Power Supply 60v 250A Repair - Page 1
Forum section: electronics / repair

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 01, 2022, 12:19:22 pm
content: Hi,Its a long holiday in my country, since I was stuck with my Wavetek 9100 Repair, I decided to take a look on a beast of a power supply I acquired some time ago.This is a TDK Lambda ESS 60 250. Its basically a 250A "bench" Variable Power supply. I got this unit defective with previous repair attempts by someone.It requires 3 Phase supply 415V So before powering up, I opened up each section, checked for shorts, lose contacts. I found a 33 ohm 25W Wire wound resistor open (marked in red). Here is the block diagram for reference:These resistors are used to soft start the PSU, in which the resistor is connected to capacitor in series to control inrush current, after a given time the relay engages and bypasses the resistor. I found it strange a big resistor like that to be open, so I checked the capacitors, they were good, the inverters were also not shorting. Anyway I removed the connection to the inverter just in case, replaced the 33ohm, and powered up. I got 300V on one cap and nothing on the other. Checking back the replaced resistor, the resistor is deadWhat else can be an issue here?The huge coil, in between?

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 01, 2022, 01:35:22 pm
content: Quote from: CJay on May 01, 2022, 12:35:43 pmFor this I have extensively checked everything to be sure, in fact I have removed the entire load section (4x inverters) before replacing the resistor. But even in this condition the resistor is dying even without the inverter sections. This indicates a very high current draw, but I don't see anything that draw huge amount of current, and in that condition, the breaker should have tripped.PS: Due to public holiday I could not get a quality 25W Resistor, I used a cheap Chinese made one also rated 25W, any chance they cant take high inrush current. A quality Vishay/Ohmite one is rated for 550V, but I am not sure about the chinese one.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2022, 01:36:28 pm
content: Try an incandescent light bulb instead of the resistor. If it stays lit with no load, there's a short somewhere.

author: bdunham7
author_rank: Super Contributor
timestamp: May 01, 2022, 02:02:49 pm
content: I don't think the differential mode choke would be an issue, but you can just test its DCR and leakage just to be sure.Assuming that it is C2 that is not getting charged up, you might have to reconsider whether it might be bad. How did you test it? Can you swap C1 and C2 relatively easily? I know those things are huge and scary! Are they connected with cables and screws or are they mounted to the board?A grossly substandard resistor might be internally vaporized by the current surge, but that doesn't explain what happened to the original. The peak current would be 10A at the very most.One other thing to consider is the rectifiers. One shorted rectifier would put one phase of AC across a huge cap and that would certainly burn your resistor, but might not trip the breaker because the resistor limits the current.

author: free_electron
author_rank: Super Contributor
timestamp: May 01, 2022, 02:23:49 pm
content: Quote from: bdunham7 on May 01, 2022, 02:02:49 pmThis. of one of the diodes in the bridge is shorted this will happen.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 01, 2022, 02:30:25 pm
content: Quote from: bdunham7 on May 01, 2022, 02:02:49 pm1. I checked the capacitance and ESR of the capacitor, ESR was low, and capacitance was well within tolerance, even used an external power supply to charge the capacitor out of circuit till 100VDC, to see how it charges and discharges, its holding the charge good, I can swap the caps, when I reinstall it back.2. Regarding the rectifier, I tested all 6 diode, Forward voltage is about= 0.48V each and no leakage

author: bdunham7
author_rank: Super Contributor
timestamp: May 01, 2022, 03:03:29 pm
content: Something may be failing under full load. The previous suggestion of putting a light bulb in place of the resistor might be a good diagnostic idea here. But be careful--these PSUs have enough energy to simultaneously cook and skin an alligator!

author: coromonadalix
author_rank: Super Contributor
timestamp: May 01, 2022, 03:05:02 pm
content: your green squares, the common connection is what i can call the ground of the psu for many sections, could be called virtual ground etc ...if the resistor is changed and doesn't blow up you will be good to take measurements but keep this ground line in mind, it can play you some tricksdo you have a link for a full schematic ?

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 01, 2022, 05:59:59 pm
content: I'd be looking harder at the rectifier if you just checked with a DMM in diode mode. Do you have access to a megaohm meter or other current limited source of voltage around 500 to 1000V to check for proper reverse behavior? It is possible for a diode to fail halfway like that, if it is in a circuit where there isn't enough current to instantly destroy it to a shorted or blown open state.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 02, 2022, 04:10:16 am
content: Update: I have a fluke 1587 Insulation tester, will be using it to test the rectifier again. Maybe like most of you commented the rectifier might be half-dead (zombie-rectifier?) and a multimeter diode tester don't have enough juice to properly test it.The light bulb is a good idea, will try that if the rectifier measures good.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 02, 2022, 09:35:51 am
content: Quote from: CrazyTiger on May 02, 2022, 04:10:16 amThe rectifier has been tested with my insulation meter at 1000V, all the diodes reverse voltage reading is about 50MΩ, hence there is no leakage, forward reads 0MΩ. The rectifier is good.I have also tested the common mode choke for any sort of leakage to the body, or to the opposite winding, bott yielded 500MΩ, so no problem with choke too.Next up will be light bulb test.

