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RocketBoy
23-06-2016, 10:19 PM
Evening Chaps,

I wondered if anyone could help me with the correct size capacitor for my PSU. The calculations come out to 11,764 uF and the voltage is 68V (allowing an additional 20% as per Gecko guide =88v) I've found a 10,000uF 100v capacitor on eBay, is this close enough or should I use three 4,700uF 100v and wire in parallel?

Many thanks

Mike

Clive S
23-06-2016, 11:52 PM
Personally I would use three as you say because they are generally cheaper. Something like this :https://www.rapidonline.com/samwha-hc2a478m35040ha-4700uf-100v-85deg-hc-snap-in-capacitor-11-3121

Boyan Silyavski
24-06-2016, 10:21 AM
A piece of advice about capacitors:

Don't buy a capacitor from non reputable seller, especially ebay. Too many reasons to explain here but in short : China, not genuine, quality, NOS etc.


Buy from Mouser or RS online, i don't know about Rapid online, but i assume as Clive pointed you there it should be good. Buy a brand capacitor- Panasonic,etc. Look for rating 85C or even better 105C rated


Plus i wouldn't save a dollar from a capacitor. A good normal one 85C is rated 2000-3000h at the temperature rating. A better one exact value, not a stack of cheaper smaller ones, that is meant especially for computer and other power supplies could be rated 105C and 20 000h . So its up to you if you will save a $ or 2 from your power supply. Questions to ask yourself: how many hours per day the machine will work, how many years you expect it to last, do you have time later to stop production and investigate eventual problems.

If it was me i would buy a single screw terminal can type capacitor, meant to be there, less space, easy to exchange.

JAZZCNC
25-06-2016, 12:09 AM
Don't get paranoid with Cap quality or go OTT it's not that critial.
Go with 3 x 4700Uf. They are cheaper and easier to find and provide less ripple than one large Cap. Even the cheap Ebay ones are ok provided you size them correctly. Give them plenty of overhead on voltage and you won't have problem.
I've built probably 100 + and just about every one used 3 x 4700 and never had any issues, Zero failure (Unless I cock up polarity.!!) The PSU running my Own machine is nearly 10yrs old and used Cheap Ebay caps, It's still going strong and as runs for 10hrs day most days.

I buy mine from Farnell.

cropwell
25-06-2016, 10:48 AM
You can buy cheap Chinese capacitors from China, or you can buy expensive Chinese capacitors from RS or Farnell. It is your choice depending on your perception of quality and service.

magicniner
25-06-2016, 08:19 PM
One large cap just means there is just one large component which, when it fails, will render your PSU broken.
Provided the conductor area of the connecting bus is large and it's length is short there is no reason not to use several smaller caps in parallel, but buy branded quality from a reputable supplier,

- Nick

cropwell
25-06-2016, 08:51 PM
I am partly retracting my former statement in the light of this article http://www.hardwaresecrets.com/how-to-identify-japanese-electrolytic-capacitors/

Rob :crushed::crushed::crushed:

Clive S
26-06-2016, 12:43 AM
Rob at our time of life if they last 10 years it's a bonus:hysterical:

JAZZCNC
26-06-2016, 02:16 AM
Rob at our time of life if they last 10 years it's a bonus:hysterical:

Ten more yrs.!!! . . . . Now't like being optimistic. :eagerness:

Boyan Silyavski
26-06-2016, 12:53 PM
You can buy cheap Chinese capacitors from China, or you can buy expensive Chinese capacitors from RS or Farnell. It is your choice depending on your perception of quality and service.

Its absolutely not like you present it.

cropwell
26-06-2016, 02:17 PM
Its absolutely not like you present it.

If you read my previous post, you will see that I have added information to enable a buyer to make an informed choice. Chinese (and Taiwanese) goods are made as cheaply as possible. This affects quality and in some instances safety. Brand forgery is rife. It does not stop major UK suppliers buying them for sale in UK and, for the time being, in Europe. Major suppliers are not immune from fakes creeping into the supply chain.

I have seen many instances of failed power supplies, with capacitors bulging with internal gassing, on the brink of spectacular failure. These are not always Chinese components.

Japanese capacitors are generally a better quality product, but to me it is a price based decision. I agree with Jazz, that in most instances where a capacitor is not stressed, it will do the job for a reasonable service life, wherever it was born.

