i need urgent help designing an inverter using the parts i have

[audioguru]

I know whenever the motor in our AC started up it drew enough current to dim the house lights.

Either your home is too far from the mains transformer or the wires to your home are too thin. My home is about 70 feet away from the mains transformer (underground wires) and nothing causes any noticeable dimming.
I guess the guy with no money and no civilization does not have running water or sewer, no garbage pickup, no mail and no school buses. In the desert I wonder where is the water he is pumping?

 

[tomizett]

I say this, not because I want to discourage you, because I don't....... I actually feel this is an EXCELLENT AND WORTHWHILE PROJECT. And many people here would help you. But your crops will be dead by the time you finish up a fully tested inverter.

I agree with Schmitt. It's a very worthwhile project, but I think you'd have to be a real export in power electronics and have a lot of facilities and a wide stock of components available to you to design an inverter like this in such a short timeframe.
Possibly a simple modified sine wave system like Tcmtech suggested could get you up and running. Do you have a suitable transformer (it would need to be very large)?

I think it might be a more practical short-term solution to try to repair your existing inverter. Perhaps you could start a new thread to look into this?

 

[tcmtech]

Do you have a suitable transformer (it would need to be very large)?

Any standard 1 KVA rated unit would handle his pump all day without breaking a sweat.

I think it might be a more practical short-term solution to try to repair your existing inverter. Perhaps you could start a new thread to look into this?

Unfortunately, his lifestyle/life choices have been questioned so I suspect he has already took his ball and went home.

 

[audioguru]

Unfortunately, his lifestyle/life choices have been questioned so I suspect he has already took his ball and went home.

Back to his cave in the desert? Animals do that.

 

[edddyyyy]

I am a city boy. I do not understand why some people live on the moon without electricity or money but have a good internet connection and maybe satellite TV.
Farms around here do not irrigate with pumps, they use rainfall. Why do some people try to grow crops in a desert?

its not desert here, in fact its very fertile. the idea of irrigation is to give the crops a start where the freshly turned soil dries out fast in the sun, killing sprouts. it also gives the crop rows an advantage over the weeds.

i carted the genny up to the field behind the elecctric buggy but on cranking the power kept failing. stripping it a bit found the last guy servicing it threw a non fitting rod in the bearing. i had some 8mm threaded rod and retapped the shaft for that and got some water.

the isolated dc-dc converters are on their way from china. i still have to think about feedback. the pic hex code didnt seem to have any implementation of that. i need to vary the pulse width without being able to edit the software.
could a 555 work to shorten the pulse code from the pic? that would totally mess up the waveform. im already having doubts about the igbt switching frequency.

enough input and tinkering will get something going with what there is even if its a bit mcguyver.
its certainly going to help my understanding of this type of power electronics. im more into ham radio really.

 

[edddyyyy]

you guys mentioning transformers, i dont see the need for one as i am starting off with a nominal 380vdc from the fuji flexis. i can add a chopper to the 24v system at a later date to add to that 380v line with 500w more.

 

[tcmtech]

im already having doubts about the igbt switching frequency.

Why? They have a <100 nanosecond rise time and <300 Nanosecond fall time giving them an easy 1 MHz + top end working frequency range.

PWM waveform shaping for a standard 50 - 60 Hz doesn't need to be much over 10x the base frequency IE 500 - 600 Hz unless harmonic noise or audible whine is and issue then jumping things up into 20 - 30 KHz PWM frequency can be used which would still be a magnitude of order or better under the IGBT's maximum hard switching frequency capabilities.

 

[tcmtech]

Relating to what I have said earlier about using a common LM3524 or SG3524 Ic and a set of High/low driver IC's to make a simple H-bridge inverter.

With mosfet power stage.

With Transistor power stage.

Here's the link to those circuits and their related build data.
https://www.instructables.com/id/250-to-5000-watts-PWM-DCAC-220V-Power-Inverter/

The only difference here is that the as shown designs are for push-pull power stages so that end of the circuit would be replaced with the driver IC's and H-bridge.