author: strawberry
author_rank: Super Contributor
timestamp: May 02, 2022, 08:31:27 pm
content: if one of bridge rectifier diode is shorted = short circuit on mains supply400V/30A and half-dead (zombie-rectifier?) = I can bet, this powersupply wont be repaired

author: bdunham7
author_rank: Super Contributor
timestamp: May 02, 2022, 08:47:06 pm
content: Quote from: strawberry on May 02, 2022, 08:31:27 pmExcellent point. I recall having shorted rectifiers take out caps, but apparently not bridges, or at least directly mains-connected ones.

author: trobbins
author_rank: Frequent Contributor
timestamp: May 03, 2022, 12:08:31 am
content: Another diagnostic option is to feed DCV in to one phase and neutral, and between phases, and confirm nominal dc current paths, and no dc current paths where it shouldn't flow due to the other bridge diodes and status of the in-rush relay.

author: fzabkar
author_rank: Super Contributor
timestamp: May 03, 2022, 02:02:30 am
content: In addition to a light bulb, it might be an idea to disconnect 2 of the 3 phases at a time. This would narrow down a faulty rectifier under load.

author: antenna
author_rank: Frequent Contributor
timestamp: May 03, 2022, 02:45:21 am
content: Try swapping the caps around and see if the other resistor blows. Being you only charged it to 100v, it could still be arcing over when it gets closer to 300v. Sure, normally caps turn into a really smelly confetti when that happens, but just maybe?

author: srb1954
author_rank: Super Contributor
timestamp: May 03, 2022, 03:05:05 am
content: Quote from: fzabkar on May 03, 2022, 02:02:30 amBut this could create more stress on the diodes in the remaining connected phase as they will be carrying the full surge current for up to half a cycle compared to the lesser average current and shorter conduction time that would occur if all phases are active.In this case it would be wise to also use a series resistor on the mains supply as well as a light bulb. The light bulb will initially have a low resistance until it is warmed up and will not limit the initial peak surge current sufficiently. The light bulb really only provides protection against prolonged excess currents as its resistance increases considerably when the filament warms up. The extra fixed resistor, sized to limit the expected peak current to an individual diode's maximum surge rating, would help protect the diodes against the shorter term excess currents.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 03, 2022, 06:23:21 am
content: So, at this point, all you're trying to do is charge the input capacitors? All the following circuitry has been disconnected? And you're trying to figure out why the original and then the replacement resistor blew?Here are some random thoughts.........A 35 ohm, 25W resistor has a full load current of ~1.2A @ 30V. Bdunham7, you said you expected a peak current of 10A. Where did you come up with that number? I'd expect a much higher number, but I have no experience with 3 phase. In any case, I'm not surprised that a 25W Chinese resistor wouldn't be happy with an 8X overload current spike and a, possibly, over 10X voltage overload. What could possibly go wrong?Note that the DF60AA120 3 phase bridge rectifier has a surge current rating of over 900A. Tiger, can you find a part number and datasheet for the original resistor? Does it have a surge rating?Why did the original resistor blow? Maybe just age? How old is this thing? It sounds like those resistors are living a very hard life. If you have the room, I'd recommend replacing both resistors with higher wattage units. Note that they have to be*rated*for high wattage, but they don't have to*dissipate*that power. The surge comes and goes so quickly that heating is minimal. So, for example, you can use a resistor that's designed to be mounted on a heatsink, but not use a heatsink - or maybe just a small one. Many years ago I used a similar circuit to soft-start a 300W projector bulb. A high quality 20 ohm 10W resistor died a quick death. A 25W resistor was robust enough to take the surge, but heat wasn't an issue.Does relay K1 operate? If not, the resistors are being stressed even more because they have to survive the complete capacitor charging cycle. Now, heat could become an issue.If all the output circuitry has been disconnected (don't forget the A600 Phase Loss board) you can slowly ramp the voltage up - either AC or DC - and see how the circuit responds.If you decide to use a light bulb, remember that the bulb has to be rated for the supply voltage. So, if you don't happen to have any 400V light bulbs kicking around, put two 220V bulbs in series. When I powered up a 33V@33A supply, I had to use a 100W bulb before it would start, but that was with all the circuitry active. If all you're doing is charging the input capacitors, it doesn't really matter what you use. The lamps will flash on and then slowly go out.

author: strawberry
author_rank: Super Contributor
timestamp: May 03, 2022, 07:36:46 am
content: soft-start relay could be faulty(high contact resistance/ or open) or not activated at allif there is no shorts after that resistorsoft-start relay could be operational even if there is excessive capacitor leakage above ~300VDC230V3f = 560VDC

