D+ supply

The fridge on my Symbol is very slow to switch off when the engine is stopped,as the van has a smart alternator I have no idea where auto sleepers get the supply from.

I think 12v supply to auto 3way fridge is designed to delay switch off with engine to stop gas immediately cutting in. One reason I can think of is at fuel station. 
If I am wrong I am sure someone will be along to suggest otherwise. I can only also suggest the supply would somehow be taken short term from battery source.

On automatic energy selection  fridges, there is a 15 minute delay before switching to gas to enable you to fuel up as KDC said, otherwise there's the danger of a naked flame at a petrol station.

Interesting, we have the Fiat automatic with a smart alternator and don’t have the fridge characteristic you mention. Can you quantify the time delay in the fridge switching off?

The supply to the fridge in its 12V mode comes from the vehicle battery but is only used when the fridge senses a D+ signal. Whether or not the vehicle has a smart alternator is immaterial in this context, though it does affect leisure battery charging which is another matter entirely.

In answer to your question the 12V supply comes from the converters socket which is in the base of the B pillar behind the driver’s seat. This connects into the Sargent EM40 panel, usually located nearby, which is the interface unit between vehicle and habitation electrical systems that AS fit. You’ll most likely find it underneath the bench seat at the cab end, see picture below. The D+ signal and fridge 12V supply are derived from this panel, via their respective fuses.

In trying to understand why your fridge is slow to switch off once the engine has stopped, you could pull the D+ fuse upon stopping and see if it makes a difference. That will then tell you whether the characteristic is due to the fridge electronics or due to an anomaly in the D+ signal to shut down. 

If the latter then I would suspect a fault in the EM40, which has to invert a D- signal (a so-called “active ground”) that Fiat provide at the converters socket. Maybe a relay that’s slow to respond. You could seek advice from Sargent, who I’ve found generally helpful in answering queries.

A circuit diagram of the EM40 is shown below.


Tim

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We don’t use the fridge on auto, having been caught out by an undetected interruption in 240V supply resulting in the gas tank being emptied. Consequently I’m not familiar with the changeover process, but I thought the 12V mode would still cease on engine shutdown and that the gas ignition was delayed by 15 mins. But I’m not certain.

Tim

Thanks for all your very helpful replies.My main problem was early on in ownership of the symbol when I ran the fridge on the 12v setting and if I stopped for a cup of coffee,say for 20 minutes,when I started the engine again the engine warning light would come and the stop start would deactivate due to low battery,I now only run the fridge on auto and performs perfectly without any engine warning issues,thanks to everyone for their input.

That’s all very odd. We don’t operate the fridge on its auto changeover setting and when the engine is turned off the fridge immediately stops operating on 12V, as it’s designed to do. On starting the engine we never get a low battery warning.

What sometimes does happen is the engine cooling fan comes on when stopping and turning off the ignition, even in cold weather. That will then trigger a low battery alert.

As for start/stop, it doesn’t operate unless the vehicle battery is fully charged.

Tim

Yes all very odd ? I am going to Sargents in 3 weeks time to have the battery to battery charging fitted  I will let them have a look at it.

Kemerton-bath wrote:That’s all very odd. We don’t operate the fridge on its auto changeover setting and when the engine is turned off the fridge immediately stops operating on 12V, as it’s designed to do. On starting the engine we never get a low battery warning.

What sometimes does happen is the engine cooling fan comes on when stopping and turning off the ignition, even in cold weather. That will then trigger a low battery alert.

As for start/stop, it doesn’t operate unless the vehicle battery is fully charged.

Tim

If my understanding is correct, the cooling fan will continue to run after engine shutdown if the particulate filter regeneration is underway. This apparently involves raising the temp of the unit to aprox 600 deg c to convert the nasties inside. This can also happen during normal driving but is less noticeable due to other noises naturally encountered whilst on the move.

Ah, thank you, I didn’t realise the regeneration would work after engine shutdown. I’ll do some homework on it.

Your experience at Sargent in having a B2B fitted will be of interest to several of us on here. Hope it’s a positive one.

Tim

I can understand the logic of a 15 minute delay before the fridge switches to gas. Quite important on a garage forecourt when buying fuel or AdBlue. But I'm not sure that ought to cause it to continue to run on 12V for 15 minutes. I assumed the fridge just turned off for 15 minutes, then switched to gas. But I've never checked.

There are TWO 12v supplies to the fridge.  

