Reverse polarity points

[spospe]

Derek Uzzell - 2013-12-18 2:08 PM

 

And, Yes, it still seems odd to me and, No, I don't understand why Airlectric NEEDS to be polarity-sensitive, and, No, I'm not going to ask Eberspacher why!)

 

 

I did ask them and they did not reply!

[pepe63xnotuse]

Derek Uzzell - 2013-12-18 2:08 PM

 

(And, Yes, it still seems odd to me and, No, I don't understand why Airlectric NEEDS to be polarity-sensitive, and, No, I'm not going to ask Eberspacher why!)

 

Oh,go on!..You know you want to.... ;-)

(..it'll only end up keeping you awake at night, otherwise. (lol) )

[Brambles]

Derek, incoming PM.....Zooooooooooooooommmmmmm ..mind your heads chaps.

 

They are German, Germans often do things a weird way, but not as much as the French. There will be a reason for it. They would not do it unless there was a reason. You have to think outside the box here, this system is not just for motorhomes but also other types of vehicle installations and possibly even boats.

[Derek Uzzell]

Brambles - 2013-12-18 3:56 PM

 

Derek, incoming PM.....Zooooooooooooooommmmmmm ..mind your heads chaps.

 

They are German, Germans often do things a weird way, but not as much as the French. There will be a reason for it. They would not do it unless there was a reason. You have to think outside the box here, this system is not just for motorhomes but also other types of vehicle installations and possibly even boats.

 

Taking your last point first, there are a few on-line inquiries about adding an Airlectric unit to an Airtronic heater installed in a boat, but I'm not sure if anyone actually did it!

 

Hopefully you've now got copies of the Airlectric Installation and Operating instructions. The purpose of the heater is described in them as follows:

 

• Pre-heating, de-misting windows.

• Heating and keeping the following warm:

– Driver and working cabs, ship’s cabin;

– Freight compartments;

– Passenger and crew compartments;

– Camper vans.

 

The wiring diagram suggests that polarity might be important, but (as far as I can see) there's no written caveat about this elsewhere in the text. The polarity sensitivity seems to be what IBM engineers would blithely refer to as an "undocumented limitation" when I was writing mainframe software that should have worked but didn't. (The other version of this was a "documented limitation" mentioned, say, in an insignificant footnote on Page 471 of Volume 17 of IBM's set of massive technical publications.)

 

I'm sure there's a reason why Airlectric is polarity-sensitive; less sure though that it's deliberate. It's plain that Eberspacher are now aware of the polarity limitation and one might have expected this to have become evident when Airlectric was being developed. Airtronic heaters are marketed throughout Europe for installation in motorhomes and an inability for the Airlectric add-on option to work only on a UK-norm EHU would seriously restrict its attractiveness to Continental-European motorhome converters and buyers. (Perhaps 'foreign' motorhome converters were aware of the polarity issue and that's why none of them appear to have fitted Airlectric.)

 

Dunno and - as I'll never have an Airlectric unit - I definitely shall not lose any sleep over not knowing.

 

Even it's not known why there's an Airlectric polarity issue, at least it's now been established that there is a general technical issue, and that it's not just spospe's and Gram's systems that are acting oddly or that Auto-Sleepers have been incompetent.

[Brambles]

Very confusing indeed as to why it is polarity consious. Makes no real sense yet as to why. I am wondering along the theory if water or moisture was to collect in the heater unit, it would be safer to maybe have the 'Neutral' parts of the heater in closer proxmity to any earthed casing should any leakage of electricity occur. But we have an RCB fitted so safety is built n anyway. Very strange and I suppose the question might be...Will it work on floating Earth systems and the difference in voltage between either conductor and Earth be enough to enable operation?

 

[Derek Uzzell]

Brambles - 2013-12-18 9:09 PM

 

Very confusing indeed as to why it is polarity consious. Makes no real sense yet as to why. I am wondering along the theory if water or moisture was to collect in the heater unit, it would be safer to maybe have the 'Neutral' parts of the heater in closer proxmity to any earthed casing should any leakage of electricity occur. But we have an RCB fitted so safety is built n anyway. Very strange and I suppose the question might be...Will it work on floating Earth systems and the difference in voltage between either conductor and Earth be enough to enable operation?

 

You are assuming, because an Airtronic + Airlectric system is polarity sensitive, that Eberspacher deliberately designed it like that for technical and/or safety reasons. An alternative hypothesis would be that Eberspacher realised at a late stage in the Airlectric development process that the system was polarity sensitive and chose not to do anything about this limitation.

 

It would appear (at least for motorhomes) that, although plenty of converters have installed Eberspacher Airtronic heaters, only Auto-Sleepers offered the Airlectric option. If that's what's happened, Airlectric's polarity sensitivity may not much matter. Spospe's experience with reversed-polarity 230V supplies and an Airlectric-equipped Auto-Sleepers motorhome seems to be unique, as other owners of A-S vehicles with Airlectric don't seem to have been aware of it.

 

(I've asked Eberspacher for further advice, but I'm not sure they'll be able to provide it.)

 

 

[Gram]

Would someone please explain this concept of a 'Floating Earth'.

 

I understand the supplies in Germany to be TT or TN. In both cases the centre point of the star 3-phase output is taken to ground and the electrical installation takes its Earth from either an electrode in the ground or a conductor that is supplied by the Supply Authority. So how does the earth 'float'?

 

G

[Derek Uzzell]

Gram - 2013-12-19 9:34 PM

 

Would someone please explain this concept of a 'Floating Earth'.

 

I understand the supplies in Germany to be TT or TN. In both cases the centre point of the star 3-phase output is taken to ground and the electrical installation takes its Earth from either an electrode in the ground or a conductor that is supplied by the Supply Authority. So how does the earth 'float'?