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 03, 2022, 08:50:15 am
content: The instrument was manufactured at 2004, so its about 18 y.o. It was used in a harsh environment and Malaysian weather is 80% humid. So anything and everything will go wrong.Today I tested it connecting back everything. I Injected 60V DC at the rectifier DC side to see if there is any loading effect. It did not load anything. I am waiting for parts now to further diagnose. I have also ordered a new rectifier, might as well change it to see it. I also thought about changing capacitor but that cornell dubilier cap is about 150 usd per piece.Regarding Soft-Start Relay, till date the relay is yet to engage, but this is likely due the control circuit have a feedback to detect the presence of 300V to turn on the Relay, the control circuit is using 4x UC3825 which I believe without feedback is at shutdown condition. The relay is turned on by a comparator where on end is a simple RC delay circuit, the other end is 5V from UC3825 Vref, which is not present since the UC3825 is in shutdown mode.Quote from: edpalmer42 on May 03, 2022, 06:23:21 amThe resistor that was found inside is Onics AH-25W 33R, i could not find a datasheet for it.Except a facebook sitehttps://www.facebook.com/onics.resistors/Looks like the resistor was made in india. Although the block diagram states 35ohm and capacitor value of 4.7mF, in the unit I found the resistor installed was 33 Ohm and capacitor installed was 6.0mF.I have ordered both 33 ohm and 35 ohm resistor from Element14.https://my.element14.com/vishay/rh02535r00fe02/wirewound-resistor-35-ohm-25w/dp/1369529?ost=35ohm+25w&cfm=true.I do have a question how does neutral work in this circuit. Why is neutral tied in between both the caps, what is the purpose of this?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 03, 2022, 10:21:45 am
content: Hi,Let me explain what is happening in this design.Here is a simplified block diagram:The input is 415 3-phase.415 is the line - line voltage.The Line neutral voltage = 415 / sqrt 3 = 240VThe peak voltage is 240 x SQRT 2 = 340VRectifier topologyBecause the neutral is connected the rectifier is a three-phase half wave rectifier. Capacitors C1 will be charged to 340V by D1-D3. C2 is charged by D4-D6 also to 340V. R1A and R1B are to limit the inrush current to around 10A.This requires a 5-wire connection to the line, 3 phases, N and GND.Inverter LoadsInverters INV #1 and INV #2 are connected to C1 and INV #3 and INV #4 are connected to C2. This limits the voltage on each inverter input to 340V.Mostly likely FaultBecause R1B is burning up, it suggests that INV #3 or #4 has a shorted input.Jay_Diddy_B

author: bdunham7
author_rank: Super Contributor
timestamp: May 03, 2022, 01:45:08 pm
content: Quote from: edpalmer42 on May 03, 2022, 06:23:21 amThe peak current in the resistor would be no higher than the peak voltage available over its resistance. The P-N voltage here is ~230VAC and thus the peak voltage is about 350V. 350/35 = 10. Unless the resistor is a total POS, any reasonable wirewound power resistor will typically tolerate peaks like that at least for a while, even though they aren't always specified for it. Still, yeah, those are big capacitors and those resistors probably see a pretty big thump each turn on.

author: bdunham7
author_rank: Super Contributor
timestamp: May 03, 2022, 02:11:47 pm
content: Quote from: Jay_Diddy_B on May 03, 2022, 10:21:45 amOP stated that he disconnected the inverters. Perhaps he could clarify?

author: edpalmer42
author_rank: Super Contributor
timestamp: May 03, 2022, 05:05:22 pm
content: Onics web site appears to behttps://powerresistor.in/, but there's more info athttp://resistoronline.com/. There's no 'AH' resistors, but there are 'AHR' resistorshttp://resistoronline.com/pdf/new%20design%20AHR.pdf. This states that overload spec is 5X rating for 5 sec. The Vishay datasheet for the resistors you ordered says the same thing. So even with those surge ratings, those resistors are too small for the job unless Lambda talked to the factory and got their signoff on the design. But perhaps the replacement Chinese resistor wasn't rated for a 5X overload.If the driver, or the relay itself as suggested by strawberry, failed in the soft-start circuit, I'd almost guarantee that the resistor would fail. While you're waiting for parts, remove and test that relay.Bdunham7, thanks for the explanation. That was way too obvious.What's unknown at this point is how much more of a surge would be caused by the rest of the circuitry. It seems odd to me that they would limit the surge to 10 amps when the input breaker is 40 or 50 amps.Jay_Diddy_B suggested that Inverter #3 or #4 could have a shorted input. Tiger, do you know if it's possible to run each inverter by itself? Some of those Lambda supplies are built up from seperate blocks so, for example, it might be possible to remove Inverters 2,3, and 4. Does each inverter have it's own internal fuse? If so, what's the value of that fuse? Does it have it's own input capacitors?One shocking fact about this thread that nobody has mentioned is the absolutely criminal lack of pictures. We demand pictures!!

