Running a Fridge on Gas on the Move?

[Brian Kirby]

StuartO - 2017-11-18 4:15 PM

Brock - 2017-11-19 5:29 AM.... or© in any other vehicle, a refrigerating appliance or an appliance which does not expose a naked flame on the outside of the appliance and which is permanently attached to the vehicle and designed for the purpose of heating any part of the interior of the vehicle for the comfort of the driver and any passengers.

 

As I understand that, any type of refridgerating gas appliance is OK.

Au contraire, I think, Stuart. The flame is outside the appliance (it is external at the rear), and is it also exposed externally (in that the ventilation grille provides free air movement through the side of the van). Consider that aftermath of a road accident in which a petrol vehicle's fuel tank had ruptured and petrol was pouring onto the road, and there you are only a car or so behind the event, safely stopped with your fridge happily running on gas. Would your first instinct be to rush back and turn off the gas? I'm not sure mine would. As Will says above - oh dear!

[BruceM]

An interesting debate, but what interests me more is why the electronics burnt out in the first place. My fridge documentation indicates that it uses 130W at 12v, so I guess that’s about 10.8A . The fridge fuse on my Schaudt Electroblock 99 is rated at 20A so the electronics should well exceed the required spec given the current drawn.

 

So what's going on? Are over spec fridges being installed?

[aandy]

Lawyers could make fortune arguing what is meant by 'outside of the appliance'. The flame is enclosed in a metal tube which, while it is outside of the physical confines of the fridge, is an integral part of it. I've not had the vents off recently, but I'm pretty sure there are other components that project further away from the back of the fridge than does the burner tube, so where precisely would the line be drawn? I suspect a strong argument could be made for the flame being inside the appliance. In practical terms, I'm not sure it's any different from a heater designed for use in motion. While the flame is unquestionably inside the heater it still vents direct to the outside so the potential for contact with flammable vapours would, presumably, be the same. That said, I wouldn't choose to drive with the fridge on gas, but I've not seen it as a cause for concern when I've inadvertently done so.

[stvekay]

One question, not safety related/or cost. If I drive with fridge on 12 volt will that limit the amount of charge that my engine and leisure batteries will receive thus having less power in them when I settle for the night?

Hope its not too stupid a question!

Thanks

Steve

[Muswell]

A gas fridge will draw in air for the flame. I wonder what happens if the air has petrol vapour with it?

[crocs]

Brian Kirby - 2017-11-18 4:58 PM

StuartO - 2017-11-18 4:15 PM

Brock - 2017-11-19 5:29 AM.... or© in any other vehicle, a refrigerating appliance or an appliance which does not expose a naked flame on the outside of the appliance and which is permanently attached to the vehicle and designed for the purpose of heating any part of the interior of the vehicle for the comfort of the driver and any passengers.

 

As I understand that, any type of refridgerating gas appliance is OK.

Au contraire, I think, Stuart. The flame is outside the appliance (it is external at the rear), and is it also exposed externally (in that the ventilation grille provides free air movement through the side of the van). Consider that aftermath of a road accident in which a petrol vehicle's fuel tank had ruptured and petrol was pouring onto the road, and there you are only a car or so behind the event, safely stopped with your fridge happily running on gas. Would your first instinct be to rush back and turn off the gas? I'm not sure mine would. As Will says above - oh dear!

I agree with Stuart. Regulation 96: 3 © allows fridges to operate no matter where the flame is and whether it's naked or enclosed.That's what it says. Whether we feel comfortable folllowing it is up to each of us.

[aandncaravan]

aandy - 2017-11-18 9:02 AM

 

"Heartening for me that not one respondee has challenged my myth breaker that running the Fridge on 12v costs and that the Gas option while driving, is not the higher expense option many probably previously perceived."

 

I'm not challenging it, since the basic rules of physics tell us you can't get something for nothing. I had, however, always assumed that the additional fuel burn resulting from any extra load on an alternator would be so small as to be immeasurable. Do you know of any tests that have been done to establish precisely how much extra fuel would be used?

 

 

Aandy, Lets say we need 150w of heat energy at the Fridge.

Propane Gas will burn and deliver that energy direct.

To find 150watts of Heat from the engine we first have to ignite the Diesel fuel in the Engine which is about 48% efficient.

That then drives an Alternator which I think is only 55% - 65% efficient, and there will also be energy loss in the drive belt pulleys, etc.

 

Losses will also occur in the cabling and the Heater element.

 

So Propane Gas is likely to result in about half the amount being used compared to Diesel.

