yep! thats right Basil only one element, it feeds off either 12v or 240v with some converting/inverting apparatus!

I have seen a couple with dual windings on one element on older less known fridges, to my knowledge the windings themselves cant be replaced so the whole element must be replaced as with the more modern one's

the newer ones use one element with no inverter/converter technology, these I'm not directly familiar with but should be more durable and easier to work on simply because of less parts

either way the element is relatively easy to replace, from memory 2 screws for the power and two to hold the element in place inside the chamber, there is also other goodies that may be at fault but this is rare, the thermostat may be faulty or maybe a loose connection but my money is on the element

the last I replaced was in a chesney about 4 years ago so memory not that good!

I will post this even though it shoots down a lot of my argument about 3 way fridges having only one element, I will amend this to state the fridges I have worked on have only one element

I found this as i was scrounging for a bit of knowledge about a different item but thought it might be of interest to some of you as well, thanks to "rays outdoors"

3-Way Gas, 240V AC & 12V DC Refrigerators


Just a brief discussion on the subject of those 3-way absorption refrigerators.

I am referring here to the Electrolux/Dometic product but would apply to other makes.
These are usually a good,*reliable product and for these units to work effectively, the makers installation and operating instructions must be strictly adhered to. There are several areas to pay attention to.
* See note at bottom of page

Having said that, once ambient temperature exceeds 40 deg C, absorption fridges are no match for compressor types.
Compressor fridges will work effectively past 50 deg C and at all temperatures will pull the fridge temperature down more quickly.

However for most people the absorption fridge is the more suitable option for long term operation (that is, more than just a few consecutive days) in the warmer summer months unless you have at least 250 watts of solar panels or always have mains or generator power available when you stop.
(Don't be talked into believing that a 12V compressor fridge can be satisfactorily operated from one solar panel and battery for more than a few of days at a time without being properly recharged unless it is a small chest type, to attempt to do so will cause the battery to cycle too deeply before it can be properly and fully charged with a significant reduction in battery life - see solar page for more details.)


Vent position & sealing



Pay particular attention to the position of the external air vents in relation to the unit as shown in the illustration.

The performance of the unit will be greatly impaired if the convection air flow is restricted around the condenser and absorber in this rear area behind the refrigerator.

The bottom of the lower vent must be level with the bottom of the unit and the bottom of the top vent level with the top of the unit.

It is also very important that this rear area behind the fridge is completely sealed from the area around the sides and top of the unit.

If, during operation you can feel the bench top above the refrigerator is warmer than ambient by more than a few degrees, then you can be reasonably sure that the rear sealing is less than perfect.

It may be worthwhile to fit a small 12V DC fan in this rear area to assist air movement during the warmer days particularly if the manufacturers installation instructions have not been strictly adhered to. There are thermostatically controlled fan kits available from caravan parts suppliers for this purpose.

A small 12V Pentium computer fan inside the food area blowing on the cooling fins circulating the air gives a worthwhile improvement also.


Voltage drop and leakage



The operation of these absorption fridges relies on a correct heat source. This heat source is derived from a gas flame, a 240 VAC element and a 12 VDC element selected, as appropriate, from the front of the refrigerator.

The gas flame is rarely a problem if serviced annually by a qualified gas fitter but there can be problems with the electrical elements.


12V element

The usual problem here is voltage drop in the cable feeding the element due to too small wire gauge.

The (nominal) 12V element is around 150 Watts which works out to 11 Amps @ 13.8V. If, as is often the case, the wire size is too small, 3-4V can easily be dropped across the supply cable leaving only 10-11V for the element.

If, for example, 3V is dropped across the supply cable, the power dissipated in the element is only 93 Watts, less than two thirds that intended by the manufacturers.

No wonder the performance on 12V can be disappointing.

To remedy this, the wire size from your vehicle alternator / battery, not just your house battery, must be taken into account and upgraded.

The easiest way to accurately measure the voltage drop is to take two measurements of the voltage at the refrigerator with a multi-meter with the engine running such that the vehicle battery reads 13.8V, first with the fridge selector off and second with the selector in the 12V position. The difference between the two readings is the voltage drop or loss across the cable. I would not like to see more than 0.5V dropped.

(This voltage drop problem associated with inadequate wire size is a problem with electric brakes also, but that's another story.)

Make sure the AC feed to your RV is unplugged prior to doing this as the AC and DC terminal strips can be in close proximity to each other depending on the model.
If you have any problem following these steps it is probably a good indication that you should enlist the help of a suitably qualified person.

