Inverter drive module overvolt fault - Page 1
Forum section: electronics / repair

author: Eamon
author_rank: Contributor
timestamp: October 07, 2022, 12:10:07 pm
content: I'm trying to determine my next steps in diagnosing and repairing an inverter drive module for a compressor in a heat pump.Pool heat pump Model Astral Pool iHP170Symptoms:Shortly after turning on and after the compressor kicks in it stops with a fault; "F10 - Inv. Input Overvolt."Apart from a range of sensors and relays, there are essentially 3 main components in the electrical side; Touch screen, main controller and the inverter drive module.There are no obviously damaged components that I can see and no residual magic smoke smell.The replacement cost from Astral pool for just the inverter module pictured is ~$2500! Repair it is.I have had no success in determining an OEM for the part or anything related to the marking on it "SA.FNB75GW.1" except for parts listings in the various manuals for this heat pump presumably rebadged under a few names.The main drive chip is amitsubishi pss35s92f6-ag, other component numbers can be provided where relevant.I have determined that the communication between the controller and the compressor Inverter drive module is ModbusRTU over RS485.After sniffing a bunch of the communication between the boards I have managed to reverse engineer enough of the communication protocol to control the inverter drive board directly from a laptop using a small application I wrote which polls the state of the module every 100ms.I can instruct the inverter module to control the compressor on/off state, compressor frequency and fan speed and the inverter module will report:"AC plate voltage", "Inverter DC Voltage", "Compressor frequency", "Compressor Current", "IPMTemperature" along with a bunch of error codesWhile powered and with the compressor and fan off the drive module reports the AC voltage ~220v which is about 15v less than I measure on the terminals with my EEVBlog BM786 multimeterit also reports the DC voltage as ~320v which seems to be about right for the given AC voltage.When I send the "on" signal for the compressor, a few seconds later I see a jump in the reported compressor current and another few seconds later the compressor frequency begins to rise.After around 5 seconds with the frequency generally about 25Hz, the reported AC voltage jumps from ~220v to ~320v; pretty much the same value being reported for the DC Voltage.About 5 seconds later, the compressor cuts out and the "Inv. Input Overvolt" error is reported, at the same time the AC voltage drops to ~255v where it stays for the next 10 seconds or so before returningto ~220v. The DC voltage remains around 320v throughout.I've tried setting the initial compressor frequency to a number of values from 20Hz to 100Hz (all within range of the compressor's specs) and the behavior is fairly consistent.So that's about as far as I can go on the software side, now I need to get into the electrics but not sure where to start.The numbers above are all as reported by the inverter module itself via Modbus, not independently measured values.Using the multimeter I do not see the spike on the AC input terminals reported by the module so I need to determine where the metering circuit might be on the module.This is where I need help from more seasoned experts. Any suggestion on what to check next or where the AC metering circuitry might be would be very welcome.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 07, 2022, 12:30:19 pm
content: So there's obviously nothing broken there, just a malfunction of the AC input measurement.This is good news, as you don't need the expensive replacement kit - which I would suggest to get if something within the power stage was blown.There's probably very little chance to get a schematic of the inverter module, so one would have to reverse engineer the AC input until you locate the components that are in charge for AC input voltage measurement. Most probably that's just a bunch of resistors or other smallish components. You'd have to follow this path until it ends up in some ADC input of the MCU, and locate the fault within this signal chain.There's some hazards with this, as I cannot judge from the picture alone whether the MCU is isolated from mains or at "DC-Link minus" potential, and the serial (Modbus communication) port is isolated. I'd expect for this kind of application most of the PCB at live potential.So this is just some general information, basically how I'd go on with this issue, based on my options and experience. You already did some great work to help locating the fault by analyzing the behaviour of the inverter stage at the communication side. Now it's about time to dive into component level electronics.Looking at the photo, you can see a string of SMT resistors left hand side of an orange capacitor. This is probably part of the circuit that measures the DC link voltage. The AC voltage measurement might look similar. Look for strings of resistors connected to L and N input. Otherwise, regarding all the cost saving effort that goes into todays products, there might be some totally other circuit that "estimates" (in contrary to measure) the AC input voltage in some other way (ATM I don't have an idea what this could look like). Anyway, I wonder why there's an AC input voltage measurement circuit at all, since it's not required for such kind of inverter to work at all (I've got some experience working together with engineers that designed such kind of power stages, my part was rather at the MCU side).

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 07, 2022, 01:40:55 pm
content: I would suggest checking the noise filtering on the AC sense circuit, could be as simple as a cracked ceramic capacitor.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 07, 2022, 04:17:27 pm
content: After a while, I've got another thought:Check the internal (low voltage) MCU and analog supply voltage(s) for excessive ripple

author: Eamon
author_rank: Contributor
timestamp: October 07, 2022, 10:49:12 pm
content: Quote from: NiHaoMike on October 07, 2022, 01:40:55 pmThanks, any idea where the "AC sense circuit" would be from the image?

