Aircon

[Passera]

Hello all

First of all to introduce my wife and I who have recently purchased a 4 year old Lunar as our first venture. We take delivery on July 1st and hands up we are complete greenhorns at this point in time.

 

However we basically reside in Spain and will be using this as a basis for our travels and looking forward to a whole new experience.

 

To our query. The Lunar had no aircon whatsoever and after long discussions with the dealer we opted to have installed a Dometic B2200 Blizzard 2200 12v/240v ac/dc.

We were quite clear that this would give us full aircon when travelling albeit not the traditional method of cab aircon. We also understand that we will have full aircon with electric hook up but nothing if wild camping.

 

We were quoted 1650 GBP for cab aircon and 2150 for ac/dc all fitted. On the basis of where we live aircon when travelling is a number 1 priority and we felt the extra 500 was well spent to give us aircon throughout.

 

All well until a friend flagged up that in his opinion the aircon would not operate as we expect when travelling. He said the battery would not take the power required. I have checked with the dealer again and he assures us it will work fine. I know it runs off an inverter. I am unsure whether this means it runs from the engine battery or the leisure battery (my friend said I need to add another leisure battery). Each leisure battery is 100Amp and the recommendation for the aircon is 200Amp. But if it pulls from these batteries as we are travelling then how are the batteries topped up?

In fact as I type I am confusing myself due to lack of knowledge in this field.

I have noticed on the internet that some aircon models are recommended for use whilst stationary only but not this model.

 

I have tried to call Dometic but after 3 messages still no one calls us back.

Can anyone help please and give me an idiots guide on what we will get and how. It is reassurance we need thanks. (?)

[Guest JudgeMental]

It is the alternator that takes the strain using 12v a/c when driving......you may well have to upgrade the alternator to a heavier duty model, then it should be OK.... just live with it for a while and if it works OK forgetaboutit :-D

[Passera]

Thanks for info.

I did ask about the fuel consumption when using the aircon on the road and the reply was " It does not use any as it uses the inverter".

If you say the power is from the alternator then does that make the above statement incorrect?

[Brian Kirby]

I suggest you go here http://tinyurl.com/328l8wq and look for the A/C unit brochure to download. 

In that you should find a section entitled "Extras for a refreshing experience", which shows 12VDC kits for air conditioning while driving. 

Your dealer should be installing either DC-Kit-2 or 3.  From Dometic's blurb, both are designed to ensure the load is shared between starter and leisure batteries, and alternator.

You will see, under the A/C unit details, that the Kit 2 has a recommended minimum battery capacity of 250Ah, and the Kit 3, 200Ah.  Since the dealer is assuring you that the installation will be OK, ask him to confirm which kit he is using, and that the installed battery capacity is adequate.  When you go to pick up your van, get him to demonstrate it working, and to show you where the 250/200Ah of batteries are.  Bear in mind that one of these will be the starter battery.

You will not need to run the A/C all the time while driving, depending on weather and time of year.  However, when it is running it may be wise to keep its output below maximum, because it will be working the batteries, and the alternator, quite hard.  If you are using the A/C while driving, I would advise using campsites and paying for mains hook up on overnight stops, to be sure the batteries start each day fully charged.

Under the circumstances, I think it will be essential to monitor closely the state of charge of the batteries after driving with the A/C on, and to get them on mains charging as soon as possible after you stop.  Assuming a proper leisure battery is installed for habitation purposes, this will be particularly important for the starter battery, as they have lower tolerance of being left discharged.  For this reason, check that the on-board charger charges the starter battery when on hook-up, and if it does not, get this rectified.

[Brambles]

The reason you need larger battery striaght forward.

 

Just checked the 2200 model and it says 910 watts consumption for cooling.

Using 12 volts for the supply and say 15% loss in invertor its is a curemt of approx 87 amps. You probably have a 150 Amp alternator which is fine when engine is running fast, but when it is idling or not got high revs it will not supply the power or current required for everthing. The battery is needed to supplement the power when the altenator is not running fast enough. I have worked it out and 200Ah battery is about right to avoid drawing too much current from the battery beyond typical capabilities.

