 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Electronics : PSWGT-300 efficiency boost
  Page 3 of 4   |
|||||
| Author | Message | ||||
| Alasdair Regular Member  Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Karl It does sound bad, but I think it's just a warranty gamble. These cheap inverters are good value if they work, and it seems that if they last more than a week, they will keep on going. I have two that are both doing about 200watts each and show no signs of distress, however I bench tested them to the limit, and the 300 watt rating is a bit of a stretch. The efficiency drops sharply past 200 watts output and the losses turn into heat. I think the 300 watt rating is only safe when taken as input power, not output. I call it 'chinese deration'. Divide claimed performance by two thirds and your safe. Your 500 watts a day only gets you 10c daily or $36.50 a year providing you get reliable sun. Most mono crystal panels should give at least 20 years service, so keep your fingers crossed for the inverter. After three years your in the green or sooner if power costs keep rising. Cheers, Alasdair. Amc-elec |
||||
AMACK Senior Member  Joined: 31/05/2009 Location: AustraliaPosts: 184 |
Hi all, I have been looking at a new GTI inverter and this one is Australian standard aproved. (As4777) It is a 24 volt 2000 watt Solar worx made by invertek. Jaycar sell them for $2,799 but I got onto a bloke that can do me one for $2,100. It is an Australian company in sydney too. Some of it is made in Taiwan but most stuff is china or Tiawan now days anyway. They also do a 12, 48 and 96 volt version too. If you have a look at the specs on them they are a good little unit when conected up to a combi unit. They can be stacked and with the combi unit the GTI can be used as a stand alone inverter to feed the house when the grid power goes down too, unlike oner GTI's. Amack *Note to self 1. Make it thick 2.Make it heavy. 3.Make it stronger than it should be. 4. Don't rush the first job as the second job will cost more and take mor |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Amack I knew it wouldn't be long before an Aust standard approved model was passed. The only problem I see is the J..... supplier. My experience with their products, and knowing one of their Electus buyers is that quality is totally irrelevant, mass buy price governs the range and claims are sometimes difficult. I'd bet the units they sell will be no better than Jack chang for quality and reliability, but you do get a counter top to bang your fists on, instead of your keyboard. Regards Alasdair. Amc-elec |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
I have just found one of my PSWGT-300 GTI's has gone u/s. It was on 200 watts of solar panels, and had a pretty easy life, it had logged 160kwh, and it's output suddenly dropped to 25watts. I opened it up, checked all mosfets okay, but found one odd one that had obvious signs of being replaced at some time, meaning Jack chang has passed off a second hand warranty return to me as new with a bodge up repair. I found the two controlled avalanche diodes on each pair of primary mosfets were cactus, one cooked to white, and the other split in two. How this can happen with the snubber caps in spec and output never going much past half way is beyond me, unless they were pre baked before delivery, it was the primary mosfets that had one of the four replaced. I tested pre drivers and no fault, so I'm hoping to fix fault by sourcing replacement transient supressor C/A diodes. I tried lower voltage ones from parts bin but they smoked instantly so I'll have to order 440 volt originals. I'll also replace the four mosfets as a set, and repair damaged tracks from previous dodgy repair, it looked like a blowtorch was used. It's probably worth keeping an eye on these front end parts, as they seem to be working at the outer limits. My other GTI cooked the two 4.7 ohm resistors, and I upgraded them to 1 watt carbon film, and that unit is past 200 kWh logged and still going ok. I'll keep you posted on repair. Regards Alasdair. Amc-elec |
||||
| VK4AYQ Guru  Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdiar I cooked one of mine the other day when the amp meter shunt cooked subjecting it to high voltage direct from the alternator with no load. It blew the input cap to bits and the 20 amp input fuse, cant see any damage to other components at this stage, the two resistors you mentioned are intact and on spec so maybe yours got cooked at the earlier problem, I have just pulled the top off and haven't removed the board yet, from a visual inspection it is a good little board and well worth playing around to get it going again, I was quite impressed with the board construction and the simple design, I don't know what is under the board yet so I hope that is as good. I had ordered new resistors but seeing they are OK after that melt down I will leave the original for the moment. It was up around 100 volts when it blew so maybe the fuse did its job. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Wow, that will sure blow it. The board is good, but the gate tracks are mighty thin and as I found with mine one had been damaged and a blob of solder was sculpted across to the free gate leg. There are a couple of lsi surface mount chips under the board, and someone has done a number with a belt sander to remove part numbers, along with anything else standing off the bottom of the board. I thought they would be micro's, at least one is, so it makes you wonder why they wouldn't just embed the firmware, rather than physically grinding off part numbers. Maybe a truckload went missing from the factory.. Amc-elec |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair Mine doesn't appear to be butchered on the top anyway, haven't looked under it yet. They may have ground the numbers of the ic so it cant be replaced by outside service people. I would love to get my hands on a circuit of these things instead of swimming in the dark. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Yeah, I have considered drawing it out, but those micro's make it pretty fruitless, and I hate drawing multi layer boards. It does look pretty simple, all the hard work is done in the code, they've just assigned INS and outs to drive both ends and track input voltage and line frequency. The smaller pic looks like it does the display and therefore MPPT for input, it talks to the bigger chip which probably tracks line frequency and drives output mosfets to match available current from switchmode source. I think it step drives high voltage DC through that toroidal inductor against both sides of the mains cycle, the inductor absorbs the sharp transient steps and smoothest the current cycle. Much the same as those cheap and nasty faux 'sinewave' inverters do in their crude sinewave generation end. That also explains the huge emi noise and high loss at high current. Amc-elec |
||||
| leeyn Newbie  Joined: 21/03/2011 Location: Posts: 5 |
I am surprised at the slight lack of engineering with these units, as the mods are cheap and easy, and the bigger caps on dc side can only improve the slew rate of the mosfets by lowering their source impedance。。。 Buy RS GoldRunescape GoldRS Gold |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair Over the last 12 months I had purchased a total of 10 of these units, as I said I cooked one and one is running away on my old mill, so I thought I had better do a load test on them all before utilization on my next project, and guess what 6 of the ten are US, so I started pulling them to bits one will accept DC but not AC one other one is Ac but not DC the other four where shorted out with blown fuses, bypassed the fuse with variable power supply and there are a shorts on all DC inverters. Two others worked as they should with cut in and out volts as it should be 14 volt to 30 volts input and with the cap input deliver 280 watts input 315 watts. A closer examination indicates they where used units probably throw outs re sold on ebay, they had no quality control stickers as did the working ones, so could have also been factory rejects, Caviet Emptor. All the ID numbers have been removed as yours was so there isnt any chance of repair so looks like a junk box addition to me. It is such a shame as the basic concept is good but the Quality control is non existent. I tested all the 600 watt units and they all have quality control stickers, I run them up and down the range with a variable power supply and they do what they are speced to do except a bit down on power, the larger cap on the input helped but they draw more amps than my power supply can give so no definitive conclusion for maximum output. It is a shame for the company as the lack of QC has ruined a good little unit. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Bob It looks more and more like Russian Roulette buying these things. I'd almost bet they are another brand device who's warranty or defective QC failures have been, or are being patched up and fobbed off with a green sticker on top as a new product. There is no way the two I bought were new products, the boards were butchered, odd brand components, and texta written 'OK' on both units looks more like some backyard truckload of reject rubbish picked over and fixed (partially) just enough to test OK and sell on eBay. A few peoples warranty claims have resulted in replacement boards being sent, with obvious signs that they were patch jobs ex secondhand again. Buyers Beware! Have you pulled the power semi's off the boards of your failed units? Test them if you can with an Atlas or similar semi tester for performance match as well as actually just working. When these balanced switching circuits are running hard, they need well matched devices for stability, and this may explain why their cheapo fix ups don't last, they just replace one device from a different manufacturer to save a buck. If you find any dead or shorted devices, as you probably will, replace all four together from the same stick. The P75NF750's are pretty robust but throw odd gate capacitances and on curves at them at full tilt in a set and watch them fail. I used to repair Sony gear and a lot of their high end supply boards were deemed too unstable after repair to hold warranty due to unmatched semiconductor performance, so they wouldn't even supply parts, just fit a whole board instead we were told. Codec forbade us from fitting repaired supply boards and threatened all kinds of repercussions if we dared fix one. Jack Chang on the other hand... You may find them pretty cheap to fix properly, as long as those scrubbed out micro's are alive. Try checking for gate drive with a cro without the P75 devices fitted, you may need mains connected, so be careful. I'd use an isolating transformer, I think it wont try to drive them without mains, as it just goes to sleep. Also check the surface mounted driver transistors, they are there to slam the gate as fast as possible and overcome gate capacitance slowing the switching time and making heat. The shottky diodes on the HV side should be checked off board as well, I test these with a function generator running at max frequency and compare hold off using the cro again. This gives much more reliable results than a dc junction test and is just about as