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Old 12-11-2003, 09:54 PM   #16
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Charlie,

Do you know why LRP states that the power capacitor only helps in performance, and does nothing for the speed control? Is this also because LRP and Novak speedos operate in a different way?
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Old 12-11-2003, 10:25 PM   #17
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Do they have a life span? I mean, should I replace mine after running it on my TC2 for 1.5 years?

Thanks!
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Old 12-11-2003, 11:42 PM   #18
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Quote:
Originally posted by Charlie
Wow again? I got an email requesting some clarification to this link so here you go.

Power caps explained. Again. (Futureal keep this posted someplace maybe the tech section)

This may sound Like a Novak Add or something, but that is were my experience is. The statements apply to most ESCs.

The power cap on a Novak ESC is there to prevent the ripple current that is created by the ESC from damaging itself. It's not really for any full throttle response, as when the ESC is at full throttle, it is not switching, it turns into a "junction" only. It would be like soldering the wires directly from the battery to the motor. Full power is full power is full power.

The Power cap is actually there for partial throttle operation. When you are using anything other than full throttle the ESC is switching very fast. A Novak ESC switches faster than most (not the drive freqeuncy, but the switching used to create that drive frequency) so the problem is more severe. Due to the high rate of the switch process a ripple current is created. This means the voltage is flowing into the fets so hard and fast, that when the ESC switches to off, the current continues to flow and heats up the parts. This is probably an over-simplified explanation, but you get the idea right? So the Power Cap absorbs the ripple current, prevents the heating of the ESC and feeds the stored voltage back to the motor on the off cycle. That inturn creates a much cooler ESC and vastly improved mid range throttle response.

You can easily test this, but running your motor at partial throttle, then removing the power cap, the motor will slow down, when you reconnect the power cap the motor revs up a little.

Power caps are not for full throttle acceleration, I can see why that mistake is often made, it makes a little sense, but is not correct. They may have an effect on it, but are not there for that reason.

After that people want to know why you have to use a special Cap. Reason for that is that the capacitor has to be the correct "performance". If the cap is the wrong ESR value it will not do anything in the system, so it doesn't provide any protection. Problem is capacitors don't spec the ESR, it is usually indicated by the manufacture in a "series" or line of parts. The Radio Shack cap will damage your ESC.

Next question is usually about schottky diodes.

A schottky diodes is an electronic one way valve for voltage. When your motor free spins it creates voltage that is fed into the ESC. A schottky prevents that voltage from getting to the ESC. As a side effect you get more consistant breaking. They are still required even if you don't use the brakes, becuase the are stopping damage that happens every single time you lift off the throttle. Schottky diodes also increas motor voltage in a similar manor to power caps. My understanding of that isn't as clear, but similar RPM gains are noticed.

Currently Novak has been developing our ESC dyno. We have been working on ESC comparisons and what does what. What we have found for sure, is the problem does not come from the ESC or what it's doing, motors from only a couple years ago are more efficient and create much smaller issues. Today's motors may seem great, but the truth is they are less efficient overall. There are always acceptions so don't jump on me if I've said something you don't agree with or have different experience.

Anyfurther questions directly to me, please shoot me an email.

Thanks
Charlie
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I see what you mean with the ripple current, only, the current used to DRIVE the FETS should be very small. This wouldn't require such a big value in capacitor.
My experience, with an MRT VTRAC (english-made) esc, is that when I use the capacitor, my car gets a shove in the back coming out of the corner at full throttle. This is a slightly slower switching esc than a Cyclone though.
About the Shottky, Novak now has a new Shottky module, which is claimed to be the equivalent of 10 shottky's. It's used, from what I've heard, to prevent the new GT7 esc from malfunctioning, or even being damaged during operation. My question is: what does it improve over a regular SB540 or SB550? Is it the resistance when it's in operation mode (don't know how to properly say this in english), or is it the threshhold voltage? What manufacturer and partnumber is it? Would it improve the functioning of my newly acquired cyclone?
Thanks for your response!
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Old 12-12-2003, 01:10 AM   #19
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Pro ten Holland, I'm not sure what you mean by "current used to drive the FETs." Any and all current that passes through the ESC to the motor will pass through the FETs; you can think of them as gateways between the battery and the motor.

