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What is the alternate for 2.2uf 400v capacitor

keychain

New Member
Thanks, yes a normal electrolytic cap.

I mean, can we use 4.7uF 450v, 4.7uF 350v, 4.7uF 250v as an alternate for 2.2uF 400v cap in the same circuit?
 

alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO!
It all depends on what the circuit is. Some might be over-stressed by too high a capacitive load.
Post a schematic of your circuit (or at least tell us more about the circuit).
 

keychain

New Member
Hi, thanks.

AC to DC circuit. A bridge rectifier.
I use:
4 x 1N4007 diodes
1 x 474J/K polyester cap
1 x 2.2uF 400v cap (now that I couldn't get this and needing a best alternate)
 

alec_t

Well-Known Member
Most Helpful Member
What is the AC RMS voltage?
 

ChrisP58

Well-Known Member
Most Helpful Member
230 Volts RMS has a peak voltage of 325 Volts. So your capacitor must be rated for at least that voltage.

230 Volt AC lines are often actually 240 Volts, which has a peak of 340 Volts, so a 350 Volt cap will just barley make it. But if there are any transient voltages on the line, then you could blow the cap.

400 Volt caps are the standard for most 240 Volt line derived power supplies. 450 Volt caps gives you more safety margin.
 

keychain

New Member
Okay out of the following 3 caps which will be the closest best alternate
4.7uF 450v
4.7uF 350v
4.7uF 250v

Since, uF value is 4.7 instead of 2.2, can we use 250v?
 

Ramussons

Active Member
I think he has a idea to make a transformerless supply.
That 2.2 uF has to be a 400 V AC capacitor - non polarised.
 

ChrisP58

Well-Known Member
Most Helpful Member
Okay out of the following 3 caps which will be the closest best alternate
4.7uF 450v
4.7uF 350v
4.7uF 250v

Since, uF value is 4.7 instead of 2.2, can we use 250v?
No.

The cap's voltage rating needs to be greater than the peak voltage that will be applied to it. That doesn't change for any uF value.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
230 Volts RMS has a peak voltage of 325 Volts. So your capacitor must be rated for at least that voltage.

230 Volt AC lines are often actually 240 Volts, which has a peak of 340 Volts, so a 350 Volt cap will just barley make it. But if there are any transient voltages on the line, then you could blow the cap.

400 Volt caps are the standard for most 240 Volt line derived power supplies. 450 Volt caps gives you more safety margin.

The supposed 230V mains is an equipment specification, not an actual mains voltage - which pretty well didn't change at all, the UK is still 240V and most of the rest of Europe 220V, although supposedly a few countries have changed to 230V. It's simply that the 230V specification has different tolerances depending on the local mains voltage.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Possibly; it still depends on the overall circuit and load current etc.
400V or 450V would probably be safer.

I would agree, 350V is 'pushing it', and modern electrolytics don't handle even a slight over voltage well - if it says 350V that's what it means, not 351V :D With much older electrolytics you could push them a fair bit past their ratings, with no problem at all.
 

schmitt trigger

Well-Known Member
Most Helpful Member
I do remember that older caps had "surge ratings".
But that practice has disappeared.

I would say that nowadays it makes good engineering practice to use a capacitor with at least 10% higher rating than what you would calculate as its maximum voltage.
 

ChrisP58

Well-Known Member
Most Helpful Member
Hi, thanks.

AC to DC circuit. A bridge rectifier.
I use:
4 x 1N4007 diodes
1 x 474J/K polyester cap
1 x 2.2uF 400v cap (now that I couldn't get this and needing a best alternate)
As alec_t asked way back in Post #4, Please post a schematic of your circuit, including what the input and output are connected to. A list of components, without something to show how they're connected, isn't very informative.
 

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