R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 02-15-2007, 01:17 AM   #1
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default Power caps concern and questions

Hi all

I just want your opinion :

Is it still worth to put power caps (low ESR and high ripple caps) attached to pos and neg battery lead on the latest ESC (ex. Sphere comp. 007, GTB, GTX, VFS-1, etc. ) ?


Thanks for you answer / comment ....
akuhon is offline   Reply With Quote
Old 02-15-2007, 01:24 AM   #2
Tech Addict
 
AngryAsian's Avatar
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 550
Trader Rating: 4 (100%+)
Default

In a word.. YES

Can't speak for the others but the GTB in particular is designed to operate with a large 4700uf 10v cap in order to improve efficiency.

Actually, do to the high Amp draw of modern low turn motors, it's advisable to run caps in any situation to smoothen the voltage ripple that occurs during hard usage.

Novak recommends running the cap at all times, and even running a second cap wired in parallel for improved performance.
AngryAsian is offline   Reply With Quote
Old 02-15-2007, 01:55 AM   #3
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default

Quote:
Originally Posted by AngryAsian
In a word.. YES

Can't speak for the others but the GTB in particular is designed to operate with a large 4700uf 10v cap in order to improve efficiency.

Actually, do to the high Amp draw of modern low turn motors, it's advisable to run caps in any situation to smoothen the voltage ripple that occurs during hard usage.

Novak recommends running the cap at all times, and even running a second cap wired in parallel for improved performance.
Thanks

So the more caps installed in parallel, the better ?
Ex. I added 10V 3300uf, so the voltage will stay and the capacitance will increase to 8000uF ....

By adding another caps, will the ESR decrease and ripple increase ?
akuhon is offline   Reply With Quote
Old 02-15-2007, 02:36 AM   #4
Tech Addict
 
AngryAsian's Avatar
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 550
Trader Rating: 4 (100%+)
Default

I'm not sure about the ESR ratings to be honest...
All I know is that the lower the ESR, the better the cap is. Both in quality (as they are hard to produce), but also in terms of usefulness in a high frequency application. Lower resistance is a good thing!

As for ripple currents, I THINK in RC use, we're talking quite large ripple currents. So the applicable capacitor type is the electrolytic type. I don't see any other type of cap used in rc. Not sure what the effect it when used in series, but I think it's more to do with the application than anything else.

There is also a relationship between ESR and ripple voltage. The higher the ESR the higher the ripple voltage. The relationship is inverse (I think - can't remember).. So ESR impacts the operation in that regard. Big ripples are bad.. This is something that I don't really understand.

I think the general gist is: A cap is rated for a certain ripple. Ripple is bad as it "works" the cap harder.

Lastly: More caps = more better! The voltage dips experienced by the esc under high amp loads are quite large. More caps effectively adds to the capacity and I'd assume takes the same time to charge due to the parallel wiring.

**I'm not in any way an electrical engineer. So please take all of the above with a grain of salt. Internet forums! Bah!**
AngryAsian is offline   Reply With Quote
Old 02-15-2007, 03:03 AM   #5
Tech Addict
 
Skill's Avatar
 
Join Date: Apr 2003
Location: Doncaster, England
Posts: 537
Default

If you wire the capacitors in series then you will actually get less capacitance, but I would imagine you would be able to throw a higher voltage through it (pointless in R/C as the voltages are relatively low and we already have 10/16V capacitors that are sufficient).
Skill is offline   Reply With Quote
Old 02-15-2007, 08:09 PM   #6
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default

Thanks for the info...

If I use it with silver can or tamiya sport tuned motor, does it give any slight difference than without the caps ?
akuhon is offline   Reply With Quote
Old 02-15-2007, 09:18 PM   #7
Tech Elite
 
schmelme's Avatar
 
Join Date: Mar 2003
Posts: 2,294
Trader Rating: 13 (100%+)
Default

Doesnt a mosfet or transistors efficiency go way down as voltage drops or when it dip significantly. The cap helps to combat the dip in voltage seen by the esc keeping the it cooler and more efficient.
schmelme is offline   Reply With Quote
Old 02-15-2007, 09:55 PM   #8
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default

Quote:
Originally Posted by schmelme
Doesnt a mosfet or transistors efficiency go way down as voltage drops or when it dip significantly. The cap helps to combat the dip in voltage seen by the esc keeping the it cooler and more efficient.
Means caps protect ESC
akuhon is offline   Reply With Quote
Old 02-15-2007, 09:56 PM   #9
Tech Rookie
 
Join Date: Feb 2007
Location: Virginia
Posts: 16
Default

Is there a chart or table somewhere that helps me match the right caps to the motor turns and winds, wire gauge, and esc?

thanks!
PseudoScience is offline   Reply With Quote
Old 02-15-2007, 10:04 PM   #10
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default

I think, it should be related to the internal resistance (IR) of the ESC rather than motor turn, winds and wire ....

The caps should have ESR near the IR of ESC ..... That's what I think ...

Any comments ?
akuhon is offline   Reply With Quote
Old 02-16-2007, 12:13 AM   #11
Tech Master
 
akuhon's Avatar
 
Join Date: Feb 2006
Posts: 1,155
Default About parallel power caps made by Straight Ltd., Japan

While searching for good caps, I have found out what's exactly attached to this ROK-90S4 Layer Capacitor made by Straight Ltd., Japan

Also for ROK-90V8 Layer Capacitor


According to the website, they are connected in parallel.
And you'll see on top of the caps, the ROK-90S4 use 680 uF (not sure about this 'cause I don't have the caps yet and the pics on their web is not so clear.. unless someone who has it can confirm about it) and ROK-90V8 use 220 uF (it's clear from the pic)

Both are using nichicon caps products, vertical chip-type capacitor, with the datasheet you can find here
(see the "UD" series on top of the caps).

My questions are :
1. Is it low ESR same with low impedance, cause I always see in the capacitor datasheet, they always refer to impedance not ESR

2. Looking at the datasheet tabel for 220 & 680 caps, the lowest impedance for 220uF is 0.17 at 25V/35V and for 680uF at 0.09 at 10v/16v
Some say (in other thread ) low ESR should be max. 0.05 ohm for ESC
If the caps put in parallel, the capacitance will be multiplied but will the total impedance (ESR) be divided (decrease / lower) ?

3. How about the ripple in parallel caps, will it be divided or multiplied or remain the same ?

4. What are the advantage and disadvantage of putting the caps in parallel ?

I hope someone could enlightenment....
Really sorry to ask this 'cause I'm not electrician or have knowledge about power caps....
akuhon is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Power Caps & Schottky's ??? JohanZ Electric On-Road 4 03-16-2006 08:28 PM
power caps for escz xray racer Electric On-Road 3 01-07-2004 06:10 PM
power caps addicted2rc Electric On-Road 0 05-25-2003 04:26 AM
Power Caps nerdling Australian Racing 36 03-18-2003 01:39 AM
power caps was ist los? Electric On-Road 0 03-29-2002 11:36 PM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 04:20 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net