What your ESC is actually doing is turning the FETs on and off quite rapidly as you are changing the throttle of your car. If you are at 50% throttle, then it means that your FETs are "on" half of the time and "off" half of the time. The drive frequency determines the number of times each second that the FETs are switching, so they are actually doing more work at 50% throttle than they are at 100% throttle (where they would just stay in the "on" position).

A lot of the advances with ESCs in the mid/late 90s had to do with better FETs and higher drive frequencies. Earlier ESCs had drive frequenches of like 60Hz or somewhere thereabouts. As a FET switches from "on" to "off" there is a region where current is lost (or fed back, hence the ripple? Charlie or someone, correct me if I'm wrong on this). Actually by "lost" we are talking about going somewhere other than the motor; remember those big heatsinks we'd have on the FETs? That is where some of the heat was coming from. So with the newer FETs, not only can they handle higher frequencies, but they switch much faster.

Charlie, when I have some down time during the Holidays I will try to create a Tech section on ESCs or something similar. Maybe a forum with some stickied threads, like a FAQ. That's one of the things I've been meaning to do for some time...!
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Old 12-12-2003, 04:10 AM   #20
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Correct me if I am wrong, but doesn't the cap also keep the battery voltage the motor "sees" more consistant?

Like when you grab the throttle exiting a turn, the energy in the cap is released to keep the voltage stable instead of say being drug way down for that second or two (or whatever the time frame is). The cap adds it's stored energy to the mix whenever the batt voltage is pulled low.

Is that correct, or close? LOL!
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Old 12-12-2003, 01:53 PM   #21
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This is true in a power source -> capacitor -> device setting, but I'm not sure if it works in the same manner with an ESC. I have never looked inside one, so I'm not even sure that the capacitor is directly connected to the input (as opposed to somewhere else).

Generally, you want to use a capacitor when you want to provide a smooth, consistent flow of current OR you need to store more current that your power source is capable of delivering. Usually in the latter case, you are charging the cap, draining it, and then re-charging, but I don't think that setup is good in a constant-current application.

You'd have to get Charlie or someone more knowledgable on it to answer that one.
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Old 12-12-2003, 02:22 PM   #22
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what power cap specs would you reccomend to give me max performance with a stock motor ( monster stock )
thanks alot

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Old 12-13-2003, 05:25 AM   #23
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Quote:
Originally posted by futureal
Pro ten Holland, I'm not sure what you mean by "current used to drive the FETs." Any and all current that passes through the ESC to the motor will pass through the FETs; you can think of them as gateways between the battery and the motor.

What your ESC is actually doing is turning the FETs on and off quite rapidly as you are changing the throttle of your car. If you are at 50% throttle, then it means that your FETs are "on" half of the time and "off" half of the time. The drive frequency determines the number of times each second that the FETs are switching, so they are actually doing more work at 50% throttle than they are at 100% throttle (where they would just stay in the "on" position).

A lot of the advances with ESCs in the mid/late 90s had to do with better FETs and higher drive frequencies. Earlier ESCs had drive frequenches of like 60Hz or somewhere thereabouts. As a FET switches from "on" to "off" there is a region where current is lost (or fed back, hence the ripple? Charlie or someone, correct me if I'm wrong on this). Actually by "lost" we are talking about going somewhere other than the motor; remember those big heatsinks we'd have on the FETs? That is where some of the heat was coming from. So with the newer FETs, not only can they handle higher frequencies, but they switch much faster.