The only downside or concern here would be that the DC power source needs to be capable of supporting more than the continuous duty power consumption of the pumps which if yo have 500 watt pumps running at 800 watts the supply side had better be capable of supporting at least a 1000 watts for extended periods and 3X that on pump start up which rules out direct solar panel drive.

In your thread over on AAC you say your 400 VDC solar panels are only rated for 600 watts which means that some sort of battery power buffer is going to be needed between the panels and the inverter in order to get the pump started plus drive the 800+ watt load.

Dang those numbers and reality again.

 

[bountyhunter]

Either your home is too far from the mains transformer or the wires to your home are too thin.

Induction motors have HUGE surge currents at start up. That's why they have "start capacitors" that kick out via relays to help them start. Even with start caps, they can have enough surge current to visibly dim the lights for an instant when they start.

 

[tcmtech]

Induction motors have HUGE surge currents at start up. That's why they have "start capacitors" that kick out via relays to help them start. Even with start caps, they can have enough surge current to visibly dim the lights for an instant when they start.

My central air is a 5 ton system with a 1970's compressor that draws roughly 5 KW continuous and hits the better part of 80 amps on start up.

Even with that my lights don't dim and I am on the far end of 350 feet of 4/0 aluminum service line when it starts. The worst voltage dips I have seen are still less than 5 volts at that.

I agree with AG. You got wiring or supply issues.

 

[edddyyyy]

i have some capacitors to give 10000joules per second to cover starting, although most commercial units to do this job have a slow start to build up the voltage and frequency to avoid storage banks and get away with a reasonably matched pump/solar panel system. when my friend does the long drive out here with another 8kw solar (glass cracked so for free )
there will be no worries except the pumps overheating due to the lift distance. they do cut out after 30 mins or so.

so getting back to the isolated supplies for the igbt:
i have these 4x15v and 4x9v 1w psu arriving in a couple of weeks or sooner if im lucky. 2 of them will directly feed each driver hybrid module and 2 driver per igbt half bridge brick. i need to keep short leads and low inductive paths to the gates.

am i missing any more important issues or will that section be ready to box up with a lump of box section ally as a water cooling pipe for the igbts ( i think they are isolated case) and that big lump can be fed from whatever i want to output my 4 optoisolated signals for switching.

how sure are we that igbt bricks: https://www.littelfuse.com/~/media/electronics/datasheets/power_semiconductors/littelfuse_power_semiconductor_igbt_module_mg06100s_bn4mm_datasheet.pdf.pdf can work at 1mhz? most info i read states 20khz as a practical limit to keep gates fully saturated, and thats a lot of heavy charge/discharge cycles of the gates that the little 1w psus have to supply (yeah i wish i read about the 3w) but there are 2 per gate so they share the load up and down.

80 ns delay time plus 20 ns rise time, plus 290 ns turn off delay, plus 70 ns fall time =460ns per smallest pulse completed but thats dependent on the driver system being able to shove enough drive though 3.3 ohm gate resister into a 6.2nf gate.
besides those figures really are the limit because that speed of switching gives NO saturated working pulse as all the time is going up or down and in the wasteful and heat generating linear zone. i assume i need at least a 0.5 μs gap from my pulse generator between switching one igbt off and the opposite igbt on or they will short out the supply for 460ns.

my spwm pic is giving 20μs minimum pulse width. at mark/space 50% its 320μs per cycle so at about 3khz i am not really pushing into undefined realms. (i say about because im measuring a spwm wave on an analogue scope: cue suggestions to buy a new HP dso) theres some 20mhz breakthrough from the clock but nothing bad.

i have to see to the geese first, then back to crunching some more numbers to see how much power i will need to drive the gate, how much power i will lose, and if i can stick with the pic, or change it or look for another hex file.,

 

[audioguru]

Induction motors have HUGE surge currents at start up. That's why they have "start capacitors" that kick out via relays to help them start. Even with start caps, they can have enough surge current to visibly dim the lights for an instant when they start.

