16 minutes ago, Coulomb said:

The AC full bridge (four IGBTs generating L and N outputs) are bidirectional. They can push or pull power depending on the phase of the sine wave with respect to the utility's, and push or pull VARs (reactive power) depending on the amplitude of the sine wave compared to the utility's. So for utility battery charging, or indeed any charging with these models, the firmware manipulates the phase to cause the power flow direction and amplitude (power amplitude, number of watts) required.

But that power ends up in the bus capacitors, since that's at the other end of the full bridge (a DC <-> AC converter). If nothing loads the bus capacitors, they will quickly overvoltage, and other parts of the inverter have to step in and trip everything. But before that happens, the DC-DC converter, which is also bidirectional. pushes power towards the battery, keeping the bus voltage withing reasonable bounds.

But the DC-DC converter has a fixed voltage ratio, set by the transformer turns ratio. Typically this is 8:1 or 7:1, though more recent models use something like 7.2:1. And the bus voltage is being buffeted not only my the full bridge running in reverse, but also the PV boost converter(s). The bus voltage can't be more than a volt or so lower than the present PV voltage. So the bus voltage is fluctuating. How to regulate the battery charge current in this situation? That's what the buck converter is for.

When power flow is from the bus to the load, this converter is "straight through", i.e. the DC-DC high-side voltage is very near the bus voltage. But when the power flow is the other way, i.e. towards the battery, i.e. charging the battery, the buck converter is controlled to regulate the charge current. But the buck converter can only buck, never boost, so the transformed battery voltage always has to be less than the bus voltage. In other words, the bus voltage mustn't be allowed to fall too low. This can be done by fine tuning the exact power demanded from the full bridge. You can see that the inverter firmware is juggling a lot of balls at once.

Really insightful and clever design. thanks for the explanation. So i went troubleshooting the idle AC charging consumption (50w when battery is basically full), as i suspect that it may be abnormal, I have a usb multimeter and measured the ripple current, isnt this abit high at a delta of 1.5v for a 12v system? also switched on the unit with no battery, the waveform that rises up is the measurement at the DC terminal during startup, it looks to me like the ripple increases with voltage increase. does this mean anything and could it explain the high consumption during the float phase of charging. Or is this all normal?

Edited August 3, 2025Aug 3 by soulfreeze
repetition

Just now, soulfreeze said:

Did some preliminary troubleshooting, Not sure what to look for, but i did notice there seems to be quite some ripple on the charging dc output, both with battery connected and with battery disconnected. could it be possible that I have faulty Low voltage side electrolytic caps? something else to look at? or is a >1.5v ripple voltage normal?

Really insightful and clever design. thanks for the explanation. So i went troubleshooting the idle AC charging consumption (50w when battery is basically full), as i suspect that it may be abnormal, I have a usb multimeter and measured the ripple current, isnt this abit high at a delta of 1.5v? also switched on the unit with no battery, the waveform that rises up is the measurement at the DC terminal during startup, it looks to me like the ripple increases with voltage increase. does this mean anything and could it explain the high consumption during the float phase of charging. Or is this all normal?

the particular unit has a weird buck converter design, which what appears to be a synchronous buck, but with 3 IGBTs, with two paralleled together. in place of where you would have the diode. Assuming all this is being done for efficiency reasons, but cant understand why one half of a synchronous buck converter would need twice the power handling capacity.

On 2023/02/04 at 1:41 PM, BritishRacingGreen said:

Capacitors :  Why ESR Matters

If we look at the  inverter on its components level ,  we find mostly solid state  devices , electromechanical devices like the relays , electromagnetics eg. transformers , film capacitors and electrolytic capacitors.  Of all these the electrolytic has a deterministic lifecycle of degradation , even gracefully , and this has to do with its construction . The electrolyte is embedded in paste between the layers of aluminium foil , and it is fluid .  The capacitance and performance of the device depends on the quality and quantity of the fluid.  unfortunately , in the ambient environment of the high power  inverter , temperatures get high , conditions gets dry , ripple currents are high , working voltage is close to max voltage and with it the electrolyte dries out over time. In fact the manufacturer will state as a spec the number of hours that the capacitor can operate. This is typically 5000 hours , but you do get very high quality at > 10000 hours. This 5000 hours may seem very short , but it only 'counts' when the operating temperature reaches above certain high temperature thresholds  .So that means if the capacitor runs relative cool , it can last many years , although other factors also influence the degradation as previously stated.

