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Now then, for everybody who is still on board here, we have established that the main killer of an inverter longevity is heat. The most prevalent failures are Capacitors and Mosfets because they do the heavy lifting in the inversion process and run hottest. This statement is backed up by an SMA tech repairman I talked to here in Denver and makes total sense to me. There will always be one-off failures of other components but they are relatively rare.
If you want to read about capacitor and semiconductor lifetime vs heat, this is a good place to start:
http://www.illinoiscapacitor.com/tec...lculators.aspx
It's obvious why the fanless inverters come that way because the MFGs produce these by the hundreds of thousands and a lot of them will be installed in outdoor environments. Having a fan outside would cause all sorts of failures (in the fan) and so they avoid it at all cost. Furthermore, the mfgs are all in competition and need to keep cost low. As such, imo, they just want their inverters to outlive the warranty. If an inverter is installed indoors in a relatively benign environment then it has a greater chance of living longer. The assumption here is that what causes an inverter to die of old age is the ramping effect at the end of the bathtub curve. Sooner or later, either the caps or fets will hit that and thus failure. So the idea of cooling the inverter in an indoor environment should be considered imo.
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Totally agree that cooling should be considered, and that the chances it helps probably outweighs the chances it hurts (vibration, fouling, etc). I think any suggestion that inverter life will double with the addition of a muffin fan is ridiculous.
I wouldn't rule out outdoor installations... better natural airflow could actually result in lower temps relative to inside. Also keep in mind that IGBT failures are up there with caps and fets in the possible failure modes.CS6P-260P/SE3000 - http://tiny.cc/ed5ozxComment
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Definitely. Heat is only one of the many factors in determining longevity of any electronic device.
And in cases where it the inverter is mounted inside an unvented garage, average temperatures could well be higher.I wouldn't rule out outdoor installations... better natural airflow could actually result in lower temps relative to inside.
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high temperatures are the worst enemy to the lifespan of inverters, here in Egypt even the best quality solar inverters hardly last for more than 2 years due to high temperaturesComment
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A comment or 2:
1.) While it seems that heat is probably better removed from electronic devices than not, the benefits in terms of improved service life and lower service requirements seem at best not well or easily quantified. I'm not sure a process cost analysis is worth it for the cost of ~~ $20/yr. of electricity spent to extend (??) an inverter life by an unknown and probably unknowable number of years.
2.) Depending on the cooling scheme used - from a window fan under the inverter in a garage blowing up, to mounted outside w/ access to a breeze, to a sophisticated cooling system, for the cheap methods, the cost of power for aux. cooling ranges from zero (mounted outdoor) to the cost of a window fan and 40W of power, to whatever for more sophisticated methods. If the cost is from zero to cheap, cooling may not hurt provided done in a common sense and safe manner. The PITA/noise factor will probably trump. the power/equipment cost.
3.) Two things to perhaps consider with cheap, open system cooling (e.g., window fans): The additional air blowing past any cooling fins will probably cause the fins to foul w/dust/crud/etc. and work less efficiently, increasing the inverter temp. in a general way, and somewhat working against the goal of lower inverter temps. A lot of times, access to the cooling system is difficult/impossible. Also, depending on how and mostly when the aux. cooling is introduced, there is the situation of thermal cyclic stress put on components from differential thermal expansion. An already hot inverter that gets relatively abrupt forced cooling air cooling introduced will have some higher risk of problems than one that has the cooling already present before heating. Often, a strong contributing factor to equipment failures is not entirely one of elevated temps., but also up/down temp. cycling, and is somewhat a separate issue from the failures caused by continuous heat (component cooking) in and of itself.
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4.) As for elevated temps. of an enclosed space, A 5kW system under full load will probably add about a 150 W load to the space. If an uninsulated garage, the interior temp. will increase in proportion to the added load divided by the enclosed space heat loss rate. Bottom line for my uninsulated garage case, that adds about 2 deg. F. to the garage temp., +/- a degree or 2. Just sayin.Comment
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I would deffinitly consider outside for fan less outdoor rated inverters. If the higher power units have fans then consider attempting to retrofit the higher power units fan.
The main concern with this hypothesis is the assumption that " it can't hurt". I would say that as suggested ( high speed unregulated fan) it deffinitly can hurt.
Just take a look inside an old server that has been on steady for two plus years. The amount of dust and surface dirt stuck to the heat sources inside is great. A few mm of dirt is very insulating greatly increasing the heat build up on the parts that specifically need to be cooled. Heat syncs are like filters and. Clog first wi any forced air.
Units designed for convection cooling have larger heat syncs that are generally more convoluted allowing more surface area to dissipate heat more easily in the slow moving air. This larger surface area is going to clog quickly with dirt.
The units that have fans have thermal couplers and variable speed fans to cut down on the dirt build up as much as possible and heat syncs designed to trap less. What is important for the curves as dis used is the temerature of the components so insolation is unwanted.
I would suggest that if you attempt this forced air retrofit that you use a thermal coupler, variable speed fan, and annual shut down with cleaning. Of course the cleaning could result in higher failure rates as well particularly if performed by untrained personal, but better than trying to go decades with out.OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNHComment
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I guess the luck takes big place of inverter life. I keep mine in air conditioned garage/storage and I'm on my 3rd SMA 6000TL-US-12 in 2.5 yrs. The 2 failures has to do with design/human error besides the inverter itself. More simple it gets, longer life it has.Comment
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I don't think it has to do with its quality.