author: Eamon
author_rank: Contributor
timestamp: October 07, 2022, 10:59:23 pm
content: ok, I have taken some voltage measurements with the module powered but not with the compressor set "on", I've used the ground pin on the blank fan connector on the left of the board as my 0v/ground reference.I was surprised to find 380v at one particular point as shown in the image.Also not sure what the 130vAC is for? but in addition the bottom right has a second bridge rectifier that appears to be unpowered, the + and - and both ~ pins are all at 0v relative to my ground ref.The MCU isTMS320F28027PTT, I'll check out the datasheet. I assume it is likely to be one of the ADC pins that is measuring the AC voltage?As for checking for ripple, I have an analog discovery 2 USB Oscilloscope so I'll try to get some more detailed readings.As for that, this would be a whole lot easier if I could do it at a desk/bench rather that in place at the heat pump unit itself however if I disconnect the compressor from the drive, I can't replicate the fault as it errors with a "Comp. Driver Failure" error instead. Could I connect something else in place of the compressor? I have a spare 3 phase motor available, but it is 415v, could I use that?

author: capt bullshot
author_rank: Super Contributor
timestamp: October 08, 2022, 10:33:00 am
content: Quote from: Eamon on October 07, 2022, 10:59:23 pmThe 380V test point most probably is part of that small auxiliary SMPS - maybe part of the snubber circuit. If so, it's probably not relevant for your issue.Yes one could connect any 3 phase motor to the output, and the motor should run if you command the inverter to do run. Supposed both the compressor and the spare motor are the same type (e.g. induction motor, or PMSM) Your typical "spare 415V 3ph motor" probably is an induction motor (or asynchronous motor) - but I don't have any idea what type of motor is inside the compressor. If it is a PMSM or similar (permanent magnet synchronous motor) it might not start nor run. But most probably neither the motor or the inverter will die from a short "wire it up and turn it on" experiment - but don't nail me on that. The exact voltages might not match, that shouldn't matter too much for short term operation.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 08, 2022, 10:39:00 am
content: If you connect your "scope" to the 9V and 15V circuits, consider the "GND" potential most probably is at "DC Link minus" in such type of inverters.This means for the "GND" there's a large negative DC voltage superimposed with half wave line AC voltage in reference to Earth, that'll kill your Analog Discovery in a few milliseconds.Typically best way to deal with it: Use a proper isolation transformer to supply the inverter board, and connect said reference GND to Earth, then apply the scope measurements for ripple etc.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 08, 2022, 10:48:38 am
content: Reading your first post again (didn't see the additional information at my first reply here) -I doubt "AC plate voltage" directly relates to the AC input voltage at all, and there might not exist any AC input voltage sensing circuit at all.Usually there's no need for such kind of inverter to monitor the AC input voltage, especially if it's just single phase (for three phase and higher power you want to monitor the input to detect a lost phase condition).I've got no idea what "AC plate voltage" means in this context, where's the origin of this term?Do you have means to operate the inverter board at somewhat lower AC input voltage? Some kind of autotransformer or variac to reduce the mains voltage by some 10 Volts?One can use an ordinary e.g. mains input and 12V output transformer by some simple but tricky wiring to reduce the mains voltage by 12V - the 12V output winding just has to be able to supply the nominal current of the load, not the nominal power.

author: Eamon
author_rank: Contributor
timestamp: October 08, 2022, 11:33:12 am
content: Quote from: capt bullshot on October 08, 2022, 10:39:00 amI was planning on using a pair of 100x probes for this and not connecting the ground leads of the probes to anything. I believe the analog discovery can handle up to 50v on the probes so with the 100x probes I figured I'd have plenty of headroom? I don't have access to an isolated transformer, but have considered buying an entry level differential probe if the 100x probes wont work.

author: Eamon
author_rank: Contributor
timestamp: October 08, 2022, 12:04:29 pm
content: Quote from: capt bullshot on October 08, 2022, 10:48:38 amI mis-typed it slightly but "Inverter plate AC voltage" is the term the touchscreen uses. When I was reverse engineering the modbus protocol, I had the controller and touch screen connected to my computer acting as the Inverter module and would send back various values for the requested registers and see how they would represent in the touchscreen. One particular register always matches the value the touchscreen represented as "Inverter plate AC voltage", this is the value represented in the chart in the first post (I added the PCB back and the chart images a bit later).Also, the fault code reported in the touchscreen interface is "Inv. Input Overvolt." which is why I'm assuming it's a measure of the input AC voltage but I agree that there does not seem to be a need for such a measure.Quote from: capt bullshot on October 08, 2022, 10:48:38 amAre you suggesting running the inverter at a lower voltage permanently as a workaround or as part of diagnosing the problem? Could probably just drop the AC voltage by running about 50m of 2.5mm2 extension cable if it's just a test, wouldn't want to run it permanently like that though.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 08, 2022, 12:43:34 pm
content: Yes, 100:1 probes could do the job as the AD has differential inputs anyway, and your setup should be safe. Just ensure to properly adjust and match them."Inverter plate AC voltage" is as meaningless to me as "AC plate voltage", and the almighty internet doesn't give meaningful results, too.I guess it's some literal but not meaningful japanese/chinese/korean to English translation.Reducing the input voltage: My intent is for testing, to see whether the error message disappears or the measured value changes according to the change in input voltage. The extension cord won't drop the voltage in standby, so the latter one wouldn't work.

author: Eamon
author_rank: Contributor
timestamp: October 08, 2022, 10:41:02 pm
content: Well I tried to connect the motor in place of the compressor and while nothing blew up, the motor barely turns at a very slow speed with a bit of a high pitch for a second or two before the inverter faults out with a "PFC fault". Time to find a plan B for a load to replace the compressor.Can you give me some insight as to the 12v transformer trick to reduce the voltage?Also just occurred to me that I have an old stick welder that is essentially just a giant iron core variable step down transformer, turn a handle to move the secondary winding further into or out of the primary. I'll investigate what the voltage is on the lowest current setting....

