Fridge/Freezer – and the Battery.

[Keithl]

IIRC there should be a delay of possibly 10 to 15 minutes before an AES fridge switches from 12 volts with engine running to gas to prevent it 'lighting up' when you pull in for fuel.

 

Does this help explain things?

 

Keith.

[lennyhb]

Keithl - 2014-11-07 3:15 PM

 

IIRC there should be a delay of possibly 10 to 15 minutes before an AES fridge switches from 12 volts with engine running to gas to prevent it 'lighting up' when you pull in for fuel.

 

Does this help explain things?

 

Keith.

 

No that's does not effect running off the leisure battery.

[Brian Kirby]

lennyhb - 2014-11-06 7:00 PM

 

Brian, when I added the drawing the tex got lost:-

 

The 3rd fuse from the left controls it, marked Kompr./AES.

Is that fuse fitted in your van Brian?

Short answer, Lenny, don't know! Mine also has an EBL29, and the fuse position is present, but I don't know if a fuse is fitted to the holder.

 

The Hymer manual doesn't cover the "AES" type Thetford actually fitted, covering only the "MES" type. It is clearly stated that 12V power to the fridge is only available when the egine is running. This is how ours is wired. The AES function hunts for 12V, then 240V, then gas (pauses for a while before trying to ignite) and then panic! It is only a problem for tunnel / ferries. Otherwise, when the gas is on, it just switches between power sources automatically.

 

I note that when describing the Dometic 8 series AES fridges it states as you say, that the fridge will draw power from the hab battery when the engine is turned off if no other source is available. It also implies that if solar is connected via the EBL, that source will be prioritised in preference to the hab 12V. But it further implies it will use solar in preference to all other sources, which seems plain daft. I think things are getting lost in translation!

 

However, I'm afraid this will probably only be relevant to the OP if he happens to have a Hymer with a type 8 Dometic fridge.

[Derek Uzzell]

Operating and Installation instruction documents are available on-line for the Dometic RMD 8505 AES fridge/freezer fitted to Solomongrundy’s motorhome.

 

The Operating Instructions are (as far as I’m concerned) ambiguous about whether or not the appliance is intended to run using leisure-battery power when the 12V option has been manually selected (ie. Automatic operation has not been chosen). Advice regarding Automatic operation is as follows:

 

"Upon switching on, the electronics automatically selects one of the three possible energy types: 230V - 12V - liquid gas. The control electronics automatically ensures that the refrigerator is supplied with the optimum source of energy in each respective case.

 

Sequence of priority:

 

1.) Solar (12V -)

2.) 230V ~

3.) 12V -

4.) Liquid gas

 

If sufficient mains voltage is available (more than 195V), this power source is selected as prime option. If a solar system capable of powering the refrigerator is installed, the solar 12V supply takes priority.

The 12V operation is otherwise only effective while the engine is running.”

 

However, the Installation instructions seem more clear-cut and the “Electrical installation” section includes this advice:

 

"Provide a 16 A fuse to protect on-board 12 V circuit.

 

In order to ensure that the 12V power supply is shut off when stopping the engine (otherwise the battery would discharge within a few hours), perform the power supply to the heating element (cf. page 30, connection A/B in wiring diagram) in a way to have the 12V supply only live while the vehicle ignition is switched on.

 

The connection C/D (interior light, electronics, cable black / violet) must be permanently provided by a 12V DC power supply to be protected by a 2A fuse.”

 

The inference seems to be that it’s the installer’s responsibility to ensure that the appliance is incapable of cooling on 12V (unless there’s a sufficiently powerful solar input) when the motorhome’s engine is not running. Basically, that the installer should introduce a relay into the 12V cooling power-supply to the fridge/freeze that would prevent power reaching the appliance when the vehicle’s motor was stopped. Presumably Hymer has chosen not to do this.

