On 2024/02/05 at 2:28 PM, Scorp007 said:

What is interesting for me is that a 10 uF cap weighs less than a 1 uF.

Capacitors ain't capacitors. (cf. that old advertisement of the mafia guy saying "oils aint oils"). They (capacitors) have different voltage ratings, some are electrolytic, some film, some mica or other types. Electrolytics are quite compact because they use aluminium oxide as the separator (if I understand correctly). But they generally need to be polarised.

Even within the class of electrolytics, they can be optimised for service life, ripple current rating (or often both), or economy.

Then there are the X7R and similar ceramics that can barely be called capacitors; they have insane capacitance densities but very ordinary performance. Just fine for bypassing and the like, just don't use them for critical timing applications.

 

Hi,

 

Thanks for this repair. Saved me lots of money, I’m sure. Needed a 100W soldering iron to melt the existing solder The caps didn’t look damaged at all. I changed the two caps and inverter is up and running again. Should have changed the fans while the inverter was stripped. Powered up and only one fan is working. 
 

 

I found this thread because I have exactly the same model of inverter (Voltronic Axpert MKS 5kVA) which exhibited the same fault condition. I want to say thank you for all the posts here because this helped me to fix my inverter quickly and it didn't cost me anything.

I am electronic engineer in South Africa with 30+ years experience in hardware and software design. I have also designed a 1kW switch mode battery charger using active power factor correction. I performed my own solar inverter installation around 5 years ago with the above mentioned Axpert 5kVA. It also has the same printing on it as per @Plaasjapie 's post (TheSunpays.co.za). It suddenly exhibited the same fault. I disassembled and found the two guilty capacitors C78 and C79. It would seem that this is a common failure point on this design.

From my analysis of the reason for failure of the components is either because they have insufficient voltage rating or they have insufficient ripple current rating, or both. The capacitors are used for smoothing on the output of what appears to be an auxillary power supply supplying +5V and -12V to the circuit. This can be deduced from that switch mode transformer nearby, the output diodes feeding the capacitors and the 7912 and 78M05 regulators. The 7912 regulator is a standard -12V linear regulator and given the dropout voltage required for it to operate the input voltage would need to be around -14V or lower. The capacitors on my board were 16V rated. This is way too close to the maximum rated working voltage of the capacitors. They should be at least 25V rated or higher. Just to respond to the comment by @Coulomb about operating electrolytics at 80% of rated voltage. That is not quite correct:

To begin with the way the maximum rated working voltage of an electrolytic capacitor is determined during testing is they crank up the voltage and measure the rate of spark through events on the dielectric. When the rate of spark through events reaches a certain value that is how they determine the maximum safe working voltage. So in essence at the maximum rated voltage the capacitor is already failing, just very slowly. So it's definitely a good idea to have quite a margin when it comes to working voltage. Also the value tolerance of most electrolytic capacitors is +/-20%. No circuit should be designed using an electrolytic capacitor where an accurate value is required. In this case the electrolytics are used for smoothing so the value chosen should be "enough" to perform adequate smoothing but doesn't need to be an exact value, more is better. The choice of value might also affect the corner frequency of the control loop for the switch mode, but again the design should allow for a wide tolerance of capacitance value. But what is more important is the capacitors should be of the low ESR type (low equivalent series resistance). All capacitors used in switch mode circuits where high frequency ripple currents are involved must be chosen for low loss and have sufficient ripple current ratings for the design. In addition the ripple current rating is reduced at high temperature. Another indicator that the capacitors are handling high frequency ripple currents are the small ceramic chip capacitors solder directly between the pins of the capacitors on the underside of the board. They are there to handle the very high frequencies where the electrolytics impedance starts to climb because of parasitic inductance. But this doesn't mean that they handle the bulk of the high frequency ripple currents.

The capacitors I found on my board were 16V rated and appeared to be made by a company called yst. There are no other markings to indicate which series they are. I googled yst and the information is sketchy on the manufacturer. I replaced the capacitors with some Rubycon YXF series 1000uF 35V capacitors I had in my stash and the inverter is working fine now. I just didn't have 25V rated capacitors but it didn't matter. Rubycon is a reputable manufacturer and the YXF series are low ESR 105C rated capacitors with long life. I've used Rubycon YXF for years and they've never failed me. I do not want to have to replace the caps again in 5 years time. You can use any capacitors from a reputable manufacturer that are specifically Low ESR and high temperature rated, such names as Rubycon, Nichicon, Panasonic, TDK Epcos, BHC Aerovox, Wurth etc come to mind. They only cost a little more than standard grade but its worth it. My guess is the yst capacitors used on the board are just standard grade capacitors and with insufficient voltage and ripple current rating, thus the failure and it's clearly happening on a lot of these inverters so it's a design flaw, not a random failure.