author: Eamon
author_rank: Contributor
timestamp: October 08, 2022, 11:12:57 pm
content: Well I don't think the welder will be useful directly as the maximum output voltage is ~45v with input of 236v, but it may be useful in place of a 12v transformer that you mentioned previously, it will certainly handle the current of the inverter and the load even. If you could provide some more details of the "some simple but tricky wiring" that would be helpful, in the meantime I'll google a bit and see what I can find.

author: florentbr
author_rank: Contributor
timestamp: October 09, 2022, 04:00:07 am
content: This reminds me of an SMPS driver that was randomly shutting down.The waveform of the input rectified DC had voltage spikes, which I assume was causing an over-voltage shutdown (OVP).I removed the PFC switching transistor and the issue never reappeared.I didn't check the capacitors since the rectified DC under load was steady without the PFC.I suspect that the ESR of the capacitors went out of spec.In your case, the reported voltage seems to be correct when on standby, so I don't think it's a sensing issue.Since it takes an inductor to raise a voltage, I would pay attention to the PFC stage.Among those TO-264 you'll find a switching transistor and two diodes for the PFC.For more information, search for "PFC boost converter design guide".

author: capt bullshot
author_rank: Super Contributor
timestamp: October 09, 2022, 11:10:01 am
content: See the attached sketch for the basic idea of using a "standard mains step down transformer" to add / subtract its secondary voltage from mains. Load current shall be lower than the ampere rating of the secondary.Previous posters thought about the PFC stage: I have to agree, this is plausible. There are components that look just like a PFC stage, and said "plate voltage" might have something to do with the PFC stage. Disabling the PFC stage could work - e.g. by removing the transistor. In general the inverter is able to run without a PFC stage, it is required for compliance, not for function. Depending on how it is done, the inverter might throw other errors if one disables the PFC.Once you've started investigating, scoping the waveforms at the DC link capacitors and at the switching node of the PFC might give some insights.

author: Eamon
author_rank: Contributor
timestamp: October 11, 2022, 01:45:49 pm
content: I've spent a fair bit of time trying to reverse engineer the schematic and have what is attached so far. I have a little more around the gate drivers for the two PFC MOSFETs but not sure its too important here; it's essentially aucc27524with some resistors and an unidentified SOT-23 transistor.The three 150k resistors in series head off on a trace that jumps back and forth through vias and ends up in a sea of smd passives and a few SOT-23 diodes near the MPC. I can't identify the pin arrangement on the diodes as the only marking on D5 is "HA7" which is not much use for searching, but the "idle" state voltage at the end of the 3 series resistors is 2.08vThe three 200k resistors that come out after the first choke also head off to a bunch of smd parts and becomes hard to follow but given that I think this is the only path the MPC could potentially measure an AC signal, I'll try to follow it further.If there is a problem with the PFC circuit, what is the most likely culprit?No progress finding a compressor substitute so I'll probably just have to put the module back into the heat pump and put the scope on it in place. Are there particular points in the circuit I should focus on?

author: capt bullshot
author_rank: Super Contributor
timestamp: October 11, 2022, 02:41:11 pm
content: The R3 ... R5 string might be the startup supply for the PFC controller IC, or the other auxiliary SMPS.Doesn't look like a typical AC sense circuit at a first glance.The R54 ... R99 string most probably is an input signal to the PFC controller, as these need the actual half bridge rectified voltage for their control loop.If you have a stable DC voltage at E1 ... E3 that is higher then the peak value of the input AC voltage, the PFC should be considered OK. I'd recon the controller turning on/off the PFC stage depending on the compressor motor stage (PFC off while motor is off to save energy). So the voltage across these capacitors might actually rise when the motor starts.The UCC27524 is a simple gate driver, not a PFC controller. My guess the PFC is done by the MCU in software, as the inverter control loop and modulator is done there too. You could measure the voltage across the electrolytics (with a multimeter) to see if it matches one of the reported voltages, or if this voltage rises unexpectedly high (whatever a "normal" voltage would be, one can rely on guesses only - I'd consider 350V for a PFC DC-Link "normal").

author: capt bullshot
author_rank: Super Contributor
timestamp: October 11, 2022, 02:47:31 pm
content: Another thought:TI publishes quite a few reference designs using their chips. You might want to search for motor control reference designs using the TMS320F28027 (or similar) maybe even including a PFC stage. There are designers out there, that use these reference designs as a guide or copy parts of the schematic. This might ease the reverse engineering and help understanding the circuit.

author: florentbr
author_rank: Contributor
timestamp: October 11, 2022, 04:43:23 pm
content: The AC input voltage in question could be measured at R94 even though it's rectified.What's strange is that the inverterDCvoltage is supposed to rise well over 320v when the PFC is turned on, but your measure doesn't show that.If the reported AC voltage jumps from ~220v to ~320v, it could indicate that the output DC is finding it's way back to the output of the bridge rectifier. I might be wrong, but I don't think it's supposed to.I would remove and test C53A, Q1, Q2, D1, D2 and DB2.DB2 is not used as a bridge rectifier but as a single diode.The PFC from your schematic seems to match this one:https://www.digikey.be/de/articles/hvac-dual-ac-motor-control-with-active-pfc-implementation-using-piccolo-mcus