Charlie, when I have some down time during the Holidays I will try to create a Tech section on ESCs or something similar. Maybe a forum with some stickied threads, like a FAQ. That's one of the things I've been meaning to do for some time...!
Ah yes, now I know what you mean! You want the current running through the fet in the'on' state to go into the capacitor, in stead of burning off as heat in the fet. And with the high frequency used, you'd need a capacitor that's quick enough.
Correct if I'm wrong, but wouldn't a capacitor with a smaller capacity be faster than a big one?
The increase in punch out of the corner is a nice bonus though.
Another question: I've heard about esc's from Tekin, which were designed not having the need of a shottky diode. Does this work by sending the power created by the motor during braking and coasting to be send back to the battery? I think that would be an interesting concept.
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Old 12-18-2003, 01:32 AM   #24
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Quote:
I've heard about esc's from Tekin, which were designed not having the need of a shottky diode. Does this work by sending the power created by the motor during braking and coasting to be send back to the battery?
There are two answers to this. The answer from Tekin in the day was that they had built in shottky diodes, so they didn't need one mounted on the motor. But, they also claimed their ESC's had "Battery Regeneration Technology", so when you hit the brakes the motor would act as a generator and "charge" your battery slightly. If that was the case, I can't see how there could be an internal shottky. I still own a number of Tekin Speedos..no offense to Charlie or Novak, but I wish they were still around. They had by far the best Torque limiter on the market, where you could see what it was really set to with a voltmeter. Very acurate, and very repeatable. Plus the competition between Novak and Tekin was fun to watch.
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Old 12-18-2003, 03:05 AM   #25
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Would recharging the battery under breaking harm your pack..? Wouldnt this send a spike of voltage back to the battery.
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Old 12-18-2003, 04:46 AM   #26
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Well I have done the following test (that contraries my belief)!!
OK, before throughing everything against my test, I think it could put some light on that matter.
I have put a 12x1 Core stopped and then running at 3V, 5V and 7V with my GFX. I have measure the rpm with a GlooBee digital gauge. Attached to the mtotor was a small propeller to absorb energy. Then a charged different caps, all of them 16V, 105ºC, ranging from 1000uF to 10000uF. Then I disccharged the caps on motor and see any differences on rpm.
Results:
. with motor stopped - nothing happened but sparks on contact
. with the different voltages applied to the motor the difference was so small that the reader doesn't measure it.

Conclusion - after that test I believe that the power cap is most used to protect the ESC rather to add any punch.
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Old 12-18-2003, 11:46 AM   #27
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The power cap IS added to the battery circuit in an ESC. Just like the cyclone series, the GT7 capacitor is attached to the power circuit, only INSIDE the speedo. If you want to be actual, the battery has more storage than the capacitor EVER could, so its effects would be on the speedo, not overall (100%) motor performance. The only way the cap would prevent any glitching due to low wind motor use, is if it was added to keep the voltage up or constant (ripple-free as Charlie mentioned) for the internal voltage regulator in the speedo that provides current for the servo and receiver. The easiest way to avoid this without all the "popular" capacitor addons (3 and 4 of them that you see alot of team drivers adding in an elaborate fashion) is using a receiver pack that powers your servo and receiver, taking the main battery/speedo out of the equation alltogether. If you then still glitch, you have other issues not related to low wind motor use. I personally use the smaller capacitors available when the TC2 was out, on my GT7. I never use frequencies above 7KHZ, the GT7 is smoother than the Cyclone ever could be because of all the throttle steps added. Using anything above 7KHZ seems redundant and too soft for throttle response. (IMO) I was however unfortunate enough for the standard GT7 cap to pop off in a nasty landing off of a BIG double jump running a 10X2 in my B4 during a qualifier. Throttle response seemed to drop to half, and top speed suffered, almost like i dropped a cylinder in a real race car, losing just as much power and the engine running rough. (which made no sense in light of the current discussion, as far as top speed is concerned) When i pulled the B4 off to the side (i thought i had a hung brush in the motor) the speedo was QUITE warm... and one lead had popped off of the cap, the cap retainer popping off the side of the speedo... stressing the wire till it broke. I rebuilt the motor, having only two runs on it, so i cannot say if a hung brush was the culprit of the power loss or not, i did not make the capacitor fix as my only change to be able to tell. I have since added the smaller TC2 cap to the GT7 in both my B4 AND TC3, and they run flawlessly with good midrange punch and smoooooth throttle feel, with the case temp never going above 100*, or ambient temperature, depending on the weather. I really think now that technology has gotten sooo advanced, with added runtimes and better motors and speedos, fans should be an everyday addition to these cars. I know it seems like a sales gimmick, but nothing runs better than a cool speedo/motor. My .02c !
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Old 12-18-2003, 05:41 PM   #28
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Hey Guys, I kept checking back for this thread but never saw it after my first post sorry I missed so much. Next time somebody email me to come back.