I hope this explanation helps.

Edited June 24, 20251 yr by Pilot

On 2025/06/23 at 12:57 AM, Pilot said:

I disassembled and found the two guilty capacitors C79 and C79.

I assume you mean C78 and C79.

On 2025/06/23 at 12:57 AM, Pilot said:

The 7912 regulator is a standard -12V linear regulator and given the dropout voltage required for it to operate the input voltage would need to be around -14V or lower. The capacitors on my board were 16V rated

This is possibly because The Sun Pays is a clone, not a Voltronic inverter with other branding. In a standard Voltronic inverter, C116 (at the input to the 7912 -12 V regulator) is 1000μF 25 VW.

On 2025/06/23 at 12:57 AM, Pilot said:

My guess is the YST capacitors used on the board are just standard grade capacitors and with insufficient voltage and ripple current rating, thus the failure and it's clearly happening on a lot of these inverters so it's a design flaw, not a random failure.

The capacitors used in genuine Voltronic inverters are so-so, typically rated at 2000h at 105°C. What you'll find in clones will vary tremendously, most likely at the low quality end of the spectrum.

I certainly agree that it's worth spending a little more and replacing with decent quality capacitors.

Hi @Coulomb

"I assume you mean C78 and C79."

Ah, yes, I corrected that.

"This is possibly because The Sun Pays is a clone, not a Voltronic inverter with other branding. In a standard Voltronic inverter, C116 (at the input to the 7912 -12 V regulator) is 1000μF 25 VW."

The company I bought the inverter from said that they are all cloning each other, so you never know what you are really getting.

"The capacitors used in genuine Voltronic inverters are so-so, typically rated at 2000h at 105°C"

That's not very long, quite honestly the better quality capacitors really don't cost much more, I never design in cheap components when I'm doing a design.

"If asking me for Axpert firmware updates, please quote your existing firmware versions (main/DSP/U1 or display/MCU/U2)."

What can you tell me about the firmware updates? Is it worth it? I find the software in these inverters to be really crap. I control mine from a Raspberry Pi that I have written an intelligent application on to manage the inverter and frequently there is a CRC error on the packets sent from the inverter which indicates a bug in the CRC calculation in the firmware. It's annoying but I just work around it.

Edited June 24, 20251 yr by Pilot

On 2025/06/25 at 4:19 AM, Pilot said:

The company I bought the inverter from said that they are all cloning each other, so you never know what you are really getting.

There are a fair few clones about, but not as many as in earlier years. Most are made in the Voltronic factory, and the resellers send Voltronic the artwork to put on the cover. So most are "genuine" Voltronics, despite the different brand names. Voltronics likes the resellers to handle warranty work and customer enquiries.

On 2025/06/25 at 4:19 AM, Pilot said:

What can you tell me about the firmware updates? Is it worth it? I find the software in these inverters to be really crap.

I and others find that they are "just barely good enough". Sometimes you have to patch the firmware to get reasonable results.

With the CRC errors, you are possibly running into a bug with Arduino USB comms where you have to split up ascii commands longer than 8 characters (including the trailing carriage return and two CRC characters) into two strings. And/or the special case when a CRC character would result in a carriage return, linefeed, or open parenthesis character (in which case that character is incremented by 1).

It used to be that the next inverters up (in quality) from Axperts cost twice as much or more. That's no longer the case, and hence Voltronic no longer dominate the lower priced end of the market.

On 2025/06/22 at 4:57 PM, Pilot said:

small ceramic chip capacitors solder directly between the pins of the capacitors on the underside of the board.

@Pilot My unit started to flicker on the weekend so I decided to open it up to try and fix it myself.

Sure enough C79 had popped. It was repaired by a company about 18 months ago and I see that there are no ceramic caps between the pins.

Could this have been the cause of the failure? And do I need to replace them or will a higher voltage cap be enough to compensate for them?

The blown capacitor is also a YST brand btw.

I am by no means an electrical engineer, far from it. Just trying to save myself a few bucks...

Many thanks in advance.