[Brambles]

Passera - 2010-06-09 2:05 PM

 

Thanks for info.

I did ask about the fuel consumption when using the aircon on the road and the reply was " It does not use any as it uses the inverter".

If you say the power is from the alternator then does that make the above statement incorrect?

 

If you supply electrical power from the inverter it has to come from somewhere and that is the 12 volt input which ultimately comes from the alternator, and will be to the tune of 1 kilowatt. The alternator is powered by the engine so, yes, your fuel consumption will go up. There is no way it cannot go up.

 

p.s. You are going to ask how much now aren't you. Oh gosh! I am going to have to guess here. in a petrol car could be around 4 or 5 mpg, as the power required to drive a van is a lot lot more then proportionaly I would guess 2 or 3 mpg. I do have a book next to me which will allow me to work it out exactly in litres diesel per hour but at this time of night I can't even find the right section, let alone find what I did with the cork for my wine bottle........shall just have to finish it by having another glass!

[Guest JudgeMental]

Brambles - 2010-06-09 11:45 PM

 

but when it is idling or not got high revs it will not supply the power or current required for everthing. The battery is needed to supplement the power when the altenator is not running fast enough.

 

I have a WAECO 12/230 volt a/c unit and it tends to cut out a bit when idling but fine once revs pick up. not worried as we dont really use it on the move as Ford cab air is excellent......

[Brian Kirby]

Passera - 2010-06-09 2:05 PM Thanks for info. I did ask about the fuel consumption when using the aircon on the road and the reply was " It does not use any as it uses the inverter". If you say the power is from the alternator then does that make the above statement incorrect?

Try looking at it another way.  The A/C will be doing work, and so consuming power.  That power is all electric power and, when driving, is met from the inverter, which converts 12VDC to 220VAC.  So, the inverter must now have 12V power fed in, to be able to feed the 220V power out.  It gets this from a combination of the leisure and starter batteries, and the vehicle alternator.  However, any power that is taken from the batteries must be replaced by the alternator, otherwise they will become "flat".  So, ultimately, all power consumed by the A/C unit must be supplied by the alternator so, to supply that power, the alternator must work.  The engine drives the alternator so, as the work done by the alternator rises, the demand on the engine rises, and it has to work harder.  To work harder it requires more energy, and its energy comes from its fuel, so it will consume more fuel.

Ultimately, it is the vehicle engine that drives the alternator, that powers the inverter/charges the batteries, that supply the electricity to the A/C.  Work out = energy in.  Switch on the A/C, and the fuel consumption will, inevitably, rise.  Trouble is, they don't teach motorhome salesmen elementary physics.  :-)

Truly, there ain't no such thing as a free lunch!

[Passera]

First of all sorry to take so long coming back. Been on an airport run today and then following up all the info.

Anyway my grateful thanks to Brian, Judgemental and Brambles who all took the time out to help put our minds at ease. I only hope that for Brambles it was worth that extra glass of wine. We buy it in 5 litre plastic bottles here but it never seems to last long. I love the local Jalon valley wine despite a recent newspaper report that described it as having all the subtlety of a JCB!!.

Anyway I digress.

It appears from all the info that we are unnecessarily concerned. I followed up the Tinyurl link thanks Brian and have since established the accessory kit installed is DC2 which has the minimum capacity of 250A.

The MH is a Lunar H592 premier with a Renault chassis and that is listed as having an auxiliary battery with a split charger relay of 85A. I cannot find any reference to the alternator or starter battery capacity.(I assume aux battery is the leisure battery).

I am following the points you all make but am a little confused.

Brian you say the 250A must come from the starter and leisure batteries and that means the starter battery needs to be 165A correct?

Brambles you talk about probably having a 150A alternator and then mention calculating that a 200A battery is about right. Don't sigh but the 200A battery is that starter, leisure or both- I am assumimg it is both as that sort of fits in with Brians calc. Is the alternator ampage usually the same as the starter battery Ampage? and how does that fit in with the above calc.