There is way too much for me to answer one at a time, so I'll cover what I can for now.

Now, the current I was talking about was used by the motor, not to "drive" the fets. I don't want to be rude to anyone, but my description is correct, and verified over and over again. Anything related to a Power Cap and a Novak ESC is for the reasons I listed ONLY, all other effects are benefits of what is going on inside the ESC.

The power cap is not for under acceleration, I SWEAR IT, it's not. Maybe in a junky ESC with a crappy BEC it will help, but that's not what it is for in a modern Novak ESC. Drives me nuts when folks get that wrong because it is totally incorrect. If there is a difference, it may due a problem in the ESC.

If you cap falls off during a run, it is usually damaged, the effect after was do to the very quick damage to the ESC.

We have a minor update posted on our site regarding new motors and the use of proper drive frequency.

Newer motors (about 2 years) have been found to not really like higher drive frequency. We've worked very closely with top-level team drivers and the newest motors and have found that using only profile 5 offers MUCH better throttle response. It is explained by many different terms, but technically what is happening is the motor is more linear. This is because at the higher frequency the motor won't run as well, due to its "not wanting" to accelerate at low voltage. This is because newer motors are very in efficient. Stock motors are almost as bad. I can get a most P2K2s or a Monster to draw over 16 amps with off the shelf brushes and springs. That's not good at all.

New motors are also the cause for the huge schottky. They create a very bad EMF that heats up the ESC whenever you lift and coast. We can't get a big enough one inside the ESC to provide enough protection, so we put a huge one on the motor. I can't tell you how many "other team drivers" come to us for these diodes at big races. We have some things in the works to rid us of these horrid Diodes. Next ESC will likely not need them, but I'm sure by the time we finish, the motor manufactures will have a new breed of multi super magnet, misshapen wire- too much brush- run it one time and rebuild motors that will ruin our plans. We don't want to have to add this stuff, but the truth is even if you don't need it, it helps. No matter what you think, it helps performance. ESC is cooler and motor response is significantly improved.

The Power cap is soldered to the battery leads inside the GT7 just like the C2 and TC2; we just use heavier and shorter wire due to today’s motors. Power Caps are not there to add punch; they are there to improve throttle response.

Again, if you experience different, that is fine, your brand of ESC is not switching at the speeds we are, the GT7 is a huge step up from what we had before regarding it's technical capabilities. All team drivers gave rave reviews when they received them.

I've worked here for about 4 years now and have spoken at length with our engineers on many occasions. Novak Electronics never really try's to "market things up" or Gimmick things. If we say it's better, it really is, we may give it a funny name, but that is for the kids, moms, and less than serious racers that make up 90% of this industry.

I even spell checked this time.

Well everyone, we'll be closed the rest of next week, and I'm going out of town tomorrow so I'll see you all around the 29th for more updates and answers. You can also email me directly. [email protected]

Thanks
Charlie
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Old 12-18-2003, 07:22 PM   #29
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let me say thank you Charlie and Team Novak for taking the time to come on here and explain this to us. thanks
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Old 12-18-2003, 11:41 PM   #30
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Keep up the good work Charlie! You're appreciated!
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