Double the lifetime of an inverter?

[jflorey2]

Inverters are still full of electrolytic caps. The mfgs are trying to eliminate them but it's very difficult as no other technology has the charge density that aluminum electrolytics have, so they are still in your inverter and mine and if we can cool them they will last longer.

Well, EDLC's have far higher charge density, but have similar problems.

However, the path towards elimination is not replacement with an equal charge density, more reliable part; it's removing the need for them to begin with. Capacitors are needed in inverters because energy storage is needed, and energy storage needs are inversely proportional to frequency. In general, an inverter with a switching frequency (not inversion frequency) of 500KHz needs one-fifth the bridge capacitance of an inverter that runs at 100KHz. Once your frequencies get high enough, electrolytic caps can be replaced by film caps or even ceramics, both of which have much longer lifetimes. For example, SolarBridge (recently acquired by Sunpower) uses only ceramic and film caps in their microinverter designs.

[DaveDE2]

EDLC's also have a max voltage rating of just a few volts so would never be considered for bridge capacitance.

Whilst increasing the switching frequency by a factor of five decreases the needed bridge capacitance it would also increase the switching transistor power dissipation by a factor of five assuming the rise and fall times are the same, so there are a lot of trade offs.
Inverter manufacturers probably care a lot more about efficiency than increasing longevity at this state of the art.

[bcroe]

Just 2 cents. Thermal cycling is inevitable in a PV inverter every day. So perhaps any efforts to limit the max temps
reached each day will lower the temp delta & cycling stress. And switching converters truly stress the caps in the
power conversion section; we are still working on taming this beast. Bruce Roe

[J.P.M.]

Just 2 cents. Thermal cycling is inevitable in a PV inverter every day. So perhaps any efforts to limit the max temps
reached each day will lower the temp delta & cycling stress. And switching converters truly stress the caps in the
power conversion section; we are still working on taming this beast. Bruce Roe

As has always been the case, and as in most things of that sort, methods of cooling equipment come down to knowing/learning what's going on, defining goals, knowing/finding how to best meet the defined goals, and meeting those goals in a safe, serviceable and cost effective way. An ongoing process as you note.

[jflorey2]

Whilst increasing the switching frequency by a factor of five decreases the needed bridge capacitance it would also increase the switching transistor power dissipation by a factor of five assuming the rise and fall times are the same

Only if the devices themselves are the same - and they are not. MOSFETs are much faster (and less lossy at high frequencies) than the bipolar devices they replaced. And gate capacitance energy (the primary loss factor in non resonant switchmode power supplies) keeps going down as new MOSFETS are released. Resonant gate drives eliminate most of the gate capacitance loss in MOSFET designs. New devices (like GANFETs) reduce capacitances by another order of magnitude, making a 1MHz design no more lossy from a switch perspective than an older 100KHz design.

And all the above make it that much easier to move away from electrolytics to film and ceramics. Which is why you are seeing fewer electrolytic caps in inverters today.

Inverter manufacturers probably care a lot more about efficiency than increasing longevity at this state of the art.

I think they care about efficiency, longevity, size and cost. Enphase would go out of business quickly if local dealers stopped carrying them because they were getting sick of frequent warranty repairs on their inverters.

[DaveDE2]

I agree with everything you say here with the added comment that a 10x power reduction improvement (in the fets and drive circuitry at a given switching frequency) is a tall order and the smaller devices always seem to make advances more quickly than the larger ones. Micro inverters can benefit from this sooner than large string inverters, which is great, then again they really could use that because they really bake up there on the roof. Non-micro inverters evidently are not there yet because (for example) the latest SMA inverters still have lots of electrolytics. I'm not saying we'll never get rid of the electrolytics but as of now all conventional inverters have them.

[Sunking]

You can build an Inverrter for any electrical or electronic equipment to last a Life Time. Super easy to do. Most just cannot afford it. Not to say they are not made because they are. Utilities, commercial, and Industrial, and Military customers have the deep pockets to do that. Consumer grade products are made cheap so they can sell, and keep reselling to you.