First failure is immediately after panel addition with disturbance AFCI error (human error)
I think within 3 months, 2nd failure with no error code. I did see the burn mark on L1 input and also found water in J Box (another human error)Last edited by silversaver; 06-11-2016, 06:38 PM.Comment
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I believe that the lifetime of a semiconductor or capacitor doubles for every 10C temperature decrease. This is based on all scientific data I've read including the two documents I referenced. If someone can show me other-wise then please do. This assumes that the electronic design of the inverter is done properly and all components are operating within the manufactures specified limits including max voltage, current, junction temps etc. I agree with you that if a small fan can not reduce the operating temperature of those devices by 10C then the assertion is ridiculous but so far my measurements hold promise there and I'm going to pursue it (I used a 10W fan to see an 18C decrease, but this is not average operating temp, investigation to be continued).
As far as outdoor installations, I ruled that out from the git-go here because of the risk of premature failure due to increased stress of environmental thermal cycling (solder joints), moisture ingress, etc. There may be an ideal climate where an outdoor installation would prevail but it sure isn't here in Colorado.
jflorey2
Please tell me what the other mechanisms for electronic failure are for a device in a properly designed circuit as described above.
@JPM
Good points, but in my situation the the inverters have a heatsink with large straight fins approximately 1/2" apart and will probably never clog from dust and can easily be blown clear of any surface dust with my garage air-hose. Good point about dust though and I can see doing that once per year or so just for piece of mind.
I'm planning on giving the secure power supply something to do by having it supply fan power. So when the sun is up the fans are on, sun down they are off. I can't see how this could cause thermal stress.
ButchDeal
There is no comparison between forced air cooling of my inverter fins and computer servers. I own a large restaurant that has a server and 12 other point of entry computer terminals. Each one of them is a PC which draws air into its innards and across the components, then in most cases exhausted by the power supply. Yes, they get very dirty with dust and have to be blown free of it a few times per year so that premature temperature related failures do not occur. In the case that I'm talking about here, forced air convection only occurs on the exterior of the box (heatsink) so there will be no clogging whatsoever.
I've attached a photo of the inverter fins.Comment
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Well, you didn't list any mechanisms; you listed an observation, which is that higher temperatures increase failure rates. The mechanism is what causes that increased failure rate. For example, one common temperature related failure mechanism is dopant diffusion. Dopants are intended to be stationary with respect to the semiconductor structure; if they move around, the characteristics of the device change and it eventually fails. Increased temperatures increase diffusion rates within semiconductors. There are several other failure mechanisms like this one which obey the general relationship described by the Arrhenius Equation, which describes an exponential increase in failure rates with increasing temperatures.
We have known about this relationship for decades. During that time we have been working to reduce its incidence by improving passivation, ohmic connections within semiconductors etc. In modern semiconductors - especially power electronics - they are now well controlled. That means that other failure mechanisms that depend on other factors begin to have a larger influence. Some examples include:
Electromigration. This depends on temperature as well as voltage stress and current density. Thus voltage, as well as temperature, plays a role in lifetime. A scheme that attempts to reduce operating temperatures by operating at higher voltages (a common engineering tradeoff) may therefore increase failure rates.
Die fracture. This occurs when differing thermal expansion coefficients cause microcracks in a semiconductor substrate. This is caused by _changes_ in temperature, rather than absolute temperature. Thus a scheme that attempts to minimize average temperature by cooling the device more rapidly may increase, rather than decrease, failure rates.
All of which means that following the belief that semiconductor lifetimes always decreases by a factor of two for every 10C increase in operating temperature can get you in trouble. If, for example, you aggressively cool a device and by doing so increase the range of temperatures it sees (and the rate at which it is warmed and cooled) you might cause the very problem you are seeking to avoid.
That being said, the primary failure mechanism in electrolytic capacitors _is_ very closely tied to the Arrhenius Equation. Thus keeping 1990's-era inverters cool was pretty important; they were full of electrolytics, and I saw at least two inverters that failed due to capacitor failure. As technology improves, and especially as operating frequencies increase, manufacturers have used fewer of these devices, and the link between temperature and failure rates has become weaker.
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Thank you.
Everything you have argued here indicates that temperature is the primary conduit to failure, and that "we have known about this for decades". Touche!
Some of the stuff in your argument depends on thermal shock; electromigration, die fracture, etc. Running a fan across a massive aluminum heat sink on the outside of the box is hardly going to thermally shock anything. It takes a long time, on the order of 30 minutes or so for said system to stabilize. Who's trying to use a "scheme that attempts to reduce operating temperatures by operating at higher voltages (a common engineering tradeoff) may therefore increase failure rates"? I'm not. Say what?
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.Last edited by DaveDE2; 06-12-2016, 10:27 PM.Comment
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The flow will probably never be "blocked". It's the dust buildup on the fins that reduces their effectiveness. depending on the nature of the dust in the air, the fouling layer need only be a fraction of a mmm. to inhibit performance and negate some or all of the improvement afforded by the increased film coefficients afforded by the increased velocities of forced convection.
It's a bit complicated, but using a natural convection design and then imposing or forcing more air past the fins will change things some in ways I spent a good part of an engineering career working with, through and around. In general, more cooling will be effected, but there are some considerations often overlooked, such as cleaning, and the idea of thermal shock, which is often more a function of the rate of cooling change introduced, and also when that change is initiated (usually, turn the fan on before the inverter as you seem to suggest). Blowing the fins with an air blast 1X/a while will probably be adequate as a cleaning expedient.
BTW, forced convection may also help keep critters like spiders out of the fin portion of a heat sink. They seem to like heat, or maybe the lower air velocities of nat. convection catch more bugs in the nets.
Take what you want of the above. Scrap the rest.Comment
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