My router/modem runs from a 9V 9VA AC wart, and has its own bridge rectifier and 1000uF 16V 150°C smoothing cap; this feeds a couple of regulators, 3.3V and 5V.
The original no-name cap showed swelling after some months in service so I replaced it with a low-ESR 1000uF 25V I had in stock; runs fine, but too hot to touch for more than a second. OK, it's 105°C rated and the ripple spec is 1.7A so maybe I should ignore it, but I had the thought to feed the bridge with regulated and smoothed 12V DC from another adaptor (9V RMS = 12V peak, near enough), thinking the cap temperature would show a big drop; it didn't, still too hot to touch. I've dropped the supply to a regulated 9V DC, feeding the bridge input, the router runs fine but the cap's still hot. (Regulators are a lot cooler though
)
What's going on? Do the bridge diodes in each supply rail between the caps prevent the adaptor smoothing and router smoothing from "sharing" the heat produced, or am I misunderstanding why a smoothing cap gets hot?
The original no-name cap showed swelling after some months in service so I replaced it with a low-ESR 1000uF 25V I had in stock; runs fine, but too hot to touch for more than a second. OK, it's 105°C rated and the ripple spec is 1.7A so maybe I should ignore it, but I had the thought to feed the bridge with regulated and smoothed 12V DC from another adaptor (9V RMS = 12V peak, near enough), thinking the cap temperature would show a big drop; it didn't, still too hot to touch. I've dropped the supply to a regulated 9V DC, feeding the bridge input, the router runs fine but the cap's still hot. (Regulators are a lot cooler though
)What's going on? Do the bridge diodes in each supply rail between the caps prevent the adaptor smoothing and router smoothing from "sharing" the heat produced, or am I misunderstanding why a smoothing cap gets hot?
No red herrings - nothing wrong with the cap wiring, the hot cap is in the router, not the wart; it's its own heat, not picked up from adjacent components, the warts get warm (as they usually do when on 24/7) but they're sealed units so I can't say what temperature the wart caps are running at.
At 12V DC input I've used both SMPS and 50Hz linear supplies, no apparent difference.
Obviously to rate a cap at 105°C it's expected to run hot; I'm just surprised that post-smoothing a regulated voltage still gives such a rise.
At 12V DC input I've used both SMPS and 50Hz linear supplies, no apparent difference.
Obviously to rate a cap at 105°C it's expected to run hot; I'm just surprised that post-smoothing a regulated voltage still gives such a rise.
SY said:
Surely not the only reason for using 105°C caps? I can't think of too many environments that hot. My motherboard certainly isn't and it's crowded with them.
Maybe the high-frequency on/off loading of a wholly digital circuit?
I guesstimate "idle" temp as around 60°C (140°F), several degrees hotter during prolonged downloading. Not alarming, but routers are on 24/7 and cap life goes down with temp head. Plus routers seem to be the one PC peripheral that often fails, judging by any "What's a good router?" thread elsewhere.
My DSL modem (fed by a wall wart) also gets hot inside. Don't expect a cap to get hot by itself unless it has to absorb a lot of ripple current. This shouldn't be the case with a simple 60Hz type supply. The thing that I see happening most often is the cap heating up due to heat transferred through the traces from the rectifier(s), as well as operating in an elevated ambient due to a hot chip set in a small box. Using a larger rectifier or adding some copper foil heat sinking to the rectifers will help the one, more ventilation will help the other. Unfortunately, good layout practice dictate a small loop area for the rectifier and filter. This makes for good heat transfer between the rectifiers and the filter caps. If you are using axial rectifiers, they have no place to dump heat except into the PC traces.
Or use good low ESR caps from a well known brand. I experienced such a phenomenon in cheap switchers ( especially gear from 2000-2002 ) and solved it by using quality material. However, your PS runs on 60 Hz which should generate less/no heat. Strange.