 

I note you use cab aircon which unfortunately we do not have.

 

I think I am coming to the conclusion of Judgemental mentioned inasmuch that it is borderline but perhaps to be safe have a second leisure battery fitted. If you could just help me a bit more so I can understand the detail.

Also thank you Brian for the tip about the on board charging to include the starter battery.

 

I have moved from wine to home made Sloe Gin right now so here's to you all

 

 

[Guest JudgeMental]

You can find out the amperage of the alternator by ringing a Renault dealer and giving them your VIN/chassis number. Or look and see what is stamped on it....... I assumed you had 2 leisure batteries and am surprised the fitter did not recommend this.

 

when you pick it up test a/c on tick over, if the stops and starts and alarm beeps the system probably needs a bigger alternator (if 2 batteries fitted)

 

 

[dwaviation]

I understand that the DC kits are 'smart' inverters and will cycle the AC in order to ensure that the battery charge is preserved

[Brambles]

"when you pick it up test a/c on tick over, if the stops and starts and alarm beeps the system probably needs a bigger alternator (if 2 batteries fitted) "

 

 

If I may, I would like to change this to......

If it stops and starts then a bigger alternator or a 2nd battery needs to be fitted.

But it could equally also be alternator belt is loose and batteries are not in good condition.

 

 

Aldo clarify what I said which was "200Ah" battery( not 200A) , it is its capacity not the current it can output. 200Ah could be made up of more than one battery.

Jon.

 

 

[Tony Jones]

Brian Kirby - 2010-06-10 3:48 PM

 

The engine drives the alternator so, as the work done by the alternator rises, the demand on the engine rises, and it has to work harder.

 

This is the bit I've never understood. I fully realise that

there ain't no such thing as a free lunch!

- I just don't understand why, in this case.

Does the alternator actually become "stiffer," therefore harder to turn, when it's putting out more power? Cos otherwise I can't see how it creates more work for the engine.

Intuitively, it seems the alt ought to turn just as freely, whether anything was connected to it or not - you'd just find that it didn't produce enough electricity if it wasn't going fast enough. But that can't be right, as it WOULD mean a free lunch.

I know this is no help to the OP (sorry for the hijack!) but it's always puzzled me.

[colin]

Tony, you will proboly have heard alternators working harder, esp in winter, starting from cold or after pulling up at junctions with lights etc on many cars have squeeling drive belts as the load on alternator increases.

[AliB]

Tony, think of trying to move two magnets apart. The stronger the magnets the more effort you will need to pull them apart. An alternator uses electro magnets or coils of wire. The current through these coils varies according to the load placed on the alternator. Hence increasing or decreasing the strength of the magnetic fields. Under normal loads the difference is minimal so you will not see any significant improvement in fuel consumption if you turn off the radio.

Cab air conditioning is different as the compressor is usually belt driven. When the a/c is turned on the engine management system will increase the idle speed to compensate for the extra load. Typically belt driven a/c can decrease fuel consumption by 2-3mpg.

As stated in previous replies an alternator driven a/c system will put a huge strain on the alternator and big batteries are needed to compensate.

[Brian Kirby]

AliB - 2010-06-11 12:08 PM Tony, think of trying to move two magnets apart. The stronger the magnets the more effort you will need to pull them apart. An alternator uses electro magnets or coils of wire. The current through these coils varies according to the load placed on the alternator. Hence increasing or decreasing the strength of the magnetic fields. .............  As stated in previous replies an alternator driven a/c system will put a huge strain on the alternator .............

With apologies for the deletions, but I think the above is clear and relevant - after which AliB seemed to digress a bit!  :-)

This increased strain on the alternator will take the form, as stated, of higher currents in the alternator coils, hence stronger magnetic fields, hence greater force to keep pulling them apart (i.e. turning the alternator rotor), hence more work for the engine to do, and so increased fuel consumption.  Hope this helps!

