capacitors: what are they for and how many is enough?

[morewattsnow]

I'm building a 34.5" Aeromarine Sprint Cat with a Neu 1527 1Y with a full length aluminum water jacket, a Castle Hydra 240 HV and an Octura 442 sharpened and balanced. Batteries are 5000 mah with 4 of them wired 6s2p. I have 2 sets- Polyquest 30c and Thunder Power 45c. The motor/ESC/prop setup is straight off the Castle web site.

Earlier this summer I ran this same boat/ prop/batteries with a Neu 1521 1Y and a Hydra 240 LV. It ran well, went like stink and one day it let ALL the smoke (and I mean ALL)out, burning the ESC and motor to the ground. So for some reason I want to do all I can to protect my new stuff from meltdown.

I've seen extra capacitor sets on the OSE website and would like to know when they should be used, if at all. Also, a little discussion of capacitors in general would be useful.

I have extensive RC boat experience, all with nitro power. I have some understanding of the basics- bigger prop=more amps=higher temps, wet boat=more amps=higher temps but am just learning about life at high power setups in these boats. Any help would be greatly appreciated.

[dana]

capacitors are for storing power from your batteries that isnt being used. they help protect your esc. adding them certainly doesnt hurt. i use extra's just to be safe. i would say mixing different battery makes with different C ratings is a bad idea. just my two cents

[NativePaul]

If you have more than 8" of wire Total between your battery and ESC (that includes the series link between your 2 3s2p packs) then you need more caps, adding more caps wont hurt anything even if you don't need them, as long as you have the space for them.

[morewattsnow]

Dana- You're absolutely right, not a good idea to mix different batteries. What I meant was I have 2 full sets, 4 TP's and 4 Polyquests. I think I'll install some of the high voltage caps sold on OSE. And keep the wiring as short as possible. Question- does installing more caps increase the snap when connecting the batteries and do any of you guys use a resistor to reduce this?

[Fluid]

I don't like the idea of resistors. Without the snap it is not possible to be certain your caps are working. They are an expendable item and will go bad over time. No snap means bad caps and a soon-to-be bad ESC. I'll accept the connector damage from a high voltage spark - replacing a pair of bullet connectors a few times a year is far cheaper and easier than replacing a blown ESC.

I see guys soldering a bunch of tiny caps all over their ESC, why? Large caps are available, with five to ten times the "capacity" of the caps used on most ESCs. One cap is neater and easier to install than 4 or 6 and gives better protection.

Here is one I use - shipping is rather high so if you order get a handful and split the cost with others. These are good for up to 7S, others are available for higher voltages.

http://www.alliedelec.com/search/pro...0203#tab=Specs




.

[Rumdog]

You're going to want WAY more prop than a x442. X452 minimum. The x455 will get you into the sixties.

[7500RPM]

I don't like the idea of resistors. Without the snap it is not possible to be certain your caps are working. They are an expendable item and will go bad over time. No snap means bad caps and a soon-to-be bad ESC. I'll accept the connector damage from a high voltage spark - replacing a pair of bullet connectors a few times a year is far cheaper and easier than replacing a blown ESC.

I see guys soldering a bunch of tiny caps all over their ESC, why? Large caps are available, with five to ten times the "capacity" of the caps used on most ESCs. One cap is neater and easier to install than 4 or 6 and gives better protection.

Here is one I use - shipping is rather high so if you order get a handful and split the cost with others. These are good for up to 7S, others are available for higher voltages.

http://www.alliedelec.com/search/pro...0203#tab=Specs




.

I am on board with some of your comments Jay, but, having such a large spark, current surge will prematurely destroy the capacitors as it distorts the plates inside the capacitor, also using smaller capacitors have a much better lower ESR and therefore will filter out the High Frequency Ripple that is present on the power supply rail when the speed control is in operation. This in it's self makes the speed control operate much cooler as it protects the FET's in the controller.( When I use to modify high end power supplies in home audio equipment we use to use small capacitor values but more of them with lower ESR values and you could actually hear a difference in sound reproduction when the mod was complete, using the same test parameters. When picking a capacitor you need to pick one designed for switching power supplies and the lowest ESR and at least 105 degrees operating temp and a voltage at least double to tripple what you are using. I have scoped the ripple on speed controls and you can get very high voltage spikes and this needs to be controlled, as the motor is an Inductive load.

