Cap pack?

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Don't take me wrong I am looking into them also and it's question of understanding how them Jewls work. I like the idea of adding them but what I am trying to understand is the load to the amount of caps or uf. I believe like joostin42 in doing everything to ensure the best performance
I'm trying to understand this as well. I'm an electronics engineer in the DC to DC converter realm for 15 years. This is why I want to do bench testing. I suspect that ESR is more important than the amount of uF. Meaning the caps ability to deliver high current for short durations is more important than the ability to deliver lower currents for longer durations. The only way to know for sure is to hook up my scope in the lab and see what is really happening. Duration and amplitude or current spikes and resulting dips in voltage.
 

Drtybird

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I have read on one site that caps take away radio frequency but what I know about about caps on a amp it takes voltage spikes and balances it. Wouldn't there be a particular uf to either volt or amp draw
 
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No. uF is simply the capacity of the cap. Like the battery. More uF means it can deliver current for longer. If the spikes are short before th current draw settles down to its nominal running current then a lot of uF isnt needed. The battery will deliver the running current.
 
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ok,... There are two main factors contributing to the voltage drops at the ESC. the Resistance and the Inductance. The resistance is a combination of the resistance of the wire and the ESR of the lipo pack itself. The inductance which is mostly the wires though there is some inductance in the pack and the cells themselves.

The resistance.

Resistance drops the voltage relative to the current through it. So (V) volatage drop = CUrrent (I) x Resistance(R). For example say you have 50A current draw and overall resistance of 10mOhms. this means you will see a voltage drop equal to 0.01(R) x 50(I) of 500mV or 0.5V! at the ESC. during the startup of the motor they have a much higher and short duration startup current. for example, say you have a 300 amp start up current. so you will see a voltage drop of 0.01(R) x 300(I) of 3V at the ESC. now these numbers are all hypothetical at this point.

The inductance.

Ill leave out the math here. Think of your wires as inductors. Inductors store energy in the form of magnetic fields. while the field is charging the voltage at the other end drops. your battery can only deliver so much current and some of that is being sucked up by the inductance. once the field charges fully this effect goes away and only the resistance drop is present.

To counteract these effects you can do a number of things. the best is to shorten the wires and make them bigger. this lowers their resistance and their inductance. they have less resistance and cant store as much magnetic energy. The other thing to do is to provide a current supply right at the load (the ESC). This is where caps come in. they supply low esr/inductance current during the inrush and while the inductance is charging. if your caps are connected via big wires then they are much less helpful as you are adding back in inductance and resistance to those current supplies. they still help because they are in parallel with the battery and helping to supply some of that current. with the case of electrolytic caps their ESR plays a much bigger role as well as they tend to be in the 100mOhm range compared to the 6-10mOhms of your Lipo pack. Since these spikes tend to be short you don't need a ton of capacitance to absorb them. its better to have much lower esr and Inductance. this is why smaller polymer caps placed right at the ESC would be much more usefull and compact. Polymer caps are in the 15-30mOhms range.
 

jamesbcn

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ok,... There are two main factors contributing to the voltage drops at the ESC. the Resistance and the Inductance. The resistance is a combination of the resistance of the wire and the ESR of the lipo pack itself. The inductance which is mostly the wires though there is some inductance in the pack and the cells themselves.

The resistance.

Resistance drops the voltage relative to the current through it. So (V) volatage drop = CUrrent (I) x Resistance(R). For example say you have 50A current draw and overall resistance of 10mOhms. this means you will see a voltage drop equal to 0.01(R) x 50(I) of 500mV or 0.5V! at the ESC. during the startup of the motor they have a much higher and short duration startup current. for example, say you have a 300 amp start up current. so you will see a voltage drop of 0.01(R) x 300(I) of 3V at the ESC. now these numbers are all hypothetical at this point.

The inductance.

Ill leave out the math here. Think of your wires as inductors. Inductors store energy in the form of magnetic fields. while the field is charging the voltage at the other end drops. your battery can only deliver so much current and some of that is being sucked up by the inductance. once the field charges fully this effect goes away and only the resistance drop is present.

To counteract these effects you can do a number of things. the best is to shorten the wires and make them bigger. this lowers their resistance and their inductance. they have less resistance and cant store as much magnetic energy. The other thing to do is to provide a current supply right at the load (the ESC). This is where caps come in. they supply low esr/inductance current during the inrush and while the inductance is charging. if your caps are connected via big wires then they are much less helpful as you are adding back in inductance and resistance to those current supplies. they still help because they are in parallel with the battery and helping to supply some of that current. with the case of electrolytic caps their ESR plays a much bigger role as well as they tend to be in the 100mOhm range compared to the 6-10mOhms of your Lipo pack. Since these spikes tend to be short you don't need a ton of capacitance to absorb them. its better to have much lower esr and Inductance. this is why smaller polymer caps placed right at the ESC would be much more usefull and compact. Polymer caps are in the 15-30mOhms range.
Sethman, did you manage to test those peaks and find which kind capacitor suits better? this way we can buy bulk of first class caps and make our own cap-packs. Thx!
 
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I haven't had a chance. Had surgery the day after Christmas so I've been down. I may borrow a portable scope from work and do it at home.
 

Drtybird

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I haven't had a chance. Had surgery the day after Christmas so I've been down. I may borrow a portable scope from work and do it at home.
What are variables of loads? Does kv and voltage very when motor is not running at based rpm?
 
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joostin420

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Searched for 5x months for the 40mm nitro exhaust boat mounts to use as motor mount/braces like I used in my Kraton with the tp 4070cm 2200kv. Finally found a seller in England and bought the last 3x he had real fast ;)
AFB0AF84-BC8F-4E27-889B-64BFB2878796.jpeg
EB0B5B84-1B1D-4A8A-8601-5653437F9BC8.jpeg
 
Thread starter #52

joostin420

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I have a 45mm brace as well that is going to be used for something else since it was much too large. It may be too wide and hit the rear center driveshaft.
 

Drtybird

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I have read a post about someone looking at the TP motor but said something about the cans breaking or coming apart. Such a long motor the mount seems to be needed
 
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