 

But remember most 12v systems bypass the Temperature control so are on 100% of the time versus the Gas system which will probably be 'active' for half that time, so the Gas used should be half that again. Maybe even more dependent on the Fridge Insulation. So a big difference in operating a Fridge on Gas versus Diesel..

 

If the Gas is Butane, which burns 'hotter', the Fridge will either be more efficient, or use about 15% less again

 

If you then factor in that Gas is half the cost of Diesel,..............

 

But to counter that, the Alternator will be driven at times when the throttle is closed, like going down hill when the 12v power will be free

 

The difference is still massively in favour of Gas operation, plus better Fridge efficiency, especially on Butane.

The same applies in charging batteries from the Alternator, especially using a big B2B and a big battery bank, in that it will take power from the engine and that will cause more Diesel to be used.

 

 

 

"I have left my fridge running on gas and drove with out thinking, remember about 3 miles up the road and stopped to turn it off and it had gone out!"

Paul2, It is established fact that many Fridge's are not installed as the Fridge manufacturer suggests.

 

 

 

 

Stvekay, There might be occasions where a Fridge/Freezer drawing 12v, and as much as 17amps, may reduce the charge to the batteries, indeed we have seen Forum posts to this effect.

However, there is usually a fault somewhere or other associated with this.

 

 

 

 

BruceM, Generally the issue is the connectors which are not rated high enough for the job, particularly when connectors at the back of the Fridge corrode/become loose.

 

Later Schaudt units use a 3 pin 40amp rated plug/socket.

Recent, upgraded, Nordelettronica also use high rated plugs/sockets. Photographic evidence of the changes to the units can be found on our "Add a Second battery?" web page : http://www.aandncaravanservices.co.uk/add-a-second-battery.php

 

 

 

 

 

[aandncaravan]

lennyhb - 2017-11-18 12:29 PM

 

It is against the Road Traffic Act (I think its the 1986 act) to run any gas appliance with a naked flame in a vehicle. The fridge has a naked flame so the answer is NO you can't run it on the move.

I also find it quite alarming that someone of Alan's experience has suggested this also no mention of the safety requirements for using gas on the move such as crash protection regulators & ant-rupture hoses.

 

Lenny, if the flame is within the appliance, which all Fridges are, it is legal.

Although the Chimney sits out from the main body it is still part of the Appliance, the flame enclosed within shielding and within the Appliance is legal and considered safe.

.

So having established it is legal in Germany, Holland, Spain, Italy, UK, Hollan, Portugal, etc, and that legislation in the the UK and EU allow it. Also that Dometic design it in and don't talk of any safety issues, then it is probably BECAUSE, " someone of Allan's EXPERIENCE has suggested this" is an Option?

 

That doesn't mean we recommend any one does it, a big difference.

 

 

As for talk of crash protection I think it crazy that anyone differentiates between Gas and Petrol, they are both very volatile, both highly dangerous, both ignite readily at the temperatures of a modern Turbo or Cat, so why stipulate 'Extra' protection should be taken on a Motorhome and not campaign for 'anti burst' hoses on every UK petrol car? The risk is there, there are a mass of electrics on a Petrol car that are capable of causing ignition of any vapour, yet accident statistics show that injury from Fire following a car RTA is almost zero, despite there being millions more cars on the road than MH's.

 

 

If you, or anyone, can provide statistics that UK Motorhomes crash everyday, burning the occupants to Death from gas fires, then I will have a rethink of what I believe.

But as pointed out, in the ULTRA safety conscious North Americas, running the Fridge on Gas while on the move is normal.

 

Despite all the responses, no one has presented ANY evidence that injuries have resulted from gas fires in RTA's.

Nor have they presented any figures that the risk is anything but exceptionally low.

Just lots of "it's dangerous because it's gas"' without actually having any real evidence if it is or not.

 

Ingrained in the culture like so many myths, errr, just like the one running a Fridge on 12v is 'free' maybe?.

 

 

 

 

 

 

[Alanb]

BruceM - 2017-11-18 5:06 PM

 

An interesting debate, but what interests me more is why the electronics burnt out in the first place. My fridge documentation indicates that it uses 130W at 12v, so I guess that’s about 10.8A . The fridge fuse on my Schaudt Electroblock 99 is rated at 20A so the electronics should well exceed the required spec given the current drawn.

 

So what's going on? Are over spec fridges being installed?

 

 

Bruce seems to have missed my earlier post in which expressed my doubts as to the rating of the Mate-n-Lock connectors, as used on CBE DS300 and DS520. I have carried out some research and find that thequoted maximum current per pole on a 9 way connector is 11.5A at a maximum temperature of 120C, allowing for a 30C rise in contact temperature. This rating is for a fully populated connector, with the same current in all poles, so as this will not apply in practice, a slightly higher current may be possible.