Rob

Clive S
26-06-2016, 04:37 PM
Well said Rob:beer:

Boyan Silyavski
26-06-2016, 05:23 PM
Well said may be,but i would not put a chinese capacitor in my audio or my cnc for the sake of saving what, almost nothing.

Just an example (http://www.diyaudio.com/forums/parts/109130-hitachi-hcg-fa-capacitor.html) of what happens if you buy the "Hitachi" capacitor from ebay. Which is just a couple of euros cheaper than a real one from Mouser. See what a guy that bough it says and at bottom the guy that distributed them.


I just don't know what exactly you are promoting here guys? You want to be right for the sake of rightness or what?


Its one thing pointing people to buy chinese spindle, VFD or similar where substantial savings are made, and other thing pointing them to buy crap to save a $ for a beer. So sb will spend 3000 euro for 900x600 DIY router and will save 5 euro from capacitors?

JAZZCNC
26-06-2016, 06:45 PM
Its one thing pointing people to buy chinese spindle, VFD or similar where substantial savings are made, and other thing pointing them to buy crap to save a $ for a beer. So sb will spend 3000 euro for 900x600 DIY router and will save 5 euro from capacitors?

Boyan while I agree upto point with what your saying where do you stop with the " For few more" this is better.? This could be said about every part and aspect of the CNC machine .!

Lets keep it relavant with the The point being that for DIY CNC if Sized correctly even the Cheap Caps are plenty good enough. For Hi-usage Industrial CNC or HiFi then maybe not but this is DIYCNC. 5 x 3 (Pounds because EU won't deal with us anymore!!! ) saved on something that 99% chance won't fail is enough saving.

Then you have the other way to look at it.? If worst happens and "one" fails it's cheap, available and easy to replace. The other two will keep you running until replacement arrives. . . . . If ONE BIG one goes Boom then your dead in the water.!

cropwell
26-06-2016, 07:09 PM
Have a look at this page :http://uk.farnell.com/epcos/b41231c9228m000/cap-alu-elec-2200uf-100v-snap/dp/1839293

Note the country of origin

Look at the suggested alternatives and note their countries of origin.

Make you own mind up about quality and price.

I am currently trying to find out the inductance values of 5 of these capacitors as against 1 large one to the same value 11,000 uF, it affects ripple, but you can always compensate with ceramic disc caps. Not that I am building a power supply at the moment, just curious.

BTW anyone want a 1F (yes 1 FARAD !) 5v dual layer capacitor? It cost me 10 and also an obscure ancient static RAM chip, that cost me 30, all for a job on some equipment of mine that turned out not to be worth repairing.

:chargrined:Rob

Boyan Silyavski
27-06-2016, 10:43 PM
OK, maybe i am too spoiled because usually i buy capacitors for audio, and as i said i would not put that thing in my amp, but for mere 5euro there is Cornell Dubilier cap in Mouser, which is USA made.

Clive S
27-06-2016, 10:50 PM
OK, maybe i am too spoiled because usually i buy capacitors for audio, and as i said i would not put that thing in my amp, but for mere 5euro there is Cornell Dubilier cap in Mouser, which is USA made. OK can you please put a link up to the caps that YOU would use in a standard 68V non linear power supply and the price including delivery.

Boyan Silyavski
27-06-2016, 11:21 PM
OK can you please put a link up to the caps that YOU would use in a standard 68V non linear power supply and the price including delivery.


I don't know what exactly you are asking Clive? you could just go to Mouser and find it.


But if you are asking what exactly I will use- I will not buy it from Mouser. I will go downtown, drink a coffee and visit the local repair guy and buy from his shop the needed capacitor, saving on shipping fees. yes, i will pay them a bit more expensive, but he helps me so i help him. Last time he repaired my 3kw Siemens VFD for 15 euro, and i payed him 20, from shame. At same time people wanted 90 euro just to open it and look what the problem is. So i like personal contact with nice people.


Look at the photo below, just did it in the workshop. These caps are exactly for some CNC PSUs. As you see Nichicon cap.~12 euro per piece.

18799



Added bonus when I was buying the caps was that he went back and sold me 2 toroid transformers x 20 euros each, which i was going to buy for 100euros each /shipping included/ . So my point is personal contact pays off.



But at the same time now i need for my amp 2x 22000μF cans with exact height and width, so i have to buy them from Mouser and yeah, 40 euro each.