Aircon running without the engine

[dave_aber]

Just a thought for the summer (I'm planning a trip to Europe).

I bought a 2-box portable aircon unit which runs off 240v hook-up. All very good, but in honesty it's going to take up too much valuable space when we are touring.

So, I am re-selling it and plan to use the funds to investigate a way of running the Bongo's perfectly good dual aircon system without running the engine.

Current thoughts :

1. Replace the a/c compressor with a 12v DC powered one, and use the electromagnetic clutch wiring to pull in a solenoid to power up the 12v compressor.
2. Mount a DC motor (somewhere) such that I can belt-drive the original aircon compressor.
3. Plumb a second compressor (12v DC) into the system, and use that when parked up.

Now, I reckon that any of these will need to draw 20 or 30 amps when compressing, so I'm looking at powering the compressor from the L/B via some heavy wiring, and only using this when on hook-up. As the a/c cuts in & out the overall consumption will be in the order of 6a @12v equivalent or so. I'll probably swap over the digital heating controls to the L/B as well, so I don't need the ignition switched on. The Willinton will keep both batteries topped up when I'm on hook-up in either case.

So, any aircon specialists out there who can advise me if there are 12v powered aircon pumps available? I'd prefer not to try mounting an additional 12v motor and belt, as I doubt there is space.

Is it feasible to have a second compressor in the system? (one used at a time)

Someone please put me out of my misery and convince me I'm mad.

Cheers
Dave

[winchman]

I will ask the one who sits next to me tomorrow

[francophile1947]

Someone please put me out of my misery and convince me I'm mad.

Seems a reasonable request
Based on the fact that powering aircon uses quite a bit of engine power, I would have thought that any 12V motor would need to be very powerful and consume vast amounts of battery power It'll be interesting to see what someone who knows comes up with.

[dave_aber]

From what I have researched so far, it takes about 10bhp to spin the a/c compressor. I'm thinking it would be something like a starter motor - which probably rules out getting a single unit which is both motor and compressor.

I'm hoping that the L/B and Willinton can 'keep up' when I'm on hook-up. I'm not considering this when off mains. I do still want to be able to use a/c when I'm driving though, so I don't want a 240v pump / motor.

[Northern Bongolow]

have you looked into the truck top models, or caravan top models, you dont like the sunroof much do you

[dave_aber]

I looked at roof-mounted campervan ones initially - all mega-money though.

[francophile1947]

Aren't starter motors about 2KW?
If so, you're gonna need a heck of a battery charger to keep up with that for any length of time - it'll probably give off more heat than the aircon can cope with

[markoos]

HI Dave, your mad, lol.
AC in bongos is not my speciality, however, I was a refrigeration and air conditioning engineer for 15 years and now i am service, maintenance and technical director for a large refrigeration and Air Con company, not that i have an answer for your problem.

Issues as i see it, installing an additional compressor would need a bypass arrangement for each compressor, commercial vehicles have a AC motor and a PTO (power take off) unit for running off an engine, this would seem the best arrangement to get in to a bongo, the highest electrical pull would be the initial starting on the electric motor, so you may need to run the engine first to bring down the suction pressure first then switch over to the power hook up, depending on belt pulley arrangement you could get it down to reasonable running amps.

Have you looked into a small adiabatic / evaporative cooler, water pump and fans, they are very simple

http://www.ebay.co.uk/itm/Amcor-Amcor-2 ... 1e6209140f

[Dodgey]

Aren't starter motors about 2KW?
If so, you're gonna need a heck of a battery charger to keep up with that for any length of time - it'll probably give off more heat than the aircon can cope with

That was exactly my thoughts. No battery charger is going to keep up wit the power requirements for this.

[dave_aber]

That might be a more sensible answer!

Last time we toured Europe, we only had one evening when it was unbearably hot (in Munich), and we sat all closed up with the engine running for half an hour or so to cool down.

This year we are heading to Budapest in August, which will be hot, then South to Croatia. I got a bit carried away buying a £400 aircon unit which has an outside compressor / exchanger and an inside condenser / fan. It's overkill, and too big / expensive. So, my thoughts then turned to getting the van's built in aircon working for me. It may be wise to go cheap - I can make ice as I drive in the fridge / freezer and use it in something like the one you linked to.

Ady - Further research indicates that starter motors are about 2.5Kw. More worryingly, if my 10BHP estimate is right, is that 10BHP is 7.5KW, so I'd be looking at a huge motor. This may well be a dead end!

On the other hand, my fridge runs a danfoss compressor drawing 1a @ 12v, and cools the plate in the fridge to -10° with no problems.

There has to be a solution somewhere in the middle ground......

(or I am really mad, which is just as likely! )

[francophile1947]

On the other hand, my fridge runs a danfoss compressor drawing 1a @ 12v, and cools the plate in the fridge to -10° with no problems.

There has to be a solution somewhere in the middle ground......

Sit in your fridge
To be fair, your fridge is a lot smaller than the inside of a Bongo

[Northern Bongolow]

have a look at the peltier unit, basic phyisics stuff but you can reverse the useage.
this is how the cheap coolboxes work.
look up ECOFAN on the net they use the same principles running backwards.
ive made my own out of computer parts for the top of my log burner.
put in volts get heat or cool. put in heat and cool can give volts.
strap 20 cheap units to the exhaust gives good voltage to charge batts but more important to you ,gives you ccoling plates of alluminium use the voltage created to power small fans.

hey presto d i y aircon

[dave_aber]

Here's an alternative and perhaps more practical idea.

I'm not really concerned with efficiency, as this will only be used on hook-up. Ultimately of course there is a limit to the power available on hook-up (6A @ 240v - 1.5Kw, minus losses etc)

I am more concerned with the space used.

So, if I swap over the supply to the car's heating / aircon system I can use the existing front & rear vents and fans on the L/B - lots of functionality and no loss of space.

If I then install a peltier plate in the cold air ducting to the top vents in the rear, I should have cold or at least cool air from them - at a load of, say 4A for the plate and 2A for the fans. I'd only be running this for a percentage of the time, so the hook up - charger - L/B should be able to keep up OK.

At least these peltier plates are cheap enough to experiment with - but the downside is that at 40x40mm they may be pretty ineffective.

[g8dhe]

You will nee to duct away the hot air as well otherwise that will start to warm the van internally!

[dave_aber]

Ah, of course, they have a hot side as well as a cold side.

I might just run the engine!