author: Eamon
author_rank: Contributor
timestamp: October 11, 2022, 11:44:44 pm
content: Quote from: florentbr on October 11, 2022, 04:43:23 pmFirstly, thanks for that link, it does look strikingly similar to my board's circuit apart from specific component values (though DB2 does not seem to have a reciprocal part in the diagram). And reading the article was a bit enlightening too, I think I have identified the phase current measurement blocks as a result (3 x MV7221 OP-Amps connected to the low side shunt resistors from the IBGT driver)Just double checked with the multimeter in DC mode and I don't see more than about 3V variation at the start of the resistor chain at R94 when the compressor starts and the inverter reports the big jump in AC voltage, unfortunately every time I try to measure the voltage at the end of the resistor chain after R99 as the compressor starts, the inverter reports "PFC Failure" code. Hopefully the oscilloscope will be more of a passive observer when I get the chance to set it up and try.Quote from: florentbr on October 11, 2022, 04:43:23 pmHow high is "well over"? I double checked the +vDC plane serveral times with the multimeter in DC mode and the highest I have seen is about 325V. Is there something I can do with a multimeter to check if the PFC circuit is turning on? My assumption from reading the article you provided is that it will be running at a frequency too high for a multimeter to be of much use?Quote from: florentbr on October 11, 2022, 04:43:23 pmMy thoughts are similar; the reported AC voltage when it jumps is almost exactly the same as the reported DC voltage, i'm just not sure where to measure to test that theory. Hopefully when I can get a scope onto it I'll learn more.Quote from: florentbr on October 11, 2022, 04:43:23 pmDe-soldering is not a strength of minetrying to avoid if possible. though if the problem is the +DC leaking back to the output of the bridge rectifier, it would seem that C53A could cause that?

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 12, 2022, 12:42:08 am
content: The inverter supply of 320vdc should not rise above that value, unless the compressor pressure/piston is pushing back against the motor, causing it to be become a generator rather than a motor. This can lead to overvoltage trips and this may be a sign of a bypass valve not opening for startup to reduce the pressure to allow the use of smaller motors. Don’t know what the refrigeration system schematic looks like but it should be easy to locate anything in the refrigerant lines with wires on it. It might be a pressure switch but you should be able figure out if this is going to an input or output on the control board.Your approach of trying to run the inverter with a different load is good idea but even better, the inverter may run without a motor. If not, a suitable load can many times be made with three 220v incandescent light bulbs wired in delta.

author: Eamon
author_rank: Contributor
timestamp: October 12, 2022, 01:47:04 am
content: Quote from: WattsThat on October 12, 2022, 12:42:08 amI've disconnected the heat pump controller board and I'm turning the inverter on an off directly with a small application I wrote using a USB to rs485 converter. I've reverse engineered enough of the communication protocol between the heat pump controller and the inverter module and that I can disconnect the heat pump controller and drive the inverter and compressor directly from a laptop so none of the various other sensors related to the refrigeration system should matter. The application essentially just polls the inverter for its state and sends the compressor on instruction in response to me pressing a toggle button on the laptop. I'm pretty confident that the compressor is not faulty.If I try to run the Inverter without anything connected to the U, V and W outputs of the inverter module it faults with a "Comp. Driver Failure", I've tried the only 3 phase motor I have at hand and it caused the inverter to report "PFC Fault" instead. I'll see if I can try 3 resistive loads in delta, but I suspect it will not work as I believe the inverter would be using the phase differences on the three inputs to measure frequency or rotor position or something like that?

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 12, 2022, 02:48:41 am
content: Is there any feedback from the motor back to the inverter? Some motors use three Hall effect sensors to tell the inverter where the rotor is, needed for proper switching. If there are no sensors/feedback, it should run with a resistive load so long as the current is close to that of the compressor load.

author: Eamon
author_rank: Contributor
timestamp: October 12, 2022, 04:24:03 am
content: Quote from: WattsThat on October 12, 2022, 02:48:41 amNo, the motor has only three wires, the three power phases from the inverter.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 12, 2022, 05:49:53 am
content: Quote from: Eamon on October 12, 2022, 04:24:03 amMy conclusion from this and other observations is - there's some kind of synchronous motor inside the compressor, and the inverter uses "sensorless feedback" for its control loop. The inverter won't run with anything else than a similar synchronous (PMSM) motor.Is 320V above the peak value of your normal mains AC voltate (e.g. 230V * 1.414 -> 325V)? If the PFC is active, the voltage from DC+ to DC- should be larger than this value. In practice, the rectified voltage from mains is somewhat smaller than this theoretical value, so 320V could mean the PFC isn't active. I'd expect 350V (ballpark value) while the PFC is active. If there's something wrong with the compressor, causing it to feed back energy into the DC-Link, voltage could easily rise up to 380V ... 400V before an error message is thrown. This is at least some general figures, I've got no experience with this particular appliance.

