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Forum Index : Electronics : 6Kw Ozinverter build
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| Author | Message | ||||
Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Odd, not so on my version. There is no way 50V from the drain leg (pos rail) can show at the gate terminal unless the mosfet is faulty or the snubber cap is shorted. But then, I do not have a schematic for your board, about time one of you traces it out for the benefit of all newbie builders. Klaus |
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| johnmc Senior Member  Joined: 21/01/2011 Location: AustraliaPosts: 282 |
checkout " A newbie ozinverter build" by tinyt on page one tinyt has produced a very good schematic pdf file of both the power board and the control board . As Revlac has said the gate source paralleled bleed resistors my power board gate source has a effective bleed resistance of approx 3k3 ohms cheers john johnmc |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Pins 3 & 8 are the low side gate drive, I have not put a meter on it but I would have thought they would be closer to ground than 50V. Mark what voltage do you get on pins 4 & 7?  2018-05-03_220947_2018-02-16_025148_EXP_POWER_BOARD_SCHEMATIC_P1.pdf There are only 10 types of people in the world: those who understand binary, and those who don't. |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Pins 4 and 7 nothing, only pins 3 and 8 do I get voltage and of course the two parallel pins at either end, between 1,2 and 10,9 Cheers Caveman Mark Off grid eastern Melb |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Thanks for pointing that out John, I must have missed the original posting. Now I can see what you guys are talking about  That schematic version mad posted is a bit confusing with all these gate diodes, I think one Schottky diode is plenty here  . Klaus |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
You are right to use the schottky 1N5817 instead of the signal diode 1N4148. Even though the schottky has a higher leakage current and slightly higher Trr, I think it is better for this application because of the lower forward voltage drop at higher forward current. The 1N4148 is a flow down from the EGS002 schematic and I just kept it. From wikipedia: 1N4148 - switching signal diode Vf = 1V @ 10mA If(avg) = 200 mA (average rectified forward) Trr = 4 ns (reverse recovery time) From M.C.C. datasheet: 1N5817 - fast schottky diode Vf = 0.45V @ 1.0A If(avg) = 1A Trr = 10 ns (reverse recovery time) |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Doubt the forward voltage is important, as the HY4008 turns off below 2-4v, so the extra .5v is not material. I would keep the 4148 and throw away the schottky. 4148 is 250% faster, so any hysteresis in the system will come down faster.... ie we are closer to real time. Forward current pulse is 2000ma for the 4148, repetitive is 500ma.... and we are only getting rid of 31nC of charge... in parallel with a 5r6 resistor.... and we only need to get it below 2-4v for full turn off. The EGS002 folks think the 4148 is fine.. and I think so too. I like this one, but can't seem to see the 4uf bypass cap for the bulk caps  That cap is important. .......oztules Village idiot...or... just another hack out of his depth |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Mad, you are correct, I was looking for a complete circuit. I was testing pos and where else it completed a circuit. So pos and pins 3,8 gave 50v. I think this inverter is cursed and it has it in for me, I just went out to look at it again and lent my hand on the bench and I got stabbed by a turfed 2110 that was sitting on the table with the pins up.   Cheers Caveman Mark Off grid eastern Melb |
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| tinyt Guru Joined: 12/11/2017 Location: United StatesPosts: 438 |
I think this is my latest circuit trace of that design. This now has that missing capacitor. 2018-05-04_074827_Oztules_Control_PCB_and_Power_Board_Schematics.pdf |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
So a dead cockroach got you :) I had assumed you would be measuring from ground to the pins to see what voltage is present. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1026 |
Mark I found a short on my board that i didn't see in the dark last night So it's worthwhile checking every thing through, is it easy enough to take the fet out and try the voltage again? Putting the battery leads the wrong way around gives me that result as well without the fets in Nice schematic there tinyt. Cheers Aaron Off The Grid |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Nice work there Tinyt.... I will steal this for my files... ... even if I think better with the circuit board view.........oztules Village idiot...or... just another hack out of his depth |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Oztules, could you please enlighten me as to *why* that cap is important? I'm missing something here, 4uF in parallel with several times 10,000uF?? FYI, my inverter does not have this 4uF cap, never saw it mentioned or shown on a schematic here. Yet my inverter works now fine without it, could that be the reason of my initial problems? I do have 2 x 0.22uF bypass caps there instead. Klaus |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