 

Yes, 10.8A at 12V, but 12.72A at 14V assuming that the resistance is constant. This is greater than the quoted 11.5A, and the heating of the connector is proportional to the square of current.

 

I will continue to use my fridge on 12V, but as previously stated I have paralleled both connector pins, designated by CBE.

 

Alan

[Guest pelmetman]

Cant say I've noticed having the fridge on 12 volt makes much difference to my mpg? :-S .........

 

Still seem to be getting 30+ mpg B-) .......

 

 

[aandncaravan]

Someone has sent us this from the Delco Remy website on engine/alternator efficiency which backs up what we said about the expense of running a fridge on 12v versus Gas :-

 

"Electrical power on a vehicle is not free. It comes as a direct result of consuming fuel within the engine to drive the alternator. With a typical engine efficiency of 40%, a belt efficiency of 98% and an alternator efficiency of 55%, this leads to an overall energy conversion efficiency of only 21%".

 

Big advantage in favour of Gas and that is before the thermostat swings it even further in favour of Gas.

 

 

 

[aandy]

Having nothing better to do, I've tried to convert Alan's figures into actual costs. I'm not clever enough to come up with a formula that anticipates the many variables so have assumed the fridge is working constantly and that the engine is constantly under load (i.e. no down hill stretches). I have also assumed that the engine is running at its maximum power (which of course it won't be), and is returning 30mpg at 60mph.

 

The 150 watts the fridge needs will, at an overall efficiency of 21%, take 714w from the engine, which is 0.95 horsepower or .76% of the maximum output of a 130 horsepower engine. Assuming the additional load increases fuel consumption in direct proportion, that equates (at £5.50 per gallon) to 8 pence an hour. My handbook says that the fridge uses 16 grams per hour which, if using 6kg Calor bottles at £22 per refill, equates to 6 pence per hour. As I said at the start, far from scientific, but it wasted 20 minutes.

[Alanb]

Alanb - 2017-11-18 8:33 PM

 

BruceM - 2017-11-18 5:06 PM

 

An interesting debate, but what interests me more is why the electronics burnt out in the first place. My fridge documentation indicates that it uses 130W at 12v, so I guess that’s about 10.8A . The fridge fuse on my Schaudt Electroblock 99 is rated at 20A so the electronics should well exceed the required spec given the current drawn.

 

So what's going on? Are over spec fridges being installed?

 

 

Bruce seems to have missed my earlier post in which expressed my doubts as to the rating of the Mate-n-Lock connectors, as used on CBE DS300 and DS520. I have carried out some research and find that thequoted maximum current per pole on a 9 way connector is 11.5A at a maximum temperature of 120C, allowing for a 30C rise in contact temperature. This rating is for a fully populated connector, with the same current in all poles, so as this will not apply in practice, a slightly higher current may be possible.

 

Yes, 10.8A at 12V, but 12.72A at 14V assuming that the resistance is constant. This is greater than the quoted 11.5A, and the heating of the connector is proportional to the square of current.

 

I will continue to use my fridge on 12V, but as previously stated I have paralleled both connector pins, designated by CBE.

 

Alan

 

I forgot to add the fact that the 11.5A rating is with 14 AWG / 2 sq.mm. conductor which is the largest size that can be accommodated in the general run of connector pins. 2 sq.mm. thinwall pvc auto cable is rated at 25A, so the connector is the weakest link.

There is a larger size of connector pin available which will take up to 10 AWG / 5 sq. mm. cable. With this combination a maximum current of 13.5A is given, when used in a 9 pole connector. The increased current rating is due to the larger the increased ability of the larger cable to conduct heat away from the connector. (I believe that this larger size connector pin is used in the output connector of CBE CB-516 chargers, which has only two high current poles, and where larger cable is used to improve voltage regulation.)

I am begining to suspect that fridge 12V power connecting cables have been sized for current rating, and not to suit the thermal requirements of the connector. At maximum current rating there is also a specified minimum length of conductor, which increases with conductor size, However there is also a requirement to design the pcb with large tracks in order to conduct heat away from the connector.

 

I suggest that it could be sensible to install larger cable on fridge 12V connections. I will now have to locate my fridge 12V -ve supply, and inspect it.

 

Alan

 

[aandncaravan]

aandy - 2017-11-19 10:14 AM

 

Having nothing better to do, I've tried to convert Alan's figures into actual costs. I'm not clever enough to come up with a formula that anticipates the many variables so have assumed the fridge is working constantly and that the engine is constantly under load (i.e. no down hill stretches). I have also assumed that the engine is running at its maximum power (which of course it won't be), and is returning 30mpg at 60mph.

