and if it can keep a 40' container refrigerated it can probably cool your boat!