[lennyhb]

Derek Uzzell - 2014-11-07 6:44 PM

 

The inference seems to be that it’s the installer’s responsibility to ensure that the appliance is incapable of cooling on 12V (unless there’s a sufficiently powerful solar input) when the motorhome’s engine is not running. Basically, that the installer should introduce a relay into the 12V cooling power-supply to the fridge/freeze that would prevent power reaching the appliance when the vehicle’s motor was stopped. Presumably Hymer has chosen not to do this.

 

With the engine running the fridge takes power from the engine battery, when 12v is selected the fridge takes power from the leisure battery, the fridge relay is inbuilt into the Elektroblock.

[Stitches]

lennyhb - 2014-11-07 3:11 PM

 

Just been having a play with mine, I put the fuse back in and set the fridge running on gas, I then turned off the gas, it did not switch to the leisure battery but tried to relight on gas, after a predetermined time the fault light came up. Switching to manual to battery it runs off the leisure battery if the engine is not running. I also tried the options after running the engine same result.

 

Not sure how Nick came to his conclusion on his Exsis i578 (assuming he has a Dometic fridge) but it certainly does not do that on mine, the battery light on the fridge stays on for the 15 min after switching off the engine but it is not drawing any power from the leisure battery.

 

On my previous van the 7 series fridge would run off the leisure battery in auto mode as does my mates new Carthago.

 

I do have a solar panel fitted but have not tried out the 'switch' over in a variety of situations ie when panel is not causing a charge

 

 

 

[Robinhood]

.....I haven't got time at the moment to fully trace the block diagram, but my suspicion still falls on the addition of solar to the EBL (which would account for differing behaviour where solar is not fitted).

 

If you trace the "starter battery" feed from the solar connection, it would appear (at least to me at a quick glance) that this triggers the fridge relay(s) in a way that would connect the leisure battery to the fridge.

 

Patently, this should mean that the leisure battery is also being charged, but not at the rate of consumption of the fridge.

 

l may be mistaken, and there may be something else in the diagram that negates this - I'll have another look later.

[Derek Uzzell]

lennyhb - 2014-11-07 7:12 PM

 

With the engine running the fridge takes power from the engine battery, when 12v is selected the fridge takes power from the leisure battery, the fridge relay is inbuilt into the Elektroblock.

 

Whatever electrical system Hymer has chosen to fit and whichever battery the Dometic fridge gets its 12V cooling power from, I still maintain that anyone with a basic understanding of what motorcaravanning is about and with a logical expectation of how a 3-way fridge in a motorhome should behave, would not anticipate a 3-way fridge being installed so that it can place a heavy drain on a 12V battery when that battery is not being recharged.

 

I’m not doubting that this 12V drain occurs with a Hymer + EBL + Dometic AES-fridge combination (or with a Carthago + CBE system + Dometic AES-fridge combination) when 12V operation is selected manually. I’m just saying that I believe any right-thinking motorcaravanner would consider such behaviour ‘wrong’. And - based on Dometic’s own documentation - it would seem that the fridge manufacturer also takes that view.

 

I think you see Hymer through rose-tinted glasses. This is the company that, until quite recently, could not be bothered to fit windscreen wipers with an efficient RHD pattern to their expensive A-class motorhomes destined for the UK, and gained a well-deserved reputation for installing Truma heaters inaccessibly. I’m certainly not suggesting that Hymer is the sole culprit when it comes to motorhome manufacturing idiocy, but Hymer is no paragon of virtue either and definitely not infallible.

 

That you’ve highlighted that Dometic AES fridges in Hymers (and in other marques) have the capability to flatten the motorhome’s leisure-battery is a valuable warning. (I’ll be checking what the Thetford SES fridge in my forthcoming Rapido does in that resprect.) But it still begs the question of why Hymer permits this potentially harmful capability ito be present when the simple addition of another relay would prevent what must surely be considered a nuisance not a benefit.

[Brian Kirby]

Hmmmm. Don't want to throw petrol on the fire :-), but I think Lenny said he installed the solar himself? I believe he also said he did this with his previous van. Could it be that, when installing solar at the works, Hymer wires the solar somewhat differently, or adds something, to the way Lenny did/does, and that explains the difference?