[DaveDE2]

You can build an Inverrter for any electrical or electronic equipment to last a Life Time. Super easy to do. Most just cannot afford it. Not to say they are not made because they are. Utilities, commercial, and Industrial, and Military customers have the deep pockets to do that. Consumer grade products are made cheap so they can sell, and keep reselling to you.

...and you could make it last a DOUBLE life time (think grand kids) by then cooling it by 10C...

[Sunking]

...and you could make it last a DOUBLE life time (think grand kids) by then cooling it by 10C...

That is easy to do. Install it in the shade with good air circulation.

Dave I understand what you are driving at. But today is a very competitive market which forces manufactures to take short cuts, and use loose tolerance components.

Go back to the 50's and use electric fans as an example. Most still work today because they are built like tanks. You might have to replace the Cotton/Asbestos power cord, but mechanically they are tough. Hell even the ole Western Electric Rotary dial phones still work if you can find them.

Today you have four grades of product quality. Consumer, Commercial, Industrial, and Military. You as a consumer can buy any grade you want. Most likely you will buy the 4000 watt $2000 Consumer grade Grid Tied Inverter vs the $6000 Industrial grade model, or $10,000 GI Joe model.

[DaveDE2]

Right on! (fans) ...

[DaveDE2]

Sunking, I get what you're driving at too but I don't understand the logic.

This new SMA inverter (6.0) is the most highly engineered thing I've ever seen excepting an iPhone. It must have hundreds of thousands of engineering hours poured into it, a culmination of 20 years of innovation by dozens of engineers. On the other extreme, a military inverter (if not actually produced by a mfg like SMA or SE for the govmt) is in comparison likely a hack job produced from scratch with a limited govt budget by some contractor such as Lockheed or Raytheon for a specific application with probably a team of five to ten or so engineers within 2-5 years, etc. Do you think they could produce a more reliable inverter (or cell phone) than SMA (or Apple)? I think not.

Sure, for a space (or some military) job the development would be upscaled and the components would be tested to death to weed out any infant moralities but would it be any more reliable over the long haul? Doubtful. Electrolytic caps are not allowed in space applications. Tantalums (except for wet) are frowned upon, it's mostly all ceramic now, so they would most likely increase board space and load it up with ceramics. Barring that, I'd put my money on any SE or SMA inverter to outlast a military unit.

[jflorey2]

...and you could make it last a DOUBLE life time (think grand kids) by then cooling it by 10C...

Incorrect, again. Temperatures are only part of the story - and some poorly thought out mitigations to try to make that happen might result in HALF lifetime (think before your kids are in college.)

[DaveDE2]

... or they might result in 1/4th, 1/8th or 1/16th! Where's the beef? Where's the data to back that statement up? I've provided you data, where's yours?

I'm tired of this and have better things to do with my time. You once stated that you believe that (at least) capacitor lifetime follows Arrehius. Now apparently you don't.

I'm just trying to help extend inverter lifetime for anyone interested. I'm taking data and installing small fans. Anyone else can do what they want.

[Sunking]

Do you think they could produce a more reliable inverter (or cell phone) than SMA (or Apple)? I think not.

Then you would be wrong. Military would use the same top manufactures. The difference is the specs of components used. Example consumer grade temp range is -10 to 50C, Military would have to be -55 to 125 C. Same circuit designs, just better cases, switches, display, and component tolerance. There is nothing special about an Iphone. The only thing Apple makes for it is the Operating System. Take out Iphone IOS and replace it with Linux Kernel and you have an Android.

[DaveDE2]

Actually, commercial parts are rate 0 to 70C, industrial grade -40C to 85C and military -55 to 125C.
They're mostly the same parts, made the same way, just screened (tested) to different levels. The mil and space parts are usually hermetically sealed.

Does SMA have a military division?

I don't care if you're an iPhone fan or android. In any case, one has to admit the smart phone is highly engineered and a marvel.

[Mike90250]

Sure, for a space (or some military) job the development would be upscaled and the components would be tested to death to weed out any infant moralities but would it be any more reliable over the long haul? Doubtful. Electrolytic caps are not allowed in space applications. Tantalums (except for wet) are frowned upon, it's mostly all ceramic now, so they would most likely increase board space and load it up with ceramics. Barring that, I'd put my money on any SE or SMA inverter to outlast a military unit.