I forgot. My AC is high efficiency and uses a variable speed DC motor for its in the home air circulation fan. The compressor motor outside might be capacitor start but it does not cause the lights to dim for a moment when it starts.

 

[edddyyyy]

my AC has higher efficiency than yours: its called 'deal with it like a man' and it works from -40c to +50c with the addition of a little 'antifreeze' (beer, wine, rum).

 

[edddyyyy]

https://tahmidmc.blogspot.bg/2012/11/feedback-in-sine-wave-inverter-pic16f.html

is it really not practical to work out the pwm on the fly rather than tables? can anyone discuss the pros and cons?

 

[tcmtech]

Most of us do deal with it like a man and work to gain the resources to be able to afford the luxury of not living like our sod house dwelling predecessors did or homeless bums on the street do today.

Having central air costs me maybe $40 a month during mid-June to mid-September which in my oil field fracking job that's maybe 4 - 5 hours of my take home pay out of my 3000+ hour work year.

 

[edddyyyy]

Most of us do deal with it like a <sheep> and work to gain the resources to be able to afford the luxury of <being a pussy>.

Having central air costs me maybe $40 a month during mid-June to mid-September which in my oil field fracking job that's maybe 4 - 5 hours of my take home pay out of my 3000+ hour work year.

i love fracking and anything else that keeps the price of LPG low, especially if the only consequences are the odd american school or hospital falling into a giant sinkhole LOL.

anyway we can discuss our lifestyle choices on a thread i just started. should help keep this thread on topic.
https://www.electro-tech-online.com...-lifestyle-choices-that-are-different.148317/

 

[tcmtech]

Fracking puts material (sand and fine aggregates) into the ground not takes it out thus it can't form a sinkhole nom matter how hard you try..

Also. sinkholes are a shallow surface phenomenon (typically less than 300 feet deep) and related to large underground naturally formed or localized man-made cavities like sewer and storm drain lines or mines collapsing.

Fracking happens at depths of thousands of feet and covers areas up to hundreds of square acres and add volume to the ground not removes it.

I can respect others lifestyle choices if the can reset mine but I have little tolerance and no respect for blatant ignorance and outright stupidty of subjects that I know intimately one that have very well documented factual data available freely to anyone willing to open their eyes and look at and learn about.

Prove me wrong and give me one valid credible link to any story that shows that fracking caused a sinkhole anywhere regardless of whether it was under a hospital or school or out in an open field. Extraordinary claims require proof otherwise they are just idiotic scaremongering stories continually retold by fools and idiots who are too stupid or self-riotous to actually learn the real facts about what it is they claim to hate/fear so much.

 

[schmitt trigger]

https://tahmidmc.blogspot.bg/2012/11/feedback-in-sine-wave-inverter-pic16f.html

is it really not practical to work out the pwm on the fly rather than tables? can anyone discuss the pros and cons?

It all depends on you processing power and available memory.
With a general purpose microcontroller, I would think a table is more efficient.
If you have a full fledged DSP, then it may be best to synthesize it.

 

[edddyyyy]

It all depends on you processing power and available memory.
With a general purpose microcontroller, I would think a table is more efficient.
If you have a full fledged DSP, then it may be best to synthesize it.

so far this was my first attempt at programming a pic, or uploading to it at least. i just got a hex file from the web and dont have any source code so i dont know how the pic i am using works.
i do have a variety of pics quite a few of which have pcm outputs, none have proper dsp.
a lookup table would have advantages of being programmable like a pcm function generator with a choice of frequency.

at 3.3khz switching could i maybe use the headphone output of a computer? i have an olinuxino imx233 on the shelf running some bastardised arch linux. this board also has lots of gpio and i think some of those have pcm.

 

[edddyyyy]

https://www.industrial-electronics.com/images/elec-pwr_7-15a.jpg
i just saw this and wondered, why are they driving the second module a separate waveform instead of the spwm lines crossed over from the first module. am i being more stupid than usual, or is it for gate drive efficiency?