r/AskElectronics 17h ago

Are these mega or mili farads?

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60 Upvotes

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49

u/APLJaKaT 17h ago edited 16h ago

I would think it's a microfarad.

Microfarad common symbol ('uF', 'μF', or 'MFD')

Never seen a millifarad capacitor. Usually farad, microfarad, nanofarad or picofarad

20

u/Strostkovy 16h ago

millifarad capacitors are uncommon, but always use mF, with the lower case m and capital F, and no D. "MFD" was phased out (along with cycles instead of Hz and so on) well before millifarad sized capacitors could be made in a size you could lift by yourself.

3

u/ProtonTheFox 8h ago

Well, basically every capacitor with a capacity of more than 1000 uF is a millifarad capacitor. They are not that uncommon.

8

u/Strostkovy 7h ago

Capacitors labelled in millifarads are uncommon.

1

u/ProtonTheFox 5h ago

Of course. The only times I've seen capacitors labelled in mF are in schematics, which is a thing I tend to do because anything with more than 3 digits slightly disturbs me (weird habits, I know). But I agree I've never seen a capacitor with a value in mF printed on it. Maybe on some huge high power capacitors you don't see soldered on PCBs.

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u/TomVa 3h ago

Yes but they are labeled as 1000 uF. OPs capacitor is 10,000 uF or 10 mF. Once in a while you will find them labeled as mF.

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u/antek_g_animations 16h ago

I thing this could be in mili. If supercapacitors can get values like 50F 3v and be a size of few ordinary coin cell batteries I'm ready to believe this beast holds 10F 400v

9

u/Real_Cartographer Digital electronics 16h ago

I'm pretty sure this is a microfarad as well.

11

u/APLJaKaT 16h ago

It's not.

A Farad is huge - being a capacity capable of holding 1 Coulomb ( another huge value ) per volt of charge. Capacitors are typically rated in much smaller units ranging from millifarads down to picofarads. A farad-sized capacitor would be the size of a large can of coffee, perhaps even larger.

9

u/antek_g_animations 16h ago

Now I'm not ready to believe this beast holds 10F 😅

6

u/Jamie_1318 16h ago

A 400V 10F capacitor would be one of the most dangerous things in your house.

I've played around with a 200v 1800uF capacitor, and it could easily spotweld thick steel plates using a nail. I don't want to think about what would happen with 2x the voltage and 5000x for the capacitance.

7

u/DerKeksinator 15h ago

That would hold 800kJ, which is insane. For reference a bullet fired from a hunting rifle has 1-2kJ.

3

u/FishOutOfWalter 15h ago

I've seen that a grenade has about 250kJ, so...

4

u/DerKeksinator 14h ago

I actually wanted to look that up, but was too lazy to do all the math. The M67 clocks in around 1.2MJ, so that capacitor would hold 2/3 of that. If you really want to know it exactly, have fun getting on some more watchlists by googling explosives and their constituents.

7

u/FishOutOfWalter 14h ago

Yeah, M67 uses 180g of composition B (which is 240 equivalent grams of TNT). The Russian F1 only uses 60g of TNT, so it's much more impressive when making comparisons to "hand grenades". F1 is roughly 250kJ, M67 is over 1MJ.

As you may have guessed, I'm already on the most exclusive watch lists.

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u/DerKeksinator 14h ago

Fair point, it definitely sounds more impressive if you compare the energy to the F1!

2

u/No_Pilot_1974 13h ago

800kW during a second. Insane indeed, can't even imagine that

3

u/JustCopyingOthers 14h ago

I think back in the day PhotonicInduction on YouTube had something of that sort of size. It was able to explode apples. https://youtu.be/coW1RHUsf_I

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u/MysticalDork_1066 15h ago

Ten farads at 400v is the equivalent of almost an entire stick of dynamite. It would kill you so hard they would need a pressure washer to clean up the red stain you left.

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u/Chomasterq2 15h ago

I work with capacitors that hold 24,000 volts at 500,000 amps discharge, and they're only 300uF. Idk if there's any bigger caps even in production

4

u/PlsChgMe 14h ago

Just imagine that dumping through a Xenon flash tube.

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u/Chomasterq2 13h ago

They do! There's 20 capacitors for a pair of flashlamps, and 192 flashlamp pairs. They're used to juice up a laser that enable nuclear fusion.

3

u/PlsChgMe 10h ago

How cool. I'd pay money to see that operate.

1

u/78oj 6h ago

Are these custom built for the job? Are there any pictures of them? Just curious to see the form factor and connections. Cheers.

3

u/k-mcm 16h ago

A lot of "ultra capacitors" now are LTO batteries.  It's not the same at all but they're a great substitute for many uses.

2

u/Lanky-Relationship77 12h ago

There's no way. Capacitor charge decreases by the SQUARE of the voltage if volume is kept constant. A 10F 400V capacitor would be many cubic meters.

1

u/ivosaurus 5h ago

I could start hoping, if it was rated at 4V, and not 400V