Which type and brand do you use now ? Did you measure/change the diodes ( yet ) ?
Which type and brand do you use now ? Did you measure/change the diodes ( yet ) ?
jean-paul said:
The original (swollen) 16V 1000uF cap was a CTC one, listed at badcaps.com as a dodgy brand; no datasheet I can find. I'm assuming that to get bulged it ran even hotter in the 17 x 10mm dia. size than the replacement 25 x 12.5mm dia. Suntan CD287, (not a well-known brand, but at least they give a datasheet and on paper a similar spec to a Panasonic FC; ESR 0.038 @20C/100kHz, ripple 1690mA) but it did fit in the router case without butchery)
I've a Dubilier I'll try, same size though not quite as good a spec (0.041 ESR, 1430mA ripple) and some bigger Suntan 1000uF 50V that may fit. But as said, the router runs perfectly, I don't think there are any broken components. But I'll have another look at the PSU circuit.
CTC is utter garbage, because of the stolen electrolyte issue in 2001. CTC is often found with bulged heads.
I would not bet on Suntan either ( what a name ). Just order a decent Panasonic FC/FM from Farnell and look again. A normal supply with a hot cap just is not right. Things would have been different with a switcher as said before.
I'll be away for 2 weeks but I could send you one cap after that if you're on a budget. Send me a PM.
I repair computer gear with blown caps sometimes to see if my skills are still OK. Wonderful those multilayer boards. If there is CTC/ISSI/Jackcon/Capxon/Lelon in it with datecodes of 2001/2002 I just change them all as I know they will blow one day ...
I would not bet on Suntan either ( what a name ). Just order a decent Panasonic FC/FM from Farnell and look again. A normal supply with a hot cap just is not right. Things would have been different with a switcher as said before.
I'll be away for 2 weeks but I could send you one cap after that if you're on a budget. Send me a PM.
I repair computer gear with blown caps sometimes to see if my skills are still OK. Wonderful those multilayer boards. If there is CTC/ISSI/Jackcon/Capxon/Lelon in it with datecodes of 2001/2002 I just change them all as I know they will blow one day ...
I again repeat I did not receive any mail from you. Also I wish to make clear that if there is a mail/technical problem in communication it is not normal to post this in another thread. That is called threadjacking and it is against forum rules to do so.
You can contact the mods for such problems. Please stop posting that I do not reply mail from you as I did not get mail which seems a perfect valid reason to me. It is not hard for me to reply mail as many members can confirm. In your own language: sizden posta almadim. Almadigim posta cevapliyamam.
You can contact the mods for such problems. Please stop posting that I do not reply mail from you as I did not get mail which seems a perfect valid reason to me. It is not hard for me to reply mail as many members can confirm. In your own language: sizden posta almadim. Almadigim posta cevapliyamam.
ok, jean-paul.
Sorry about having bothered you. The point is that I am a new user in this site and may not have been understood some rules or even items, such as "the mods". so I see now that I have misunderstood you at the beginning, when you replied to my first mail under the thread about Akai CD 55, which was nothing to do with my inquiry, either!.. In my own language: sizin ilk olumlu yaklaþýmýnýzdan dolayý ve tecrübenizi de gördüðüm için yardýmýnýzý rica etmiþtim, belki bilgi tamam ama yanlýþ "insan" ile diyalog kurmaya çalýþtýðýmý görüyorum..
Sorry about having bothered you. The point is that I am a new user in this site and may not have been understood some rules or even items, such as "the mods". so I see now that I have misunderstood you at the beginning, when you replied to my first mail under the thread about Akai CD 55, which was nothing to do with my inquiry, either!.. In my own language: sizin ilk olumlu yaklaþýmýnýzdan dolayý ve tecrübenizi de gördüðüm için yardýmýnýzý rica etmiþtim, belki bilgi tamam ama yanlýþ "insan" ile diyalog kurmaya çalýþtýðýmý görüyorum..
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