inverter double wound transfromer overheating

[bahnfeldt]

is there any way of producing a filter to reduce the harmonics produced in a 5kva pure sine power inverter( step up transformer)

i know this is a manufacture design issue but i have getting no sense from the supplier

under very little load ie a standard refrigerator running from this inverter the inverter after a 24 hours from cold will cut out on over temp on the step up transformer

with the frig load connected start up current is approx 6 amps

running current is 1.0 amp on the 230 ac side

i measured the temperature its gets to with the safety disconnected i could not believe that it got to 125 deg Celsius

the transformer is a double wound copper  dry type

i have searched the net trying to find any way of dealing with this, i have a 3 kva type inverter of the exalt same type winch  is fine  

 so i am presuming that there is a harmonic being caused from the pwm switching causing a harmonic in the transformer that it is causing this

the main board heat sink stays cool

with the thermostatic controlled fan kicking in only when you  load it up

with no load at all connected the transformer gets very warm but does not cut out on over temp

is the fridge responsible with any of the harmonic

any suggestions  apppreciatied

cheers Arny

[electronbaby]

I was going to suggest that you try some bypass caps on the xfmr to ground to get rid of some harmonics, but are you sure that the double wound xfmr isnt a ferro-resonant xfmr? This would explain the heat build up. They like to run hot. They work pretty good for regulation, but suck as far as conversion efficiency goes...probably not what you want on an inverter based system.

Just a thought...

[bahnfeldt]

yes you may be right i am also thinking the iron leaves maybe not up to a high quality

heat = energy that comes from batterys in this case so not good ,the temp staying the same under all load conditions say what though

[electronbaby]

The core of the xfmr (in a ferro-resonant design) is meant to reach saturation quickly and prevent any sharp changes (increase or decrease) in flux from the primary. This effectively regulates the output and tends to hold the voltage and frequency somewhat stable. The downside is that they draw quite a bit of power to hold the iron in a saturation state. This power is dissipated as heat in the core due to eddy currents. It will heat up even when you are not pulling power out of the secondary. There is a good explanation here:

http://tristate.apogee.net/pq/qrsvfer.asp

This may or may not be your problem. Not sure what type of transformer you have.

[donald77777]

I may not be reading this right however, you say the inverter is cutting out from heat. Wouldn't a fan help your situation? Disconnect the inverter pull off the top if not in warranty, cut out an 80 mm fan hole. Attach a fan.

[wpowokal]

Arny, can you post information about your system ie inverter type modle number, how the AC side is connected, how the DC side is connected and where your earths are.

I smell a fault somewhere, I just can not see how even a cheep inverter (not saying your's is) correctly installed should trip on high temperature on low load.

allan down under

[bahnfeldt]

eys me either

it seems that the saturation of the core with the heat build up as i have 5 of these machines do the same thing,the Chinese when testing probably do not see the fault it takes at least 8 hours from cold to happen, the same model in 3000va get hot but not ot fault level, so it seems all transformers are not created equal