easy. Regards Alasdair. Amc-elec |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair Thanks for the advice on these little monsters, I have ordered a smd air solder thingo to try to do the dismantle without wrecking anything else. I am sure you are right about the regurgitated junk issue as there are signs of rework on them, and the only ones that have worked OK are the ones with an inspection sticker on them. A bit of advice for anyone purchasing one of these, check it right away and don't be like this idiot and leave it sit in the box till the warranty runs out not that their warranty is worth a hoot, but at least you can give a negative feedback on eBay and they hate that, as much as I hate their deception of selling reworked inferior products to us idiot Aussies. Good point on the Russian roulette, but in this case it is with one empty chamber not one loaded one. I am at present building a new shack in the shed incorporating a active work bench as the wife is sick of burnt holes in the table cloth on the kitchen table, the hot weather and rain has slowed progress a bit 36 deg again today and stifling humidity. In reality I am just fooling around with them as i think they are beyond me to fix without a circuit and most of the control circuit bits I can hardly see, had a call from Gordon today and he encouraged me to have a go just to learn a bit about how it all happens, hence the order for the hot air doover. I will destroy the one I cooked first for practice and work through the others for fun. I have a 20 watt isolator transformer so should prevent me loosing magic smoke cant find my function generator either so may have to lash out for one or make a square wave generator to test switching, more fun. For now i think they can go in the to be kept junk box until I finish the LG generator, as i want to run it on High voltage into a conventional GTI for an experiment, I have all the bits coming to make some big HV caps for that so it is a project within a project. I am getting my Chev Blitz going to mount it on for testing so i can drive it up and down the runway so I don't have to wait for wind. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Bob The blitz sounds like a perfect testbed, but any onlookers will probably think you have an air powered truck, or tell them it's a new type of hybrid, the wind turbine drives the motor which drives the truck to drive the turbine, 'you know.. perpetual motion'. I'd give the PSWGT-300's a go, I just received parts to hopefully fix mine (I'll keep you posted) and the four mosfets Q1,Q6,Q7,Q2 were only $5 each and $1 for the 440 volt diodes, D31,D32. The high voltage mosfets are even cheaper and easily upgraded, I'd also change caps C15,C16, as part of the snubber they work pretty hard, one of my 'new' inverters had a blast mark on the board under one of these (C15) and evidence of replacement so I'll upgrade them from cheapo mylars to polystyrene. 25 bucks might bring it back to life, and hopefully better than before. Regards Alasdair. Amc-elec |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair I would appreciate that, I might have a go at them in the winter when long nights give me a bit more time in the evening. If you can get it going for $25 it would be worth it for sure. have the blitz going now and the winch working so next thing is to get a tripod made for the mill, trip to the second hand steel yard coming up. People around here reckon I am crazy so can tell them anything and they will believe it, if i leave it by the road with the mill going and tell them its charging up the motor, they will leave me alone. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi there again The saga of this PSWGT-300 inverter goes on. Against my desire to waste any more time on this thing, and a partially successful repair now completed, I decided to look a little closer at how this thing works, so for anyone craving a circuit diagram, sorry I haven't gone quite that far yet, but I can break it down a bit. The unit is best broken down into blocks which are all fairly simple but a few secrets remain. The front end (low voltage side) does the work of mppt, there are three surface mount chips, U1,U2 & U3, clearly marked, U1 provides clock base and display LEDs and fan control, based on input voltage, it talks to U2 which drives SMPS mosfets via Q4 and Q5 and is able to regulate the drive into this array via MPPT with a fixed delay ramp programmed in. U3 looks at mains voltage via four 1.2meg resistors R37-40, then R35-36 and C32-34, this chip enables the inverter section to work and probably controls U1 for 'fault' led etc. The secondary side of the main transformer T1, is rectified using D7,8,9,10 in conventional bridge format, but both my units, being 240 volt have been hacked at before purchase, and modified from two stacked rectifiers, from two separate secondaries to stacked windings and one rectifier, filter and choke. I assume this is cost saving, but the diodes do have more voltage to deal with so no bonus there. The high voltage DC is then loosely coupled via choke L1 and C17 (filter) to the high voltage mosfets Q8-11. These are tied directly to the mains and looking at the way it's done, the gates are triggered via Q12-13 and track the waveform using C22-23 and a myriad of diodes D15-20 to and resistors to pull it back at zero crossing, so the mosfets are not controlled by any external timebase, just the input mains. Inductor L1 would spread the current peaks from the HF to allow the small value filter capacitor C17 to store minimal charge energy for 'anti islanding' and L2 despite being clagged with glue seems to soften current