Below the ripple voltage chart explanation is an email thread that I thought would be interesting to share. Note, permission was provided to reprint it here. The subject of the email is: Fat Caps & Ripple Current…
The following ripple voltage chart is provided for reference material.
Understanding the Ripple Voltage Drawing Above
The faster the capacitor discharges, the more ripple will be present. If the capacitor in the circuit is underrated or completely bad, it will not properly hold a charge, and thus the electronics circuit will have maximum ripple present. When a capacitance filtering circuit is faulty, picture the valleys on the voltage being very deep relative to the peaks, and the ripple current will shoot up proportionally in the circuit, with the result of a major increase in heat being generated in all the circuits supplied by the power supply voltage that should be a regulated level DC, which would now effectively be an AC ripple voltage. This will quickly result in thermal breakdowns in various components on the circuit boards, causing a cascading component(s) failure(s) affect.
Picture Courtesy of HyperPhysics Department of Georgia State University – Development of Ripple Expressions
I thought it would be interesting and educational to hear from an expert in the engineering and circuit design field. The following is the email dialog conversation I had with Dean Palmer, engineer/owner of MicroDyne Engineering, LLC, an electronics research, design, and development services company, located in Queen Creek, Arizona, USA.
Dear Jim,
I stumbled upon your very informative “Capacitors” web page today and enjoyed your article on DIY lead free soldering and circuit repairs. I too encourage people to try to service their own stuff where possible. And this leads me to the following question:
I have a Panasonic DVD player/recorder (Model DMR-ES15) that has a recurrent “U61” error that, in the owner’s literature, is stated more or less to be a power related problem. So I open up the unit and discover a single (but large) aluminum electrolytic cap on the main power converter sourced directly from the DC rectified AC mains. A check around the Web and I see that many owners of this product have been experiencing similar “U61” problems with their units; some failing after only a few months of operation; most just after their 1 year warranty expires. So I get my trusty Tek 2467 scope on the circuit and I see a HUGE amount of ripple at the pins of the capacitor, yet the capacitor tests good! I replace it anyway with a good quality low ESR hi-temp Nichicon and still there is terrible ripple on that node. The power supply seems to have a load related voltage regulation problem and there is a lot of ripple and harmonic noise on the output. Doubling up on the capacitor even though there was no room on the board (had to dead-bug it) was the only way I could quiet down the circuit.
After visiting your page, I too thought that this part (or others) had possibly been damaged by the lead-free thing and the higher heat production methods used to build this unit – there is lead-free solder everywhere, even though the date of manufacture was 2006. But now I’m convinced that the part was actually under-designed for the requirements of the circuit. And, I’ve seen high ripple on computer mother board caps from time to time that caused all sorts of malfunctions and random errors/reboots, and also in a couple of LCD displays I worked on. In addition, there is an under-designed heat sink on the video processor chip in this DVD player – it gets seriously frying hot when playing back or recording a DVD – which cannot be good for the chip or it’s tiny ball grid array solder connections.
So my question to you is, why are manufacturers under-designing the circuitry in these products? Are these companies so desperate to maximize profits that they apply MTBF and service data back into the manufacturing process to find ways to cut back on design quality and circuit components to just get them through the warranty period? I’ve heard they can actually tweak this down to a granularity of weeks. Or, are we just seeing rampant designer incompetence all across the board – engineers who do not know how to do simple calculations for ripple current and thermal dissipation? Could these guys even balance their check books? What are they teaching in the EE programs these days???
I would be very interested in your thoughts on this! At any rate, Ha, it keeps me in business.
Thanks very much!
—
Dean Palmer
Engineer, NPDMicroDyne Engineering, LLC
Queen Creek, Arizona
USA
480.888.0600
www.microdyneeng.com
—
Jim W. wrote back:
Hello Dean,
Wow, you got my mind filled with all types of thoughts. First off, my experience in the electronics field goes back more years than I care to imagine: http://jimwarholic.com/about.