[Tony Jones]

Got the picture now - it's the magnetic field the engine has to "fight." That makes complete sense - what a helpful bunch you all are!

Thanks. And apols to Frank for borrowing his thread to sort out a long-standing puzzle!

 

T

[AliB]

Tony Jones - 2010-06-11 11:07 AM

 

But that can't be right, as it WOULD mean a free lunch.

.

 

Now we've sorted that out can we talk about the free lunch :-D

[Brian Kirby]

Passera - 2010-06-10 9:30 PM ........... It appears from all the info that we are unnecessarily concerned.

I think you are rightly concerned, but should not panic!  :-)

I followed up the Tinyurl link thanks Brian and have since established the accessory kit installed is DC2 which has the minimum capacity of 250A. .........

No, the kit does not have a capacity of 250Ah, it requires batteries of 250Ah total capacity to service it.  That is to say, the leisure battery and the starter batteries must have a combined storage capacity of 250Ah.

Brian you say the 250A must come from the starter and leisure batteries and that means the starter battery needs to be 165A correct? Brambles you talk about probably having a 150A alternator and then mention calculating that a 200A battery is about right.

Again, I'm afraid no!  You are confusing, as Brambles says, Amps with Amp hours.  The A/C unit requires 900 Watts in cooling mode.  Remember Watts = Amps x Volts?  To work the A/C when driving, it is fed 220V AC power via the inverter.  The inverter takes 12V DC power, and converts it to 220V AC power.  To feed the A/C the inverter must develop about 4 Amps at 220V AC, and to do this it will require 80 + Amps of power at 12V DC (900 W = 4 A x 220 V, or 75A x 12V, plus inverter losses).  So, you now have to put in 80 + Amps of 12V power.  All things being equal, the alternator, with a power output of, sat 150 Amps, can cope, but must also run your fridge, plus possibly headlights and windscreen wipers, and charge the batteries.  So far so good, but then you get to the traffic lights and stop.  The engine speed falls to idle, and alternator now cannot generate its 150 Amps.  This is where the kit installation begins feeding the A/C current from the batteries, to supplement the alternator's depleted output.  It uses both batteries, because the potential load is high, and sharing the load across both prevents damage to either.  Batteries store electricity, and their storage capacity is measured in Amp hours (Ah).  Thus, you will see figures like 80Ah on batteries.  Battery capacity is measured in a particular way, in fact over a 20 hour period, so what this means is the battery can produce, when new and fully charged, a current of 4 Amps for 20 hours (4A x 20hrs = 80Ah).  The problem is that this does not mean, due to battery chemistry, that you can extract 80 Amps for one hour (it would be nearer 20/30 minutes), which in the end is why Dometic say you'll need 250Ah of battery to feed the A/C.

Don't sigh but the 200A battery is that starter, leisure or both- I am assuming it is both as that sort of fits in with Brian's calc. Is the alternator amperage usually the same as the starter battery Amperage? and how does that fit in with the above calc. ..............

It is 250Ah, and yes, it is the combined capacity of starter plus leisure batteries.  Forget the alternator for now, that produces Amps and this is about Amp hours.  :-)  Your van is 4 years old, and so presumably, are its batteries.  Neither will now be capable of providing their full rated capacity, so whatever they say on the case, will not be there.  This is an inevitable consequence of ageing.  I think what you have found is that the leisure battery is of 85Ah capacity (but less now).  There is not a cat in hell's chance that the starter battery is of 165 Ah capacity, so your van does not have the battery capacity to feed the inverter as Dometic recommend.  I think you will need to add leisure battery capacity and, since the existing battery is presumed 4 years old, that will mean discarding it (because simply adding a new battery to an old one won't work), and installing two new batteries of, I would guess, about 100Ah each.  They will need to be accommodated somewhere, so space for these needs to be found.  Over, I think, to your dealer!!

I think I am coming to the conclusion of Judgemental mentioned inasmuch that it is borderline but perhaps to be safe have a second leisure battery fitted. If you could just help me a bit more so I can understand the detail. Also thank you Brian for the tip about the on board charging to include the starter battery. ..............