author: bdunham7
author_rank: Super Contributor
timestamp: May 03, 2022, 05:41:50 pm
content: Quote from: edpalmer42 on May 03, 2022, 05:05:22 pmThis topic has been debated before. If you insist upon specific datasheet approval for something like a 100X (power) surge for 1ms, you'll have a much harder time finding a part. But typical wirewound power resistors will shrug that off, and if you need proof you can characterize it yourself or consult the manufacturer. 5X (power) for 5 seconds would be similar to 25X (power) for 1 second and so on, but of course you might want a bit more margin as you go down that route. And of course 25,000,000,000X (power) for one nanosecond might be problematic even if you weren't over the voltage limits, so there will be limits to the principle. 5X 25W x 5 seconds is 625J. Charging that capacitor to 350V will dissipate about 280J in the resistor. Some WW resistors could experience limited life or resistance change as a result of that, but I wouldn't expect them to blow up on the spot.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 03, 2022, 07:15:59 pm
content: Quote from: bdunham7 on May 03, 2022, 05:41:50 pmFor you and me in our workshop - absolutely!That's exactly what I did for the soft-start circuit I used. For a company like TDK-Lambda with military contracts and liability insurance - not a chance!If anyone suggested running beyond specifications without a signoff from the manufacturer, the corporate lawyers and accountants would beat them to death on the spot! You can't characterize it yourself because the manufacturer could change their processes and totally negate your testing. Since they don't know what you've done, they won't know that their change will sabotage your design.But I think we can agree that these resistors were being used in a manner that was not specified in the datasheet. It worked well enough that it lasted for 18 years so it wasn't a horrible decision. At this point, it's an open question whether the replacement resistor failed because of the current surge or some other fault that is yet to be discovered.

author: bdunham7
author_rank: Super Contributor
timestamp: May 03, 2022, 07:43:45 pm
content: http://htr-india.com/design-notes/pulse-surge-capability-resistors/Many mfrs will have published a supplement like this so that you don't have to bother them. If this company was the mfr of a 35R 25W WW power resistor, I think this document would show that it was sufficient in this case.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 03, 2022, 09:36:05 pm
content: Quote from: bdunham7 on May 03, 2022, 07:43:45 pmWouldn't it be nice if every manufacturer did this?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 03, 2022, 11:03:48 pm
content: Hi,If the soft-start is working correctly and there is no load on the capacitor during starting theEnergydissipated in the soft-start resistor is always:E = 1/2 CV2In this design the energy isE = 1/2 x 4700u x 340 x 340 = 271 JoulesJay_Diddy_B

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 04, 2022, 01:25:53 am
content: Hi All,Here are some pictures I have taken of the Inverter, Rectifier, Resistor section. I will take more picture later today. I am working on this power supply in my other house, the house is empty, and comes with 3 phase, but i am traveling daily to visit the PSU.all the markings, is not made by me, so I believe someone tried repairing beforeI have removed the 33ohm resistor here, you can see the other resistor at the edgeGood news is I managed to find the entire circuit diagram yesterday night, will scan and post it later. Regarding Inverter 3 and 4, it was isolated prior to turning on after resistor change.The inverter does have a fuse, which is tested good. I have also fed 60 V directly to each inverter to see if there is any short and it has none. 60V is the maximum my PSU can deliver.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 04, 2022, 03:27:23 am
content: Hi,Can you check the capacitor in a circuit like this:The Incandescent lamp will limit the current. The capacitor may be bad.The capacitor should charge up to around 320V and there should be be no light from the lamp if the capacitor is good.You can check them first with your 60V power supply.Regards,Jay_Diddy_B

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 04, 2022, 10:07:26 am
content: Hi,I will do the test as Jay_Diddy, suggested for the caps. I have also pulled out all the 4 inverters out for further checking. I will be testing the IGBT's off circuit to see if it actually switches, but nothing is shorted for sure. At least I can eliminate the inverters once and for all. Here are more pictures.The power supply front lookThe resistor in question, the red box is where the resistors belong, I have taken out the defective one.The control boardInverters:

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 04, 2022, 10:32:58 am
content: Hi,You should try and find a wire-wound resistor that is this style:What did the original resistor look like?It is described as having a Silicone coating. It is not the vitreous enamel coating. The vitreous enamel, glass, coating will crack if there is a high power surge, as there is in this application.The aluminum resistors are not very good. They tend to blow out of the ends !!It looks like there is a fuse on each of the inverter boards. I think the fuse would be blown if the IGBTs are bad. I think the soft-start burns without the inverters connected? This would mean it is not the inverters.Jay_Diddy_B

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 04, 2022, 12:05:35 pm
content: With the little experience I have, all wirewound resistors on a ceramic form are very capable of handling significant overloads during a short time.Those cemented resistors in a rectangular ceramic block also.I've had very bad experiences with the gold colored aluminium resistors which are made to fit on a heatsink. These tend to blow at the slightest overload. Even to a point I suspect that they fuse by design.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 04, 2022, 12:36:27 pm
content: Quote from: Jay_Diddy_B on May 04, 2022, 10:32:58 amThe resistor you are suggesting makes sense, I have had this doubt too wondering if it was replaced. Reason is I have basically opened the PSU to bare body, any high powered resistor inside the unit looks like the one you are suggesting except the two resistors for the soft-start circuit which came with Aluminum Casing. It might have been replaced before, but the heat shrink that came with the resistor feels and looks the same with the existing heat shrink on other cables and component, so we will never know unless someone have the same PSU. I am finding the type you suggested so far no matches.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 04, 2022, 01:15:59 pm
content: This looks good, rated 30W, close enough, not sure about minimum order quantityhttp://htr-india.com/wp-content/uploads/2021/01/HFOM.pdfSorry Link fixed