I constantly see problems related to component failures more and more frequently. I honestly believe that everything is designed with a time value. Capacitors have a certain time value to heat rating. If you operate a capacitor near its maximum rating, the capacitor will last X amount of time. If you operate a capacitor at 1/2 the maximum rating, you will likely get 2X life or more out of the capacitor. So, it comes down to the engineers specifying the ratings on the capacitors without fully understanding the time value. The differences in costs are very very minuscule if anything at all. But, when they call for a value of 2200 uF cap at 10 volts because the maximum voltage might be only 10 volts, but the circuit is actually operating at 10 volts, then in essence the capacitor is operating at 100% of its maximum voltage. They could just as easily installed a 16 volt capacitor, that might be slightly larger, (though they would have had to design for this larger size) but would have lasted probably more than twice as long, because it would have only been operating at 63% of its maximum operating voltage, and more than likely would have operated at a cooler temperature too. So, the engineers need to take into account the time value, which is probably not being stressed at all.
These power circuits generate tons of heat on their own, and that also is not being taken into account. This causes a cascade effect, which causes more heat, and more breakdown, and more heat, etc.
Here are a couple of pointers to consider when troubleshooting power supply circuits. Most power supply circuits start with full wave rectification. If only one half of the rectification process is working, the capacitors will not be able to filter the voltage properly. Also, there are many times the regulator circuits are failing. So, the voltage drops under load, the regulator can not keep up and therefore the caps try to maintain the voltage, but heat builds up due to excessive current draw.
With the push towards smaller, more compact designs, this causes the engineers to simply go with the smallest of the specs that they can get away with. So, when the final design comes out, and it goes out for build, the builder (assembly house) simply follows the component specs and then gets its supply of components sent from the manufacturer. Once again, at each leg of the manufacturing process, the specs are used as the guide. If the specs are just of a minimal value, and the manufacturer supplies the component with that value, the question comes down to, who’s fault is it?
Did the engineer look at a data sheet of components and see that the standard is a 2000 hr. rated capacitor at TEMP, OP. MAX:105(DEGREE C) and in essence say that will be good enough? Probably. Did the manufacturer of the component, simply target the minimum standard? Probably.
Have computer companies looked at the life cycle of computers being somewhere between three and five years, and say, that if it lasts for four or five years it’s probably good enough? My guess is yes.
However, computers have gotten to the point where even if you go twice as fast for most activities, it really doesn’t matter much. So, more and more of us are keeping our computers for a longer period of time.
Does the manufacturer hold some degree of responsibility for a design that should last longer than the warranty period? And if so, how long? The short answer, is yes. However, the long answer is much more complex than meets the eye. There is always a trade off between price, design, and life expectancy.
I was really ticked off, and still am ticked off to this day, when my Apple failed, two months out of warranty, and the Genius Bar folks said, “Why don’t you just buy a new iMac? The price of a new one is only several hundred dollars more than the parts for the old one.” It was at that point, I had to taken action in my own hands. http://jimwarholic.com/apple
Thank you for listening. Maybe I will post this online, without adding your name to the mix.
Regards,
Dean Palmer wrote:
Thanks Jim for answering my question! I appreciate your comments very much. And I am right with you on being very upset that your MAC dies right after the warranty period is up. I think that manufacturers should be held accountable for the quality of their products. I know that in reality, it’s “Buyer Beware!” – “If you don’t like my brand, buy someone else’s” … but really, is that the way you’d want YOUR company to do business? The whole attitude out there seems to be “make as much money as you can with as little cost as possible put into it…” – that seems to be capitalism at its worst where greed and lust for wealth and profit creates an environment where crap is king and corporations are driven to make things as cheap as they can get away with! But in the end, we are ALL consumers of products and services. Even the CEO Of SONY, or Toshiba, or in my case, Panasonic – all are consumers. When he goes to buy his Mercedes Benz, would HE be satisfied that it just (barely) meets the warranty period before some major failure occurs? No! He’ll be on the phone to Mercedes to raise hell about it!
