CurtPalme.com Home Theater Forum

Sparky015 · Posted: Thu Nov 12, 2009 8:22 pm Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Ok, next I guess we'll look at ripple currents and how the affect cap life. Some say that ripple current has little affect and others will say it has great affect. So lets see if we can understand why.

Basically its not the ripple current itself that causes issues but what affect it has on the capacitor. The more ripple current the capacitor has to deal with the higher the core temperature of the capacitor will get.

Now as discussed earlier, temp has alot of influence on cap life. So temp doesn't just pertain to ambient temp but also core temp. This is where the life chart still applies. If a capacitor is in an ambient temp of 45 degrees C but the core temp is higher, say 65 degree C because of high ripple current, then the life is dependent on the higher temp, which is the core temp of 65C. So if we look at the chart for a 85C/2000 hour cap at 65C we can see an expected life of app. 8000 hours. Even thought the ambient temp of 45C would indicate 32,000 hours. The cap is still running warmer because of the core temp.

The same applies if the ambient temp is high and the core is low, the higher (ambient) temp would apply for affect on cap life.

Now the reason some say ripple current has little affect on cap life is because its controllable. The is part of the design factor. A good designer will attempt to control these currents to increase component life. Plus the circuit reacts better. So if the original design showed a high core temp on a cap then the circuit could be altered to reduce this current affect.

Even if ripple currents were causing a core temp equal or lesser then ambient temp, then the ripple current would have no affect and only ambient temp would affect cap life.

Let me also say that most higher ripple currents are produced in power supplies (low voltage and high voltage) and horizontal drive circuits, but are also very controllable with a good design and will keep core temp very low.

Also, most capacitors in a device have very little if any ripple currents so would only be affected by ambient temp.

If you look back at Ile's thermal pictures you can see that there are very few hot spots and none jump out as caps. If a cap was running hot from a high core temp it would stand out in a thermal image.

Let the games begin....... Cool

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

Ile · Posted: Sat Nov 14, 2009 11:24 am Post subject:

mp20748 · Posted: Sat Nov 14, 2009 2:56 pm Post subject:

One of the best threads ever posted on the forums.. Thumbs Up

Sparky015 · Posted: Sat Nov 14, 2009 3:43 pm Post subject:

Did I really see that right in the last picture? They packaged a 35 volt 2200uF cap in a bigger package and called it a 50V 6800uF? Wow! Even if the reason was to cut costs, I can't imagine all that repackaging is cheaper than installing the right cap to begin with. I've never seen that before.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Ok, just got back after being gone for the weekend. I'll right some thing up either later or tomorrow for the next subject. It also pertains to something Ile just posted above so I'll respond to that later also...... Stay tuned..... Very Happy

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

**AnalogRocks** · Posted: Mon Nov 16, 2009 2:31 am Post subject:

Mac, I have a question will storage temperature affect capacitor life? For example if I have two radios that are in storage. One is stored in a closet beside the hot air return and the closet is 90 degrees the other in a normal room at 70 degrees. Both non operating.

Will that affect capacitor life?

km987654 · Posted: Mon Nov 16, 2009 3:21 am Post subject:

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Some manufacturers even quote storing at 40C or under is fine but I used the lesser to make everyone happy.... Very Happy

**AnalogRocks** · Posted: Mon Nov 16, 2009 6:42 am Post subject:

Hmmmmm Maybe that's why allot of my stuff craps out. I have high humidity here most of the time. Hi heat too.

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

**AnalogRocks** · Posted: Mon Nov 16, 2009 4:32 pm Post subject:

Ohh I'm not sure. I seldom have time to take it all apart. It's a matter of putting something away for a while. Taking it out and finding out the closet gremlins broke it while it was in storage. Wink

macgyver655 · Joined: 22 Aug 2007 Posts: 8508

Ok. Next we're going to discuss operating voltage vs rated voltage. Originally I wasn't going to get to involved in this because for the most part this has little affect on cap life. This is because as long as the cap is operated below the rated voltage there is pretty much no affect. But if you put a cap in a place where the operating voltage is above the rated voltage then the cap has little chance of survival.

However, the more I thought about this I believe there are situations where understanding voltage affects could be important.

I'm going to try my best to explain this so everyone can understand.

Lets first think of electricity as water. If you have a garden house with water running you have 2 things. You have pressure and volume. Pressure in electricity is voltage and volume is amperage. Now if you were to double the size of your hose you would double the volume(amps) and would fill a bucket twice as fast. Your pressure would also drop but for this discussion were mostly interested in volume. Now if you put a nozzle on the larger hose the pressure would then increase but you would loose volume again. This would be a restriction in the volume. Pretty simple, no?

Now if we take this scenario to house electricity the pressure would be your voltage (lets use 110 for this part) and your volume would be amps. So if you had a device that uses less the 20 amps you would use a 20 amp breaker and 20 amp wire(12 guage). So as long as your device is using less then 20 amps every thing is fine. But if you unplug that device and install a device that draws 30 amps, what will happen. Breaker would trip. So you change the beaker to 30 amp. Now if you run the device the breaker wont trip but if you feel the wire it will be warm (temp). The device is trying to draw more volume of electricity then the wire is capable to pass through is. Amps is also consider current so what you have is a high current draw causing the wire to heat up. If your device was drawing 40 amps (volume) and breaker again was 40 then the wire would get real hot and possibly cause a fire. To solve the problem you need to increase the wire size to allow the device to draw the required amps (volume) it needs.

Now if you had a device that requires 110 volts but you plug it into a 220 socket what happens? Instant failure. More voltage then the device is capable of handling.

So when it comes to capacitors, if one was placed in a circuit running more voltage then its rated it will run warm or hot and cause failure. This can also apply to currents. Capacitors also have a max current rating (ripple current) but its not usually discussed much because higher current ratings are a given with higher voltage ratings.

Think out it like this. A higher voltage capacitor has everything larger from the internals to the leeds which also means the case is usually larger. Now remember the hose and house wire. If they are larger then they will pass more volume(current). Same applies here. Larger components for higher voltage also allow for more current (amps or volume).

Now I know newer technology capacitor sizes are getting smaller with the same voltage rating but its the ratings that apply not the size when figuring date of technology. If it will carry the voltage, it will carry the current.

I'll stop here for now in case I didn't explain it clear enough and you can ask questions.

Does your head hurt yet?????? Laughing

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

Great explanation Ron, I think everyone should understand that.

Athanasios

Sparky015 · Posted: Tue Nov 17, 2009 1:17 pm Post subject:

Yes, nice explaination. Funny, my basic DC classes in college used the same water analogy. The other is around electricity looking for the easiest path to ground, which when you think about it, applies to just about everything. Everything is looking for the easiest path. Anyway, I read your post and thought, this guy sounds like a professor! Thumbs Up

Nashou66 · Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY

He did say he did some teaching in the past. Very Happy

Athanasios