transients between the mosfets and mains, probably to stop fast switching causing gate feedback and self destruction. A quick check showed the HVDC part of the circuit is unreadable on a meter in DC mode due to the imposed current swing from the load, hence the presence of D1, but on AC around 130v would indicate all is well here, removing D1 for the test should give a much higher reading (around 360v). These will vary according to input voltage (DC). I hope this may help anyone trying to fix one of these 'unreliable' things. Regards Alasdair. through R41 Amc-elec |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi all, I have since discovered another fault that seems to creep up on these inverters, and that is the fan controller, which seems to be embedded in one of the surface mount chips. Both of mine failed following bizarre fan speed switching for a couple of days, then nothing. This cooked the transformer in one which I am rewinding, the other I heard the same erratic speed changes, so I removed the lid and caught it before it stopped totally and saved the transformer in this one. They get really hot without airflow and in both units it would have been terminal. I fixed the fan with a stick on temp switch and a 7809 regulator, even though the fan is 12 volt, it screams at this voltage, so 9v will lengthen is life and still gives plenty of airflow. I tested the surface mount fan driver transistor and found it okay on both units, just no output from the lsi chip. Hey Bob, I found an identical inverter (non powerjack) and surprise surprise it is rated at 250watts, no green label, the only visible difference is a supply voltage selector switch on the panel next to the IEC. It's probably the original source of our '300' watt fakes. I found it on you tube but can't remember the name. I'll let you know. Amc-elec |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair I have seen some of these 250 watt units advertised also but haven't tried one as I am working on the once bitten twice shy principal. The output sounds to be more realistic so it may be better or just another useless clone, only time will tell. On my 300 watt units I have the same fan problem and am cutting a hole in the top plate and fitting a 4 inch fan 12 volt computer case cooler hooked to a 50 degree thermo switch direct to the input line with a 12 volt regulator. I will find the hottest spot on the board with laser thermometer to put the thermo switch. I am just wondering if it is worthwhile persisting with these units. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Bob good idea with the pc fan, I should do same. I won't buy another of these things, but I want to at least force the two I have to pay for themselves. I think you'll find that little yellow switchmode transformer will be the hotspot, they cook even at moderate power levels without airflow. One of mine is arcing internally which I'll try re-winding, I have a machine to do it on, so it shouldn't be to difficult, I'll also add some secondary turns to get it up to 240 volts instead of 220 as made. It may improve efficiency a bit more. You should be able to get a few of your dead ones up and running pretty easily, and with your fan mod, at least get some long life. Amc-elec |
||||
| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Alasdair I have four that are still working out of the batch so i will do the fan mod on them for the moment, that will give me one per phase and a spare with the others for spares. I wonder if it is worth my time to fiddle with them, after I get the next mill up I might give them a go for the interest. At the moment I am trying to make a modular down converter for that mill, I want to run it on higher voltage, 100 to 300volts AC and switch that down to 28 volts DC, I have tried a switch mode power supply and it works alright in principal but only 14 amps out and I need at least 50 amps to load the mill but with a front end that works like a MPPT from 100 to 350 volts, all I have so far is a bit of magic smoke. At least I can see the bits I am using so when they smoke up its not hard to find. All the best Bob Foolin Around |
||||
| Alasdair Regular Member Joined: 12/01/2011 Location: AustraliaPosts: 62 |
Hi Bob It sounds like you need a high voltage PWM regulator. I designed one years ago which used 600 volt mosfets which are controlled at about 20khz using a standard pwm controller chip, looking at output voltage (you peel off a reference voltage through a high speed diode and small value cap, into a trimpot and to v-ref pin of pwm chip) The AC can be rectified with a high current bridge able to stand whatever ac voltage x1.41 + margin then chop the negative side through the MOSFET source/drain to a LC filter and it will give perfect regulation within 1% and accept input voltages between output V+10% and max gate source V of the mosfets. You could also use IGBT devices for more current, modern ones behave almost like mosfets anyway with fast switching and low gate current and capacitance, but you can pull 50 amps from a single device. I built a controller for my TIG welder using these (HG20N60) and it's a brute. Four transistors comfortably switch 150 amps at over a hundred volts in nanoseconds I put a cap and choke on the output and using a UHP halide lamp striker, impose about 7kv across the output for HF striking. The IGBT's haven't blown yet and don't get all that hot, and they're cheap, about $4-5each. PS, you may not hear from me after this post, it's been like pulling teeth to log on, and I keep getting 'access denied', all getting a bit hard, ok to read though. Amc-elec |
||||
| Page 3 of 4 |
|||||
 Print this page |
