Cap pack?

Drtybird

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Did anyone get to find out about rating to voltage for cap packs? Are they only useful in HV loads with high gearing? Would they be useful with max6 ESC and TP 4070 around 1730kv
 

Raji

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Yes, they are helpful they will give you more punch. Also they will reduce speed control heat.
I have one on my outcast. man it's flips even if the battery almost dead.

Did anyone get to find out about rating to voltage for cap packs?

I didn't understand could you explain more please
 

Tumbleweed30

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@joostin420 how is your cap pack working out for you? Been having some electrical issues and I was recommended a cap pack and was running about doing mine up like yours with the XT-90. Any thoughts after all this time? Do you recommend the one from kill mode?

Thanks for your help man. I purchased the HR Diff Cups and Diff Housings on your recommendation and LOVE them.
 

joostin420

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The killmode cap packs are working great. I am using one in my x-bug x-maxx, and in my senton build as well. All 3x are the 13,200uf 6-pack units. Each is wired to a hw max 5 esc the same way with leads via xt90 connectors.

In the Kraton it is mounted on the original esc plate and location. In the senton it will be mounted in the original esc location but standing upright (have to shorten leads when finalized). In the x-maxx I have it mounted under my cf electronics plate.

Using 6s graphene in the Kraton and senton, 8s (2x4s) graphene in the x-bug.
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Drtybird

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Does the cap packs help in the cogging at low speeds
 

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The killmode cap packs are working great. I am using one in my x-bug x-maxx, and in my senton build as well. All 3x are the 13,200uf 6-pack units. Each is wired to a hw max 5 esc the same way with leads via xt90 connectors.
How are these working for you? Can you tell a difference? It seems to be a little overkill. With that MAX5 esc I wouldn't think it was needed since it was developed for a 1/5 scale motor and you are using an 1/8 scale motor. However these things are not always that cut and dry. If it makes a difference I would consider it for my MAX6 esc. I'm not sure if the motor or servo cares about voltage "ripple" but getting a little more consistent performance throughout the battery charge sounds worthwhile. Please let me know how this is working out for you. I am new to the cap pack idea and am very interested to know if it will be an actual benefit to me.
 

slick2500

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How are these working for you? Can you tell a difference? It seems to be a little overkill. With that MAX5 esc I wouldn't think it was needed since it was developed for a 1/5 scale motor and you are using an 1/8 scale motor. However these things are not always that cut and dry. If it makes a difference I would consider it for my MAX6 esc. I'm not sure if the motor or servo cares about voltage "ripple" but getting a little more consistent performance throughout the battery charge sounds worthwhile. Please let me know how this is working out for you. I am new to the cap pack idea and am very interested to know if it will be an actual benefit to me.
Not sure if it is relevant or not, when I picked up my Max8 it came with an optional cap pack, I installed it anyway.
I'm with you on the 6 pack probably being a bit overkill, the 4 pack from killmode would probably be just fine in a 6s setup, I would think you would only ever see any befits from the 6 pack in a speed run car or a EDF plane/jet.
 

Krathead

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Interesting that they give you a cap pack with the esc.
 

joostin420

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better safe than sorry; with all the money invested I also want the best performance out of all my projects :geek:

plus the 4pack 8800uf is $45, and the 6pack 13200uf is $55; its kind of a no-brainer.

My redcat be6s has a max8 esc and 4274 2200kv. The max8 esc came with small cap pack already attached. I don’t think it is enough though.
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Sethman919

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Wow. I need to get into the cap pack business. Just an bunch of caps soldered together and shrink wrapped. You have multiple caps because electrolytic caps has a lot of ESR that limits the amount of current they can deliver. Distributing the current across multiple caps helps solve that issue. With a single large cap you would be drawing all current from a single cap with more capacity but similar ESR limiting how much current that cap could deliver. If you really wanted the best performance you would use polymer caps. They have much lower ESR than electrolytics. Whether it is needed or not remains to be seen. I need to get a scope probe on the ESC input and see what's going on there. The caps help you because when you initially mash the throttle the startup currents for the motor can be massive. That same ESR is in your lipo pack. It's what dictates the c rating of the pack. Think of it as a current limiting resistor in series with your power source. This causes your voltage to dip during the huge transients of startup currents. The caps should help absorb these spikes by distributing the current across the caps. To maximize the performance keep leads as short as possible to the cap pack. The effects of the parasitic inductance and resistance of the wires and connectors is a whole other lesson.

That first ebay pack is about $7 worth of caps at 500pcs quantity. Nichicon caps.
 
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Sethman919

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I did some modeling this morning. While not perfect I did check the effects of high current transients on a battery pack. The parasitics of the wire play a lot more role in this than my model shows, but it really looks like the ESR of these Purely electrolytic cap packs is severely limiting their ability to minimize voltage dips from these transients. These packs really need to have a bank of ceramic caps to help with this. I really need to get my car in the the lab and see how bad it is real world and test some cap packs with and without ceramic caps.
 

Drtybird

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What is the difference in the ceramic over the electrolytic caps
 

Sethman919

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What is the difference in the ceramic over the electrolytic caps
ceramic caps typically have significantly lower ESR which allows them to deliver a lot more current. but they have much smaller capacities so they cant deliver that current for as long. I played with my model some more. Im not sure how accurately it models the inrush current of the motor, but my model produces a 300A 2uS spike with a 50A constant current. I found that you would need a significant amount of ceramics to make a big difference. I did find that a bank of polymer caps which are also a lot lower ESR produced much better results. Reducing the dip by another 400mV over the purely electrolytic cap pack. these caps would be significantly smaller than the all electrolytic caps packs as they are much smaller capacity. depending on duration of the real spikes in the car the ESR is much more important than the capacity. The down side to the polymer caps is they are more expensive. If the spike from the motor is much longer in duration then i may have to rethink which cap is better. there will be two spikes to worry about. the basic commutative spikes from energizing each field of the brushless motor with a PWM and then just the initial inrush current of cranking up the motor. I suspect the inrush current may be the one we are worried about here and may have a longer duration.
 

Drtybird

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Some of these guys are running higher amp motors with high speed gearing wouldn't your model need to be tested at 80-100 amp
 

Sethman919

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Some of these guys are running higher amp motors with high speed gearing wouldn't your model need to be tested at 80-100 amp
The base current is really unimportant here. It's Inrush current spikes that are more important here. I just need to test to get a better idea of the current profile of these motors.
 

Drtybird

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With higher volts the amp draw is less but when running larger motors and higher gearing won't the spikes be at longer times with higher loads
 

Sethman919

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With higher volts the amp draw is less but when running larger motors and higher gearing won't the spikes be at longer times with higher loads
For the most part that is correct. I just need to know what they are in the real world and I can scale the numbers from there as well as understand the roll the parasitic inductance plays. I suspect this parasitic Inductance plays a bigger roll than the even the ESR. This would mean that shorter and bigger wires would be more beneficial. Allowing you to simply get more out of the already very low ESR of your Lipo pack.
 

Drtybird

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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
 
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