So if we receive a machine that has been running for 4 years already , do we need to change the caps as a qualitative measure ?  Not necessarily  , as the caps could have been subjected to good operating condition as described above. So the question arises , can we measure the level of degradation . Fortunately we can , by measuring its Effective Series Resistance  (ESR)   . While this is never a silver bullet , it does provide a good measure . The ESR of a capacitor is a resistance that can be seen as being in series with the capacitance . So the higher this resistance is , the less is the device capable of filtering , and under ac circuits it can influence the reactance. This ESR value is typically in the order of tens / hundred of  milliohms when the capacitor is good , but as the electrolyte dries out , this resistance increases , and values approaches 1 ohm or more will be a telltale that the capacitor has degraded to a level that it needs replacement.

I am pretty new to the  subject of ESR and it is difficult just to measure ESR as an absolute value and  qualify it as good or bad . Fortunately I have some good new capacitors to expermiment with as to provide a basis of comparison.

So how is ESR measured ?  The capacitor within this model consist of capacitance in series with the internal resistance. An ESR meter employs a low voltages ac oscillator to generate a 100hz square wave signal . if the Capacitor Under Test (CUT) is exposed to this ac circuit its own reactance will be very close to zero ohms , given a 100khz frequency and a high value of capacitance. If the reactance of the CUT  is near zero all is left is the ESR , and this we can measure using voltage divider circuit.

Unfortunately I have not yet layed my hands on a commercial meter , and the one that is available in local store is in the order of R6000-00 . So I decided to cook up a homebrewed circuit , based on DIY designs on the web .  Below is a circuit diagram of my crude ESR meter:

 

I am using a Raspberry PI Pico to generate the 100khz square have at 3.3V . This signal drives 6 logic inverters in parallel , each inverter feeds a 270R resistor. So the effective  source resistance of the generator is about 45 ohms.

The output is low pass filtered by C3 and feeds R7 , a 10 ohm resistor.  This provide about 450 - 500 mV at point A , and this depends on the drive capability of the generator , which is not optimum in my case , but good enough.

The CUT is terminated by R8 , 10R to ground. So you can see that the voltage at B will get lower as the ESR of CUT gets higher. Currently I am using an oscilloscope across points across points A and B to get a measure of ESR magnitude.  When A and B is short circuited , I read about 6mV or lower . When I connect a 1R resistor between A and B I read something in the order of 30mV across A and B . This is some crude calibration.. So anything between 7mV and 30mV provides an ESR of 0 to 1 ohm. That's the range i am interested in. 330 milliohm is about 10.6 mV.

Below is an image of the ESR voltage level for a new 470uF 63V electrolytic. You can see that at 7mV the ESR is very low.

 

Here is a 1000uF 16V one removed from inverter . 

 

At nearly 750 milliohm (22mV ) its bad . I say its bad because I have tested good 1000uF 16V devices and I get far better results than this. Now here is the interesting thing about this CUT : the capacitance reading on cap meter is 1023uF !!!!  , which implies its ok , but BEWARE , the ESR shows its bad , and its probably going to fail in not so distant future !!!!

 

The next sample is also a 1000uF 16V , also removed from inverter , this is one is even worst :

 

And next is what the ESR looks like when the capacitor has ran dry : its virtually open circuit !

 

I will continue this post in a next one , cover in-circuit test of ESR .

 

It's a little late to complain since this post is from 2023 ..but..

Almost all you wrote is ok, but you really have "overengeneered" the measurement.

The ESR Tester from ludens.cl which was the hint from me, isn't a measuring device, it's build for fast tests. You don't even need a calibration on the meter which gives you numbers..you can use the instrument of an old VU meter or some such to get a fast good/bad test. Some experience is needed for identifying bad caps, but after a short time you know how a good cap is looking like on the meter.

That thing that I'm regularly use has an resistance value of approx max 20 Ohms it can display and sometimes I misuse it to check source resistors in PSUs..they are ok .. or they are bad. An yes/no decision. Same as for electrolytics.. I don't want to "measure" values, I want to know if they are ok oder bad.

The meter needle has to be in the zero range, all other positions identify a bad cap (except for 0,47 or 1µ Values).

The ludens.cl Tester does a good job for this. I have a large stack of TL084 Opamps and made a small pcb for those testers ..using an precision rectifier..that was nonsense. It works better with the simple circuit with the two diodes for his purpose.

I have the gear to do precise measurements at different frequencies and different polarization Voltages, but this HP 4285A Meter is more a furniture then a test device and it takes much longer to get yes/no results.

just my 2 Cents,

holm

Edited August 3, 2025Aug 3 by holmoe

On 2025/08/02 at 4:36 PM, Coulomb said:

No, that seems too low to me, assuming that the voltmeter can be trusted to within one percent or so. The voltage of the 12 V rail is determined by the width of the pulses in the main power supply. I would suspect parts around the 3-terminal voltage reference and the associated opto-coupler.

But of course it could also be that something is still drawing too much current from the 12 V supply, and that's overloading it. Those sorts of faults can be a nightmare to fix.