author: Eamon
author_rank: Contributor
timestamp: October 12, 2022, 09:33:50 am
content: Quote from: capt bullshot on October 12, 2022, 05:49:53 amYou are probably right about the motor but for all intents and purposes the fact that this is a heat pump and that the load is a compressor is irrelevant to the problem at hand I believe; this is a variable frequency driver for a 3 phase motor that uses as you said "sensorless feedback". I agree that I'm unlikely to have much luck using anything other than the actual compressor it is built for as a load. In any case, there's a real chance that a different load might not exhibit the fault for various reasons and ultimately I need it to work with the compressor not some other load so I'm somewhat resolved to do my testing in place at the appliance even though that is outdoors and means a bit of setup and packing up each time I want to take some measurements.My nominal AC voltage is "230 volts +6/-2%" according to regulations. In practice I see it vary a bit throughout the day (there is a high penetration of roof top solar where I live, including my own house). What I measured with the multimeter (BM796) this morning was nearly bang on 230v.I was playing around a little with the Analog Discovery 2 USB scope and the 100x probes at my desk. When I put them across active-neutral, the AC signal was not a pure sine wave; it appeared somewhat clipped. Image attached. I don't think this is likely to be a contributing factor to the fault, just that it might mean the peak DC voltage would be a little different than expected for pure sine wave 230v RMS signal. Over about 5 minutes I recorded a range 225V-233V, my multimeter recorded almost exactly 1V less. max and min are also recorded in the image.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 12, 2022, 12:34:05 pm
content: Your 230V waveform looks pretty normal. It's not an ideal sine wave, but rather a bit "clipped" as you see. This is the reason why I said, the actual peak voltage is lower than the theoretical value.A "short" (up to maybe 5...10m) cable from the inverter to the compressor/motor most probably works, at least for testing purposes.

author: florentbr
author_rank: Contributor
timestamp: October 12, 2022, 01:13:47 pm
content: QuoteCheck this one:https://www.ti.com/lit/ug/tidu249/tidu249.pdfQuoteI don't know how much higher it's supposed to be.All the PFC I've tested were around 370v (small SMPS) and all the literature I came across is showing a significant difference between Vmax input voltage and output DC.If you check the previous pdf, there's an example at the end showing Vrms=230V and Vbus=390V (DC-link).This paper says that it must have an output voltage greater than 380v:https://www.ti.com/seclit/ml/slup390/slup390.pdfQuoteTo determine if the PFC is ON, measure the voltage or frequency at the transistor's gate.You should measure something even if the frequency is too high.QuoteMeasure the DC voltage at the output of the bridge rectifier and at the output of the PFC (DC-link).QuoteIf C53A was defective, it could have an impact on the measured voltage at the output of the bridge rectifier.I have no explanation for the InverterPlateACVoltage switching between 225v, 320v and 255v.If there was a path back to the rectifier, the InverterPlateACVoltage should be the same as InverterDCVoltage, on standby or PFC on. It's not the case and your curve shows 3 distinctive states.

author: Eamon
author_rank: Contributor
timestamp: October 12, 2022, 08:04:20 pm
content: Quote from: capt bullshot on October 12, 2022, 12:34:05 pmI hadn't even considered a longer cable. The run will be more like 30m but it's worth a shot.

author: Eamon
author_rank: Contributor
timestamp: October 15, 2022, 09:34:13 am
content: ok, so with a much longer cable, I have just over 2 ohms phase to phase now instead of 1.1 ohms but it runs and triggers the fault the same. I can use the scope on the desk now so will try to get some traces. Just have to work out the safest way to go about this as the scope is a USB scope with earth ground and the inverter is mains earth connected with the common ground as the -DCI've ordered a USB isolator but that will take a couple of weeks to arrive I think. I am reading that I should probably be using an isolated transformer to power the inverter? The full load of the inverter would require a fairly expensive transformer, but as it faults at around 30Hz which is well below full load I will probably get away with something smaller.Also the scope can be powered externally rather than USB powered. The inverter has a 15V line for the fan (relative to -DC/common ground), If i were to convert that down to 5V the scope uses would it be the way to go as that would put the scope and the inverter on a common ground? (assuming I use the USB isolator)

author: capt bullshot
author_rank: Super Contributor
timestamp: October 15, 2022, 10:12:30 am
content: An USB isolator is fine. Some of them have capability to power up the connected USB device - don't know if this is enough for the AD. If not, I'd recommend a quality external power supply for the AD, these should have enough isolation to cope with -DC potential (don't use a lab supply). I wouldn't recommend powering the AD from the inverters internal supply, as 1. it might not provide enough power, and 2. the AD powers down when you disconnect the inverter mains supply, this might be really inconvenient. Third reason: You'd connect the AD GND to -DC anyway in this scenario, but you'd better ensure no power supply current flowing through this connection as this might induce "interesting things" to your measurements.Alternatively, use an isolation transformer and connect -DC to protective earth. The AD should work then without any further isolation (in theory at least, in practice one could discover what kind of funny things EMI is able to kid on youin such kind of setup).The isolation transformer must not be rated for the full power of the inverter, as at the lower motor frequency the load is lower and your typical isolation transformer can be short term overloaded by single digit multiples of their rated power. It just heats up faster, if you cut off the power before it overheats and wait for it to cool down again, it'll work.

author: Eamon
author_rank: Contributor
timestamp: October 16, 2022, 08:24:57 am
content: Ok, I think the isolation transformer is the way to go and I will then tie -DC to earth, along with the Analog discovery's ground.I came across a couple of step up/down transformers for cheap and had the thought that I could step down through one and up with the other to get isolation but turns out they are both autotransformers so no luck there, however the input can be switched between 240v, 220v, 200v and 110v with both "110v" and "220v" outputs, net effect is that if I switch it to 240v input, I get 210v on the "220v" output rather than my normal 230v so I can try what you originally suggested of feeding it ~20v lower voltage, I need to source a US style plug first, but I'll give that a go while I wait for the isolation transformer.

