Cap swap question  - Page 1
Forum section: electronics / repair

author: Crambone
author_rank: Frequent Contributor
timestamp: June 27, 2020, 12:14:37 pm
content: I have a bad 473Z Ceramic Capacitor Does the Z on 473Z stand for +80% -20% ?Can I use a .047uf film cap at 10%? It’s in 500v service.

author: aqibi2000
author_rank: Regular Contributor
timestamp: June 27, 2020, 12:19:57 pm
content: Believe you would require a 1kv cap if swapping like for like.Z means to allow the tolerance to be + and - 20% of the specific value so nothing wrong with using a 10%

author: login
author_rank: Contributor
timestamp: June 29, 2020, 03:31:28 am
content: no you can't. ceramic caps are measured in pico farads ( pf ) not microfarads (uf ) so the values don't match. The tolerance of the ceramic @ -20% + 80% means it can wander form it's nominal value to those two extremes without affecting the operation of the circuit. This allows for temperature fluctuations in the circuit that a 10% cap doesn't allow for and won't survive. Stick with the same value the circuit was designed for.

author: bdunham7
author_rank: Super Contributor
timestamp: June 29, 2020, 04:28:55 am
content: Quote from: login on June 29, 2020, 03:31:28 amThe third digit is a multiplier exponent, 3 means a multiplier of 10^3. 47 x 10^3 = 47000pF = 47nF = .047uF, so that part is right.QuoteThe first sentence I understand. The second makes no sense at all. I think you may misunderstand the term 'tolerance' as it is applied here.

author: login
author_rank: Contributor
timestamp: June 29, 2020, 04:37:31 am
content: ahh I'll have to concede that first point as I didn't do the maths. however there is a reason the tolerance in this instance is given as two figures not one. Can you explain why you think that is?

author: bdunham7
author_rank: Super Contributor
timestamp: June 29, 2020, 05:57:59 am
content: Quote from: login on June 29, 2020, 04:37:31 amDo you mean the -20/+80% ? Capacitors for power supply reservoirs, decoupling and so on need to be at least some minimum, but it isn't generally a problem if they are bigger. So caps manufactured with this in mind won't be rejected for being over, just under. Capacitors in circuits like RC filters need to be close to the specified value and being too big is just as bad as being too small, so the circuit will specify a cap with a symmetric tolerance of +/- 10% or 20% or whatever. It's just a different binning process for different applications. There's never a problem using a tighter tolerance part than specified.

author: login
author_rank: Contributor
timestamp: June 29, 2020, 06:45:38 am
content: that really makes no sense in this regard. this particular ceramic cap has a Z rating and as I tried to explain earlier refers to two parameters, not one. Not all caps have two parameters so I'll ask you again, Why do you think that is? Perhaps it is you who misunderstands in this instance what this paticular tolerance refers to. it seems you are generalizing instead of being specific.

author: bdunham7
author_rank: Super Contributor
timestamp: June 29, 2020, 02:15:00 pm
content: I'm not sure what you mean by 'two parameters'. They aren't parameters at all, they are bounds and each has two--an upper and lower.A 'J' rated capacitor has a lower limit of 95% of its nominal value and an upper limit of 105%A 'K' rated one has a lower limit of 90% and an upper of 110%A 'Z' rated cap has a lower limit of 80% and an upper limit of 180%.The 'Z' rated ones can be asymmetrical because of their intended use, as I explained.