author: SeanB
author_rank: Super Contributor
timestamp: May 04, 2022, 01:33:15 pm
content: Using a local link to the datasheet is kind of going to be hard to see though, perhaps better to link to the manufacturer website instead?Quote from: CrazyTiger on May 04, 2022, 01:15:59 pmhttp://htr-india.com/wp-content/uploads/2021/01/HFOM.pdfAnd yes the 10x short term overload capacity will work, though probably better to use the 40W versions instead of the 30W, though it may be a bit hard to fit in the available space, which the 80W definitely will not do.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2022, 02:28:29 pm
content: Quote from: Doctorandus_P on May 04, 2022, 12:05:35 pmWith that design, I suppose they can put a smaller element in it and just let it run quite hot internally. I would have thought that this would be the case with no-name eBay parts. A look at a few datasheets for 'good' versions shows that some state 'high pulse capability' and so on without much specificity--these are probably as robust as I claimed WW resistors to be generally. However, there are some name-brands that quite clearly give much lower pulse/overload limitations and would be greatly in excess of them if used in the OPs PSU. So I'll have to withdraw my statement of WW being universally robust when it comes to this style.https://www.mouser.com/datasheet/2/414/TTRB_S_A0012496756_1-2565697.pdf

author: strawberry
author_rank: Super Contributor
timestamp: May 04, 2022, 03:16:45 pm
content: https://eu.mouser.com/ProductDetail/Vishay-Dale/FSOT5509E30R00JE?qs=JsD2jqDDQCxJ79D6QFrdTQ%3D%3DFSOT5509E30R00JE

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 04, 2022, 03:17:41 pm
content: Been searching internet for an inside picture of another PSU made by lambda, found a video, its a different model but architecture seems the same.At 0:10 we can get a glimpse of the resistor, its definitely not a Aluminum housing, seems more like a cement type or something radial.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 04, 2022, 03:48:47 pm
content: Sometimes it works to put in a DC current of a few amps and then measure where the current goes by measuring voltage drops over tracks.You can also connect a function generator and generate a sinewave current a a few amps and then pick it up. Maybe with a small inductor, or with a head from a cassete recorder.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 04, 2022, 04:34:40 pm
content: You can also get high power resistors in a case that looks like a TO-247 or TO-220 transistor. That would be an example of my earlier comment where you don't actually have to dissipate the rated power. A small heatsink or just a block of metal would be all that's required. Actually, if you mounted it to almost anything, that would provide enough of a heatsink for this application. This particular one is 39R @ 100W, but there are others at different values and power ratings.https://www.mouser.ca/ProductDetail/TE-Connectivity-Holsworthy/MPT100C39RF?qs=sGAEpiMZZMtlubZbdhIBINNjBjh6UlIP%252B9ccrjePZE4%3DI didn't see any info on surge ratings in the datasheet, but if you go with the 100W version it might not matter.

author: bdunham7
author_rank: Super Contributor
timestamp: May 04, 2022, 05:31:13 pm
content: Quote from: edpalmer42 on May 04, 2022, 04:34:40 pmThe peak power might be as high as 3500W and TF resistors aren't the best for that. I'm a bit surprised to see that there are more than a few WW lines that seem to have diminished pulse withstanding, presumably because they have used thinner, shorter wires and thus less mass. They seem to have high joule ratings only for very low resistance values. Here's an example of a line where the 10W version would barely work but the 25W aluminum-housing version would not.https://www.ohmite.com/assets/docs/res_30.pdfMetal oxide or ceramic composition resistors may actually be better for this application if they've cheaped out on WW models. Here is a series where the 2 watt (!) version can withstand 275kilowatts for 1 ms. Now that is a surge rating!https://www.ohmite.com/assets/docs/res_oc.pdfI'm starting to think that the OP might in fact just need some different resistors.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 04, 2022, 05:51:57 pm
content: Quote from: bdunham7 on May 04, 2022, 05:31:13 pmI'm concerned that he said that the relay has never operated. That almost guarantees that the resistor will fry - both the original and the replacement. I'd suggest replacing both resistors rather than just replacing the blown one.Tiger, if I were you, I'd be collecting incandescent (or halogen) bulbs and sockets to use as inline surge limiters. That will allow you to power the unit up and continue troubleshooting. With the bulbs in place, you can jumper out the contacts on relay K1 to bypass that part of the circuit. If there are problems further down the line, the bulbs will glow bright. If you have one available, you could also consider using a small 3-phase breaker (maybe 5 amps or less) in the power feed in addition to the bulbs.Since you're dealing with 400V AC 3-phase, don't just throw something together. Mount everything on a piece of plywood or similar, use good quality wire, etc. 100W bulbs might not be enough to allow the unit to start, so plan for bigger bulbs, if necessary.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 04, 2022, 08:26:17 pm
content: Hi,The energy dissipated in the soft-start resistor is equal to the energy stored in the capacitor during starting.It is also equal to the energy dissipated in the resistor if you discharge the capacitor.Charging takes longer, because the line voltage has to be more positive than the capacitor voltage, so it less severe.If you can discharge the capacitor without breaking the resistor, it is probably good enough.Summary for CrazyTiger:Theory 1The resistor is weak and doesn't survive the inrush current.Theory 2The capacitor is bad and the dissipation in the resistor is high because the capacitor is faulty.Jay_Diddy_B