author: Eamon
author_rank: Contributor
timestamp: November 06, 2022, 10:12:50 am
content: Ok, I haven't given up on this and I'm finally in a position to use the oscilloscope on the inverter (isolation transformer, USB isolator).Also, while waiting for the USB isolator to arrive I've painstakingly mapped all the ADC pins on the MCU.I've put probes on all the ADC inputs and none appear to exhibit the pattern reported by the "AC Plate voltage" value reported by MODBUS when I run the compressorThat said, there is another characteristic that might provide some clues; when powering off the inverter there's enough power in the capacitors that the 3.3v rail holds for another 15 seconds or and continues to power the MCU and I can continue to read the values for this period. The DC voltage drops in a fairly linear fashion until about 160v at which point the MCU cuts outBUTthe reported "AC Plate voltage" drops immediately to 190v and stays exactly at that until the MCU cuts out. In fact, regardless of what input voltage I feed the inverter (using a step up/down transformer I have been able to generate 250v, 217v and 210v in addition to my current line voltage of 227v) and consequently where the "AC Plate voltage" starts when the power is cut (it always seems to read 14v lower than I measure at the terminals with a DMM), it always drops abruptly to exactly 190v for the remaining duration before the MCU cuts out.One reason this behavior is useful is that I have probedeverypin of the MCU while powering off the inverter from idle and the only two pins that show any real change between power off and the MCU cutting out are pins 6 and 9.Pin 6 (ADCINA7) drops from about 1.6v in a linear fashion to about 0.8v before the MCU cuts out (pin 6 is connected to DC+ through 4 x 470kΩ resistors and I'm fairly confident this is where the DC voltage measure is taken)pin 9 (ADCINA2) drops from about 2v much faster, more of an exponential decay. Maybe not directly converted to the "AC Plate voltage" but certainly suggests its it involved.My guess is that because the "AC Plate voltage" does not directly track any input it is some sort of calculated value (with a floor of 190v) but I'm at a bit of a loss as to where next?I was thinking that maybe I should I try manipulating the voltage on pin 9 with an external source and see what it reports as the "AC Plate voltage"? What sort of supply would be suitable for this?

author: capt bullshot
author_rank: Super Contributor
timestamp: November 06, 2022, 10:24:24 am
content: The supply must be capable to override the voltage at pin 9. So it needs to have a lower output impedance than the circuitry that brings the signal to pin 9. I'd recommend to investigate / reverse engineer the circuit driving this pin at least partially to see if it's driven from a resistive divider or an OpAmp output.In the latter case, be careful when applying external voltage to that node, as it could (thermally) overload the driving OpAmp.For a supply, keep in mind it has to be able to source and sink current to overdrive the voltage, and should be of low output impedance. In a former job, I've used a purpose designed amplifier to achieve that, but there was low risk, as I easily could get a fresh or repaired target board if I blew the device by mistake. For whatever reason (most possibly some kind of reversed murphys law) I didn't blow up a target.https://www.eevblog.com/forum/testgear/show-the-homemade-equipment-you-are-using-now/msg1983056/#msg1983056

author: Eamon
author_rank: Contributor
timestamp: November 06, 2022, 11:14:59 pm
content: This is what I can determine the circuitry feeding pin 9 looks like:Not sure exactly what "D5" is, it has "HA7" written on it (no luck find the part on google) and it looks like this:I've drawn it as a regular diode and assumed the polarity because the opposite makes less sense but not sure of the purpose of it, is it just to prevent pin 9 going -ve or is it actually a zenner diode to prevent too high a voltage on pin 9?Anyway, I put this into LTSpiceand it corresponds with the measured voltage at pin 9 and it shows 706.40177µA through R44 (not sure of the input impedance of pin 9).The analog discovery 2 has a power supply capability between 0.5v and 5v in 0.001v increments so I'm hoping I can use that? Not sure how to determine what its output impedance is though?

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 07, 2022, 12:18:28 am
content: Maybe worth checking C53A.

author: Eamon
author_rank: Contributor
timestamp: November 07, 2022, 03:34:42 am
content: Quote from: shakalnokturn on November 07, 2022, 12:18:28 amFor short? (Pretty confident it's not shorted) or do you mean to check that it's value matches what the label says? I was hoping to go as far as I could without needing to de-solder anything first.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 07, 2022, 06:25:04 am
content: I'm expecting a low value. This capacitor gets some harsh current spikes when the PFC is active. MKP capacitors tend to degrade by slowly loosing capacity. A value too low could cause more switching noise to reach the MCU's "AC" sense.If you must desolder use an iron with sufficient power.Edit: If desoldering is a problem, for testing you could add a 2.2μF parallel to the existing one see if it makes any difference.

author: Eamon
author_rank: Contributor
timestamp: November 07, 2022, 09:57:31 am
content: I can confirm that Pin 9 is the direct input for the "AC Plate voltage" value. I connected my analog discovery 2 power supply to the end of the 150k resistor chain and varied the voltage observing the effect on the "AC Plate voltage", sure enough as I varied the voltage, the reported AC voltage varied between a floor value of 190v (at 1.83v or lower) up to a 255v ceiling (2.45v or higher)Quote from: shakalnokturn on November 07, 2022, 06:25:04 amThanks, I think I'll try that first as my de-soldering skills leave a lot to be desired. Now to source a suitably rated capacitor.This is the existing one:Not sure where I previously determined that it was 2.2uF but will need to verify that before I can try another in parallel. But that part number seems hard to find any datasheet for best I've found is this linkhttps://world.taobao.com/item/585823361132.htm?spm=a21wu.24122187-tw.recommend-goods.6which has a picture with the same markings on it and says it's 2.2uF. Does that seem like a reasonable value for such a capacitor?Edit: the "G>" symbol on the capacitor suggests its from "Xiamen Faratronic Co. Ltd" and that took me tohttp://files.faratronic.com/book/2022/C35-1.pdfwhich Ithinkmeans that it is in fact a 2.2uF 630v Metallized polypropylene film capacitor