So whatever happened to having pride in your product and its quality of workmanship? As you pointed out, for just a few cents more, a better suited capacitor could have been used in the circuit and this would have avoided thousands of upset consumers and calls to service centers. The way I see it, it’s a reputation thing as well as being an ethical matter. When I do a design for my Clients, I want my design to be the best it can be. I was raised by a very demanding and “military authoritative” father who insisted on perfection; to do the best job you can do – or don’t do the job at all. So it’s in my makeup to give my Clients 110 percent on every project that crosses my desk. I will cut corners in design or materials ONLY if they tell me to do so, but with great reservation and reluctance. And for the money I pay for a new TV set, I expect it to last for many years. My parents had an old Motorola Quasar “Works In The Drawer” TV that we had for probably 12 or more years. It was a hybrid design made with tubes and transistors, and a couple ICs. It lasted until the picture tube finally gave up. Wow! But these days, this kind of quality and reliability just isn’t seen anymore. It’s very sad really, especially in the light of technology being so advanced – you could build a DVD player that should last 20 years. And as consumers, have we, for the most part, become used to mediocrity in everything we buy?
No matter what brand I choose, it’s gonna have problems? There just has to be a balance between profits and getting your new gizmo to market before the competition, and building a product of decent quality and reliability. And it seems that the consumer public – you and me included – needs to drive this shift in corporate paradigm by DEMANDING high quality and exceptional reliability from manufacturers. And by the same token, we should also be willing to pay a little extra for it. If I want to buy some off-brand TV set for 79 bucks at Walmart, I can do that, and I’ll get what I get. But when I pay $895.00 for a bran new shiny SONY with all the bells and whistles that even pours me coffee, I EXPECT it to last and last and last. Maybe I’m too much the old school, I don’t know. But I would NEVER design in a 10 volt capacitor into a 10 volt circuit! I “might” design a 20 volt part in there if I’m in a good mood. But I’ll probably and most likely use a 50 volter! And really, what does that do to the end cost of the product? Not much.
There are so many other factors that go into the total cost to manufacture and sell an appliance. One of the biggies is that damn paranoia about lead in the environment (RoHS)! For God’s Sake, don’t people know that lead comes from the ground in the first place? How much of this is political and how much of it really makes sense in the name of public health and the environment? And a lot of the cost to make a product comes from efficiency and the internal structure of the company. Some companies are so wasteful and inefficient that they could build their products lined with gold if they’d just cut out the waste and inefficient practices, and perhaps limit those million dollar bonuses to CEOs. The list is endless, but taking such clean up measures would pay for a better capacitor, diode, or heat sink a thousand fold. And personally, I will pay more as long as I KNOW that I am buying quality. The tires on my car and the brakes I use are the best money can buy. There are some things you just don’t cheapen your way out of! I can buy a cheap DVD player if I want. But I probably won’t. I want good quality at a reasonable price. And I adhere to the Three-To-One policy: for a one year warranty, a product should last three years at the very minimum! Really, warranties are to protect the consumer from DOAs and accidental defects that can sometimes occur in manufacturing or materials. It should NOT be an indicator as to how long I can expect the product to work!
I’ve enjoyed our conversation Jim! Thank you for allowing me to rant. And you may use my name in connection with any of my comments you wish to publish. I hope if you do publish this dialog, it will get people visiting your site to thinking – and demanding – quality and reliability. Next to a fair price, what else matters?
-Dean Palmer
Dean Palmer
Engineer, NPDQueen Creek, Arizona
USA
480.888.0600
www.microdyneeng.com
“MicroDyne Engineering provides Electronics Design, Research and Development (R&D) and Prototype Design and Assembly services to customers and clients who wish to bring a new technology product idea from concept to actual hardware realization. Their goal is to provide clients and customers with product designs and solutions for markets and applications that would benefit from innovation and value-added product designs.
Reverse-Engineering services can also be provided for existing technology products and devices where the original documentation and component sources are non existent or no longer available.”
Thank you Dean for sharing your insight into the wonderful world of electronics research, design, and product development, with this first hand look into engineering and design of electronics’ products. The mind of an engineer is …
I would also like to extend a big thank you to Dean for granting permission to reprint this here.
Note, all copyrights are reserved.
Regards,
Jim Warholic