DIY & Home Improvement

intrepidity

(7,892 posts) Thu Feb 9, 2023, 02:40 PM Feb 2023

Capacitor question

Trying to replace a capacitor with specs: 20+10uF 300v

But can only find (Amazon) one with 370v, all other specs matching.

This is a dual start capacitor for two 300v motors. Will it burn the motors? Is there a simple modification to reduce the voltage? I'm just learning this stuff, so excuse my ignorance..

ETA: I just asked chatgpt and it said it is fine. Is AI trying to kill me?

ETA2: Uhoh, after grilling it for awhile, now it says this:

Yes, it is both "generally safe" and "potentially dangerous" at the same time. Replacing a 300VAC capacitor with a 370VAC one can be done safely as long as all other specs are the same, but it is important to make sure that the new capacitor is rated for the same voltage as the original one, to avoid any potential damage or fire hazard.

9 replies

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Capacitor question (Original Post) intrepidity Feb 2023 OP

The ability of the capacitor to charge up to a higher voltage than called for mahatmakanejeeves Feb 2023 #1

this? IbogaProject Feb 2023 #2

The capacitor will only discharge up to the voltage level that is applied to it Shermann Feb 2023 #3

Sorry for the delay...but what do you mean by intrepidity Feb 2023 #5

If you apply "X" volts to a capacitor when it is charging Shermann Feb 2023 #7

But this is AC intrepidity Feb 2023 #8

Basic concept applies regardless of AC or DC nt Shermann Feb 2023 #9

Should be fine. usonian Feb 2023 #4

Thanks for that link intrepidity Feb 2023 #6

mahatmakanejeeves

(60,949 posts)

1. The ability of the capacitor to charge up to a higher voltage than called for

Reply to intrepidity (Original post)

Thu Feb 9, 2023, 02:42 PM

Feb 2023

should not be a problem. It's the underrated ones that will fail in service.

Did you try Grainger?

Where did you find a 300-volt motor?

IbogaProject

(3,652 posts)

2. this?

Reply to intrepidity (Original post)

Thu Feb 9, 2023, 03:36 PM

Feb 2023

https://www.mouser.com/ProductDetail/Hartland-Controls-Littelfuse/CAP-20-10-440R?qs=TuK3vfAjtkUyLxwJ9ZQ9%252Bg%3D%3D

Shermann

(8,642 posts)

3. The capacitor will only discharge up to the voltage level that is applied to it

Reply to intrepidity (Original post)

Thu Feb 9, 2023, 04:21 PM

Feb 2023

If all other specs are the same, it should be suitable as a drop-in replacement.

I'm not familiar a "dual start" capacitors but believe it is effectively two capacitors.

intrepidity

(7,892 posts)

5. Sorry for the delay...but what do you mean by

Reply to Shermann (Reply #3)

Mon Feb 13, 2023, 04:33 PM

Feb 2023

"voltage level that is applied to it"?

And yes, a dual means it has two hot leads with different ratings, in my case, one each for 10uF and 20uF, to start two motors (like a compressor and a fan).

Shermann

(8,642 posts)

7. If you apply "X" volts to a capacitor when it is charging

Reply to intrepidity (Reply #5)

Mon Feb 13, 2023, 05:34 PM

Feb 2023

...it will then only output up to "X" when discharging.

The voltage rating only specifies how big "X" can be. So, you can use a capacitor with a higher voltage rating as a drop-in replacement without risk of it discharging a higher voltage.

It's really better to play with breadboards with 5V or so than 300-volt motors. This is kind of an unusual thread that way.

intrepidity

(7,892 posts)

8. But this is AC

Reply to Shermann (Reply #7)

Mon Feb 13, 2023, 05:36 PM

Feb 2023

So 120v

Shermann

(8,642 posts)

9. Basic concept applies regardless of AC or DC nt

Reply to intrepidity (Reply #8)

Mon Feb 13, 2023, 07:11 PM

Feb 2023

usonian

(13,836 posts)

4. Should be fine.

Reply to intrepidity (Original post)

Thu Feb 9, 2023, 06:33 PM

Feb 2023

Take note that a capacitor's voltage rating is not the voltage that the capacitor will charge up to, but only the maximum amount of voltage that a capacitor should be exposed to and can store safely.

http://learningaboutelectronics.com/Articles/What-does-the-voltage-rating-on-a-capacitor-mean

intrepidity

(7,892 posts)

6. Thanks for that link

Reply to usonian (Reply #4)

Mon Feb 13, 2023, 04:39 PM

Feb 2023

Although in that page, it seems to only discuss DC power. Mine is AC, so I'll have to see how that might alter things.

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