author: capt bullshot
author_rank: Super Contributor
timestamp: November 07, 2022, 07:47:30 pm
content: The capacitance code 225 means 22 and five zeros pF -> 2200000pF -> 2.2uF

author: Eamon
author_rank: Contributor
timestamp: November 07, 2022, 09:41:00 pm
content: Ok, so it's going to be a little while before I can get a replacement capacitor for C53A, but I have a much larger electrolytic capacitor (labeled 820uF but tests at 730Uf with my DMM) here that has a suitable voltage rating so I was wondering if I could wire it in parallel to test.I assume there is a good reason that they used a metalised-polypropylene capacitor with a relatively small value here instead of a larger electrolytic capacitor, but can I add an electrolytic capacitor in parallel in this circuit with a much larger capacitance and see if that prevents the fault?Also, if I do just end up de-soldering C53A to test it, is the capacitance test function on a DMM sufficient?

author: Eamon
author_rank: Contributor
timestamp: November 08, 2022, 10:31:00 am
content: Well this is frustrating; I've ended up de-soldering C53A and testing it and it looks good so I'm back to the drawing board for the root cause of the problemI've tested the C53A capacitor with both the DMM (which reports 2.18uF) and as it turns out the analog discovery has an Impedance Analyzer function that I used to measure the capacitance from 10Hz up to 100kHz and it was within 1%-2% of the 2.2uF nominal value between 10Hz and about 50kHz and within 10% from there up to 100kHz so I am reasonably confident that the capacitor is good, at least at low voltage (AD2 test was done at 5v). Is it possible/likely that the capacitor might still be bad but only at AC line voltage?Is there any other test I should do before I put the capacitor back in circuit?I can manipulate the reported AC voltage by varying the voltage at pin 9 between about 1.8v to 2.5v and this corresponds to linear change in reported voltage between 190v to 255v, but everything from 2.5v to 3.3v remains at 255v like it was a ceiling value (3.3v was as high as I was prepared to go as that is MCU datasheet say to keep the ADC inputs below 3.3v), but when running the compressor, the reported voltage jumps higher than this (usually up to about the DC voltage) and I observed the voltage at pin 9 actually dropping (but getting noisier) when the compressor kicks in and the "AC voltage" jumps up.Where to next?

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 08, 2022, 02:31:51 pm
content: I doubt the capacitor would behave badly at higher voltages, nothing else I'd check before re-fitting.Sorry for giving you hope, at least it's checked.So if in "bench test" conditions the AC voltage measurement is behaving correctly and I would suppose that 255V is a sensible high limit anyway, then the problem must be noise getting to the wrong place.Others have previously mentioned some of these points:-MCU supply voltage(s) decoupling (ADC Vref. voltage if externally generated or decoupled.)-Snubber capacitors/networks on the motor output.-"Y" capacitor on the small SMPS.-Wrong grounding.

author: florentbr
author_rank: Contributor
timestamp: November 09, 2022, 10:49:12 pm
content: QuoteThe output of the bridge rectifier DB1 should be 320v DC (flat) when the PFC is off (no load) and 230V DC (rectified sine, 320v peak) when the PFC is ON .Maybe it's simply the software reporting the voltage as Vavg/1.41 when the PFC is turned off and just Vavg when ON.Assuming the PFC is failing to pull the coils L1/L2 to ground with Q1/Q2, that would explain the ACPlateVoltage rising from 220v to 320v and why the InvertDCVoltage doesn't rise.I don't think it's a sensing issue since the reported values are stable and they match either Vrms 230v or Vpeak 320v.Check the voltage on the gate/drain of Q1/Q2 with and without load.

author: Eamon
author_rank: Contributor
timestamp: November 10, 2022, 10:13:29 am
content: Quote from: florentbr on November 09, 2022, 10:49:12 pmEureka!The voltage on the gates did not move one bit when turning on. I had assumed that the PFC was turning on as the outputs from the MCU suggested that was so but I should have measured at the final target!The MCU is driving pins 1 and 8 (Channel A and B enable pins) of the UCC27524 gate driver to 3.3v about two seconds after I send the compressor on signal, then just over a second later the MCU sends a ~48kHz 90% duty cycle 3.3v square wave signal to pins 2 and 4 (channel A and B Input)BUToutput pins 7 and 5 remain at 0v. pin 6 (VDD) has ~13v and pin 3(Gnd) is 0v.Output pins 7 and 5 are each connected through a 100Ω resistor to the gates of the two 34NM60N Power MOSFETs (Q1 and Q2 in the schematic).13v VDD is within spec (-0.3v to 20v) and outputs should be VDD +-0.3v so I think it's safe to conclude that the gate driver is bad?Quote from: florentbr on November 09, 2022, 10:49:12 pmSo a bad gate driver here fits with this theory too then I guess?I'll source a replacement and get it changed over and provide an update once done.In the meantime, a big thank-you to those who persevered with me through to this point, I've learnt heaps and it's been fun (and frustrating).Special thanks tocapt bullshotandflorentbr