One is a permanent feed from the leisure battery that is there whether or not the PSU is switched on or the engine running.  This supplies the fridge control panel so that the fridge can be operated on gas without EHU, habitation 12v or engine run.  When the fridge has automatic fuel selection invoked, the control panel will manage a delay between losing the 12v engine supply and enabling gas.

The second 12v supply is from the starter battery/alternator (and with a split charge rather than B2B charge, also the leisure battery).  This supply energises the 12v elements that cool the fridge (careful choice of words here) and is switched on/off by a relay whose operation is controlled by the D+ output from the alternator.

The D+ also tells the habitation electrical control system that the engine is running to disconnect that system from the habitation load, retract the step etc. (in some MES systems its a motion detector that controls fridge and step supplies).

I don't know is their is a difference in operation between auto fridge operation between Thetford and Dometic and the first auto fridge I've had is the current Thetford - another of several facilities that I swore I would never use.... until I found out how useful it is, particularly on foreign sites with dodgy electric supply.

Not all vans have a 12v LC feed that is direct from the leisure battery. Mine was fed from the EC500 and was disconnected if the EC500 was switched off. I ran a permanent 12v feed myself to the fridge control panel to overcome this.

I never thought this this D+ subject would cause so much interest,thanks. Regarding the trip to Sargents,we live only 25 miles from Beverley,Sargents leisure is next door to Sargents electrical and can carry out any repair on motorhome and caravan.

Dbvwt wrote:Not all vans have a 12v LC feed that is direct from the leisure battery. Mine was fed from the EC500 and was disconnected if the EC500 was switched off. I ran a permanent 12v feed myself to the fridge control panel to overcome this.

This is the same with the EC700.  The fridge is only able to work off mains, gas or the VB/alternator when the EC700 PSU is not shutdown.  If its shutdown, no 12V gets to the fridge and it's dead.  

My fridge is set to auto.  When I stop driving the VB/alternator supply immediately stops.  I know this because the fridge gas tap is usually shut which means the fridge display flashes until I connect to an EHU.

Dbvwt wrote:Not all vans have a 12v LC feed that is direct from the leisure battery. Mine was fed from the EC500 and was disconnected if the EC500 was switched off. I ran a permanent 12v feed myself to the fridge control panel to overcome this.

I was certain with previous vans but have never switched my EC500 off. Not messing with anything at the moment as need to resolve an airbag fault indication before next week.

Peter Brown wrote:
I was certain with previous vans but have never switched my EC500 off. Not messing with anything at the moment as need to resolve an airbag fault indication before next week.

I'm quite the opposite.  My EC700 is shutdown most of the time.  I only turn it on when I'm using the van.

Caraman wrote:
I'm quite the opposite.  My EC700 is shutdown most of the time.  I only turn it on when I'm using the van.

I agree with you on shutdown, just wondering why people use fridge when not using the van. Extra fridge when at home maybe?

I had to go and try and found that when my EC500 is shutdown it does remove the permanent supply from the fridge AND from the Truma wiping all stored settings and the time!

None of my previous van Sargent systems had a shutdown facility and permanent supplies were permanent (I teed off the fridge to give a permanent supply to motorhome wifi) but I had an excellent dual channel solar system maintaining the batteries. I leave this one hooked up on the drive as the smart charging ensures neither battery gets overcharged and I'm in the van most days for one thing or another.

I find the real beauty of the auto fridge is that when in a hot europe, visiting a town, chateaux, etc. I don't have to remember to do anything with the fridge (or gas bottles, having a fixed lpg tank)

Peter Brown wrote:I had to go and try and found that when my EC500 is shutdown it does remove the permanent supply from the fridge AND from the Truma wiping all stored settings and the time!
.....

Yes - the loss of settings on the Truma is a bit of a nuisance.  I don't bother with Truma's clock or its time switch but occasionally I get caught out with the heat source setting which reverts to gas.  Its not really a problem though.  Like you I'm also in and out my van when its out of use on the drive but I much prefer it not to be permanently connected to the mains with the EC700 consuming 7Ah every day for no real benefit.  Shutting down prevents the fridge consuming power (mains or gas) and if the EHU is turned off, anything else that has been left on by accident.  I find the 80W solar panel and dual battery MPPT regulator is enough to keep both batteries topped up providing the EC700 is shutdown.  You may have noticed that when the EC500/700 is shutdown, the habitation step stops working.  This is not a problem if you ensure its in the out position before shutting down.