1 hour ago, OzzyMozzy said:

@Pilot My unit started to flicker on the weekend so I decided to open it up to try and fix it myself.

Sure enough C79 had popped. It was repaired by a company about 18 months ago and I see that there are no ceramic caps between the pins.

Could this have been the cause of the failure? And do I need to replace them or will a higher voltage cap be enough to compensate for them?

The blown capacitor is also a YST brand btw.

I am by no means an electrical engineer, far from it. Just trying to save myself a few bucks...

Many thanks in advance.

Hi @OzzyMozzy , that seems like an oversight on the part of the company that repaired your inverter. You definitely should have the ceramic caps between the pins, the reason for them being there is because at very high frequencies (greater than say 10 MHz) the electrolytic capacitor looks more like an inductor than a capacitor. The ceramics are there to catch the high frequency components of the currents, which helps to reduce the ripple current stress on the electrolytics. I don't know the actual value of the ceramics used, but typically 100nF X7R should be fine and you should use at least 50V rating. I would also select better electrolytic capacitors than the YST brand. If you need some assistance in choosing a replacement I'm more than willing to help point you in the right direction. I understand you also want to save some money, which was the case with me, so my acknowledgement again goes to @Coulomb who originally started this post which has been very helpful.

Hey, thanks for the advice, would you know where I could get the ceramic caps from locally and more importantly quickly?

And yes, thanks to @Coulomb for his post on which caps to buy and what brand as I was in Australia earlier in the year and bought them according to his list. The man is a legend!

And thank you for responding!!!

6 minutes ago, OzzyMozzy said:

Hey, thanks for the advice, would you know where I could get the ceramic caps from locally and more importantly quickly?

And yes, thanks to @Coulomb for his post on which caps to buy and what brand as I was in Australia earlier in the year and bought them according to his list. The man is a legend!

And thank you for responding!!!

If the caps are the normal 0.1uF 50V then you can buy on line from Communica. Then you have them real quick as well. Not an expensive item and courier will be more than the caps.

11 minutes ago, OzzyMozzy said:

Hey, thanks for the advice, would you know where I could get the ceramic caps from locally and more importantly quickly?

And yes, thanks to @Coulomb for his post on which caps to buy and what brand as I was in Australia earlier in the year and bought them according to his list. The man is a legend!

And thank you for responding!!!

May I ask which country you are based in? Communica is an option in South Africa, otherwise RS components. They will sell you a small strip and as @Scorp007 says the courier fee will be more than the components. Look up RS Stock code 698-3263 or anything similar will do.

I’m based in Pretoria but work in Joburg so will see what they have available.

Thanks once again.

6 minutes ago, OzzyMozzy said:

I’m based in Pretoria but work in Joburg so will see what they have available.

Thanks once again.

Ok, you have some options then, Electrocomp is one, Communica, Mantech, RS Components etc.

Errr, so as I didn't have a sample with me I managed to buy the wrong caps...

Also looking at the PCB I'm not sure if it is worth the effort, has a lot of scorching on it so maybe not worth it?

I am also not sure how many of the caps (just C79?) needs the ceramic caps as it all just looks so messy.

Thoughts?

Time for a new inverter perhaps?

And as usual, time is not my friend so any thoughts greatly appreciated.

24 minutes ago, OzzyMozzy said:

Errr, so as I didn't have a sample with me I managed to buy the wrong caps...

Also looking at the PCB I'm not sure if it is worth the effort, has a lot of scorching on it so maybe not worth it?

I am also not sure how many of the caps (just C79?) needs the ceramic caps as it all just looks so messy.

Thoughts?

Time for a new inverter perhaps?

And as usual, time is not my friend so any thoughts greatly appreciated.

You board doesn't look too bad from what I can make out in the photos, I think it's still worth trying to fix it (I certainly would). I don't have a photo of the underside of my board so can't say which electrolytics had ceramics across them but I would say definitely you should put them across C78 and C79 as those are the caps which fail most commonly. There is no harm in having ceramics across other electrolytics, all that they will do is reduce the impedance at high frequencies which is always desirable. It looks like you have bought 1206 capacitors, that is fine, just get them to fit in between the pins.

I ended up fixing mine when it failed when we had an extended power failure lasting almost 2 days and I had to sit in the garage using a small 500W inverter to power my soldering iron from the car battery, so I understand the time pressure to get it working again.

Edited August 6, 2025Aug 6 by Pilot