It is not the size that matters this time, as much as it is the type of cap. Electro's have good low frequency behavior but lousy high frequency characteristics. We have two primary frequencies, and probably myriads of harmonics to boot... so the electro does it's bulk thing, and the ceramics do their HF thing. Remember, we need to present the DC as a low impedance to the fets to quench voltage spikes, and as we switch at over 20khz, we expect that frequency and harmonics of that frequency to be prevalent.. The electro's won't help much here. They will with the 50hz though. So to help stop the ripple in the big caps from these frequencies, and help keep the DC source looking low. Keeping ripple in the big caps low is good. We have the bypass caps of ceramic type... cheap and low impedance to high frequencies compared to aluminum electro's. Your low esr caps will help enormously here to keep the temp down as you have no 4uf cap. The switching noise will be also quelled, but the Madness totem's will help here too. Thats why I like them, even if I don't need or use them. They are a better idea I think.... better noise immunity. The unit will do mostly ok without the 4uf, as you have found, and it will even do ok without the 40000-60000uf too,( but not for more than maybe 500w-1kw....) mine gets into the 30hp ( 22kw) range starting the lathe.... not sure what would happen up there with yours...should be fine.... but would feel better with the 4uf in there, and we don't need more ripple in your big caps if we can avoid it easily. So it is a frequency thing... trying to emulate a loudspeaker box... a tweeter for the highs, and a woofer for the lows... and a midrange if you want to go that far. Heavy leads and tracks make the job of the electro's slightly easier, as the battery is the low impedance, but the high frequency will still be there, as the impedance in the leads will be markedly higher for the high frequencies, and thats why we place it as close to the dc bus as we can. I don't see this as a cause for your previous blow ups though. Warpspeed may have more to add or corrections, as there will be plenty of nuance there I'm sure. ......oztules Village idiot...or... just another hack out of his depth |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Very comprehensive explanation there oztules, I like that and you convinced me to fit such a cap next time I open the cover. Thank you for this detailed reply. My lathe has only a one Hp motor and no sweat staring that up. I think the abrasive cutoff saw demands a bigger kick to get going. Its nice to have an inverter that works so well and now in the cooler time of the year its fan has not been turning on for a couple of months. Klaus |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Well Poida was very helpful, what a top bloke. He found two issues with my control board. A burned track and a crap solder joint. That got sorted out. I took it home and tested with the power board with 4 fets and no caps. All went well, no issues, nice wave with a tad of ripple in the wave, but no blips at all. Put the caps in and the wave cleaned up perfectly, however, the machine kept restarting, I was watching the cro, the wave would stop and restart again, it would build up and bam stop again, the process kept repeating. I went to check the 5v supply and BAM! yep fets blew again. These boards have copped a pretty hard time, God knows what burned out bits of track are unseen below, they have been a good training tool, however I have conceeded that since my first and subsequent mistakes with them, they are just plain rooted, and not worth the effort to perservere with. I'll start fresh with new boards when they come. Next time I'll be a lot more careful not to stuff up anything. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Mark you have probably worked it out but I will say it anyway. Until you get it running properly leave the caps out and run it with a resistor in series. It will save you from becoming shell-shocked from the exploding FETs. It can have a really horrible waveform but won't go bang with the safety net of the resistance and no caps. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yes and I really need a proper Oscilloscope. I quoted really really high on a job I didn't want the other day, if that goes ahead I'll buy a digital storage scope. It's odd how the crap jobs I don't want and quote high, I seem to still get them. That's how I justify extravagant expenses to the wife, as it's basically extra money from unwanted crappy jobs, (usually many stories high and a tad dangerous) Cheers Caveman Mark Off grid eastern Melb |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yeah I actually did do that and it ran fine, when I took it to the forklift battery then I ran it without the resistor to test some loads, that's when it had the restarting problem, it didn't do that with the resistor/s. Millions of possibilities, I'm done with those boards, not wasting any more time on them. I'll be happy to see the new boards. Cheers Caveman Mark Off grid eastern Melb |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
A secondhand 20MHZ CRT CRO will do the job for you, take your wife out to dinner with the money you save and she will let you play with your toys. I unwound 2 cores today getting ready to build another inverter, both had the same label made 3 1/2 months apart the second one is black as and about 30MM bigger. Had windings that were all joined together halfway, first one I have seen like that. I will leave that one aside and unwind another tomorrow. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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