Your 25v capacitor may last longer than a 10v one because its internal resistance will be slightly lower. But, unless it's a "low ESR" (with the ESR value stated) it's still not low enough. What did it actually measure?
I forwarded your comments to Satcure and here's Martin's immediate reply:-
I've been doing electronics design and repair for 50 years+ (since I was 10) so I know a bit about it. The stated ambient temperature and hour ratings of capacitors are no more than a loose guide and, since it's the ESR that matters in applications where there's a high, fast-risetime, current pulse density, they are irrelevant when applied to general purpose capacitors.
Still, he's not the only person who fails to understand the difference between ambient temperature and internal heating. Here's an analogy that might help:-
It's rather like saying that ordinary tyres will be absolutely fine on a racing car, provided that it doesn't exceed the stated 105 mph max speed for more than a few hours. This is nonsense since the more important consideration is the extreme cornering force, which will rip an ordinary tyre apart because it causes overheating of the flexible tread.
Likewise, with an ordinary "General Purpose" electrolytic capacitor, any "high cornering forces" (high, fast-risetime, current pulse density) will destroy it, regardless of any ambient temperature rating. The reason for this is that the internal resistance is high so the high current causes internal heating. This has very little to do with ambient temperature rating.
If you've followed me so far, you may now understand that a general purpose capacitor is fine for applications where there are no high current pulses and, in those applications where there is no internal heating effect, the hour/temperature ratings are a reasonable guide to longevity.
However, high current pulse considerations override all other ratings and must be taken into account where applicable. This is a point which many young Power Supply designers completely fail to understand, which is why there's so much equipment being scrapped due to bad capacitors. Even Alan Sugar's Technical Director failed to understand this and it cost the Amstrad company big money.
Unfortunately, it's a fact of life that low ESR capacitors are more expensive, just as racing tyres are more expensive than ordinary ones. SatCure won't compromise on quality and reliability.
Frankly, I simply can't understand people who do a shoddy job. I've had one lad write to me to boast that he got THREE capacitors off eBay for the price of one of ours. But why would he need spares? Why would anyone want to replace the same part over and over when the capacitors we sell are guaranteed for 3 years (but will probably last for at least ten)?
BTW this penny-pinching outlook is peculiar to Britain. People walk into a shop and ask "how much is that TV?" But in Germany they ask "how reliable is that TV?" and they wouldn't dream of having a TV programme called "rip-off Germany". They expect to pay for good quality and reliability.
BTW our low-ESR capacitors are manufactured by Panasonic. We don't advertise this fact because all the eBay sellers will rush out to get general purpose Panasonic capacitors and claim "The Same As SatCure Sells", which would be a lie. We are very selective in our choice and some have to be ordered from America.
Firstly, thank you for taking the time to bother to reply to the somewhat throw away (and correct) comments that I ventured in the hope that I might be able to help someone a little bit and also for involving your chum Martin. I genuinely don't know why you have singled me out for such attention but I'm not flattered by being repeatedly accused of shoddy work by strangers who know nothing about me.
Let's get down to some facts.
1. This is a DIY forum not an electronics forum. My comments are designed to help someone make a good choice without having to get a degree in electronics first. DIY normally involves saving money so my advice was on how to buy the right thing at a good price not the absolute best thing at any price.
2. I am not a TV repairman. I needed to get a TV working for an elderly lady who uses the TV as more or less her only source of entertainment and company. I do not charge the elderly for repairing anything. Curry's TV repair service, for example, costs £95 plus parts. This is two thirds of a week's state pension. I successfully repaired that TV in 2 elapsed days at no cost at all to the user. Do you understand why I found your comments offensive?
3. You assert that the working temperature range and endurance characteristics of a capacitor are meaningless because it says that on the Satcure web site. Furthermore you assert that the only meaningful parameter is that of equivalent series resistance. To add insult to injury you also say that if I don't believe you and your chum Martin that I will be guilty of doing bad repairs that will quickly fail again.
4. Martin of Satcure (presumably) has told us that he buys Panasonic capacitors but that he doesn't let people know what they are buying from the web site so Satcure cannot be copied. Satcure make a big pitch about ESR and generally specify the impedance of their capacitors (at 100 kHz at 20 deg C) although the working temperature and endurance are also often specified despite being 'meaningless'.
I'm going to have to guess here but if we take the case of a 470uF 25 volt radial electrolytic with a 0.03 ohm impedance from that site I'd think it may be from the FR series and likely a EEUFR1E471L. If so this is, indeed, a very fine capacitor. We can tell this without knowing that the impedance is a very low 0.03 ohms.
The AC ripple current is high (good) at 1560mA and its endurance is a splendid 9000 hours at 105 deg C.
We can also see what its overall efficiency is by looking at its data sheet and finding the value for tan δ (0.14 where lower is better). The tan delta is an expression of the overall loss of energy to heat; ESR is an important factor in the calculation of tan delta but not the only factor.
And now for the take home message.
Aside from physical characteristics, values and tolerance the most MEANINGFUL things to know about a capacitor are:
Working temperature range
Endurance at temperature
Ripple current
Tan delta and ESR
If you visit Panasonic’s capacitor site you will find that ESR isn’t even included in the parametric picker – you get the other stuff right first then pick up on things like cost and range preference (FR and FM have the same ESR’s anyway).
It's just not good enough to take a statement like the only thing that counts is ESR but I'm not going to tell you what I'm selling you - trust me I'm very experienced.
Martin/Satcure may well be jolly good chaps but they do not have divine or prophetic powers of wisdom as you suggest. Rather they want to sell stuff for more than they bought it for. That’s a perfectly honest thing to do. It is not honest to tell people that all other metrics bar their chosen one are meaningless.
Look at the datasheets yourself. Weigh up the prices. Look at hidden costs like postage. If someone doesn't let you see the evidence you may wind up fighting a war in Iraq. Don’t be so naïve.
Just in case you are still interested or, indeed, awake here are the RS part numbers of the caps that I bought to do the TV job.
571-858
756-7806
704-8046
This is the last time that I'll be writing to this thread.