( I don't use the 12V facility at all, I use the 240V position even when driving, it works much better. See my Batteries & 3-Way Fridge Problems page. )


240V element

Voltage drop is not a problem with 240 VAC side. The current with a 150W element is only 0.625 Amp and the minuscule voltage drop is an extremely small percentage of the supply. (In marked contrast to the 12V side where 3V is a large percentage of the supply)
However there can be another problem.

The heating element consists of a resistance wire inside, and insulated from, an outer metal tube casing. So long as there is no electrical connection between the resistance wire and the outer casing, all is well.

A situation can arise, and probable will in time, where a partial circuit will form between the resistance wire and the outer casing which is earthed. This can be caused by partial breakdown of the insulation between the two or an ingress of moisture.

If this happens it will cause RCDs (safety switches) to trip out if a leakage current of greater than 30 mA flows. (See page describing Safety Switches)
Even if you don't have an RCD in your RV (and you should), many caravan parks now do and this will result in your 240V power tripping off every time you turn you fridge to 240V.

If the leakage is due to a breakdown inside of the element, you will have to have it replaced. This is a simple job that can be accessed by removing the lower exterior vent.

If it is due to moisture in the element, you can try drying it out by running on gas for a while. However, prevention is a better option. If you run your fridge on 240V on a frequent regular basis, it will prevent the moisture build up.

Remember, all work involving 240V and gas must be done by a suitability qualified person.


Level



Absorption refrigerators must be levelled to work efficiently and can be damaged if operated out of level for more than a short time. Mobile operation out of level is OK since it will be level on average. This is extremely important.

Circular 'bulls-eye' spirit levels are ideal. I have one on the drawbar and one on the bench above the fridge.

Fore and aft levelling is done with the jockey wheel and sideways levelling with a nifty tough plastic ramp made for the job by Fiamma. There are two ramps in a set each measuring 500x200x90mm. Also, make sure you buy the optional matching chocks that lock in to the ramp.


Other problems



Whilst absorption fridges do not have any moving mechanical parts, they are not without their problems.

The cooling system relies on a complex ammonia/water/hydrogen cycle.
Faults can occur due to pipe corrosion, blockage, leakage and air locks.

In the event of cooling failure, where the heat source is not at fault, the entire cooling system will need to be replaced. The cost of a replacement system is in the vicinity of 60% of a new fridge. Reconditioned cooling units are available but are still approximately 50% of the new fridge price and usually with a shorter or no warranty.

If you are very lucky, the problem may be an air lock. In this event, try inverting the fridge for several hours and giving it a bit of a shake and when right way up again, try operating on 240V. This often works and if it does you will have saved $600-700.



Update

*
Jan 07

Based on recent personal experience and several emails, I am not so sure the statement on reliability is accurate.

We have been told (or we assumed) that no moving mechanical parts equals good reliability and long life.
I have personally just recently been associated with two Dometic 3-way fridges that failed, one at 8 years and the other 4 years.
The former was used continuously for 8 weeks per year and monthly for several days at a time the rest of the year. The latter was run continuously for 4 years.
Both suffered the same fate, rusted pipes causing loss of coolant.
The cost of repairs (new cooling unit needed at 60-70% of new fridge cost depending on repairer) and in some instances, lack of worthwhile warranty of the repair meant both were scrapped.

To my surprise, authorised repairers have told me 10 years is a good life expectancy.
Obviously this is planned obsolescence since a metal not subject to corrosion could be used.

Pretty disappointing for a $1300 fridge (depending on state, Qld was cheapest, SA dearest, in fact when I enquired, it worked out more than $100 cheaper to buy in Qld an freight to SA than buy in SA).

If my new one fails anytime soon, I can't see myself getting another one.

My recent experiences and several email criticizing my comment on their good reliability have prompted this update.

hope that helps a little!

I'm still trying to get my head around the single element operating on both 12v dc (or 13.8 - 14v dc) and 240v ac without there being either an inverter to supply the 240v from a 12 volt input or a power supply to supply 12v (or more likely 13.8v) from the 240 volt ac mains to the element. Maybe the promotional material for the fridge simply promotes the single element operation without being specific as to how this is achieved.

It is interesting to note that the site you obtained the details above from actually recommends using the 240 volt option (via an inverter) when travelling in preference to the 12 volt option, something I alluded to as a possibility earlier in this thread. The site also suggests this as an option for charging the van battery (batteries) using a "smart" charger in conjunction with this arrangement. One would need to do their sums regarding the current requirements and wiring adequacy before committing to this set up. I'm not in a position to comment on the merits of this idea from a "real world" practical stand point as I haven't tried it.