[lennyhb]

Derek Uzzell - 2014-11-08 9:48 AM

 

Whatever electrical system Hymer has chosen to fit and whichever battery the Dometic fridge gets its 12V cooling power from, I still maintain that anyone with a basic understanding of what motorcaravanning is about and with a logical expectation of how a 3-way fridge in a motorhome should behave, would not anticipate a 3-way fridge being installed so that it can place a heavy drain on a 12V battery when that battery is not being recharged.

 

I’m not doubting that this 12V drain occurs with a Hymer + EBL + Dometic AES-fridge combination (or with a Carthago + CBE system + Dometic AES-fridge combination) when 12V operation is selected manually. I’m just saying that I believe any right-thinking motorcaravanner would consider such behaviour ‘wrong’. And - based on Dometic’s own documentation - it would seem that the fridge manufacturer also takes that view.

 

I have never said anything to the contray and if you read my posts you will see I have said on many occasions that I remove the fuse that allows this behaviour so that it behaves as most of us would expect and my posts have been made to alert people to problem.

 

I think you see Hymer through rose-tinted glasses. This is the company that, until quite recently, could not be bothered to fit windscreen wipers with an efficient RHD pattern to their expensive A-class motorhomes destined for the UK, and gained a well-deserved reputation for installing Truma heaters inaccessibly. I’m certainly not suggesting that Hymer is the sole culprit when it comes to motorhome manufacturing idiocy, but Hymer is no paragon of virtue either and definitely not infallible.

 

No, I just know a lot more about Hymer's than other brands. I agree to you to some extent about the wipers but their are probably more LHD A class Hymer's in the UK than RHD and from there point of view probably not economical viable to change for the small quantity involved.

The Truma installation in my last van was OK the one in current van wastes valuable space has a whole double seat box to itself now you compare that to Mike's (Joe90) problems on his Rapido I think Hymer have done a pretty good job.

 

That you’ve highlighted that Dometic AES fridges in Hymers (and in other marques) have the capability to flatten the motorhome’s leisure-battery is a valuable warning. (I’ll be checking what the Thetford SES fridge in my forthcoming Rapido does in that resprect.) But it still begs the question of why Hymer permits this potentially harmful capability ito be present when the simple addition of another relay would prevent what must surely be considered a nuisance not a benefit.

 

Agree.

Hymer being the largest manufacturer in Europe means that a very large percentage of the vans on the road are wired like this and the first the owners know about it is when they get a flat battery, that is the reason I try to make people aware of it.

At least on the latest vans it only appears to happen if you select manual mode, one assumes they consider you would only select manual 12v if you had adequate solar, but there are a lot of people like me out there who prefer to use the fridge in manual mode. Also not many people would have enough solar power to support the power requirement, I certainly would not even think about with my 190 a/h of batteries and only 200 watts of solar.

[Robinhood]

Robinhood - 2014-11-08 9:26 AM

 

l may be mistaken, and there may be something else in the diagram that negates this - I'll have another look later.

 

...as you were. I've now blown the diagram up, and can read it a bit better.

 

The solar supply doesn't seem (at least directly )to affect the relays.

 

I can certainly see the (removable) 20A fuse and understand what that does to overcome the issue.

 

I could also possibly rationalise that (if the D+ signal is passed on to the AES fridge, as it appears it should be) that the fridge might work properly in "auto" mode (i.e. not select 12V when the engine isn't running), but might select 12V (from the leisure battery) when manually switched to 12V. (as this probably bypasses the fridge auto logic which will look for a D+ signal).

 

Maybe the clue as to "proper" working is that the AES fridge supply is also tagged as relevant for a compressor fridge, this latter requiring to be powered from the leisure battery when the engine is off.

 

There does, however, appear to be a different connection for a (non-AES) absorber fridge, (which doesn't appear to have the capability to run off the leisure battery, and without further study, I can't see why you wouldn't connect all absorber fridges to this (the compressor connection to the leisure battery I can understand).