Make sure the charger has the capacity to charge whatever is the newly installed battery capacity.  The charger needs an output (in Amps at 12V) of approximately 10% of the battery capacity in Ah.  So for 250 Ah of batteries, you'll need a mains charger delivering a charging current of about 25A.  Now Brambles can correct me where I'm wrong!!  :-D

[Passera]

Thanks Brian

 

I just said to my wife I think i need a good lesson in electronics and mechanics.

Think I just received one!!

 

I have ascertained the dealer "always fits an extra leisure battery with a/c installations" but am waiting for them to call me on most of the points you raised.

Will advise in due course but again thanks to everyone for help. Been 3 weeks trying to get some help so should have started here first.

[Brian Kirby]

AliB - 2010-06-11 1:29 PM

Tony Jones - 2010-06-11 11:07 AM But that can't be right, as it WOULD mean a free lunch. .

Now we've sorted that out can we talk about the free lunch :-D

Only if it's a liquid lunch!  :-D

[Brian Kirby]

Passera - 2010-06-11 2:46 PM Thanks Brian I just said to my wife I think i need a good lesson in electronics and mechanics. Think I just received one!! I have ascertained the dealer "always fits an extra leisure battery with a/c installations" but am waiting for them to call me on most of the points you raised. Will advise in due course but again thanks to everyone for help. Been 3 weeks trying to get some help so should have started here first.

Forgot to say re differing ages of batteries - if the first battery has been in use for less than one year, it is OK to add a further battery, provided it is of the same type.  If the difference in ages is more than one year, the pairing is not advisable.

Basically this means, providing the max one year age difference is respected, a "flooded" battery can be paired with a "flooded" battery, an AGM battery with an AGM battery, and a Gel battery with a Gel battery.  An AGM may be paired with a gel, but advice from the manufacturers should be sought. 

A starter battery should not be paired with a leisure battery.  Beware the term marine battery, because a number of these are, for want of a better term, semi-starter batteries, having more the characteristic of a starter battery (to deliver a big whack of power in one short hit) than of a leisure battery (to release its power more gently, over a longer period of time).  Two such together would be OK, but connecting one in parallel with a leisure battery would not be good.  A number of AGM batteries fall into this group. 

The mains charger must be set to charge the battery type, generally they are switchable for flooded, and AGM/gel.  This is because the charging regime for the one type is unsuitable for the other.

[Brambles]

Brian Kirby - 2010-06-11 1:31 PM

 

  Now Brambles can correct me where I'm wrong!!  :-D

 

 

Oh no! you mean I have to go back and read all the post again and digest.

Just back from a trip to Aberdeen again, so shall make a coffee and read again.

 

Jon. :-S

 

p.s, Brian, your post immediately above this is 100% correct --- I shall just add you can mix same type but with different capacities keeping the ratio no greater than 3 to 1 being recommended .

 

Shall read your earlier post again now.

[Brian Kirby]

I await your learned deliberations, Jon! 

Blimey, it's like the school exams, ain't it?  Did I pass, did I fail?  Shall I get booted out?  I'm only the bleedin' apprentice, after all!  :-D

[tonyishuk]

I do not want to muddy the waters more than they are already but if might be wise to consider a Battery to Battery charger to aid the charging of the leisure battery when the air con has worked, but drawing the charge in the leisure battery down.

 

Basicaly a B2B charger uses electonics to boost the charge in the leisure battery.

 

I started a thread http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=19685&posts=16

 

which gives a description of what goes on.

 

If I have mudded the waters, I will withdraw my stick from the pond and watch the ripples ;-)

 

 

Rgds

 

Just to add to Brians remarks about marine batteries, they are a very different beast, a boat can have much more electical equipment generally drawing much deeper discharges and running sometimes heavy electic motors for bow thrusters. The are not just for starting the motor like a M/home but also run a lot of navigational gear reliably (one hopes !)