16v or 50v capacitor, what are the implications?

jerrah · Postby **jerrah** » Mon Jun 25, 2012 10:43 pm

I need a capacitor for my COPs (that I've taken 2 years to put together)...

I've noticed that 10,000uF 16v capacitors appear to be fairly rare but I have no trouble getting the same in 50v.

Will a 50v work fine or are there other implications?

jerrah · Postby **jerrah** » Mon Jun 25, 2012 10:54 pm

Would two 4700uF 16v capacitors give me the same joy? They're pretty cheap and common!

lee · Postby **lee** » Mon Jun 25, 2012 11:29 pm

Two 4700uF caps in parallel would yield 9400uF. It's about a 5% difference, but I'd probably rather over-do it than under-do it. I can't see any issues arising from using the 50V caps.

LuckyCat · Postby **LuckyCat** » Tue Jun 26, 2012 9:25 am

One thing to keep in mind, what will be the peak voltage in the circuit? Is the capacitor an electrolytic type? Make sure the voltage rating is more than the peak and if you use caps in parallel, their working voltage should be the same.

Try this mob: www.rockby.com.au

cheers

c

noobee · Postby **noobee** » Tue Jun 26, 2012 9:45 am

50volt wont hurt,should be dearer,possibly last longer.
2 x 4700 should be ok,close enough to 10000 as to make no difference.probably more important if you are mounting underbonnet is to get 105 degree rated caps instead of 85 degree.
Mick

droo · Postby **droo** » Tue Jun 26, 2012 12:33 pm

Automotive alternators can peak above 16 volts if their regulators have issues as well as pass intermittent spikes if the conditions permit. Engine bay temps (if the caps are mounted there) are also exposed to high ambient temperatures. Commecial grade electrolytics handle a temp rating of 80-100 degrees. Engine bay temps can "approach" that in the middle of summer depending on it's airflow, your car's body kit/front mesh etc..

Also, running under minimal electrical load, you'll be above 13 volts which is approaching the upper safe limit of the caps. By choosing 50v caps in your setup, you've got a load of headroom. A cheaper option, is using 25v caps. My setup i'm using 8x 4700uF 25v caps in parallel.

photo.JPG

photo1.JPG

Plenty of overkill, plenty of energy storage and $23 from Jaycar. I only chose 8 because it looked nicer then having 3..

Being electrolytic caps, they are made from a damp cardboard structure and need to be kept at a reasonable temperature to not over heat. When they reach tolerance levels, they expand, burst and go bubbly, and then dry out, with the potential to open circuit as well as seriously reducing their capacitance value after they've burst. As I'm keeping all of these in my engine bay (boxed beside the driver side fuse box) the near 4x redundancy in capacitance should be ok even if 6 of the 8 caps fail.

The caps can also overheat (depending on their enclosure/environment temp) if dríven at their max voltage, so yes, the implications of running 16 volt components in a 13volt and very hot environment (engine bay) essentially leaves you less margin for error.

http://www.youtube.com/watch?v=GKRZyPXP ... re=related
These videos are excessively over voltaged but impressive..

droo · Postby **droo** » Tue Jun 26, 2012 1:17 pm

here's some links to cap pricing:

10,000uF 40v (perfectly safe and small for your engine bay)
http://www.jaycar.com.au/productView.asp?ID=RU6720

4700uF 25v (grab two and hook up in parallel)
http://www.jaycar.com.au/productView.asp?ID=RE6244

Ebay has some cheaper prices but offset with 2-3 weeks delivery times on the 4700uF.. For the 10,000uF, Jaycar is better off on price.