 

The 150 watts the fridge needs will, at an overall efficiency of 21%, take 714w from the engine, which is 0.95 horsepower or .76% of the maximum output of a 130 horsepower engine. Assuming the additional load increases fuel consumption in direct proportion, that equates (at £5.50 per gallon) to 8 pence an hour. My handbook says that the fridge uses 16 grams per hour which, if using 6kg Calor bottles at £22 per refill, equates to 6 pence per hour. As I said at the start, far from scientific, but it wasted 20 minutes.

 

 

Aandy, that suggests that in your particular case, and it probably won't apply to all, is that even though Gas is still cheaper your Fridge must be under performing massively on 12v?

Assuming your argument is valid, the energy your Fridge uses on Gas must be at least double that on 12v Alternator suggesting your Fridge performs really well on Gas and exceptionally poorly on 12v?

 

 

LPG has a higher 'Heat value', 49Mj/kg, versus Diesels lower 45Mj/kg if you use two liquids to create heat for the same function and one is lower heat rating and goes through a conversion process of only 21%, there has got to be a major advantage to the one giving direct heat output.

 

If LPG is also half the cost of Diesel then that is an additional 2 to 1 in favour of Gas. If you then also factor in the thermostat will switch off the gas for 50% of the time, it is an further 2 to 1 in favour of Gas.

That is a huge difference, my maths isn't good but I make it 8 times more efficient..

 

If your gas flame is really needs to use that much Gas, delivering, say 500 watts of LPG heat, and the 12v only 150watts, you can see why they are so rubbish when running on 12v.

Even a 300watt 12v element wouldn't match the efficiency of Gas, but that would really stress the vehicle electrics. I guess that is probably why it isn't done?.

 

No wonder so many report their Fridges only just stay cool, or don't even do that, on 12v.

 

Your figures, if valid, are a real eye opener and put 'into Science' what many have thought for years.

 

 

We mentioned in the post how tired batteries, or High Maintenance batteries, gassing down their vents under the van near the Exhaust is a high danger, IMO, than LPG. Well the web link below that shows the different Heat values of LPG, Diesel, etc. list Hydrogen at 120Mj/kg, more than double that of LPG, some pretty explosive stuff in even small quantities.

Always use non gassing batteries.

 

 

http://www.world-nuclear.org/information-library/facts-and-figures/heat-values-of-various-fuels.aspx

 

 

[Will86]

aandncaravan - 2017-11-20 10:02 AM

 

No wonder so many report their Fridges only just stay cool, or don't even do that, on 12v.

 

 

OK ... so what is the benefit of a Fridge being super cool when its not being used. You can argue all day on your theories but I see no advantage when most users can connect to a 240v supply or gas when they park for the night or even a short break.

 

The world is filled with those who quote figures but in the end simplicity rules.

 

What you are suggesting may be true but its surely false economy.

 

[aandy]

Alan, my figures were not based the real life performance of my fridge or any other. All I did was crunch the numbers that you gave for the fridge's 12v consumption and the engine/alternator losses, add in Dometic's stated 16g/hr gas consumption, and come up with a very simplistic formula based on a number of rather shaky assumptions. I'm sure my figures are not valid, and their only worth was in keeping me amused for 20 minutes

 

What interests me here is not which is the cheapest way to run a fridge, but the extent to which additional load on an alternator will impact on fuel consumption. While there should, in theory, be a direct relationship between the increase in the power drawn and the fuel used, I can't help thinking that in practice it would be absorbed into, or hidden by, the various losses and inefficiencies already present. For example, your 21% efficiency figure takes account of loss in the belt driving the alternator, but in practice is that loss mostly a 'one off', or does it change in direct proportion to fluctuations in current drawn? As I think I said in an earlier post, in a crude attempt to see whether there was a discernible effect, I set the idle speed on my car to just above stalling then turned on the lights, fan, and heated rear window. I don't know what the overall load was, but the headlights alone draw 200 watts. My thinking was that with the engine running so slowly the additional load would be a significant proportion of it's output at that moment and might result in a change in engine speed or note. It didn't. I'm not claiming that proves anything, nor do I claim to know the answer. If anyone does, I'd be interested to hear it.

[bigparkie]

Excuse my ignorance but how many litres of gas are in a kg of liquid propane?

Regards Richard.

[StuartO]

bigparkie - 2017-11-21 6:20 AMExcuse my ignorance but how many litres of gas are in a kg of liquid propane?Regards Richard.