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: May 04, 2022, 09:43:05 pm
content: Maybe I missed it somewhere above, but have you confirmed the relay contacts across that resistor are clean and functioning?

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 05, 2022, 01:01:49 am
content: Quote from: Ground_Loop on May 04, 2022, 09:43:05 pmThe relay contacts are good was tested with 34401A to check for any significant resistance drop. The relay was also tested with a insulation tester to check for any contact leakage between NO and NC. Everything tested ok.I will be getting few 100W and 50W bulbs and sockets today. I will be also borrowing a 3 phase variac, at least probing can be done in a safe manner with a variac.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 02:31:54 am
content: Quote from: CrazyTiger on May 05, 2022, 01:01:49 amDid you check the coil to make sure it isn't open? In a perfect world, put 24V on the coil and confirm that the relay operates and the contacts close. There's a diode across the coil so mind the polarity.QuoteCareful! A variac does**NOT**provide isolation from the line. It only reduces the voltage.For the bulbs, remember that you'll need two 220V bulbs in series for each of the three phases. So a total of 6 bulbs & sockets.By the way, you said that you were working in your other house that has 3-phase power. Is it common for houses in Malaysia to have 400V 3-phase electrical service?

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2022, 02:37:16 am
content: Quote from: edpalmer42 on May 05, 2022, 02:31:54 amWhy can't he just put one bulb in place of the resistor? It will be a bit over voltage, but unless there is a short it should just blink at the most.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 03:15:50 am
content: Quote from: Jay_Diddy_B on May 04, 2022, 08:26:17 pmBut that doesn't include the effect of relay K1. We don't know when K1 is supposed to operate, but as soon as it does, the resistor is shorted out so energy dissipation stops at that point. If the capacitor voltage at that point happens to be 100V then that determines the energy dissipated in the resistor, not the peak charged voltage.I just checked the schematic of my Xantrex XKW33-33 power supply (33V @ 33A). It uses a similar soft start circuit. The capacitor bank is only 1500 uf @ 400 V. The soft-start resistor is 39R @ 5W. I tested it and the relay operates about 1 sec. after powerup. There's also a 0.5A fuse in series with the 39R resistor. This fuse is also shorted out when the relay operates. But that shows that in my unit, the surge is no more than 0.5A.I also see in the instruction manual for the ESS that inductor L1 limits the peak charging current. Unfortunately, they don't specify the maximum surge. Bottom line here is that we don't know what the surge current is or how long the resistor has to withstand it. All we know is that it finally gave up and we're trying to figure out why.

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2022, 03:24:08 am
content: Quote from: edpalmer42 on May 05, 2022, 03:15:50 amI was wondering about those chokes, which I would have assumed were to suppress HF noise from the inverters. Do they give values for L1A/B and L4?

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 05, 2022, 03:24:23 am
content: Quote from: edpalmer42 on May 05, 2022, 02:31:54 am1. The coil was engaged with external supply for checking.2. Each phase will need two light bulb for sure.3. A normal house in Malaysia usually comes with 230VAC Single phase, but when the house gets big, 3 Phase is provided with normally two Distribution boxes, with separate MCB&CB&RCCB provided for the ground floor and first floor, of course Electrical meter is one. Service provider assumes the entire house will likely be air conditioned, and water heaters are running, they calculate on worst case scenario, hence they started providing 3 phases. Its a overkill anyway electricians usually "try" to balance out utilization of each phase during wiring process itself.I got the house so that I can shift all my instruments to this house and make a huge electronic evil lair

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 03:26:06 am
content: Quote from: bdunham7 on May 05, 2022, 02:37:16 amWhen he flips the switch, a single 220V bulb will see the entire 400V line voltage. It will be running over it's rated voltage until the capacitors charge to something like 250V. I wouldn't expect a single bulb to survive that. If the surge-limiting resistors were in place a single bulb might survive, but we removed them to troubleshoot why they died. As I stated above, L1 limits the surge to some unknown value so that also might save a single bulb. It just seems to me that two bulbs in series is cheap insurance.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 05, 2022, 03:29:27 am
content: Quote from: bdunham7 on May 05, 2022, 03:24:08 amI did measure the inductance at 1KHz for L1A/B it was about 1700uH each coil. But could not find any nominal value.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 03:35:03 am
content: Quote from: bdunham7 on May 05, 2022, 03:24:08 amNo, this is just a copy of the user manual. It has a bit of circuit description, but no schematics or parts list. I'm surprised L1 is even mentioned. It says:QuoteThe way they drew L1 with the line connecting the two cores, I thought it was like a common mode choke.