Actually, military gear is quite well designed, much more than civilian gear. We analyze and simulate the heck out of it, we pare components down to the bare minimum, the fewer parts that can break, the better. Pioneer 10 lasted 30 years, expiring when the RTG power cells finally failed from half-life. The electronic gear (mostly analog) did pretty darn well based on solid design, not a "hack". Gear I design puts any commercial comm or power gear to shame. We have had inverters in space power supplies for years, and they make civilian models look like tinker toys. So I don't buy any of that,

[DaveDE2]

How many electrolytic caps are on that mission?

[jflorey2]

Where's the data to back that statement up? I've provided you data, where's yours?

I'll give you a case study - the Sun Tie inverter, one of the first grid tie inverters. I got one of the first ones (an ST1500) and it sucked. It would trip off-line for no good reason; it was difficult to keep it running for more than ten minutes at a time. Then they hired an outside contractor to come in and fix it - and one of the first things he did was turn DOWN the fan speed. Why? Because the fan was running full speed all the time, and very quickly clogging the fins of the heat sink. (I took mine apart to see if there was anything obvious I could fix - but outside of cleaning the fins, there wasn't really anything I could do.)

The contractor made several fixes to the design and I got a replacement. The fan barely turned over at low power levels, and didn't go to higher speeds until temperatures rose. (Thus, overall, temperatures were higher - at least at first.) It worked well for me for years before I moved. It was far more reliable, and the fins stayed much cleaner.

The original designer took a simplistic approach - "low temperatures are always better so run those fans." The result was lower reliability overall. Good electronic design is considerably more complex than "just run the fans to make the inverter cooler and it will be more reliable."

[Sunking]

Using Fans to cool electronics indicates a thermal management problem, and fans are the poorest choice you can make, but the least expensive. The issue with fans is they are high failure rate devices, dust/dirt magnets which only compounds thermal runaway problems and makes it worse.

[bcroe]

Using Fans to cool electronics indicates a thermal management problem, and fans are the poorest choice you can make, but the least expensive. The issue with fans is they are high failure rate devices, dust/dirt magnets which only compounds thermal runaway problems and makes it worse.

A good fan system varies the speed to just enough for the situation, mostly minimum. Also it detects & reports fan failures, meanwhile
upping the speed of the remaining fans as needed. And filters get regular maintenance. Bruce Roe

[J.P.M.]

A good fan system varies the speed to just enough for the situation, mostly minimum. Also it detects & reports fan failures, meanwhile
upping the speed of the remaining fans as needed. And filters get regular maintenance. Bruce Roe

For large systems,closed loop cooling systems using liquids solve a lot, but not all of problems associated with fouling caused by air cooling, including down time for maint., and a more stable temp. regime that's easier to predict/control but, depending on the application, often cost an order of mag. more $$. Cost/benefit analysis time.

Having designed industrial cooling systems for a living, and now having a window fan blowing up under my inverter for the last 2 1/2 yrs. or so, I'd suggest for a 5 -10 kW inverter in a garage, simple fan cooling will probably knock about 10 deg .C. out of a 30 deg.C. heat sink to amb. air delta T., and probably not cause enough additional fouling of the heat transfer surface to be of any concern. In my ignorance, whether or not an inverter running 10 C. cooler lasts longer Is something I'm ignorant about. I'm guessing it won't shorten the life. The additional cooling costs more in energy to run the fan than it removes from the heat sink for my application. It's probably not cost effective. Whether or not it helps or harms the equipment is unknown to me. I'm working on the belief that heat does more harm to electronics than cool. The fan fires up ~ 0600 and runs until about 1/2 hr. after the inverter shuts down, or when I get to it. That probably takes care of time/temp. thermal shocks. None of this is rocket science. I've no idea if an inverter running 10 C. cooler lasts longer or not, but I'm having fun.

[Sunking]

And filters get regular maintenance. Bruce Roe

Who the heck wants filters and maintenance. That is just poor design. Larger aluminum heat sinks and current devices require no maintenace.