author: florentbr
author_rank: Contributor
timestamp: November 10, 2022, 03:56:49 pm
content: QuoteI would change the driver and the mosfets since a leaky gate could have killed it.It's usually the power switching components failing first followed by the driver.QuoteYes it does since the voltage at the output of the bridge rectifier is supposed to decrease when the PFC is turned ON.Since it doesn't, I suppose it's the reason why the software is reporting an over-voltage.Check this simulation and pay attention to the output of the bridge rectifier with PFC ON and OFF:https://www.falstad.com/circuit/circuitjs.html?ctz=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

author: capt bullshot
author_rank: Super Contributor
timestamp: November 10, 2022, 04:28:51 pm
content: Quote from: florentbr on November 10, 2022, 03:56:49 pmI can confirm that from others (colleagues) experience with power electronics. I'd at least check whether the gates are shorted to drain or source - if not, one cannot be totally sure there's no hidden damage that'll strike again somewhen in the future. At that particular job, it was an unspoken rule to replace the whole driver / power board in case of such kind of failure.The other way 'round: In case the MOSFETs failed, they were shorted Drain-Source which obviously would blow fuses or release magic smoke in this configuration. So i'd bet they're still OK and prepared to lose my stake.Quote

author: Eamon
author_rank: Contributor
timestamp: November 10, 2022, 11:51:18 pm
content: Quote from: florentbr on November 10, 2022, 03:56:49 pmBoth power mosfets (Q1 and Q2) read exactly the same resistances in circuit:source-drain=16.5kgate-drain=27.7k,gate-source=9.75kDB2 = 12.8kWhat about the power diodes (D1 and D2,EPU3006)? is it a case of better safe than sorry? They're about $10 each but a relatively small amount given the time invested so far, just more soldering. Using my DMM Diode test function in circuit they each read 0.378v, but I assume the inductors are just a resistor at DC so they're effectively in parallel so that's about right? and in reverse the voltage just keeps climbing which I assume is because the diodes are good so not passing any current and that's just the effect of the capacitors charging.

author: florentbr
author_rank: Contributor
timestamp: November 11, 2022, 06:41:06 am
content: You'll have to remove the mosfets to check them.Since D1, D2 and DB2 are in parallel (coil is negligible), it won't show on a multimeter if one failed open. If either D1 or D2 was open, it would expose the mosfet to high voltage spikes well over the specified limit. I would just check them off circuit.

author: Eamon
author_rank: Contributor
timestamp: November 12, 2022, 04:50:50 am
content: Ok, so the three different components are not available from a single source that I can find so I'm considering substitutions.For the gate driver, there is an "A" version that says "The UCC27524A adds the ability to handle –5 V directly at the input pins for increased robustness" so I think a straight substitution here is ok.For the MOSFETs (STW34NM60N), apart from ensuring the voltage rating is 600v or above and the current rating is at or above the rating of the existing ones (34 amps), are there particular attributes that I need to match closely with the existing part? I'm thinking of using the STW45N65M5 which has a 3.5amp higher rating and a 650V rating instead of 600v.And for the diodes (VS-EPU3006), the datasheet link actually goes to the VS-EPU6006 which is essentially the same but with a 60 amp rating instead of 30 amps. Can I use the VS-EPU6006 instead?

author: Eamon
author_rank: Contributor
timestamp: November 22, 2022, 11:32:13 am
content: Well the parts arrived and after de-soldering all the power components and testing them I decided that they were all good apart from the gate driver (and an electrolytic cap that I may have inadvertently overheated so replaced that too). So I put all the original parts back in with a new gate driver and voilà, a functioning inverter compressor driver!I have the new components at hand should one of the existing ones fail but as they were not an exact part number replacement anyway I felt best to stick with the originals if they appear to function correctly.Now when the PFC turns on, the DC voltage jumps up to 380v instead of dropping slightly and at the point where the "AC plate voltage" previously jumped to ~320v it climbs to 230v and no fault occurs.I've sunk a lot of hours into this but I've mostly enjoyed it and learnt a heap, not to mention a saving of ~$2500 for a replacement part!Again, I want to give a special thanks tocapt bullshotandflorentbrif you guys have a paypal account, I'd like to buy you both a beer/coffee/drinkmsg me.

author: capt bullshot
author_rank: Super Contributor
timestamp: November 27, 2022, 10:34:17 am
content: You're welcome!Glad to see the good result of your effort, so the thing is working again with mininum hassle. I would have kept the original power components, too. But that bet could have failed in a spectacular way. My former colleagues always used a good amount of protection when powering up a repaired board for the first time - a carton box put over the DUT, shrapnel protection googles, distance and a remotely controlled power on switch - and someone else nearby to watch them and to call emergency / fire brigade in case.

author: piratebriggs
author_rank: Newbie
timestamp: August 29, 2024, 10:20:45 am
content: Hi, Sorry for replying to an old thread - I have a different heatpump to you but with the same inverter board.Mine has suffered damage to the 15v SMPS section of the board (skid marks) so I've desoldered enough components so I can feed 15v in from an external supply and the activity LED next to the mcu is blinking, however the touchscreen is still reporting "F02 - Inverter Offline" so I'd like to try comminicating with it over the rs485 port to see if that section of the board is intact.So, I was wondering if you still still have a copy of your test application @Eamon to save me the reverse engineering the ModBUS all over again!I know there are issues on the power side of the board - the DC bus is shorted/trips the breaker when the main relay turns on but I just wanted to verify that the LV side of the board is OK before putting a lot of time/unloading the parts cannon on itAnyway, there's lots of useful info in this thread to help diagnose my board already so Thx allTTFN