General ESC Theory Discussion

[MetalMan]

Why not just capacitors? I'll admit I haven't yet studied inductors much, but capacitors still seem more logical to me. As you stated an inductor in series with the positive rail between the battery and ESC will require some hefty wiring, and that alone would cost more than I'd care to spend (due to wrapping of the thick or high-strand count wires over the core). In another post somewhere you mentioned that it's difficult to get extra capacitors close enough to where they need to be on the MMM, but what about modifying the case to allow additional wires/capacitors, sized/spec'd appropriately to handle excessive ripple current?

[BrianG]

Yes, caps can help, but a good combo of both may be better. I don't want to figure out the math of it right now until someone a little more knowledgeable on the topic can chime in. I'm sure it's been thought of at some point, just thinking out loud really.

[Serum]

what exactly IS the problem? is it the internal resistance of the batteries that gets worse on a high load?

An inductor would be adding too much resistance.

What is the exact problem? if lipo's are not up the task, perhaps the voltage ripple kills the esc; in that case it might be an idea of adding these diodes that short above a certain voltage. put these between the 3 motorwires and it would prevent an overvoltage to occur.

[zeropointbug]

Is it Zener Diodes you are thinking of Serum?

About the inductor, it's kinda hard to say what that would do on an ESC; but wouldn't a large cap bank like the one I have make more sense? Looking at my eagletree results from last year when I have my monster quark running, and comparing that to the replacement quark, I have discovered that the voltage drop at a given current level is definitely less. This could possibly be an error in the eagletree, but I don't really know. Just my two cents.

[GriffinRU]

Originally Posted by BrianG

With the discussion of high ESC ripple current and the effect of using lipos that aren't quite up to the task, I was thinking of ways to help with this. What about using an inductor in series with the + battery line?

Yes, the wires would have to be quite large (probably litz wound), would weigh a few ounces, and there may be slight v-drop. But, an inductor is essentially a current storage device (via the magnetic flux), much like a capacitor is a voltage storage device. And an inductor opposes a change in current flow. So, the inductor will ramp-up/down current flow during high/low changes in current. Wouldn't thins help to reduce ripple current and voltage spikes getting to the battery? And since the ESC is constantly providing somewhat of a load (even when not driving a motor), inductor kickback should be minimal. Thoughts?

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

[tom255]

Is it possible to buy Ultracaps somewhere? How expensive they are?

[lutach]

Originally Posted by GriffinRU

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

Artur,

I'm going to get the caps I told you about. I have to try it out and see where they stand.

[BrianG]

Originally Posted by GriffinRU

No, No, No...

Only capacitors, and just a good bank of ultarcaps will convert low current LiPo into short-term (need to define voltage drop and timeframe, formulas available) high current killer power pack.

Inductor can be in motor leads, but not in power. Ripple current covered by capacitors, voltage drop can be covered by ultracaps and zeners (in one half).

Yeah, kinda figured, but doesn't hurt to ask...

[zeropointbug]

Originally Posted by tom255

Is it possible to buy Ultracaps somewhere? How expensive they are?

Maxwell Technologies has some RC size ultra caps that would work wonderful for high powered BL setups. They are C size cells, 2.5v/120Farads IIRC.

I will get link in next post...

[lutach]

Yes, www.maxwell.com, www.enerland.com and www.maxfarad.com. The ones I'll be gatting are he size of a button cell just a bit bigger then the ones found in digital watches.

Anybody have a link to some Low-ESR caps that are similar to what is on the Mamba Max ESC? I was thinking about adding a cap bank to help it run a little cooler (only gets to around 120F with a fan and a medusa 4800 kv pulling some hefty gearing). I would like it to run even better though... It's starting to get into the low 90's down here in Florida, so I'd like some extra cooling insurance.

Also, I should solder them closest to the power leads, yes?

[lutach]

You can look around www.newark.com, www.mouser.com and www.digi-key.com.

Edit: I got some Axial type capacitors that I'll be adding them up. They are the same width as most of the ESC I have and I'll probably hook it up to my Scorpion controller. They are Nichicon 50V 1000uF each. Should make a good bang when connecting .

Thanks lutach. Could I just pluck some off of a PCB I have laying around (say...from a computer's mobo?).

[lutach]

Originally Posted by Five-oh-joe

Thanks lutach. Could I just pluck some off of a PCB I have laying around (say...from a computer's mobo?).

I don't the the leads will be long enough, plus you won't know how many hours they've been working.

[zeropointbug]

Unfortunately caps from mobo's are lower voltage (~5v on mobo's)... and lot's of the time they are only lower rated 85C rated, which usually means not so low-esr.

Go on ebay and type in Nichicon low-esr 35v caps, and choose between 250uF and 500uF, they are usually the most effective for space/performance wise.

Lutach, a button size ultra-cap will have a relatively high esr, even compared to a lipo pack. You might want to look for something larger... I have found the Maxwell's to be the all around best for this.


http://www.maxwell.com/ultracapacito...l/bcap0120.asp These are the Maxwell ultra caps that I would use... 120F, 2.5V each (You will want +20% pack voltage handling), and are ~$15 each.