 

Where LPG is propane, 1kg of LPG has a volume of 1.96L. Conversely, 1L of LPG weighs 0.51kg

 

[bigparkie]

Thank you.

Richard

[Keith T]

A slightly different take on this topic, though as far as I am concerned I would never run the fridge on gas whilst driving.

 

We now have an Autotrail PVC, which has a fixed gas tank under the chassis. We were advised that there is a turn off switch on the tank, but so far have been unable to find one, and in any case, it would not be accessible unless you lay under the vehicle

.

However, we do turn off the individual isolator switches in the kitchen cupboard, but I feel this is not as safe as the Calor cylinders where you turn it off at source......which was always our procedure before driving off. Also the external cupboard door housing the calor cylinders had a gas sticker attached.

 

On the AT we have an external filler for the gas in the side of the van, which then has a fair run of piping to the actual gas cylinder underneath. Nowhere is there a sticker to say there is a gas installation....is this correct, is this allowable under regulations?? Anyone else out there with similar tanks and are there warning stickers??

[Derek Uzzell]

This 2009 MHFun discussion may be of interest

 

https://www.motorhomefun.co.uk/forum/threads/lpg-warning-labels.17523/

 

The type of fixed LPG tank generally fitted to motorhomes normally has an ON/OFF outlet-valve beneath a metal protective cover on the tank’s side (see attached photo).

 

This recent-ish thread may be worth reading

 

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Underfloor-LPG-shutoff/47760/

[Brian Kirby]

There seems to me to be a further aspect to this topic. Please follow this link to an earlier, and loosely related topic: http://tinyurl.com/ydbyha3g

 

The posters gas tank fell off. This is not unheard of, though not common. It seems to relate to ordinary mild steel commonly being used for the tank support bracket. However, with underslung gas tanks there is also a risk of damage (more probably to pipework), from debris on the road, especially during, or in the aftermath of, an accident.

 

There is a requirement when using shuttle or ferries for the gas supply to be isolated at source. Isolating at the gas cocks on the distribution manifold still leaves various pipe connections, and the pipes themselves, including the main gas cock, between the tank and the regulator, subject to full tank pressure, and those downstream from the regulator up to the distribution manifold, subject to 30mbar.

 

Whereas neither are risks with a high likelihood of occurrence, the potential consequences should the event arise are very high indeed. For example, with a tank that is partially detached to become part supported on its pipework, now strained and leaking, loaded into the confined space of a shuttle carriage.

 

It seems to me that any shut off cock should have to be placed where it is readily accessible to the user. At worst, this seems to mean no more than extending the operating shaft for the main gas cock, so that it can be operated without having to reach under the van.

 

Do buyers query gas fitters on the accessibility of the main gas cock when agreeing what is to be installed? I'm not suggesting that the gas fitters do not supply proper, gas tight, installations: just that they seem isolated from the additional dynamic risks and practical inconveniences that are presented by installing gas tanks under vehicles.

[Derek Uzzell]

This 2011 MHFacts thread relates to a retrofitted LPG tank falling off a motorhome

 

http://forums.motorhomefacts.com/145-lpg-gas/88461-urgent-check-your-gas-tank-straps.html

 

Although anyone considering having an underslung LPG tank retrofitted can quiz the fitter about how the tank will be installed and the accessibility of the tank’s On/Off outlet valve, major converters (eg. Auto-Sleepers) are now fitting an LPG tank as part of their vehicles’ standard specification. Those tanks are usually installed tranversely and accessing the outlet valve will involve slithering under the vehicle and removing a protective cover.

 

The 2nd link in my last posting above discussed how an LPG tank’s On/Off valve might be operated remotely or more easily, but (as far as I’m aware) none of the UK motorhome converters have addressed this specific issue.

[Brian Kirby]

Derek Uzzell - 2017-11-21 2:03 PM.........................The 2nd link in my last posting above discussed how an LPG tank’s On/Off valve might be operated remotely or more easily, but (as far as I’m aware) none of the UK motorhome converters have addressed this specific issue.

True, but if any of them are looking in, perhaps they should begin doing so. It seems quite inconsiderate to expect all users of their vans to get out and get under (whatever the weather) to turn off the gas at source, as required by the ferry/shuttle operators. Is any manufacturer out there? :-D

[Brock]

Auto Sleeper advertise its gas tanks as being, "hassle free practicality" and "Reliable and safety proven, extensively tested for peace of mind and fully approved under European Whole Vehicle Type Approval Legislation". Oh and it shows a 'Underfloor mounted LPG tank' sticker on the website.

 

Not sure how slithering under the vehicle and removing a protective cover fits with "hassle free."