In hot weather especially, the mains voltage in campgrounds tends to vary widely depending on how many air conditioners are running at any moment. And a hundred watt auto-transformer is not that small nor that light. The switching mode 14 volt supply will be lighter and automatic and produce less heat. It will also probably cost less than a good transformer.

 

Autotransformers typically do not raise voltages. So in an under voltage circumstance the autotransformer won't be able to increase the voltage. At least I've never seen an autotransformer with higher output capabilities. They may exist. I know I don't know everything.

 

A rather crude method would be to use a 40VA mains transformer with a 24V secondary in series with the supply to the fridge to boost the supply when necessary. It could be switched in automatically when the mains dropped to 220V.

 

Yes, you could use a 100W (or even 170W) autotransformer. It would weigh about 500g. Or you could use my circuit from post #18, which would weigh about half that.
Just a further thought, you could switch the transformer in post #18 with the thermostat, which would just give it a boost if the weather was warm.

 

A rather crude method would be to use a 40VA mains transformer with a 24V secondary in series with the supply to the fridge to boost the supply when necessary. It could be switched in automatically when the mains dropped to 220V.

You mean, like I suggested in post #18?

 

The circuit in post #18 requires manual switching. The TS wants automatic voltage regulation.

 

The circuit in post #18 requires manual switching. The TS wants automatic voltage regulation.

Autotransformers need manual switching too. Thermostatically switching the boost circuit would be even better than voltage regulation.

 

The refrigerator will run on low voltage DC. post #1) The problem when traveling is that with all of the wireing back from the car electrical system the voltage is not adequate for good cooling. Sveral posts have suggested a regulated power supply, which a switcher will be the most efficient. What is it about that concept that is so hard to understand???
A regulated supply automatically keeps the output where it is set. The switcher is lighter and cheaper and smaller than a linear supply, and since the load is a heater element it is not picky about noise or ripple.

 

Several other posts have suggested running it off gas. The gas burner has a thermostat.

 

Several other posts have suggested running it off gas. The gas burner has a thermostat.

My experience running our refrigerator off the gas tank is that it is a rather expensive choice, and so, since we are already paid for the electric hookup which provides fans and lights, that refrigeration is free. And certainly the electrical operation also has a thermostat control. In fact, for quite a few years caravan refrigerators have needed some power, usually the 12 volt circuit, to cool with gas. . And the fact is that with the higher DC voltage available from an adjustable regulated supply the cooling should be adequate. It is the lower DC voltage that prevents adequate cooling otherwise. The current at 12 volts for 170 watts of heating is 170/12 =14.17 amps, which probably is not available from the power converter and the wiring. Thus I suggest the separate regulated supply set to 14 volts. And for a heating application like this it does not need to be clean, noise free power, so a cheaper switcher could work out very well.

 

You mean, like I suggested in post #18?

Essentially, yes, but automated and having a more generous VA rating for the tranny. A multi-tapped tranny would be nice (though involve quite elaborate switching electronics), but I couldn't find one listed anywhere with the tappings you suggested, hence my suggestion of a cruder system with a standard single 24V secondary. A custom tranny would be VERY expensive I think, even though the VA rating is quite modest.

 

24V would require an 18VA transformer (load is effectively 24V @ 0.75A). Most would be centre-tapped, so that would give you two settings.
Two 9VA 6-0-6V transformers would increase that to four settings, which, in the circumstances, would probably be enough.

 

My experience running our refrigerator off the gas tank is that it is a rather expensive choice,

My caravan fridge used about 500g of butane a day. That's less than £2 worth. Compared to a pitch fee of between £15 and £25 a night, but I don't pay hook-up fees, so I might be paying less in pitch fees.