Just as an explanation and not wishing to be too pedantic about this but the usual terminology for these various little "black boxes" is.....

An Inverter......converts 12v dc up to 240 v ac for powering mains powered devices.

Power supply.... a general term but for our purposes..... converts 240v ac (mains) to a different voltage dc, in our case 12v dc (or more likely 13.8v dc)

A Transformer.... converts an ac voltage to a different ac voltage... in our case 240v ac to 12v ac

JRH wrote:

---

Jimricho, I spent many years as an electroplater and our transformers converted 500 volts ac ( 3 phase) to 15 volts dc, now maybe there are different types of transformers to do different jobs so I am happy to stand corrected if so.

---

The transformer would have been connected to your plating apparatus via a "rectifier" circuit to convert the 3 phase low voltage ac output from the transformer to the dc voltage necessary for electroplating. The terminology does at times tend to be used a little bit loosely and mostly that doesn't matter all that much.

Likewise the alternator in our vehicle also produces 3 phase ac but this too is "rectified" (i.e. converted to dc) by the diodes. "Alternator" is just a  term for a type of generator that produces ac. The "gennies" that many GNs use are also in fact alternators, they produce 240v ac, but as the term "generator" is an all encompassing one it is also quite correct, even in a pedantic sense, to describe them as generators.

(another typo another edit)

-- Edited by jimricho on Thursday 31st of December 2009 06:30:37 PM

Hi Jim
Your views re inverter for use to feed 240v element while travelling is a concept followed by many to over come undersized wiring between alternator & fridge.

Some put the inverter in the tug & run 240v to the van.Not a good idea at all in my opinion
Others put the inverter in the van but the cables still have losses which they rely on the inverter to try & compensate for the voltage drop. If the loss is too high fridge will still not get adequate voltage even on 240v

I like the rest of your post ,it may help clear up some misunderstandings

Re elecroplate sets these were usually oil cooled 415 3phase transformer rectifiers in the one tank with oil cooling.1000amps was a common size
Been a few years since I serviced them ,So may have changed.
They usually had multi position switches to adjust output voltage which in turn varied amps as the load is  resistive.

 

DeBe wrote:

---

Cant quite see how an inverter in the tug feeding the van can be dangerous, I have one permanently mounted in my Panel van. Inthe event of an acident ive seen what the emergency services does to a vehicle, first thing they do is use big bolt cutters to the vehicles wiring at the battery. Instant nothing works any more, in a large enough smash the battery is usually smashed to hence no more voltage. If the vehicle catches alight in most cases every thing is going to be history any way. Daryl

---

            Hi Daryl

          I am not so much concerned about  road accidents, but more about installation  & insulation.
          The need to absolutely insure no insulation failure to earth can occur from either line & thus forming an EN system [Waterproof fittings, protection from abrasion, all fitting & cable rated for240v+]etc
 & of course if it feeds the entire van the risks of accidents  are greatly increased [even if fitted the van RCD will offer no protection]

-- Edited by oldtrack123 on Thursday 31st of December 2009 10:20:44 PM

DeBe wrote:

---

Waterproof fittings wernt a prob, Used power lead pluged into 240v power socket on side of van tied wire to tie points along side of van down front of van & through back door of Panel Van thick door seals dont squash cord at all. thats how i used to power a 240v bar fridge in caravan when traveling. Eventually got sick of that system & fitted 80L Waeco bar frige 12V. Daryl

---

As I mentioned earlier in this thread I haven't tested this inverter arrangement so my comments are largely theoretical but I would be very "iffy" about having the inverter in the tug instead of in the van, mainly from the standpoint of safety. Also note comments both in this thread and elsewhere about "safety switches" being ineffective in this set up.

A simple relay system could  be installed so that the fridge power automatically defaults to "ground" (or "shore" or "on site") power when tow vehicle battery power is not available. This could also reduce the amount of time the fridge is not operating when packing up and setting up, particularly in the case of camper trailers. However I don't know how significant this advantage would be in practice. I guess it it would also be an advantage not to have to remember to change the (fridge) switch over to 12v.

My own set up uses a voltage booster to recover  the cable losses and provide a stable 13.8 volts to the fridge. My only (van) battery charging capability is from "shore" power which so far has been ok as I don't do much free camping. I have bush camped for a few days without "running out" of battery power.

-- Edited by jimricho on Friday 1st of January 2010 05:33:45 AM

Hi All

WELL ,it seems we will never know the model /brand of 3WAY Fridge that only has one element.
I wonder why it has to be kept secret