How to get large capacitance at lowest cost?

[poorchava]

I need to build some hefty capacitor banks, for filtering mains. I've estimated that I need at least 50 000uF that can candle up to 55V and 20A continuous current (I guess ~35A in rare peaks). Those are to be used as BIG mains filters. Obviously soft start and and bleed resistors will be used.

The question I have is how to achieve that capacitance at lowest cost? I mean is thee some value that is especially cheap (in terms of price/uF)? For example in MLCC's 100nF ones are always cheaper because they go around in much larger volumes than other values. Is there something like that for electrolytics? Eg. is it obviously cheaper to buy 10x 4700uF, or one 47 000u capacitor?

Another thing: does it make sense to use cheap chinese capacitors? I mean it's mains frequency, so I don't expect any high frequencies or high current transients and since it's a setup for an experiment only, i don't need very long part life.

[wraper]

When I've done something similar a few years ago, cheapest option seemed to make banks containing 10 000 or 4700 uF capacitors. Forget china, if you want cheap, samwha was cheapest for 10 000uF at that time (TME).

[tautech]

I've repaired some Mig welders (pre inverter types) that had banks of 20,000 uF stud mount, screw terminal, bare Ali can sandwiched between 2 mm Ali pates for parallel connection.
Seemed the manufacturer had a similar dilemma to you.

Once upon a time big'uns were available at every surplus store for very little cash.
I got a 60,000 uF 50 V for $5 IIRC
But SMPS seems to have made the large values harder to acquire.
We have a crowd here in NZ that can build to order, but their core business is pulse grade caps for electric fence units, so not sure they can do smoothing caps.

Spend some time on Alibaba and contact the manufacturers directly, introduce yourself and they will go to some trouble for you.

[wraper]

http://www.tme.eu/en/details/he1j109m40040ha/105c-snap-in-electrolytic-capacitors/samwha/#  This one is 2.64 eur ex vat for 5+ if I log in (seems that my account have some discount there)

[janekm]

I don't know about "forget about China"... If you really need low cost, it's the place to go for reasonably priced, almost certainly recycled ones: http://item.taobao.com/item.htm?spm=a230r.1.0.0.W5Pvj8&id=21113859662&ns=1#detail
75V, 72000uF, ~$5 (with Taobao, you want to look for listings that show that the seller has received feedback on the item being sold at the advertised price, there are a lot of listings for items no actually in stock / price on demand).

[DanielS]

I need to build some hefty capacitor banks, for filtering mains. I've estimated that I need at least 50 000uF that can candle up to 55V and 20A continuous current (I guess ~35A in rare peaks).

What matters for caps is the actual RMS ripple current going through its terminals; not your application's output current. You would need 4-6 caps in parallel to handle 20-30A RMS ripple. 10mF is not such an uncommon capacitor size at 50-75V but good ones do cost around $10 a pop.

[SeanB]

See if you can contact Toploser ( hasn't been on here for a while) and see if he has any big caps for you.

[eneuro]

10mF is not such an uncommon capacitor size at 50-75V but good ones do cost around $10 a pop.

When was looking for something 400V-450V I've found those 4.7mF 400V  24mESR EPCOS B43456A9478M, each of them costs about 110$ @ DigiKey, but this one is capable up to 50A ripple current and considering using 2-3 of them in pulse spot welder on transformer primary as 230VAC recified filters and energy buffers boost.

BTW: It is interesting if those 50V costs around 10$, while 400V/50V means 8x higher voltage, so it is possible store 64 times more energy @ 400V in the same 10mF caps and to get the same amount of energy using 50V 10mF caps whould require 64*10$*9.4/10 ~  600$, while using two 400V EPCOS caps we get into cost of about 240$ .
Does it means that using high voltage caps we can save a lot of money if we can use 400V high voltages in comparision to lower voltages below 100V, or those EPOCS caps are garbage?

[Smokey]

Is this something you have a budget for?  Is it a one-off or will you need a long term reliable supply?

[DanielS]

BTW: It is interesting if those 50V costs around 10$, while 400V/50V means 8x higher voltage, so it is possible store 64 times more energy @ 400V in the same 10mF caps and to get the same amount of energy using 50V 10mF caps whould require 64*10$*9.4/10 ~  600$, while using two 400V EPCOS caps we get into cost of about 240$ .
Does it means that using high voltage caps we can save a lot of money if we can use 400V high voltages in comparision to lower voltages below 100V, or those EPOCS caps are garbage?

High-voltage energy storage is usually more cost-effective, more power-efficient and more compact.

If you wanted to store the ~40 joules worth of energy from a 680µF input cap charged to 350V in an output cap charged to 3.3V, you would need a 7.6 farad cap... that's 2000X bigger than what most SMPS usually use on their 3.3V output. Such a capacitor would be about as big as a typical ATX power supply unless you used ultracaps.

[David Hess]

If this is just a one off project, then the most economical source for big aluminum electrolytic capacitors will be surplus electronics or NOS (new old stock).  Availability will determine what values you can find and how many will be needed in parallel.

[poorchava]

Just bought 24pcs of JackCon LHK series 2200 uF / 63V 18x35mm caps. I don't need a long life, so I think JackCon's are ok. Especially that LHK series doesn't belong to the notorious "low impedance" series.