[DISAR]

Adding extra caps helps in reducing esc caps temperatures? Apart from theory, has anybody seen actual results?

[morewattsnow]

So- the spark is our friend, but to big a spark can damage the caps due to surge. Perhaps a resistor that will show enough snap indicating the caps are good but not so much surge as to be damaging? How would you calculate this? What is the life expectancy of our capacitors= change every season? Not arguing, just trying to get a handle on this.

Also 7500 RPM, what is ESR?- I don't know that one.

The only stupid question is the one you don't ask.

[LiPo Power]

Ask Doby...
Long while ago he was about to get rid of some ESC's becouse they did not work.
Well, after installing new, larger capacity caps they are up and running....
Magic of caps....
Temp of ESC with installed caps will drop down a little... Caps temp way lower....

[7500RPM]

So- the spark is our friend, but to big a spark can damage the caps due to surge. Perhaps a resistor that will show enough snap indicating the caps are good but not so much surge as to be damaging? How would you calculate this? What is the life expectancy of our capacitors= change every season? Not arguing, just trying to get a handle on this.

Also 7500 RPM, what is ESR?- I don't know that one.

The only stupid question is the one you don't ask.

ESR, is the internal resistance of the capacitor ( Equivalent Series Resistance ) the lower the better!
The large spark is caused by the capacitor charging up as it is empty, just remember if this is done to many times it will over time distort the internals of the cap and failure will result. A well know speed control manufacturer says to use a resistor to charge the caps up. ( they make the biggest controllers out there Hint,Hint and No it is not CC )
To tell if you are using the correct capacitors the temps of the caps should be low, also IF your caps are starting to fail the cap temps will start going up and you will see a visual sign of the end of the capacitor will start to bulge out.
If you pick the wrong type the temps could be higher on the caps, so you can't just use any old capacitor!

[nova68]

I have a NEU 1515/1Y with a Hydra 240LV with Octura X-442 prop,batteries are 4S1P 5000mAh per battery and I run 4S 2P, what would be a good cap or caps to run ? The hull is a DF 29

[ray schrauwen]

I am on board with some of your comments Jay, but, having such a large spark, current surge will prematurely destroy the capacitors as it distorts the plates inside the capacitor, also using smaller capacitors have a much better lower ESR and therefore will filter out the High Frequency Ripple that is present on the power supply rail when the speed control is in operation. This in it's self makes the speed control operate much cooler as it protects the FET's in the controller.( When I use to modify high end power supplies in home audio equipment we use to use small capacitor values but more of them with lower ESR values and you could actually hear a difference in sound reproduction when the mod was complete, using the same test parameters. When picking a capacitor you need to pick one designed for switching powers and the lowest ESR and at least 105 degrees operating temp and a voltage at least double to tripple what you are using. I have scoped the ripple on speed controls and you can get very high voltage spikes and this needs to be controlled, as the motor is an Inductive load.

Took the words out of my mouth.

If ESC companies like Schulze & MGM show using a anti-spark resistor is good, I tend to agree.

[ray schrauwen]

Capacitors also cool off fairly quickly and by the time some people untape and check temps, they have dropped from their peak temps.

Capacitors are like toilet paper for ESC's these days...

Gotta try some new caps on some defunct esc's.... thanks for that post above Lipopower!

[7500RPM]

Took the words out of my mouth.

If ESC companies like Schulze & MGM show using a anti-spark resistor is good, I tend to agree.

And if ESC companies decided to start using better and larger FET's like Schulze controllers we would not have half the ESC failures and fires that we have now, BUT they continually keep using those crappy surface ( small package ) FET's and just parallel more of them and multiple boards to try to get the current handling they want, or try to get.