Faulty Capacitor Help  - Page 1
Forum section: electronics / repair

author: James53646
author_rank: Newbie
timestamp: July 13, 2021, 07:32:45 pm
content: Hi Guys,Been a bit of a lurker on the site for some time but this is my first post... be kind!I'm hoping you guys might be able to help me. I'm an amateur with electronics so mostly play around with low voltage DC stuff..... however!?I was passed a old heater by my parents to look at and see if I could sort it out as it was not turning on...After a little playing about I found a blown capacitor on a board. I thought, no problem, just swap out the cap and all will be well...Unfortunately..... the markings on the cap have blown off... I can see the 680nF so all good there, but the voltage rating is gone.I had a cap with a 630V rating but it's a lot bigger than the blown one.Would there be any issue leaving this bigger fella in place? I'm guessing the voltage of the original cap was much lower. The cap sits on a main voltage rail which in the uk is around 230V.I'm sure this is probably a simply question but I don't really fancy burning my parents house down because I made a daft mistake.Can't get a schematic and the company don't sell any spare parts and told me to buy a new heater when I asked for help.Thanks for the advice in advance!James

author: TimFox
author_rank: Super Contributor
timestamp: July 13, 2021, 07:38:13 pm
content: In general, on mains-frequency circuits, you can replace a non-polarized capacitor (such as a 680 nF paper or film unit) with a higher voltage unit safely, so long as you have physical space for it.However, modern regulations require safety-rated capacitors on the power lines (X or Y, look them up) which are designed to fail into a safe condition that does no harm to humans and starts no fires.

author: tunk
author_rank: Super Contributor
timestamp: July 13, 2021, 08:11:46 pm
content: Photos of old and new capacitors may help.Same with device (showing how it is connected).

author: james_s
author_rank: Super Contributor
timestamp: July 13, 2021, 08:29:14 pm
content: What does the capacitor do in the circuit? Is it a capacitive dropper for supplying power to an electronic control board? What sort of heater is this? It's very possible that there are other faulty parts that are not visibly damaged. A picture of the board will definitely be helpful in offering suggestions.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 13, 2021, 08:52:56 pm
content: Yeah, if it's a dropper cap to supply control circuitry those usually just lose capacity from self healing until they can't pass enough current, not explode. You should check for shorted parts before applying power again.

author: James53646
author_rank: Newbie
timestamp: July 14, 2021, 09:12:50 am
content: Hi Guys,Thanks for all the help so far. I've attached a few pictures of the board and the damaged cap.As far as I can tell, the board is the only one in the heater.It has a stand by where the LED comes on. An option for two heater settings. It has a remote but the parents have lost that, but it explains the receiver.Whilst I'm on, does anyone know the symbol on the blue, blown cap? The circle with the squiggle in?? Just wondering?Thanks again for all the help!!!

author: Gyro
author_rank: Super Contributor
timestamp: July 14, 2021, 10:47:00 am
content: Yep, that's the capacitive dropper for the control circuit (including powering the relay coil).The board otherwise looks in good condition, no browning or other signs of overheating. I think it has just swelled and ultimately burst due to self healing on spikes (particularly as it seems to have a fairly small body size for its capacitance and voltage rating). Shorted components downstream wouldn't significantly increase its power dissipation - and upstream failures would be very evident!Technically speaking, there is no requirement for the capacitor to carry a Class-X safety rating as it is not being used in an 'across the line' application. It also has a protective resistor and and fuse in series with it.Using a Class-X capacitor wouldn't hurt, although there is some evidence that they self heal and lose capacitance more readily than a pulse rated capacitor, requiring earlier replacement (when it can no longer pass enough capacitance to power the relay).P.S. The circle and squiggle is a manufacturer logo.

author: james_s
author_rank: Super Contributor
timestamp: July 14, 2021, 08:47:58 pm
content: Yeah nothing special about that capacitor at all, just replace it with one of about the same value and you'll be good to go.