Where can I find a 150microFarad capacitor?

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rvk2

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Hey everyone, I'm making a circuit that involves taking a steady 5V supply from 4AA batteries. The schematic can be found here:
http://www.eepn.com/locator/products/ArticleID/32149/32149.html

The problem is that I just went to Radioshack and checked their catalog, couldn't find a 150uF capacitor. Anyone know where I might be able to get one, or if they even make one of that size?

And also, in the schematic...there are two types of capacitors. one is just two straight lines, and the other is with one straight line and a curved line. I know the curved line is for an electrolyte capacitor, what are the two straight line ones?
 
rvk2 said:
And also, in the schematic...there are two types of capacitors. one is just two straight lines, and the other is with one straight line and a curved line. I know the curved line is for an electrolyte capacitor, what are the two straight line ones?
Click to expand...

Non-polarised ie ceramic, tantalum etc

as for your 150uf you may have to use several of a different value in series

ie you could use 3x 100uf, 2 in series and 1 in parallel with that
 
hmm, the series and parallel is a good idea. the only drawback is that it might take up a lot more space than I want. Something to think about now.
 
You need to consider the tolerances of electrolytic capacitors!.

They are generally EXTREMELY poor, something like -50% +100%, so it's pointless chasing a particular non-standard value!.

The capacitor value in the circuit you posted the link for isn't at all critical, personally I would use the next largest preferred value, which is 220uF, or even a 100uF would be fine (as would a 470uF).
 
If youve got some old tv, radio etc laying around youll more than likely find that value in there as its a common value.

Just make sure that you get the right voltage rating otherwise youll hear a bang as the capacitor explodes :lol:
 
Nigel, are you saying that I can use 100uF caps? If I do use that, wouldn't that affect the whole circuit? If I could get away with using 100uF, my problem is solved.
 
I would go higher than 150uF rather than lower... those caps are decoupling caps to smooth out the power input and output (absorbing transients, high frequency noise, etc)

most likely, 150uF was chosen as the smallest recommended value, and a lower value might lead to excessive ripple voltage on the input or output, but going larger (within reason) shouldn't hurt anything...
 
rvk2 said:
Nigel, are you saying that I can use 100uF caps? If I do use that, wouldn't that affect the whole circuit? If I could get away with using 100uF, my problem is solved.
Click to expand...

As evandude says, it's best to go larger rather than smaller, which is why I suggested 220uF - but 100uF will quite probably be fine, try it and see!.

150uF was probably just a value the designer had to hand, it's not often a capacitor that has it's value calculated - you just choose one which you 'know' is going to be more than large enough.

It's only a PSU smoothing capacitor, so it's not at all critical!.
 
Some sources of parts:

Jameco, Digikey, Ocean State Electronics, Debco Electronics, Mouser, MCM Electronics, Newark Electronics, Dan's Small Parts

Jameco, Mouser and Digikey are my favorites. Electronics is a hobby and these sources usually have decent prices, small order quantities and quick delivery.
 
Nigel Goodwin said:
It's only a PSU smoothing capacitor, so it's not at all critical!
Click to expand...

Yes and no, in switching DC-DC converters it can be, a lot of times they'll specify a minimum capacitance, below which the converter becomes unstable. but true, the actual value (as long as you're above the minimum, and not so high a value that the ESR becomes a problem) isn't very important.

However, you're right, 100uF probably will work OK too. After all, it's unlikely that they put the absolute minimum sized capacitor in their app note circuit; that wouldn't be very good design practice.
 
Well now I have two options:
1. Get 220uF caps from Radioshack
or
2. Order the 150uF cap from Digi-Key. The only thing is, I need the parts before Aug 22nd. Does anyone know how fast the shipping is from Digi-Key?
 
digikey does have fast shipping.

However, I would definitely say just buy the 220uF's from radio shack if you're trying to meet a deadline. the more time you spend waiting for parts for the first prototype, the less time you'll have to debug it if it doesn't work immediately.
 
yeah, radioshack is what I was thinking too. I did a search on digikey, and it came back with about 2 pages full of different types of "150uF electrylyte general purpose capacitors". Some were "cut tape" and some were "tape & reel"- basically I had no idea which one to get. Also some had a pricebreak as low as 500, which is wayyy more than I need. Would any 150uF electrolyte capacitor with lets say a voltage rating of 10V work?
 
Jameco, Digikey and Mouser ship very quickly. You might have better luck with Jameco website - they seem to have less choices and their on-line and printed catalog is a bit easier to search. All the others ship quickly too but I've had more experience with the 3 listed.
 
I hate to be such a noob, but could someone do a digikey search for this part# 565-2205-1-ND
and tell me if its the right capacitor for this circuit? Its the only one with a low enough quantity I can buy off the site...the others are selling in bulks of 500 and up. I'd appreciate it!
 
you sure you want surface mount?

check out 493-1738-ND
1/3 the price of the one you posted, and you don't have to buy in multiples of 5...

or 493-1781-ND
only 6 cents more and rated to 16v
 
rvk2 said:
Well now I have two options:
1. Get 220uF caps from Radioshack
Click to expand...

You only have that one option! - WHY would you want to order an inferior part when you can buy a better one at a local store?.

Use a 220uF capacitor!.
 
I personally think 150uF is a weird value. Higher values won't hurt, but make sure that the new capacitor has a high enough voltage rating.
 
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