 

G

 

GOOGLE-searching on "power floating earth" produces plenty of information - whether it's directly relevant to an Eberspacher Airtronic + Airlectric system is another matter.

 

I going to suggest (kindly) that there's no point speculating about why your and spospe's heating system won't operate from a 230V power-supply unless that supply has 'UK norm' polarity until Eberspacher respond to my last e-mail.

 

This is the message I sent to Eberspacher yesterday:

 

"The .pdf files you sent me indicate how Airlectric should be wired up within a leisure-vehicle, but I can find nothing in the instructions' text to warn that, if an external 230V power-supply being connected to the vehicle has its Live and Neutral reversed, Airlectric will not operate on mains power. Although this type of 'polarity reversal' would be rare in the UK, it is (as I said originally) not that unusual outside the UK and commonplace in France.

 

You have confirmed that an Airtronic + Airlectric system will operate from a 230V power-supply only if that supply conforms to the the UK standard regarding Live/Neutral polarity. Does that mean that Airlectric was designed for the UK market alone, or is there another version of Airlectric for countries with mains electrical standards that differ from the UK's?

 

I am assuming there must be a technical reason for Airlectric only working with a UK-standard 230V power-supply, but it seems very peculiar that the unit would have been designed (by a German company) with that limitation when it is well known that Continental-European campsite power-supplies have unpredictable polarity. As far as I am aware, other manufacturers' (eg. Truma) leisure-vehicle heaters that have a 230V capability are never polarity-sensitive.

 

I note that the front page of the Airlectric instructions carries pictures of two motorcaravans. Neither is UK-built and one (a Rapido) is French - this seems to suggest that Airlectric would be suitable for motorcaravans that are being built/used outside the UK. However, a polarity-sensitive system would force a French motorcaravanner (or a UK motorcaravanner holidaying in France) to take corrective action whenever a reversed-polarity power-supply is encountered.

 

I believe Eberspacher no longer includes Airlectric in its sales-catalogue. If all Airtronic + Airlectric systems are 230V polarity sensitive, I can envisage this limitation seriously restricting its attractiveness."

[Gram]

Maybe Brambles can help me out here as he first 'floated' the concept of a European Floating Earth.

 

A floating earth is used widely in electrical equipment, particularly test equipment, but not, as far as I understand, in domestic or commercial electrical supplies.

 

G

[Brambles]

Floating earth in relation to mains supplies is a term I have picked up on these forums...so not me who came up with the concept. I personally think 'floating earth' is the wrong term to use although in some earthing systems it is does apply. e.g where there is protective earth provided by the supply running all the way back to the transformer which is then earthed.

I get totally comfused by TN-C, TN-S, TT and so on in just remembering which one is which.

 

There are loads of different earthing sytems used, mainly TN-C and TT in europe and that incudes the UK.

I think what people mean by floating earth is when the earth is connected back to the center tap of the transformer. Think of a single phase transformer with a centre tap connected to earth, just like the centre tap of a star configured transformer. The two outputs of the transformer provide 220 volts balance about the centre tapped earth. Now if you run a protective earth cable to the consumer, (often the sheath of a cable is used) Then your earth is pretty much half way between the supply comductors most of the time. It can drift slightly depending on impedances and voltage drops in the cables and any faults which exist. Also how many users have connected up 110 volt equipment between only one supply and the Protective earth whether permitted or not.

Now using the TT earthing system, hope I have the right one here when I say TT , you do not have a protective earth and just connect earth to the ground near you (or is this called TI ???). There are often ground differences in potential between where the transformer is grounded and the consumer has his ground. This in effect makes the earth potential in relation to the two supply conductors drift from being at mid point.

This is what I believe is what people refer to as a floating earth. It is not really a floating earth at all in the same sense as used in wiring of appiances or electrical equipment, it is more an earth that floats around in potential relative to the supply voltages. So maybe the term 'remote' earth is better, and I am sure there is a proper term for it, but I am no expert in these matters.

 

 

[Gram]

Thanks, Brambles, I think I know where you're coming from now.

 

You are correct, it is the TT system that does not have a hard connection between supply Earth (at the star point of the supply transformer secondary, where the Neutral is earthed) and the installation Earth. The connection through the ground is not always ideal so a heavy discharge to earth could well cause Neutral and Live (Line?) potentials to drift. But I hate to think how heavy the earth current would have to be to even slightly affect the potentials at the four points of a star secondary.

 

The IT system has no earth at all at the supply (or the star point is connected to ground through a deliberately introduced impedance). But this makes the operation of protective devices rather hit and miss (probably more miss than hit).

 

I have come across the supply originating from a centre-tapped transformer on board ships (the centre-tap being well and truly nailed to the ship's hull). However, I am not sure that this system is ever used in supplies to domestic/commercial premises. Well, not in Europe anyway.

 

I stand to be corrected, however.

 

Enough of this waffle ......

 

G

[Derek Uzzell]

The simple wiring diagram for connecting a 230V power-supply to an Airlectric unit shows a 6-Amp MCB in the Live cable. Plainly, then, if Live and Neutral were reversed, this MCB would be in the Neutral feed, but I can't see that being significant on its own where the polarity-sensitivity issue is concerned.

 

The schematic showing the wiring of the Eberspacher adapter-loom that links the Airlectric unit to the Airtronic heater's control-panel is much more complex and involves an 8-way connection.

 

Wiring schematics are available on-line for Airtronic heaters, but I don't believe marrying those diagrams to the Airlectric ones offers any hope for deciding why an Airtronic + Airlectric system turns out to be 230V-power-supply polarity-sensitive.

 

Unless Eberspacher can provide more information, it would appear that polarity-sensitivity is just an inherent limitation of this system.