Replaced all caps and new 7912 now 11.90 very acceptable..still bringing voltage up will stress component if they are dodgy ...i have seen this soon as i put new caps new 7912 some thing goes down

Any body operated igbts not heat sinked...2 are at terrible tempreture...i cant touch them after 1 mint ...is that normal ..

Sorotec inverter have same fan plug i am stuck which fan goes to which plug ....one plug have fan1 written on it other plug have fan 2 written on it ...but whcich fan 1 and which is fan2

@Coulomb

Edited August 8, 2025Aug 8 by wael_fathe

9 hours ago, wael_fathe said:

but which fan 1 and which is fan2

I don't believe that it matters for most inverters. The ones I'm familiar with have the same speed on both fans. VM models do seem to treat the fans differently, but if you swapped them I don't think it would make a real difference.

On 2025/08/03 at 1:19 AM, soulfreeze said:

could it be possible that I have faulty Low voltage side electrolytic caps? something else to look at? or is a >1.5v ripple voltage normal?

Yes, battery side capacitors could be dry. But the battery should absorb most of that ripple; I suspect either the battery itself or the battery cables have high resistance.

Actually, with the ripple on the DC bus, the DC bus capacitors could be dry as well.

Unfortunately, I have no experience with the 12 V models.

THERE ARE 4 TYPES OF 06 ERROR THAT CAN POP UP IN SMALL 1-2K INVERTER AND

3-5 K INVERTER

1- BAD ZENERS CAN EASILY CAUSE 06 ERROR TO HAPPEN 1-2K

2- BAD CONNECTIONS CAN ESPECIALLY BETWEEN THE EMIITER OF MOST LEFT IGBTS ON AC AND COLLECTOR OF THE ONE BESIDE IT (WHEN YOU VIEW THEM FROM FRONT)

3- BAD COPLER .. I SOLVED COPLER SHORTED PARTLY THAT CAUSE 1K RESISTANCE TO APPEAR ACROSS ONE IGBT...THE MOMENT THE CPU SEND PULSES THE 16VDC ZENER VOLTAGE SAGS

TO 12VDC ...OTHER ZENERS ALL AT 14VDC SO I RELIZED COPLER OF THE IGBT IS PROLEMATIC CHANGING THE COPLER SOLVED 06 1-2K the boardcan be fliped and testing zener voltages while the inverteer working

4- MARGNAL COPLER ...THIS ONE IS STRANGE THE WAVEFORM APPEARS BUT A BIT LESS THAN 15VDC AND LESS THAN 5.5VDC I CHNAGED ALL COPLERS AND ZENERS WITH SAME NUMBER STILL

ALL ZENERS ARE 13 TO 13.5 AND ALL 5.5 ARE ONLY 5.3 ...ONLY WHEN I REPLACE T5130 WITH T350 THE Z DIODES BACK TO 5.5VDC AND 14.5 VDC AND 06 DISAPPEARED

5- igbt with very high input capacitance have caused the 16vdc zener in 2k 1k inverter voltage to drop to 8vdc and 06 appear

when replaced with 40 amps igbt low cappacitance 14vdc is back and 06 disappear

all those solutions are from real life rreepairs remember in 1k inverter error 53 not exist if no output ac out and no error 09 the inverter announce 06 also remeember coopler 3150 is dodgy even if new

Edited September 13, 2025Sep 13 by wael_fathe

Hello! Because you have an inspiring 29 pages of useful information ..i dare ask a question about my situation!I received an blown POWMR 3,2kw and try to get it to work for my personal use!

Error 57 few Mosfet blown and OP07 replaced and a Zener 18v....Now starts well...

but with a thermal camera i noticed 2 resistors near TX1 and TX2 overheating... bad! i checked the parts ...all good! Replaced the nearby mosfets and zeners , decoupled the other side of tx1 and tx2 (d6 and d5)

After disconecting the capacitors c15 and c14 the heating disapeared.. so the problem is on the other side...theSG3525 is new...

reconected all only left the capacitors...no heat

Edited March 25Mar 25 by edy99

1 hour ago, edy99 said:

After disconecting the capacitors c15 and c14 the heating disappeared...

Those capacitors seem to work hard, and often seem to fail with weird effects. I don't believe that they are 100 nF as shown on the schematic, I think that they are closer to 10μF (at least for 5kVA 48V models). So it might be worth replacing those with decent quality 50V parts, if you can find them in a suitable size.

The other possibility is more gate driver parts, like the bipolar transistors.

The existing capacitor were 2μF on tester i replaced with 100nF...... still the same effect! The transistors were smd sot223 i managed to squeeze full size ones! Still no success! I powered the inverter from grid and a 24v power supply..- to weak to test the standalone inverter part(gives error 52 low battery)

"So it might be worth replacing those with decent quality 50V parts, if you can find them in a suitable size."

Thank you .i.will

Edited March 25Mar 25 by edy99