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2022, 03:57:41 am
content: Quote from: edpalmer42 on May 05, 2022, 03:26:06 amTwo is fine with me, but the voltage from P-N is not 400V, that is P-P. Phase to Phase, that is, not peak-to-peak. It should be ~240VAC P-N. But while rectified AC has the same RMS value as non-rectified, the sum of the three rectified half-waves will be higher by a bit. 20% or so if my math isn't flawed.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 05, 2022, 04:02:11 am
content: Quote from: edpalmer42 on May 05, 2022, 03:35:03 amSo it's an old school "choke input filter"?They were common in the days of mercury vapour rectifiers to prevent damage to the tubes upon switch on.They weren't usually the only inductors in the filter back then, though.

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2022, 04:06:54 am
content: Quote from: edpalmer42 on May 05, 2022, 03:35:03 amQuoteAt the value measured, again assuming no math errors on my end, the effect on the resistor would not be that great, although perhaps not totally negligible. In the operating mode though, it would do what they say by spreading the intra-cycle conduction peaks and reducing harmonics. It's actually set up as a differential-mode choke, which should also suppress switching noise from the inverters. I'm not sure why L4 is separate and uncoupled with the other two, but there's probably a reason.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 04:46:14 am
content: Quote from: bdunham7 on May 05, 2022, 03:57:41 amThanks for the education. As I said, I'm not familiar with 3 phase. I'm an electronics guy. So Tiger only needs one 220V bulb per phase. If he has two per phase he might be able to put them in parallel and leave them in place when he starts the entire unit. Again, cheap insurance. Of course, when he starts to load it up the bulbs will have to be removed completely.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 05, 2022, 12:00:49 pm
content: Hi,Let me use an LTspice model to illustrate what should happen during start-up. The circuit is symmetrical I will only model half of the circuit. Under normal operation the currents in the Neutral conductor will cancel, except for the single-phase loads within the power supply. The single-phase loads are the fans and the auxiliary power supply.Start-upI have included the inductor, with a value of 1.7mH.The waveforms look like this:If I zoom in on the first 120ms:If I replace the 1.7mH with a short, there is no significant change to the waveforms. The 35resistor and the 4700uF are the dominant components.Full Power OperationAgain I am modelling half of the power supply. The other half is identical. I have applied a load of 8kW.ModelWith the 1.7mH InductorWithout the 1.7mH InductorYou can see that the voltage is higher, I adjusted the load resistor, to keep the load dissipation constant. The peak line current is higher.Unless the inductor is faulty and has a short to ground it has very impact during start-up and is used to improve the line current waveforms at full power.Jay_Diddy_B

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2022, 02:09:25 pm
content: Quote from: Jay_Diddy_B on May 05, 2022, 12:00:49 pmVery nice! On the currents in the neutral conductor, in full-power case with the inductor, they will partially cancel. Without the inductor, it appears that they would not cancel and the neutral current would be 3X. The conduction time appears to be <3.3ms and thus <60 degrees, less than 60 degrees => no overlap. With the inductor, it looks like ~5ms and ~90 degrees, which gives you some cancellation, but not total.I think L4 and the fact that L1A and L2A are coupled will also make a significant difference in this result.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 03:33:38 pm
content: Jay_Diddy_B,So what you're saying is that if it takes K1 more than about 0.5 sec. to operate it won't actually be limiting the energy dissipation in R1 because by then the capacitors will be almost fully charged and almost all the energy will already have been dumped into R1.I'm surprised those resistors survived as long as they did. It didn't look like they had any heatsinking at all.This provides more evidence that both resistors should be replaced with higher wattage units. But does it address the question of why the replacement resistor immediately failed?

author: fzabkar
author_rank: Super Contributor
timestamp: May 05, 2022, 07:30:19 pm
content: Instead of a light bulb, why not use the heating element in an electric kettle? A 240VAC kettle rated at 2200W would have a resistance of 26 ohms.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 05, 2022, 07:42:09 pm
content: Quote from: fzabkar on May 05, 2022, 07:30:19 pmA heating element has a constant resistance. A light bulb has a low resistance if the current is low (i.e. the power supply is operating normally). But if the power supply tries to draw lots of current (i.e. it has a fault) the resistance of the light bulb will increase and limit the current. It's a troubleshooting tool to help prevent the further release of magic smoke.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 06, 2022, 03:19:21 am
content: Hi,You might want the resistor to open like a fuse, especially if there is something wrong with the big capacitors.Looking at the inrush current with a current probe would reveal a lot. It should look like the simulation that I showed earlier.If there is no load on the output of the power supply, the capacitors should charge up and the line current should drop to a low value.Jay_Diddy_B

