inverter question

[adelaide]

If i had SAFE 240v batt bank could i use a circuit like end of inverter (circuit)to make 240vac 50Hz (australia) with less stand bye current and higher out put cos is cheep to bye 50a fets? , another advantage would be no inverter volt boost running all time?

[Nando]

Adelaide:

I presume that you are saying that you have a Safe ( trade name) bank of batteries with 240 Volts and use a circuit to produce 240 V @ 50Hz. ?. Right ?.

One can make a transformerless inverter to produce 240 Vac MSW ( Modified Sine Wave) with good power if you have a battery with 240 volts.

The question, how do you plan to charge the battery bank ?.

The IGBT or MosFets, for a 240 Vac output, must have 500 Volts break down -- this for  MSW wave form.

For Pure Sine wave form you will need 1200 volts breakdown for 800 volts ( 400+ - 400+ ) supply, or a bit more difficult circuit using 4 Fets and 400 Volts only.

Nando

[adelaide]

ty for reply ,i have 50 x 12v sealed lead acid gel cells   (gmb) 75 ah 600 a max peek recommended drain,

 charging is easy off say 100s f/p or the 80 / 60 need to be delterd at least maby 1/2 rota paralleled to charge.is easy that side I'm looking for help on the voltage i would need ? and maby use end part of inverter? is above my head but people hear are up to challenge i think , i know safety is nuts important cos 600a at 240v is free cremation. eg earth leakage on bat side as well (have fets that trigger much less than 1 ma) isolate dc from earth short mills disconnect bat bank in 4 places when door opened to batt room or work or sensed anomaly (latched)

[oztules]

Adelaide

A H bridge switching topology...as in a cheap inverter is possible with 240v dc. Output will be square wave. The fets will need to be at least 500v.

Nando has some good ideas using a small inverter to supply the pulse via transformers to isolate the fets and drive them, although I don't think that it would incorporate a current regulation system for the switches (may be wrong here, Nando hasn't been explicit about this). Apparently this has not been a problem to date for those who have used this system.

 As you try and emulate a smoother waveform at 240v AC out, you will require progresively higher dc voltages. Oatley electonics has a small inverter using 350vdc 1/3 off 1/3 on and delay timing on mosfets of approx 3.3ms this give you a drive wave from the inverter that has the same RMS and peak voltage as a standard 240v mains.(but still not true mains). If it were fed through a decent choke, it may well get closer.

 http://www.oatleyelectronics.com/kits/kitsall.htm kit K127 This could give your friends a starting point for better wave forms......but requires 350v DC. and still a H bridge output. For the Aus $35.00 it is a good learning tool.

Fanman also has a squarewave setup, check his dairy/comments. Last heard he is offering plans for it for free (+ postage and handling I think) Once again this would use 240vDC which may suit you, and uses a cheap inverter and small drive transformers to achieve square waveform output. I think there is no electronic current detection, and no problems reported from Dave.

Hope this helps  When I get time I will investigate a H bridge D class output, using a sine wave to drive it ......should be interesting I think. It would require higher voltages again.

...........oztules

[oztules]

Adelaide

Nando's design has current protection, and Fanmans does not.

ie:

"fanman dave here, youve pretty much hit the nail on the head, with your explanation of the transformerless inverter, i bought a radioshack 75 watt msw inverter and used it for the wave signal, that goes to four radioshack 300 milliamp 12 volt to 120 volt transformers, that circuit controls the on off signals, then the 12 volt output goes to 8 mosfets 4 in parallel that turn on for the positive half cycle and 4 that come on for the negative half cycle. and yes it all goes through a full bridge circuit. it really does work really good and guite efficintly i measure only about 4 watts idol current, it has no overcurrent protection, or no voltage regulation, so it fluctuates with voltage, but ive never had any prblems in that regards. my batteries are 120 volt so straight in and straight out, uasuly it comes out about 130 i figure thats from the rms value, im not sure. when lightning strikes all i have to do is replace the mosfets, its really easy"

and

Nando said:

"The circuit can be made quite simple.

Using a small 75 watts MSW DC/AC inverter driving a 60 HZ transformer with 4 each 12 volts secondaries to drive the full bridge.

Then another small 50 or so watts transformer with a 12 volts secondary to charge the battery driving the 75 watts MSW.

In addition a small circuit to detect the incoming DC voltage to turn the small 75 Watts MSW ON and presto a 5 KW converter

The IGBT'S have to have around 100 amps capability with 600 volts breakdown for 5 KW.

In addition current detector to protect the converter"

Sorry about that Adelaide.

Yhis should be enough to get you going if your friends are adept at this, they will know what it means.

...........oztules