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Ok, thanks for pointing that out, i must have overlooked that by not
reading all the replies
Still, i think the pulse technique will be better because of the effects
on the transformer that is probably designed for AC like 50 or 60Hz.
Since it is going to drive a resistive load (only) i think i would raise
the frequency up to maybe 100 or 120Hz, and then a square wave
would probably be ok. In fact, i might go as high as 200Hz, at least
to try anyway. The only drawback i can think of at the moment is
the audio noise that may come out of the transformer...this would
depend on the transformer and just how perfect the square wave
was as compared to a perfect 50 percent duty cycle. Losses
will be a little higher at 120Hz, but at least the transformer
would be operating more comfortably (not near saturation).
I dont know exactly what the core is made of, so i wont say
too much about this, but it does sound like it's ordinary EI
low ac frequency laminations (50 or 60Hz).
Fridges in caravans use heating elements to work, usually both electric and gas - so plug it in the mains when parked on a site, and use a gas bottle when not.
However I live in South Africa and there are many places to camp where no 220V power source is present (in the bush). Also, some of the older caravan parks have poor / under rated supply so much so that I have made an adaptor that will allow me to parallel two powerpoints.
These fridges are also significantly more efficient than people give them credit for. Incorrect levelling, installation and venting give them a bad name. I authored a two part article in our local caravan magazine in which I put to test my absorption fridge. Probably the worst failing they have is the hysteresis of the temperature controller, in my case +-7,5°C. This brought about temperature ranges in the fridge that ranged from freezing in the bottom of the fridge to unacceptably warm. I am busy looking for suitable circuits to better control the temperature range to within about 1,5°C.
on the transformer issue. It is a big and heavy puppy. I would estimate that the back of the E core is about 120mm long and that the unit weights at least 2kg's. From what has been said here it is probably 50Hz.
on the transformer issue. It is a big and heavy puppy. I would estimate that the back of the E core is about 120mm long and that the unit weights at least 2kg's. From what has been said here it is probably 50Hz.
Sounds like a 50Hz transformer.
IIRC you say its got a centre tapped primary.?
I would suggest you apply 12Vac to the secondary,load the primary with a 60W light bulb, then measure the voltage across the lamp and windings.
Thats using the transformer as a step up.
Lets know what you get
My caravan is on our farm near Port Elizabeth.. its a Gypsy 5.
Great, you know I have never been to PE? We have a Penta.
I will test the tranformer this weekend as you suggest. There is no centre tapping but is does not concern me as transformer actually has a 24V primary so I need to rewind anyway (assumimng the primary is on the outside). I am hoping that they brought out a centre tap and that it is concealed below the outer insulation then i have no problems.
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