identifiing capacitors - Page 1
Forum section: electronics / general

author: fixit
author_rank: Newbie
timestamp: November 03, 2020, 05:14:33 am
content: I like to make things work that break rather than buy new. Today the gas valve in the furnace stopped working. Normally it would be powered directly by 24vac, but this valve has a simple circuit on it to power it with dc current.I traced the leads on the board to the components and came up with a diode bridge and an electrolytic cap on the dc output side between the pos and neg. It looks very simple, 5 components.The diodes are 1n4007 and the capacitor says 220uf 50v. It has the number h401(m) and the name LELON. RJA105°CI want to replace the cap since it doesn't seem to meter correctly and one of the diodes is shorted out.Looking at replacement capacitors, I find there is a series associated with each capacitor. Is that the (M) in the number mentioned above that indicates the series?Can anyone explain what the series indicates or differentiates on capacitors?There are many capacitors on the newark web page that have the look of the one I removed. I'm thinking that this one could be the replacement I need....ECA-1HM221Electrolytic Capacitor, 220 µF, 50 V, M Series, ± 20%, Radial Leaded, 2000 hours @ 85°Conly problem is the heat temperature, mine says 105°C and this one says 85°C.The gas valve coils meter at 120 Ohms and is probably correct other are simular, but I don't have the specs on it. Rebuilding this circuit would be much better than spending $180 on a new valve.Any help would be appreciated.Rex

author: bob91343
author_rank: Super Contributor
timestamp: November 03, 2020, 06:20:18 am
content: Often the letter M specifies 20% tolerance.F = 1%J = 5%K = 10%M = 20%If I remember correctly. In this case you'd have to check manufacturer's data to be sure.I don't recommend 85 degree components; 105 degree units aren't enough more money to make a difference.

author: james_s
author_rank: Super Contributor
timestamp: November 03, 2020, 06:41:32 am
content: You're overthinking this, it is not a critical application at all. Virtually any 220uF 50V capacitor you can find will work. Selecting a 105C part can't hurt but is not really necessary either unless it's in something that gets hot. Personally I like Nichicon, Rubycon and Panasonic but the brand is not all that important either.

author: helius
author_rank: Super Contributor
timestamp: November 03, 2020, 07:10:53 am
content: Lelon is a second-tier, fairly well respected manufacturer, and available from major distributors like Mouser or Digikey. I wouldn't immediately suspect it before measuring its capacitance.

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2020, 09:22:08 am
content: Quote from: james_s on November 03, 2020, 06:41:32 amWell in this case:Quote from: fixit on November 03, 2020, 05:14:33 amQuoteSo a 105°C part is a must!

author: fixit
author_rank: Newbie
timestamp: November 03, 2020, 05:37:51 pm
content: Thanks everyone for all your posts.I'm still fuzzy on what the "series" indications is on the capacitors. Could it be the placement of the leads, the type of body the cap has, any add-ons such as a base to mount it, or could it simply be a factory run for that particular batch of caps?I have learned that this appears to be a "radial" configuration with two leads out the bottom of a round aluminum can next to the PCB.I feel that the temperature shouldn't be lessened, even though it is in a furnace, it has free air running over it all the time and the furnace heat doesn't effect it, but the heat generated from the electricity certainly does.The (M) is the tolerance of 20%, great to know.And to know that there are many choices that would satisfy this need makes choosing much easier. just keep with 220uf and 50v is the most important.Any other opinions or knowledge from your experience is greatly welcomed.Thanks Rex

author: james_s
author_rank: Super Contributor
timestamp: November 03, 2020, 06:04:43 pm
content: Any of the above, as well as lifetime, ESR, ripple current and other ratings that come into play in specific applications needing those traits. If you grab the datasheet for several different series from the same manufacture it should tell you what the series is optimized for. In this application it shouldn't really matter, but if you were working on a switching power supply, motor inverter, aircraft instrument, battery powered device, something that will be potted in epoxy, has a very long life expectancy, will be exposed to very high or very low temperatures, needs to be very compact or other specialized application then you might want a part optimized for the traits that are important to the application.Regarding the 105C requirement, the fact that the original part is rated 105C does not necessarily mean that a 105C part is needed, it simply means that the engineer who designed it chose that part, possibly on the "105C caps last longer" advice that often circulates around, or it could be what the manufacture had in stock, used in some other product that did need the high temperature it could be any number of things. In the absence of complete information I would advise going with something rated for at least 105C unless you are sure it will never get that hot.

author: andy3055
author_rank: Super Contributor
timestamp: November 03, 2020, 07:09:22 pm
content: The 105 C might be because it is on the PCB mounted on the furnace's side and is subject to the warm environment especially when the thing is in a closet of some sort. In my house the furnace is inside the house next to a bathroom. It has very little space around it like its own little room and has a door to it. Whenever I have to open it while it is running, the air feels very warm inside. Other than that, I agree with James's comments.Just a thought.

author: andy3055
author_rank: Super Contributor
timestamp: November 03, 2020, 07:13:36 pm
content: BTW, one common problem with a furnace firing and turning off almost immediately is due to the flame sensor surface getting dirty over a period of time. It is simple to clean it with some Scotchbrite after carefully removing it without breaking the glow plug/element.

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2020, 07:51:47 pm
content: Quote from: fixit on November 03, 2020, 05:37:51 pmI forgot to say, the physical dimensions are also important. You want the same pitch (distance between the leads) and it mustn't be too tall or wide, otherwise it won't fit.

author: bob91343
author_rank: Super Contributor
timestamp: November 03, 2020, 07:58:06 pm
content: This being the real world, a capacitor isn't just a capacitor. It has many properties that often compromise its operation. There is no substitute for understanding what the circuit does and how ordinary parts behave under these conditions.Calling a part a capacitor is kind of like the blind men groping an elephant. With eyes open you can see much more. You many need to know about ESR, ESL, leakage, temperature drift, self resonant frequency, susceptibility to environment such as vibration, and so on.In the final analysis, actually running the circuit to see how it behaves is important. Capacitors are cheap unless improper selection causes consequential damage.

author: fixit
author_rank: Newbie
timestamp: November 03, 2020, 10:06:27 pm
content: thanks everyone and a special thanks to james_s.This simple circuit is something that I mostly understand, a 24v ac supply into a full wave bridge rectifier with a cap across the output to smooth the dc side out somewhat. The resultant dc is fed into a dc coil that opens the gas valve for the flow of gas to the furnace. In the past, these coils were all ac coils on the solenoid.I'm finding more and more of these dc coils on valves were in the past they were ac solenoids opening the valves, so they just put this little interface board on the gas valve to get the dc input they want. Seems to me like a lot of extra effort to change such a simple device that we have used for years and years in the 24v ac systems. Most of the failures I have come across with these dc interfaces are just soldering connection at the 24vac input, but this one actually has a bad diode in it and my meter isn't giving me good result with the capacitor, so I will change it also. Since this is my own, ill fix it for myself. A return trip to a customer after a fix like this is taking too many risks and just isn't worth it.Thanks a lotjames_sfor your very much down to earth reply to some one that knows a little but not enough to get it exactly correct.

author: S. Petrukhin
author_rank: Super Contributor
timestamp: November 03, 2020, 11:17:33 pm
content: Quote from: fixit on November 03, 2020, 05:14:33 amA capacitor of this capacity has a sufficiently large charge current that can damage the rectifier diodes or the output stage of the valve control.