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 06, 2022, 12:21:31 pm
content: Hi All,More update, I am still waiting for parts, E14/Farnel been delivering things slow since covid19. Orders from UK and US takes almost 2 week to reach, it used to be 3 Days, pre-covid.Anyway I have found and fixed more issues with control board. One of the UC3825 chip was no starting causing the main relay to never engage. With that fixed and probing with my Scope, the control board seems to be working now.The relay works, It takes about 3 Second for the relay to engage. I have also replaced a defective FET(it was open) which is used to activate soft-start pins of UC38225 Chip (SS Pin).I have also pulled all the Inverters out, tested the IGBT off circuit and all the components. Inverter 2 had one open IGBT, parts ordered. Seems like Murphy Law is very much applicable in the instrument.Inverter 4 smells weird. Its not because of burned components but this is because of Rat Urine. I suppose Mickey Mouse managed to pee through the air inlet filter. I don't see any component damage on Inverter 4 and PCB seems ok, anyway I will be rinsing the board with IPA. Hopefully no further surprises.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 06, 2022, 04:39:27 pm
content: Sounds like you're making good progress.Cascade failures are not surprising. One component dies and takes out something else. It's nice that you have multiple inverters because you can compare a working one to a dead one.Keep us informed on your progress.

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 15, 2022, 01:39:48 pm
content: Update:Finally I received all the components.I have replaced all 4 UC3825 Chip on the controller board. On the inverter boards I replaced a pair of TC4429 with Max4429, Each inverter had a pair, I ended up replacing for all the inverters, so 8 in total. Both the 33ohm resistor was replaced for the soft start circuit.After securing back everything, I turned on the power supply. For the first time ever, the relay clicked and 300V went to all the inverters. The Control Error Indicator turned off and the power supply came to life. Full voltage of 60V was measured and it was spot on. I was happy for a brief moment, till I started seeing the output voltage started dropping back to zero.Powering up again the PSU behavior is same, I tried isolating the issue by removing the control cable of each inverter. When only one inverter (any of the 4) is operated alone, the output voltage seems stable. But as I add more inverter the PSU output shuts down slowly.Another observation I made is before the output dies, the output voltage fluctuates, example when PSU is set to 50V, the voltage fluctuates from 48-52V before shutting down.Will keep looking tomorrow, my suspect now is at regulation and output rectification section, at least its good progress

author: edpalmer42
author_rank: Super Contributor
timestamp: May 15, 2022, 06:02:47 pm
content: Was 'a brief moment' seconds or minutes?Could 'shuts down slowly' have been due to the output capacitors slowly discharging?Some things to check:- Remote sense jumpers- Remote programming jumpers- Overvoltage or Overcurrent protection settings- Try with or without a load

author: CrazyTiger
author_rank: Regular Contributor
timestamp: May 15, 2022, 11:43:55 pm
content: Quote from: edpalmer42 on May 15, 2022, 06:02:47 pmWith all 4 inverters, it takes about 2 minutes.All sense jumpers and remote programming jumpers are made according to default setting stated in the user manual.Overvoltage setting is set to maximum and this function worksWill put a load to test today.

author: bdunham7
author_rank: Super Contributor
timestamp: May 16, 2022, 01:29:35 am
content: Quote from: CrazyTiger on May 15, 2022, 11:43:55 pmWhat are your 300V DC supplies doing at that time?

author: CrazyTiger
author_rank: Regular Contributor
timestamp: June 08, 2022, 11:49:21 pm
content: Final Update:The power supply works,The inverter works by two complementary PWM signal being fed into 2 mosfet driver chip and the output is fed into a transformer later switced with IGBTS and rectifiers. I found one mosfet driver dies causing the inverter working in half cycle, hence the reason for the power supply to turn on for brief moment and dies.I have replaced all the original TC4429 to MAX4429 earlier after noticing one of chip had sign of being burned. Reason for placing max4429 was Farnel did not have stock for TC4429 and blind confidence that an equivalent would work.I finally figured the inverters did not like MAX4429 as the transformer driver, when I placed back TC4429, the PSU was stable. I did not see any difference in datasheet between both the chips. But testing it on the breadboard revealed MAX4429 is very sensitive to stray capacitance causing the chips to overheat and die while TC4429 is very tolerant. Another weird finding was the DCR of VCC and GND of a new MAX4429 is about 3MOhm while TC4429 is 12MOhm. Both the chips was purchased from Farnell and RS Component.So after close to 2 months, with lots of waiting in between for parts. the PSU works. If anyone in the forum ever needs a 15KW power supply in Malaysia. I have one. Till then this is going to be a huge paper weightThanks for the help

author: bdunham7
author_rank: Super Contributor
timestamp: June 08, 2022, 11:56:24 pm
content: So what caused the burned resistor?

author: CrazyTiger
author_rank: Regular Contributor
timestamp: June 09, 2022, 12:05:53 am
content: Quote from: bdunham7 on June 08, 2022, 11:56:24 pmBurned resistor was caused by combination of resistor used (someone replaced the resistor before) and the death of pwm chip which caused relay not to engage. Now the resistor used is silicone coated type.